Migrate to new Stacks REST API (#177)

* Add stack Number field to local model and schema

The new Stacks REST API exposes a human-facing stack number (shown in the
github.com UI) alongside the internal stack id. Add a Number field to the
stack.Stack model and document it in schema.json so it can be persisted in
the .git/gh-stack file. Purely additive; behavior is unchanged until callers
populate it.

Copilot-Session: 03673c26-a245-42da-93ed-dfcebc92a740

* Cut over stack operations to the public Stacks REST API

Replace the private cli_internal stack endpoints with the new public
Stacks REST API (/repos/{owner}/{repo}/stacks):
- ListStacks / FindStackForPR (?pull_request= filter) / GetStack for reads
- CreateStack, which now returns the created stack including its number
- AddToStack for delta-only appends (there is no full-replace endpoint)
- Unstack for server-driven removal (204 dissolved / 200 partial / 422)

Migrate all callers (checkout, submit, link, sync, unstack, utils) and
drop the client-side unstack eligibility pre-check — the server now
decides which PRs can be unstacked. checkout discovers stacks via the
pull_request filter; submit/link express updates as append-only deltas;
unstack adopts partial-unstack semantics, keeping local tracking when
PRs remain stacked on GitHub.

RemoteStack now carries the stack number, and stack updates resolve a
stack's number from its internal id for stack files that predate the
Number field.

Copilot-Session: 03673c26-a245-42da-93ed-dfcebc92a740

* Remove the personal access token (PAT) limitation

The new Stacks REST API is public, so any user authenticated with the
GitHub CLI (including via a PAT with repo scope) can perform stack
operations once the feature is enabled for their repository. Remove the
PAT detection and the private-preview gating:

- Delete Config.WarnIfPAT / IsPersonalAccessToken and the TokenForHostFn
  test hook (internal/config/auth.go is no longer needed).
- Drop the submit pre-flight that aborted on a PAT.
- Rename warnStacksUnavailableOrPAT to warnStacksUnavailable and simplify
  it to the "stacked PRs not enabled" message.

Copilot-Session: 03673c26-a245-42da-93ed-dfcebc92a740

* address review comments

cmd/checkout.go

@@ -188,12 +188,13 @@ func checkoutRemoteStack(cfg *config.Config, sf *stack.StackFile, gitDir string,
 		return nil, "", ErrAPIFailure
 	}
 
-	// Step 1: List stacks and find one containing the target PR
-	remoteStack, err := findRemoteStackForPR(client, prNumber)
+	// Step 1: Find the stack containing the target PR via the list endpoint's
+	// server-side pull_request filter.
+	remoteStack, err := client.FindStackForPR(prNumber)
 	if err != nil {
 		var httpErr *api.HTTPError
 		if errors.As(err, &httpErr) && httpErr.StatusCode == 404 {
-			warnStacksUnavailableOrPAT(cfg)
+			warnStacksUnavailable(cfg)
 			return nil, "", ErrAPIFailure
 		}
 		cfg.Errorf("failed to list stacks: %v", err)
@@ -205,7 +206,7 @@ func checkoutRemoteStack(cfg *config.Config, sf *stack.StackFile, gitDir string,
 	}
 
 	// Step 2: Fetch PR details for every PR in the remote stack
-	prs, err := fetchStackPRDetails(client, remoteStack.PullRequests)
+	prs, err := fetchStackPRDetails(client, remoteStack.PRNumbers())
 	if err != nil {
 		cfg.Errorf("failed to fetch PR details: %v", err)
 		return nil, "", ErrAPIFailure
@@ -245,11 +246,14 @@ func checkoutRemoteStack(cfg *config.Config, sf *stack.StackFile, gitDir string,
 		syncRemotePRState(localStack, prs)
 
 		// Case A: branch is in a local stack — check composition
-		if stackCompositionMatches(localStack, remoteStack.PullRequests) {
+		if stackCompositionMatches(localStack, remoteStack.PRNumbers()) {
 			// Composition matches — checkout
-			if localStack.ID == "" {
-				localStack.ID = remoteStackID
-			}
+			// remoteStack is authoritative for both identifiers here, so
+			// refresh them together. Updating only one (e.g. the number while
+			// keeping a stale ID) breaks later ID-based discovery when the old
+			// remote stack was replaced by a new one holding the same PRs.
+			localStack.ID = remoteStackID
+			localStack.Number = remoteStack.Number
 			if err := stack.Save(gitDir, sf); err != nil {
 				return nil, "", handleSaveError(cfg, err)
 			}
@@ -274,7 +278,7 @@ func checkoutRemoteStack(cfg *config.Config, sf *stack.StackFile, gitDir string,
 		return nil, "", ErrSilent
 	}
 
-	s, err := importRemoteStack(cfg, sf, gitDir, remote, trunk, prs, remoteStackID)
+	s, err := importRemoteStack(cfg, sf, gitDir, remote, trunk, prs, remoteStackID, remoteStack.Number)
 	if err != nil {
 		return nil, "", err
 	}
@@ -286,23 +290,6 @@ func checkoutRemoteStack(cfg *config.Config, sf *stack.StackFile, gitDir string,
 	return s, targetBranch, nil
 }
 
-// findRemoteStackForPR queries the list stacks API and returns the stack
-// containing the given PR number, or nil if no stack contains it.
-func findRemoteStackForPR(client github.ClientOps, prNumber int) (*github.RemoteStack, error) {
-	stacks, err := client.ListStacks()
-	if err != nil {
-		return nil, err
-	}
-	for i := range stacks {
-		for _, n := range stacks[i].PullRequests {
-			if n == prNumber {
-				return &stacks[i], nil
-			}
-		}
-	}
-	return nil, nil
-}
-
 // fetchStackPRDetails fetches PR details for each number in the stack.
 // Returns PRs in the same order as the input numbers.
 func fetchStackPRDetails(client github.ClientOps, prNumbers []int) ([]*github.PullRequest, error) {
@@ -418,7 +405,7 @@ func handleCompositionConflict(
 			return nil, ErrSilent
 		}
 
-		s, importErr := importRemoteStack(cfg, sf, gitDir, remote, trunk, prs, remoteStackID)
+		s, importErr := importRemoteStack(cfg, sf, gitDir, remote, trunk, prs, remoteStackID, remoteStack.Number)
 		if importErr != nil {
 			return nil, importErr
 		}
@@ -429,19 +416,26 @@ func handleCompositionConflict(
 		return s, nil
 
 	case 1:
-		// Delete remote stack, keep local
-		if err := client.DeleteStack(remoteStackID); err != nil {
+		// Unstack the remote stack, keep local
+		_, dissolved, err := client.Unstack(remoteStack.Number)
+		if err != nil {
 			var httpErr *api.HTTPError
 			if errors.As(err, &httpErr) && httpErr.StatusCode == 404 {
-				cfg.Warningf("Remote stack already deleted")
+				cfg.Warningf("Remote stack already removed")
+			} else if errors.As(err, &httpErr) && httpErr.StatusCode == 422 {
+				cfg.Errorf("Cannot unstack remote stack: %s", httpErr.Message)
+				return nil, ErrAPIFailure
 			} else {
-				cfg.Errorf("failed to delete remote stack: %v", err)
+				cfg.Errorf("failed to unstack remote stack: %v", err)
 				return nil, ErrAPIFailure
 			}
+		} else if dissolved {
+			cfg.Successf("Remote stack removed")
 		} else {
-			cfg.Successf("Remote stack deleted")
+			cfg.Warningf("Some pull requests could not be unstacked and remain on GitHub")
 		}
 		localStack.ID = ""
+		localStack.Number = 0
 		if err := stack.Save(gitDir, sf); err != nil {
 			return nil, handleSaveError(cfg, err)
 		}
@@ -475,6 +469,7 @@ func importRemoteStack(
 	trunk string,
 	prs []*github.PullRequest,
 	remoteStackID string,
+	remoteStackNumber int,
 ) (*stack.Stack, error) {
 	// Fetch latest refs from remote
 	if err := git.Fetch(remote); err != nil {
@@ -512,7 +507,8 @@ func importRemoteStack(
 
 	trunkSHA, _ := git.RevParse(trunk)
 	newStack := stack.Stack{
-		ID: remoteStackID,
+		ID:     remoteStackID,
+		Number: remoteStackNumber,
 		Trunk: stack.BranchRef{
 			Branch: trunk,
 			Head:   trunkSHA,

cmd/checkout_test.go

@@ -158,9 +158,9 @@ func TestCheckout_NumericTarget_StacksNotAvailable(t *testing.T) {
 	require.NoError(t, stack.Save(gitDir, &stack.StackFile{SchemaVersion: 1, Stacks: []stack.Stack{}}))
 
 	cfg, outR, errR := config.NewTestConfig()
-	setTestTokenForHost(cfg, "gho_test_oauth_token")
+	setTestRepo(cfg)
 	cfg.GitHubClientOverride = &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
+		FindStackForPRFn: func(int) (*github.RemoteStack, error) {
 			return nil, &api.HTTPError{StatusCode: 404, Message: "Not Found"}
 		},
 	}
@@ -184,10 +184,8 @@ func TestCheckout_NumericTarget_PRNotInStack(t *testing.T) {
 
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{
-				{ID: 1, PullRequests: []int{10, 11}},
-			}, nil
+		FindStackForPRFn: func(int) (*github.RemoteStack, error) {
+			return nil, nil // PR 99 is not part of any stack
 		},
 	}
 
@@ -243,10 +241,8 @@ func TestCheckout_NumericTarget_NewStack(t *testing.T) {
 
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{
-				{ID: 42, PullRequests: []int{10, 11, 12}},
-			}, nil
+		FindStackForPRFn: func(int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 42, Number: 42, PullRequests: []int{10, 11, 12}}, nil
 		},
 		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
 			prs := map[int]*github.PullRequest{
@@ -331,10 +327,8 @@ func TestCheckout_NumericTarget_BranchExistsNoStack(t *testing.T) {
 
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{
-				{ID: 99, PullRequests: []int{10, 11}},
-			}, nil
+		FindStackForPRFn: func(int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 99, Number: 99, PullRequests: []int{10, 11}}, nil
 		},
 		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
 			prs := map[int]*github.PullRequest{
@@ -445,11 +439,9 @@ func TestCheckout_NumericTarget_LocalMiss_RemoteMatch(t *testing.T) {
 	apiCalled := false
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
+		FindStackForPRFn: func(int) (*github.RemoteStack, error) {
 			apiCalled = true
-			return []github.RemoteStack{
-				{ID: 99, PullRequests: []int{10, 11}},
-			}, nil
+			return &github.RemoteStack{ID: 99, Number: 99, PullRequests: []int{10, 11}}, nil
 		},
 		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
 			prs := map[int]*github.PullRequest{
@@ -464,7 +456,7 @@ func TestCheckout_NumericTarget_LocalMiss_RemoteMatch(t *testing.T) {
 	_ = collectOutput(cfg, outR, errR)
 
 	require.NoError(t, err)
-	assert.True(t, apiCalled, "should have called ListStacks API when local miss")
+	assert.True(t, apiCalled, "should have queried the remote stack API when local miss")
 	assert.Equal(t, "feat-2", checkedOut)
 }
 
@@ -493,8 +485,8 @@ func TestCheckout_NumericTarget_FallbackToBranchName(t *testing.T) {
 
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{}, nil // no remote stacks
+		FindStackForPRFn: func(int) (*github.RemoteStack, error) {
+			return nil, nil // no remote stack contains this PR
 		},
 	}
 
@@ -527,11 +519,9 @@ func TestCheckout_NumericTarget_CompositionMismatch_NonInteractive(t *testing.T)
 
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
+		FindStackForPRFn: func(int) (*github.RemoteStack, error) {
 			// Remote stack has PRs 10, 11, 12 (extra PR added)
-			return []github.RemoteStack{
-				{ID: 42, PullRequests: []int{10, 11, 12}},
-			}, nil
+			return &github.RemoteStack{ID: 42, Number: 42, PullRequests: []int{10, 11, 12}}, nil
 		},
 		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
 			prs := map[int]*github.PullRequest{
@@ -590,10 +580,8 @@ func TestCheckout_NumericTarget_ClosedMergedPR(t *testing.T) {
 
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{
-				{ID: 50, PullRequests: []int{10, 11}},
-			}, nil
+		FindStackForPRFn: func(int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 50, Number: 50, PullRequests: []int{10, 11}}, nil
 		},
 		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
 			prs := map[int]*github.PullRequest{
@@ -662,10 +650,8 @@ func TestCheckout_NumericTarget_MergedBranchDeletedFromRemote(t *testing.T) {
 
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{
-				{ID: 60, PullRequests: []int{10, 11}},
-			}, nil
+		FindStackForPRFn: func(int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 60, Number: 60, PullRequests: []int{10, 11}}, nil
 		},
 		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
 			prs := map[int]*github.PullRequest{
@@ -698,10 +684,8 @@ func TestCheckout_NumericTarget_AllPRsMerged(t *testing.T) {
 
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{
-				{ID: 70, PullRequests: []int{10, 11}},
-			}, nil
+		FindStackForPRFn: func(int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 70, Number: 70, PullRequests: []int{10, 11}}, nil
 		},
 		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
 			prs := map[int]*github.PullRequest{
@@ -732,7 +716,7 @@ func TestCheckout_NumericTarget_APIError(t *testing.T) {
 
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
+		FindStackForPRFn: func(int) (*github.RemoteStack, error) {
 			return nil, fmt.Errorf("network error")
 		},
 	}
@@ -796,8 +780,8 @@ func TestCheckout_NumericTarget_EmptyStacks(t *testing.T) {
 
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{}, nil // no stacks at all
+		FindStackForPRFn: func(int) (*github.RemoteStack, error) {
+			return nil, nil // no stacks at all
 		},
 	}
 
@@ -903,34 +887,6 @@ func TestStackCompositionMatches(t *testing.T) {
 	}
 }
 
-func TestFindRemoteStackForPR(t *testing.T) {
-	mock := &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{
-				{ID: 1, PullRequests: []int{10, 11}},
-				{ID: 2, PullRequests: []int{20, 21, 22}},
-			}, nil
-		},
-	}
-
-	// Found in first stack
-	rs, err := findRemoteStackForPR(mock, 11)
-	require.NoError(t, err)
-	require.NotNil(t, rs)
-	assert.Equal(t, 1, rs.ID)
-
-	// Found in second stack
-	rs, err = findRemoteStackForPR(mock, 21)
-	require.NoError(t, err)
-	require.NotNil(t, rs)
-	assert.Equal(t, 2, rs.ID)
-
-	// Not found
-	rs, err = findRemoteStackForPR(mock, 99)
-	require.NoError(t, err)
-	assert.Nil(t, rs)
-}
-
 func TestCheckout_ByPRURL_Local(t *testing.T) {
 	// When a PR URL resolves to a locally tracked stack, no API call needed
 	gitDir := t.TempDir()
@@ -973,14 +929,14 @@ func TestCheckout_ByPRURL_Remote(t *testing.T) {
 	}
 
 	restore := git.SetOps(&git.MockOps{
-		GitDirFn:        func() (string, error) { return gitDir, nil },
-		CurrentBranchFn: func() (string, error) { return "main", nil },
-		BranchExistsFn:  func(name string) bool { return name == "main" },
-		FetchFn:         func(string) error { return nil },
-		CreateBranchFn:  func(string, string) error { return nil },
+		GitDirFn:              func() (string, error) { return gitDir, nil },
+		CurrentBranchFn:       func() (string, error) { return "main", nil },
+		BranchExistsFn:        func(name string) bool { return name == "main" },
+		FetchFn:               func(string) error { return nil },
+		CreateBranchFn:        func(string, string) error { return nil },
 		SetUpstreamTrackingFn: func(string, string) error { return nil },
-		RevParseFn:      func(string) (string, error) { return "abc123", nil },
-		ResolveRemoteFn: func(string) (string, error) { return "origin", nil },
+		RevParseFn:            func(string) (string, error) { return "abc123", nil },
+		ResolveRemoteFn:       func(string) (string, error) { return "origin", nil },
 		CheckoutBranchFn: func(name string) error {
 			checkedOut = name
 			return nil
@@ -993,10 +949,8 @@ func TestCheckout_ByPRURL_Remote(t *testing.T) {
 
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{
-				{ID: 1, PullRequests: []int{10, 11}},
-			}, nil
+		FindStackForPRFn: func(int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 1, Number: 1, PullRequests: []int{10, 11}}, nil
 		},
 		FindPRByNumberFn: func(n int) (*github.PullRequest, error) {
 			if pr, ok := prDB[n]; ok {

cmd/link.go

@@ -321,7 +321,7 @@ func findExistingPR(cfg *config.Config, client github.ClientOps, arg string) (*r
 func validatePREligibility(cfg *config.Config, found []*resolvedArg, targetStack *github.RemoteStack) error {
 	inTargetStack := make(map[int]bool)
 	if targetStack != nil {
-		for _, n := range targetStack.PullRequests {
+		for _, n := range targetStack.PRNumbers() {
 			inTargetStack[n] = true
 		}
 	}
@@ -366,7 +366,7 @@ func listStacksSafe(cfg *config.Config, client github.ClientOps) ([]github.Remot
 	if err != nil {
 		var httpErr *api.HTTPError
 		if errors.As(err, &httpErr) && httpErr.StatusCode == 404 {
-			warnStacksUnavailableOrPAT(cfg)
+			warnStacksUnavailable(cfg)
 			return nil, ErrStacksUnavailable
 		}
 		cfg.Errorf("failed to list stacks: %v", err)
@@ -392,7 +392,7 @@ func prevalidateStack(cfg *config.Config, matchedStack *github.RemoteStack, know
 	}
 
 	var dropped []int
-	for _, n := range matchedStack.PullRequests {
+	for _, n := range matchedStack.PRNumbers() {
 		if !knownSet[n] {
 			dropped = append(dropped, n)
 		}
@@ -401,7 +401,7 @@ func prevalidateStack(cfg *config.Config, matchedStack *github.RemoteStack, know
 	if len(dropped) > 0 {
 		cfg.Errorf("Cannot update stack: this would remove %s from the stack",
 			formatPRList(dropped))
-		cfg.Printf("Current stack: %s", formatPRList(matchedStack.PullRequests))
+		cfg.Printf("Current stack: %s", formatPRList(matchedStack.PRNumbers()))
 		cfg.Printf("Include all existing PRs in the command to update the stack")
 		return ErrInvalidArgs
 	}
@@ -535,7 +535,7 @@ func findMatchingStack(stacks []github.RemoteStack, prNumbers []int) (*github.Re
 
 	var matched *github.RemoteStack
 	for i := range stacks {
-		for _, n := range stacks[i].PullRequests {
+		for _, n := range stacks[i].PRNumbers() {
 			if prSet[n] {
 				if matched != nil && matched.ID != stacks[i].ID {
 					return nil, fmt.Errorf("PRs belong to multiple stacks — unstack them first, then re-link")
@@ -551,8 +551,7 @@ func findMatchingStack(stacks []github.RemoteStack, prNumbers []int) (*github.Re
 
 // createLink creates a new stack with the given PR numbers.
 func createLink(cfg *config.Config, client github.ClientOps, prNumbers []int) error {
-	_, err := client.CreateStack(prNumbers)
-	if err != nil {
+	if _, err := client.CreateStack(prNumbers); err != nil {
 		var httpErr *api.HTTPError
 		if errors.As(err, &httpErr) {
 			switch httpErr.StatusCode {
@@ -560,7 +559,7 @@ func createLink(cfg *config.Config, client github.ClientOps, prNumbers []int) er
 				cfg.Errorf("Cannot create stack: %s", httpErr.Message)
 				return ErrAPIFailure
 			case 404:
-				warnStacksUnavailableOrPAT(cfg)
+				warnStacksUnavailable(cfg)
 				return ErrStacksUnavailable
 			default:
 				cfg.Errorf("Failed to create stack (HTTP %d): %s", httpErr.StatusCode, httpErr.Message)
@@ -576,10 +575,14 @@ func createLink(cfg *config.Config, client github.ClientOps, prNumbers []int) er
 }
 
 // updateLink updates an existing stack with the given PR numbers.
-// The update is additive-only: it errors if any existing PRs would be removed.
+// The update is additive-only: it errors if any existing PRs would be removed,
+// and (because the add endpoint appends to the top) if the existing PRs are not
+// an ordered prefix of the desired list.
 func updateLink(cfg *config.Config, client github.ClientOps, existing *github.RemoteStack, prNumbers []int) error {
+	current := existing.PRNumbers()
+
 	// Check if the input exactly matches the existing stack.
-	if slicesEqual(existing.PullRequests, prNumbers) {
+	if slicesEqual(current, prNumbers) {
 		cfg.Successf("Stack with %d PRs is already up to date", len(prNumbers))
 		return nil
 	}
@@ -591,7 +594,7 @@ func updateLink(cfg *config.Config, client github.ClientOps, existing *github.Re
 	}
 
 	var dropped []int
-	for _, n := range existing.PullRequests {
+	for _, n := range current {
 		if !newSet[n] {
 			dropped = append(dropped, n)
 		}
@@ -600,13 +603,21 @@ func updateLink(cfg *config.Config, client github.ClientOps, existing *github.Re
 	if len(dropped) > 0 {
 		cfg.Errorf("Cannot update stack: this would remove %s from the stack",
 			formatPRList(dropped))
-		cfg.Printf("Current stack: %s", formatPRList(existing.PullRequests))
+		cfg.Printf("Current stack: %s", formatPRList(current))
 		cfg.Printf("Include all existing PRs in the command to update the stack")
 		return ErrInvalidArgs
 	}
 
-	stackID := strconv.Itoa(existing.ID)
-	if err := client.UpdateStack(stackID, prNumbers); err != nil {
+	// The add endpoint appends to the top of the stack, so the existing PRs
+	// must be an ordered prefix of the desired list.
+	delta, ok := appendDelta(current, prNumbers)
+	if !ok {
+		cfg.Errorf("Cannot update stack: new PRs must be added to the top of the existing stack")
+		cfg.Printf("Current stack: %s", formatPRList(current))
+		return ErrInvalidArgs
+	}
+
+	if _, err := client.AddToStack(existing.Number, delta); err != nil {
 		var httpErr *api.HTTPError
 		if errors.As(err, &httpErr) {
 			switch httpErr.StatusCode {
@@ -642,6 +653,22 @@ func slicesEqual(a, b []int) bool {
 	return true
 }
 
+// appendDelta returns the PR numbers that must be appended to current to reach
+// desired, with ok=true, when current is an exact ordered prefix of desired.
+// When desired diverges from current (a reorder or removal), ok is false. This
+// mirrors the Stacks add endpoint, which only appends to the top of a stack.
+func appendDelta(current, desired []int) (delta []int, ok bool) {
+	if len(current) > len(desired) {
+		return nil, false
+	}
+	for i, n := range current {
+		if desired[i] != n {
+			return nil, false
+		}
+	}
+	return desired[len(current):], true
+}
+
 func formatPRList(numbers []int) string {
 	if len(numbers) == 0 {
 		return ""

cmd/link_test.go

@@ -47,9 +47,9 @@ func TestLink_PRNumbers_CreateNewStack(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			createdPRs = prNumbers
-			return 42, nil
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -69,7 +69,7 @@ func TestLink_PRNumbers_CreateNewStack(t *testing.T) {
 }
 
 func TestLink_PRNumbers_UpdateExistingStack(t *testing.T) {
-	var updatedID string
+	var updatedNumber int
 	var updatedPRs []int
 	cfg, _, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
@@ -83,13 +83,13 @@ func TestLink_PRNumbers_UpdateExistingStack(t *testing.T) {
 		},
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{
-				{ID: 7, PullRequests: []int{10, 20}},
+				{ID: 7, Number: 7, PullRequests: []int{10, 20}},
 			}, nil
 		},
-		UpdateStackFn: func(stackID string, prNumbers []int) error {
-			updatedID = stackID
+		AddToStackFn: func(stackNumber int, prNumbers []int) (*github.RemoteStack, error) {
+			updatedNumber = stackNumber
 			updatedPRs = prNumbers
-			return nil
+			return &github.RemoteStack{ID: 7, Number: stackNumber, PullRequests: []int{10, 20, 30}}, nil
 		},
 	}
 
@@ -104,8 +104,8 @@ func TestLink_PRNumbers_UpdateExistingStack(t *testing.T) {
 	output := string(errOut)
 
 	assert.NoError(t, err)
-	assert.Equal(t, "7", updatedID)
-	assert.Equal(t, []int{10, 20, 30}, updatedPRs)
+	assert.Equal(t, 7, updatedNumber)
+	assert.Equal(t, []int{30}, updatedPRs)
 	assert.Contains(t, output, "Updated stack to 3 PRs")
 }
 
@@ -122,12 +122,12 @@ func TestLink_PRNumbers_ExactMatch_NoOp(t *testing.T) {
 		},
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{
-				{ID: 7, PullRequests: []int{10, 20, 30}},
+				{ID: 7, Number: 7, PullRequests: []int{10, 20, 30}},
 			}, nil
 		},
-		UpdateStackFn: func(string, []int) error {
-			t.Fatal("UpdateStack should not be called for exact match")
-			return nil
+		AddToStackFn: func(int, []int) (*github.RemoteStack, error) {
+			t.Fatal("AddToStack should not be called for exact match")
+			return nil, nil
 		},
 	}
 
@@ -158,7 +158,7 @@ func TestLink_PRNumbers_WouldRemovePRs(t *testing.T) {
 		},
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{
-				{ID: 7, PullRequests: []int{10, 20, 30}},
+				{ID: 7, Number: 7, PullRequests: []int{10, 20, 30}},
 			}, nil
 		},
 	}
@@ -190,8 +190,8 @@ func TestLink_PRNumbers_MultipleStacks(t *testing.T) {
 		},
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{
-				{ID: 1, PullRequests: []int{10, 20}},
-				{ID: 2, PullRequests: []int{30, 40}},
+				{ID: 1, Number: 1, PullRequests: []int{10, 20}},
+				{ID: 2, Number: 2, PullRequests: []int{30, 40}},
 			}, nil
 		},
 	}
@@ -244,7 +244,7 @@ func TestLink_DuplicateArgs(t *testing.T) {
 
 func TestLink_StacksUnavailable(t *testing.T) {
 	cfg, _, errR := config.NewTestConfig()
-	setTestTokenForHost(cfg, "gho_test_oauth_token")
+	setTestRepo(cfg)
 	cfg.GitHubClientOverride = &github.MockClient{
 		FindPRByNumberFn: func(n int) (*github.PullRequest, error) {
 			return &github.PullRequest{Number: n, HeadRefName: "b", BaseRefName: "main"}, nil
@@ -277,8 +277,8 @@ func TestLink_Create422(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
-			return 0, &api.HTTPError{
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 0, Number: 0}, &api.HTTPError{
 				StatusCode: 422,
 				Message:    "Pull requests must form a stack",
 			}
@@ -379,9 +379,9 @@ func TestLink_RejectsQueuedPR(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func([]int) (int, error) {
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
 			t.Fatal("CreateStack should not be called for ineligible PRs")
-			return 0, nil
+			return &github.RemoteStack{ID: 0, Number: 0}, nil
 		},
 	}
 
@@ -419,9 +419,9 @@ func TestLink_RejectsAutoMergeEnabledPR(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func([]int) (int, error) {
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
 			t.Fatal("CreateStack should not be called for ineligible PRs")
-			return 0, nil
+			return &github.RemoteStack{ID: 0, Number: 0}, nil
 		},
 	}
 
@@ -561,7 +561,7 @@ func TestLink_ReportsMultipleIneligiblePRs(t *testing.T) {
 // Regression test to ensure a queued PR that is already a member of
 // the target stack does not block adding new PRs to that same stack.
 func TestLink_AllowsQueuedPRAlreadyInStack(t *testing.T) {
-	var updatedID string
+	var updatedNumber int
 	var updatedPRs []int
 	cfg, _, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
@@ -581,17 +581,17 @@ func TestLink_AllowsQueuedPRAlreadyInStack(t *testing.T) {
 		},
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{
-				{ID: 7, PullRequests: []int{100}},
+				{ID: 7, Number: 7, PullRequests: []int{100}},
 			}, nil
 		},
-		UpdateStackFn: func(stackID string, prNumbers []int) error {
-			updatedID = stackID
+		AddToStackFn: func(stackNumber int, prNumbers []int) (*github.RemoteStack, error) {
+			updatedNumber = stackNumber
 			updatedPRs = prNumbers
-			return nil
+			return &github.RemoteStack{ID: 7, Number: stackNumber, PullRequests: []int{100, 101, 102}}, nil
 		},
-		CreateStackFn: func([]int) (int, error) {
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
 			t.Fatal("CreateStack should not be called when updating an existing stack")
-			return 0, nil
+			return &github.RemoteStack{ID: 0, Number: 0}, nil
 		},
 	}
 
@@ -606,8 +606,8 @@ func TestLink_AllowsQueuedPRAlreadyInStack(t *testing.T) {
 	output := string(errOut)
 
 	require.NoError(t, err)
-	assert.Equal(t, "7", updatedID)
-	assert.Equal(t, []int{100, 101, 102}, updatedPRs)
+	assert.Equal(t, 7, updatedNumber)
+	assert.Equal(t, []int{101, 102}, updatedPRs)
 	assert.NotContains(t, output, "cannot be added to a stack")
 }
 
@@ -633,12 +633,12 @@ func TestLink_AllowsMergedPRAlreadyInStack(t *testing.T) {
 		},
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{
-				{ID: 8, PullRequests: []int{100}},
+				{ID: 8, Number: 8, PullRequests: []int{100}},
 			}, nil
 		},
-		UpdateStackFn: func(_ string, prNumbers []int) error {
+		AddToStackFn: func(stackNumber int, prNumbers []int) (*github.RemoteStack, error) {
 			updatedPRs = prNumbers
-			return nil
+			return &github.RemoteStack{ID: 8, Number: stackNumber, PullRequests: []int{100, 101}}, nil
 		},
 	}
 
@@ -653,7 +653,7 @@ func TestLink_AllowsMergedPRAlreadyInStack(t *testing.T) {
 	output := string(errOut)
 
 	require.NoError(t, err)
-	assert.Equal(t, []int{100, 101}, updatedPRs)
+	assert.Equal(t, []int{101}, updatedPRs)
 	assert.NotContains(t, output, "cannot be added to a stack")
 }
 
@@ -678,12 +678,12 @@ func TestLink_AllowsAutoMergePRAlreadyInStack(t *testing.T) {
 		},
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{
-				{ID: 9, PullRequests: []int{100}},
+				{ID: 9, Number: 9, PullRequests: []int{100}},
 			}, nil
 		},
-		UpdateStackFn: func(_ string, prNumbers []int) error {
+		AddToStackFn: func(stackNumber int, prNumbers []int) (*github.RemoteStack, error) {
 			updatedPRs = prNumbers
-			return nil
+			return &github.RemoteStack{ID: 9, Number: stackNumber, PullRequests: []int{100, 101}}, nil
 		},
 	}
 
@@ -698,7 +698,7 @@ func TestLink_AllowsAutoMergePRAlreadyInStack(t *testing.T) {
 	output := string(errOut)
 
 	require.NoError(t, err)
-	assert.Equal(t, []int{100, 101}, updatedPRs)
+	assert.Equal(t, []int{101}, updatedPRs)
 	assert.NotContains(t, output, "cannot be added to a stack")
 }
 
@@ -724,12 +724,12 @@ func TestLink_RejectsQueuedPRNotInStack_WhenAddingToExistingStack(t *testing.T)
 		},
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{
-				{ID: 7, PullRequests: []int{100}},
+				{ID: 7, Number: 7, PullRequests: []int{100}},
 			}, nil
 		},
-		UpdateStackFn: func(string, []int) error {
-			t.Fatal("UpdateStack should not be called when a new PR is ineligible")
-			return nil
+		AddToStackFn: func(int, []int) (*github.RemoteStack, error) {
+			t.Fatal("AddToStack should not be called when a new PR is ineligible")
+			return nil, nil
 		},
 	}
 
@@ -776,9 +776,9 @@ func TestLink_BranchNames_AllHavePRs(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			stackedPRs = prNumbers
-			return 42, nil
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -840,9 +840,9 @@ func TestLink_BranchNames_CreatesMissingPRs(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			stackedPRs = prNumbers
-			return 42, nil
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -900,8 +900,8 @@ func TestLink_BranchNames_AllNeedPRs(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
-			return 42, nil
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -960,7 +960,7 @@ func TestLink_BranchNames_DefaultDraft(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func([]int) (int, error) { return 1, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 1, Number: 1}, nil },
 	}
 
 	cmd := LinkCmd(cfg)
@@ -1004,7 +1004,7 @@ func TestLink_BranchNames_OpenFlag(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func([]int) (int, error) { return 1, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 1, Number: 1}, nil },
 	}
 
 	cmd := LinkCmd(cfg)
@@ -1062,7 +1062,7 @@ func TestLink_OpenFlag_ConvertsDraftPRs(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func([]int) (int, error) { return 1, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 1, Number: 1}, nil },
 	}
 
 	cmd := LinkCmd(cfg)
@@ -1109,9 +1109,9 @@ func TestLink_MixedArgs_PRNumberAndBranch(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			stackedPRs = prNumbers
-			return 42, nil
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -1161,9 +1161,9 @@ func TestLink_NumericArg_PRNotFound_TreatedAsBranch(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			stackedPRs = prNumbers
-			return 42, nil
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -1227,7 +1227,7 @@ func TestLink_FixesBaseBranches(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func([]int) (int, error) { return 42, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 42, Number: 42}, nil },
 	}
 
 	cmd := LinkCmd(cfg)
@@ -1282,15 +1282,15 @@ func TestLink_UpdateDeletedStack_FallsBackToCreate(t *testing.T) {
 		},
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{
-				{ID: 7, PullRequests: []int{10}},
+				{ID: 7, Number: 7, PullRequests: []int{10}},
 			}, nil
 		},
-		UpdateStackFn: func(string, []int) error {
-			return &api.HTTPError{StatusCode: 404, Message: "Not Found"}
+		AddToStackFn: func(stackNumber int, _ []int) (*github.RemoteStack, error) {
+			return nil, &api.HTTPError{StatusCode: 404, Message: "Not Found"}
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			created = true
-			return 99, nil
+			return &github.RemoteStack{ID: 99, Number: 99}, nil
 		},
 	}
 
@@ -1338,7 +1338,7 @@ func TestLink_PushesBranchesBeforeResolution(t *testing.T) {
 			return &github.PullRequest{Number: n, HeadRefName: fmt.Sprintf("b%d", n), BaseRefName: "main"}, nil
 		},
 		ListStacksFn:  func() ([]github.RemoteStack, error) { return []github.RemoteStack{}, nil },
-		CreateStackFn: func([]int) (int, error) { return 1, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 1, Number: 1}, nil },
 	}
 
 	cmd := LinkCmd(cfg)
@@ -1383,7 +1383,7 @@ func TestLink_RemoteFlag(t *testing.T) {
 			return &github.PullRequest{Number: n, HeadRefName: fmt.Sprintf("b%d", n), BaseRefName: "main"}, nil
 		},
 		ListStacksFn:  func() ([]github.RemoteStack, error) { return []github.RemoteStack{}, nil },
-		CreateStackFn: func([]int) (int, error) { return 1, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 1, Number: 1}, nil },
 	}
 
 	cmd := LinkCmd(cfg)
@@ -1414,7 +1414,7 @@ func TestLink_SkipsPushForPRNumbersOnly(t *testing.T) {
 			return &github.PullRequest{Number: n, HeadRefName: "b", BaseRefName: "main"}, nil
 		},
 		ListStacksFn:  func() ([]github.RemoteStack, error) { return []github.RemoteStack{}, nil },
-		CreateStackFn: func([]int) (int, error) { return 1, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 1, Number: 1}, nil },
 	}
 
 	cmd := LinkCmd(cfg)
@@ -1453,7 +1453,7 @@ func TestLink_PrevalidatesBeforeCreatingPRs(t *testing.T) {
 		},
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{
-				{ID: 7, PullRequests: []int{104, 105, 106}},
+				{ID: 7, Number: 7, PullRequests: []int{104, 105, 106}},
 			}, nil
 		},
 	}
@@ -1636,7 +1636,7 @@ func TestLink_SkipsBaseFix_ForNewlyCreatedPRs(t *testing.T) {
 			}, nil
 		},
 		ListStacksFn:  func() ([]github.RemoteStack, error) { return []github.RemoteStack{}, nil },
-		CreateStackFn: func([]int) (int, error) { return 1, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 1, Number: 1}, nil },
 	}
 
 	cmd := LinkCmd(cfg)
@@ -1687,7 +1687,7 @@ func TestLink_BranchNames_UsesPRTemplate(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func([]int) (int, error) { return 42, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 42, Number: 42}, nil },
 	}
 
 	cmd := LinkCmd(cfg)
@@ -1742,7 +1742,7 @@ func TestLink_IgnoresSymlinkedPRTemplate(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func([]int) (int, error) { return 42, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 42, Number: 42}, nil },
 	}
 
 	cmd := LinkCmd(cfg)
@@ -1795,7 +1795,7 @@ func TestLink_PRNumbers_NoTemplateUsesFooter(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func([]int) (int, error) { return 42, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 42, Number: 42}, nil },
 	}
 
 	cmd := LinkCmd(cfg)
@@ -1828,9 +1828,9 @@ func TestLink_PRURLs_CreateNewStack(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			createdPRs = prNumbers
-			return 42, nil
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -1893,9 +1893,9 @@ func TestLink_MixedURLsAndNumbers(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			createdPRs = prNumbers
-			return 42, nil
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 

cmd/submit.go

@@ -113,16 +113,11 @@ func runSubmit(cfg *config.Config, opts *submitOptions) error {
 		return ErrAPIFailure
 	}
 
-	// Pre-flight: abort early if the user is authenticating with a PAT.
-	if cfg.WarnIfPAT() {
-		return ErrStacksUnavailable
-	}
-
 	// Verify that the repository has stacked PRs enabled.
 	stacksAvailable := s.ID != ""
 	if !stacksAvailable {
 		if _, err := client.ListStacks(); err != nil {
-			warnStacksUnavailableOrPAT(cfg)
+			warnStacksUnavailable(cfg)
 			if cfg.IsInteractive() {
 				p := prompter.New(cfg.In, cfg.Out, cfg.Err)
 				proceed, promptErr := p.Confirm("Would you still like to create regular PRs?", false)
@@ -609,7 +604,7 @@ func remoteStackPRs(client github.ClientOps, stackID string) []int {
 	}
 	for _, rs := range stacks {
 		if strconv.Itoa(rs.ID) == stackID {
-			return rs.PullRequests
+			return rs.PRNumbers()
 		}
 	}
 	return nil
@@ -661,7 +656,15 @@ func handlePendingModify(cfg *config.Config, client github.ClientOps, s *stack.S
 
 	// Delete the old remote stack
 	if state.PriorRemoteStackID != "" {
-		if err := client.DeleteStack(state.PriorRemoteStackID); err != nil {
+		number, found, lookupErr := stackNumberByID(client, state.PriorRemoteStackID)
+		if lookupErr != nil {
+			cfg.Warningf("Failed to look up existing stack: %v", lookupErr)
+			cfg.Printf("Run `%s` again to retry", cfg.ColorCyan("gh stack submit"))
+			return lookupErr
+		}
+		if !found {
+			cfg.Printf("Previous stack already deleted on GitHub")
+		} else if _, _, err := client.Unstack(number); err != nil {
 			var httpErr *api.HTTPError
 			if errors.As(err, &httpErr) && httpErr.StatusCode == 404 {
 				cfg.Printf("Previous stack already deleted on GitHub")
@@ -675,6 +678,7 @@ func handlePendingModify(cfg *config.Config, client github.ClientOps, s *stack.S
 		}
 		// Clear the old stack ID so syncStack creates a new one
 		s.ID = ""
+		s.Number = 0
 	}
 
 	return nil
@@ -761,7 +765,7 @@ func reconcileUntrackedStack(cfg *config.Config, client github.ClientOps, s *sta
 
 	// A remote stack already contains some of our PRs. Refuse to silently drop
 	// any PRs it holds that we aren't tracking locally; let the user reconcile.
-	if dropped := prsMissingFrom(matched.PullRequests, prNumbers); len(dropped) > 0 {
+	if dropped := prsMissingFrom(matched.PRNumbers(), prNumbers); len(dropped) > 0 {
 		cfg.Warningf("A stack on GitHub already contains %s, which %s not in your local stack",
 			formatPRList(dropped), plural(len(dropped), "is", "are"))
 		cfg.Printf("  Run `%s` to import the full stack",
@@ -773,8 +777,9 @@ func reconcileUntrackedStack(cfg *config.Config, client github.ClientOps, s *sta
 	// more on top). Adopt the remote stack ID — recording it locally — and
 	// update the stack with our full, ordered PR list to append any new PRs.
 	s.ID = strconv.Itoa(matched.ID)
+	s.Number = matched.Number
 
-	if slicesEqual(matched.PullRequests, prNumbers) {
+	if slicesEqual(matched.PRNumbers(), prNumbers) {
 		cfg.Successf("Linked to the existing stack on GitHub (%d PRs, already up to date)", len(prNumbers))
 		return true
 	}
@@ -799,12 +804,57 @@ func prsMissingFrom(remote, local []int) []int {
 	return missing
 }
 
-// updateStack calls the PUT endpoint to sync the full PR list for an existing stack.
-// If the remote stack was deleted (404), it clears the local ID and falls through
-// to createNewStack so the user doesn't need to re-run the command.
-// Returns true when the remote stack was updated (or recreated) successfully.
+// updateStack brings the remote stack in line with the local PR list by
+// appending any new PRs via the add endpoint. It reads the current remote stack
+// to compute the delta; when the desired list isn't a clean append onto the
+// remote stack (a reorder or a removal, e.g. merged PRs leaving the stack) it
+// leaves the remote stack untouched. If the remote stack is gone (404) it
+// clears the local ID and re-creates it. Returns true when the remote stack
+// reflects the local stack (updated, already in sync, or recreated).
 func updateStack(cfg *config.Config, client github.ClientOps, s *stack.Stack, prNumbers []int) bool {
-	if err := client.UpdateStack(s.ID, prNumbers); err != nil {
+	number, err := ensureStackNumber(client, s)
+	if err != nil || number == 0 {
+		// Can't resolve the remote stack — treat as missing and (re)create.
+		s.ID = ""
+		s.Number = 0
+		return createNewStack(cfg, client, s, prNumbers)
+	}
+
+	remote, err := client.GetStack(number)
+	if err != nil {
+		var httpErr *api.HTTPError
+		if errors.As(err, &httpErr) && httpErr.StatusCode == 404 {
+			s.ID = ""
+			s.Number = 0
+			return createNewStack(cfg, client, s, prNumbers)
+		}
+		cfg.Warningf("Failed to read stack on GitHub: %v", err)
+		return false
+	}
+
+	current := remote.PRNumbers()
+	if slicesEqual(current, prNumbers) {
+		s.ID = strconv.Itoa(remote.ID)
+		s.Number = remote.Number
+		cfg.Successf("Stack on GitHub is up to date with %d PRs", len(prNumbers))
+		return true
+	}
+
+	delta, isAppend := appendDelta(current, prNumbers)
+	if !isAppend || len(delta) == 0 {
+		// The desired list isn't a clean append onto the remote stack — the add
+		// endpoint can't express a reorder or removal. This is expected once
+		// part of the stack has landed and merged PRs have left the stack.
+		if len(s.MergedBranches()) > 0 {
+			cfg.Infof("Merged PRs have left the stack on GitHub, so it wasn't updated — your unmerged PRs were pushed and re-based onto the trunk")
+		} else {
+			cfg.Warningf("The stack on GitHub differs from your local stack and couldn't be updated automatically")
+		}
+		return false
+	}
+
+	rs, err := client.AddToStack(number, delta)
+	if err != nil {
 		var httpErr *api.HTTPError
 		if errors.As(err, &httpErr) {
 			switch httpErr.StatusCode {
@@ -812,6 +862,7 @@ func updateStack(cfg *config.Config, client github.ClientOps, s *stack.Stack, pr
 				// Stack was deleted on GitHub — clear the stale ID and
 				// immediately try to re-create it.
 				s.ID = ""
+				s.Number = 0
 				return createNewStack(cfg, client, s, prNumbers)
 			case 422:
 				// A merged branch whose ref has been deleted upstream breaks the
@@ -832,6 +883,9 @@ func updateStack(cfg *config.Config, client github.ClientOps, s *stack.Stack, pr
 		}
 		return false
 	}
+
+	s.ID = strconv.Itoa(rs.ID)
+	s.Number = rs.Number
 	cfg.Successf("Stack updated on GitHub with %d PRs", len(prNumbers))
 	return true
 }
@@ -840,9 +894,10 @@ func updateStack(cfg *config.Config, client github.ClientOps, s *stack.Stack, pr
 // three types of 422 errors the API may return.
 // Returns true when the stack was created or is confirmed already in sync.
 func createNewStack(cfg *config.Config, client github.ClientOps, s *stack.Stack, prNumbers []int) bool {
-	stackID, err := client.CreateStack(prNumbers)
+	rs, err := client.CreateStack(prNumbers)
 	if err == nil {
-		s.ID = strconv.Itoa(stackID)
+		s.ID = strconv.Itoa(rs.ID)
+		s.Number = rs.Number
 		cfg.Successf("Stack created on GitHub with %d PRs", len(prNumbers))
 		return true
 	}
@@ -857,7 +912,7 @@ func createNewStack(cfg *config.Config, client github.ClientOps, s *stack.Stack,
 	case 422:
 		return handleCreate422(cfg, httpErr, prNumbers)
 	case 404:
-		warnStacksUnavailableOrPAT(cfg)
+		warnStacksUnavailable(cfg)
 		return false
 	default:
 		cfg.Warningf("Failed to create stack on GitHub: %s", httpErr.Message)

cmd/submit_test.go

@@ -134,8 +134,8 @@ func TestSubmit_CreatesPRsAndStack(t *testing.T) {
 				URL:    fmt.Sprintf("https://github.com/owner/repo/pull/%d", prCounter),
 			}, nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
-			return 42, nil
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -194,7 +194,7 @@ func TestSubmit_DefaultDraft(t *testing.T) {
 			createdDraft = draft
 			return &github.PullRequest{Number: 1, ID: "PR_1", URL: "https://github.com/o/r/pull/1"}, nil
 		},
-		CreateStackFn: func([]int) (int, error) { return 1, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 1, Number: 1}, nil },
 	}
 
 	cmd := SubmitCmd(cfg)
@@ -236,7 +236,7 @@ func TestSubmit_OpenFlag(t *testing.T) {
 			createdDraft = draft
 			return &github.PullRequest{Number: 1, ID: "PR_1", URL: "https://github.com/o/r/pull/1"}, nil
 		},
-		CreateStackFn: func([]int) (int, error) { return 1, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 1, Number: 1}, nil },
 	}
 
 	cmd := SubmitCmd(cfg)
@@ -293,7 +293,7 @@ func TestSubmit_OpenFlag_ConvertsDraftPRs(t *testing.T) {
 			markedReady = append(markedReady, prID)
 			return nil
 		},
-		CreateStackFn: func([]int) (int, error) { return 1, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 1, Number: 1}, nil },
 	}
 
 	cmd := SubmitCmd(cfg)
@@ -412,8 +412,9 @@ func TestSubmit_ForksWhenRemoteStackFullyMerged(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			s := stack.Stack{
-				ID:    "42",
-				Trunk: stack.BranchRef{Branch: "main"},
+				ID:     "42",
+				Number: 42,
+				Trunk:  stack.BranchRef{Branch: "main"},
 				Branches: []stack.BranchRef{
 					{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 1, Merged: true}},
 					{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 2, Merged: true}},
@@ -469,9 +470,9 @@ func TestSubmit_ForksWhenRemoteStackFullyMerged(t *testing.T) {
 						HeadRefName: head,
 					}, nil
 				},
-				CreateStackFn: func(prNumbers []int) (int, error) {
+				CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 					createStackPRs = prNumbers
-					return 99, nil
+					return &github.RemoteStack{ID: 99, Number: 99}, nil
 				},
 			}
 
@@ -562,7 +563,7 @@ func TestSubmit_NoForkWhenRemoteStackHasOpenPR(t *testing.T) {
 	cfg, _, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
 		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{{ID: 42, PullRequests: []int{1, 2, 3}}}, nil
+			return []github.RemoteStack{{ID: 42, Number: 42, PullRequests: []int{1, 2, 3}}}, nil
 		},
 		FindPRByNumberFn: func(n int) (*github.PullRequest, error) {
 			switch n {
@@ -585,12 +586,15 @@ func TestSubmit_NoForkWhenRemoteStackHasOpenPR(t *testing.T) {
 				HeadRefName: head,
 			}, nil
 		},
-		UpdateStackFn: func(string, []int) error {
+		GetStackFn: func(int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 42, Number: 42, PullRequests: []int{1, 2, 3}}, nil
+		},
+		AddToStackFn: func(int, []int) (*github.RemoteStack, error) {
 			// Merged-and-deleted base branches break the chain on GitHub.
-			return &api.HTTPError{
+			return nil, &api.HTTPError{
 				StatusCode: 422,
 				Message:    "Pull requests must form a stack, where each PR's base ref is the previous PR's head ref",
-				RequestURL: &url.URL{Path: "/repos/o/r/cli_internal/pulls/stacks/42"},
+				RequestURL: &url.URL{Path: "/repos/o/r/stacks/42/add"},
 			}
 		},
 	}
@@ -627,21 +631,27 @@ func TestUpdateStack_BrokenChainAfterMerge(t *testing.T) {
 		return &api.HTTPError{
 			StatusCode: 422,
 			Message:    "Pull requests must form a stack, where each PR's base ref is the previous PR's head ref",
-			RequestURL: &url.URL{Path: "/repos/o/r/cli_internal/pulls/stacks/42"},
+			RequestURL: &url.URL{Path: "/repos/o/r/stacks/42/add"},
 		}
 	}
 
 	t.Run("merged branches present is reported calmly", func(t *testing.T) {
 		s := &stack.Stack{
-			ID:    "42",
-			Trunk: stack.BranchRef{Branch: "main"},
+			ID:     "42",
+			Number: 42,
+			Trunk:  stack.BranchRef{Branch: "main"},
 			Branches: []stack.BranchRef{
 				{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 1, Merged: true}},
 				{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 2}},
 				{Branch: "b3", PullRequest: &stack.PullRequestRef{Number: 3}},
 			},
 		}
-		mock := &github.MockClient{UpdateStackFn: func(string, []int) error { return mustFormErr() }}
+		mock := &github.MockClient{
+			GetStackFn: func(int) (*github.RemoteStack, error) {
+				return &github.RemoteStack{ID: 42, Number: 42, PullRequests: []int{1, 2}}, nil
+			},
+			AddToStackFn: func(int, []int) (*github.RemoteStack, error) { return nil, mustFormErr() },
+		}
 		cfg, _, errR := config.NewTestConfig()
 		updateStack(cfg, mock, s, []int{1, 2, 3})
 		cfg.Err.Close()
@@ -653,14 +663,20 @@ func TestUpdateStack_BrokenChainAfterMerge(t *testing.T) {
 
 	t.Run("no merged branches still warns", func(t *testing.T) {
 		s := &stack.Stack{
-			ID:    "42",
-			Trunk: stack.BranchRef{Branch: "main"},
+			ID:     "42",
+			Number: 42,
+			Trunk:  stack.BranchRef{Branch: "main"},
 			Branches: []stack.BranchRef{
 				{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 1}},
 				{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 2}},
 			},
 		}
-		mock := &github.MockClient{UpdateStackFn: func(string, []int) error { return mustFormErr() }}
+		mock := &github.MockClient{
+			GetStackFn: func(int) (*github.RemoteStack, error) {
+				return &github.RemoteStack{ID: 42, Number: 42, PullRequests: []int{1}}, nil
+			},
+			AddToStackFn: func(int, []int) (*github.RemoteStack, error) { return nil, mustFormErr() },
+		}
 		cfg, _, errR := config.NewTestConfig()
 		updateStack(cfg, mock, s, []int{1, 2})
 		cfg.Err.Close()
@@ -731,9 +747,9 @@ func TestSyncStack_NewStack_CreateSuccess(t *testing.T) {
 
 	var gotNumbers []int
 	mock := &github.MockClient{
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			gotNumbers = prNumbers
-			return 42, nil
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -751,8 +767,9 @@ func TestSyncStack_NewStack_CreateSuccess(t *testing.T) {
 
 func TestSyncStack_ExistingStack_UpdateSuccess(t *testing.T) {
 	s := &stack.Stack{
-		ID:    "99",
-		Trunk: stack.BranchRef{Branch: "main"},
+		ID:     "99",
+		Number: 99,
+		Trunk:  stack.BranchRef{Branch: "main"},
 		Branches: []stack.BranchRef{
 			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 10}},
 			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 11}},
@@ -760,18 +777,21 @@ func TestSyncStack_ExistingStack_UpdateSuccess(t *testing.T) {
 		},
 	}
 
-	var gotStackID string
+	var gotStackNumber int
 	var gotNumbers []int
 	createCalled := false
 	mock := &github.MockClient{
-		CreateStackFn: func([]int) (int, error) {
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
 			createCalled = true
-			return 0, nil
+			return &github.RemoteStack{ID: 0, Number: 0}, nil
 		},
-		UpdateStackFn: func(stackID string, prNumbers []int) error {
-			gotStackID = stackID
+		GetStackFn: func(stackNumber int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: stackNumber, Number: stackNumber, PullRequests: []int{10, 11}}, nil
+		},
+		AddToStackFn: func(stackNumber int, prNumbers []int) (*github.RemoteStack, error) {
+			gotStackNumber = stackNumber
 			gotNumbers = prNumbers
-			return nil
+			return &github.RemoteStack{ID: 99, Number: 99, PullRequests: []int{10, 11, 12}}, nil
 		},
 	}
 
@@ -783,15 +803,16 @@ func TestSyncStack_ExistingStack_UpdateSuccess(t *testing.T) {
 	output := string(errOut)
 
 	assert.False(t, createCalled, "CreateStack should not be called when s.ID is set")
-	assert.Equal(t, "99", gotStackID)
-	assert.Equal(t, []int{10, 11, 12}, gotNumbers)
+	assert.Equal(t, 99, gotStackNumber)
+	assert.Equal(t, []int{12}, gotNumbers)
 	assert.Contains(t, output, "Stack updated on GitHub with 3 PRs")
 }
 
 func TestSyncStack_ExistingStack_UpdateFails(t *testing.T) {
 	s := &stack.Stack{
-		ID:    "99",
-		Trunk: stack.BranchRef{Branch: "main"},
+		ID:     "99",
+		Number: 99,
+		Trunk:  stack.BranchRef{Branch: "main"},
 		Branches: []stack.BranchRef{
 			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 10}},
 			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 11}},
@@ -799,11 +820,14 @@ func TestSyncStack_ExistingStack_UpdateFails(t *testing.T) {
 	}
 
 	mock := &github.MockClient{
-		UpdateStackFn: func(string, []int) error {
-			return &api.HTTPError{
+		GetStackFn: func(int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 99, Number: 99, PullRequests: []int{10}}, nil
+		},
+		AddToStackFn: func(int, []int) (*github.RemoteStack, error) {
+			return nil, &api.HTTPError{
 				StatusCode: 422,
 				Message:    "Validation failed",
-				RequestURL: &url.URL{Path: "/repos/o/r/cli_internal/pulls/stacks/99"},
+				RequestURL: &url.URL{Path: "/repos/o/r/stacks/99/add"},
 			}
 		},
 	}
@@ -820,8 +844,9 @@ func TestSyncStack_ExistingStack_UpdateFails(t *testing.T) {
 
 func TestSyncStack_ExistingStack_Update404(t *testing.T) {
 	s := &stack.Stack{
-		ID:    "99",
-		Trunk: stack.BranchRef{Branch: "main"},
+		ID:     "99",
+		Number: 99,
+		Trunk:  stack.BranchRef{Branch: "main"},
 		Branches: []stack.BranchRef{
 			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 10}},
 			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 11}},
@@ -830,16 +855,19 @@ func TestSyncStack_ExistingStack_Update404(t *testing.T) {
 
 	var createCalled bool
 	mock := &github.MockClient{
-		UpdateStackFn: func(string, []int) error {
-			return &api.HTTPError{
+		GetStackFn: func(int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 99, Number: 99, PullRequests: []int{10}}, nil
+		},
+		AddToStackFn: func(int, []int) (*github.RemoteStack, error) {
+			return nil, &api.HTTPError{
 				StatusCode: 404,
 				Message:    "Not Found",
-				RequestURL: &url.URL{Path: "/repos/o/r/cli_internal/pulls/stacks/99"},
+				RequestURL: &url.URL{Path: "/repos/o/r/stacks/99/add"},
 			}
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			createCalled = true
-			return 55, nil
+			return &github.RemoteStack{ID: 55, Number: 55}, nil
 		},
 	}
 
@@ -866,11 +894,11 @@ func TestSyncStack_AlreadyStacked_OurStack(t *testing.T) {
 	}
 
 	mock := &github.MockClient{
-		CreateStackFn: func([]int) (int, error) {
-			return 0, &api.HTTPError{
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
+			return nil, &api.HTTPError{
 				StatusCode: 422,
 				Message:    "Pull requests #10, #11 are already stacked",
-				RequestURL: &url.URL{Path: "/repos/o/r/cli_internal/pulls/stacks"},
+				RequestURL: &url.URL{Path: "/repos/o/r/stacks"},
 			}
 		},
 	}
@@ -898,11 +926,11 @@ func TestSyncStack_AlreadyStacked_DifferentStack(t *testing.T) {
 	}
 
 	mock := &github.MockClient{
-		CreateStackFn: func([]int) (int, error) {
-			return 0, &api.HTTPError{
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
+			return nil, &api.HTTPError{
 				StatusCode: 422,
 				Message:    "Pull requests #10, #11 are already stacked",
-				RequestURL: &url.URL{Path: "/repos/o/r/cli_internal/pulls/stacks"},
+				RequestURL: &url.URL{Path: "/repos/o/r/stacks"},
 			}
 		},
 	}
@@ -933,15 +961,15 @@ func TestSyncStack_AdoptsExistingRemoteStack_ExactMatch(t *testing.T) {
 	var createCalled, updateCalled bool
 	mock := &github.MockClient{
 		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{{ID: 77, PullRequests: []int{10, 11}}}, nil
+			return []github.RemoteStack{{ID: 77, Number: 77, PullRequests: []int{10, 11}}}, nil
 		},
-		CreateStackFn: func([]int) (int, error) {
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
 			createCalled = true
-			return 0, nil
+			return &github.RemoteStack{ID: 0, Number: 0}, nil
 		},
-		UpdateStackFn: func(string, []int) error {
+		AddToStackFn: func(int, []int) (*github.RemoteStack, error) {
 			updateCalled = true
-			return nil
+			return &github.RemoteStack{ID: 77, Number: 77, PullRequests: []int{10, 11}}, nil
 		},
 	}
 
@@ -973,20 +1001,23 @@ func TestSyncStack_AdoptsExistingRemoteStack_AddsNewPR(t *testing.T) {
 	}
 
 	var createCalled bool
-	var gotStackID string
+	var gotStackNumber int
 	var gotNumbers []int
 	mock := &github.MockClient{
 		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{{ID: 77, PullRequests: []int{10, 11}}}, nil
+			return []github.RemoteStack{{ID: 77, Number: 77, PullRequests: []int{10, 11}}}, nil
 		},
-		CreateStackFn: func([]int) (int, error) {
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
 			createCalled = true
-			return 0, nil
+			return &github.RemoteStack{ID: 0, Number: 0}, nil
 		},
-		UpdateStackFn: func(stackID string, prNumbers []int) error {
-			gotStackID = stackID
+		GetStackFn: func(stackNumber int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 77, Number: stackNumber, PullRequests: []int{10, 11}}, nil
+		},
+		AddToStackFn: func(stackNumber int, prNumbers []int) (*github.RemoteStack, error) {
+			gotStackNumber = stackNumber
 			gotNumbers = prNumbers
-			return nil
+			return &github.RemoteStack{ID: 77, Number: 77, PullRequests: []int{10, 11, 12}}, nil
 		},
 	}
 
@@ -999,8 +1030,8 @@ func TestSyncStack_AdoptsExistingRemoteStack_AddsNewPR(t *testing.T) {
 
 	assert.False(t, createCalled, "should adopt and update, not create")
 	assert.Equal(t, "77", s.ID, "should adopt the remote stack ID")
-	assert.Equal(t, "77", gotStackID, "should update the adopted stack")
-	assert.Equal(t, []int{10, 11, 12}, gotNumbers, "should send the full local PR list")
+	assert.Equal(t, 77, gotStackNumber, "should update the adopted stack")
+	assert.Equal(t, []int{12}, gotNumbers, "should send only the new PR delta")
 	assert.Contains(t, output, "Stack updated on GitHub with 3 PRs")
 }
 
@@ -1018,15 +1049,15 @@ func TestSyncStack_RemoteStackHasExtraPRs_Refuses(t *testing.T) {
 	var createCalled, updateCalled bool
 	mock := &github.MockClient{
 		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{{ID: 77, PullRequests: []int{10, 11, 12}}}, nil
+			return []github.RemoteStack{{ID: 77, Number: 77, PullRequests: []int{10, 11, 12}}}, nil
 		},
-		CreateStackFn: func([]int) (int, error) {
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
 			createCalled = true
-			return 0, nil
+			return &github.RemoteStack{ID: 0, Number: 0}, nil
 		},
-		UpdateStackFn: func(string, []int) error {
+		AddToStackFn: func(int, []int) (*github.RemoteStack, error) {
 			updateCalled = true
-			return nil
+			return &github.RemoteStack{ID: 77, Number: 77, PullRequests: []int{10, 11, 12}}, nil
 		},
 	}
 
@@ -1058,17 +1089,17 @@ func TestSyncStack_PRsSpanMultipleRemoteStacks_Warns(t *testing.T) {
 	mock := &github.MockClient{
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{
-				{ID: 1, PullRequests: []int{10}},
-				{ID: 2, PullRequests: []int{11}},
+				{ID: 1, Number: 1, PullRequests: []int{10}},
+				{ID: 2, Number: 2, PullRequests: []int{11}},
 			}, nil
 		},
-		CreateStackFn: func([]int) (int, error) {
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
 			createCalled = true
-			return 0, nil
+			return &github.RemoteStack{ID: 0, Number: 0}, nil
 		},
-		UpdateStackFn: func(string, []int) error {
+		AddToStackFn: func(int, []int) (*github.RemoteStack, error) {
 			updateCalled = true
-			return nil
+			return &github.RemoteStack{ID: 1, Number: 1}, nil
 		},
 	}
 
@@ -1101,9 +1132,9 @@ func TestSyncStack_ListStacksError_FallsThroughToCreate(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return nil, fmt.Errorf("network down")
 		},
-		CreateStackFn: func([]int) (int, error) {
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
 			createCalled = true
-			return 88, nil
+			return &github.RemoteStack{ID: 88, Number: 88}, nil
 		},
 	}
 
@@ -1134,11 +1165,11 @@ func TestSyncStack_AlreadyPartOfAStack_FallbackPhrasing(t *testing.T) {
 
 	mock := &github.MockClient{
 		ListStacksFn: func() ([]github.RemoteStack, error) { return nil, nil },
-		CreateStackFn: func([]int) (int, error) {
-			return 0, &api.HTTPError{
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
+			return nil, &api.HTTPError{
 				StatusCode: 422,
 				Message:    "Pull requests are already part of a stack",
-				RequestURL: &url.URL{Path: "/repos/o/r/cli_internal/pulls/stacks"},
+				RequestURL: &url.URL{Path: "/repos/o/r/stacks"},
 			}
 		},
 	}
@@ -1165,11 +1196,11 @@ func TestSyncStack_InvalidChain_422(t *testing.T) {
 	}
 
 	mock := &github.MockClient{
-		CreateStackFn: func([]int) (int, error) {
-			return 0, &api.HTTPError{
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
+			return nil, &api.HTTPError{
 				StatusCode: 422,
 				Message:    "Pull requests must form a stack, where each PR's base ref is the previous PR's head ref",
-				RequestURL: &url.URL{Path: "/repos/o/r/cli_internal/pulls/stacks"},
+				RequestURL: &url.URL{Path: "/repos/o/r/stacks"},
 			}
 		},
 	}
@@ -1195,11 +1226,11 @@ func TestSyncStack_NotAvailable(t *testing.T) {
 	}
 
 	mock := &github.MockClient{
-		CreateStackFn: func([]int) (int, error) {
-			return 0, &api.HTTPError{
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
+			return nil, &api.HTTPError{
 				StatusCode: 404,
 				Message:    "Not Found",
-				RequestURL: &url.URL{Path: "/repos/o/r/cli_internal/pulls/stacks"},
+				RequestURL: &url.URL{Path: "/repos/o/r/stacks"},
 			}
 		},
 	}
@@ -1225,13 +1256,13 @@ func TestSyncStack_SkippedForSinglePR(t *testing.T) {
 	createCalled := false
 	updateCalled := false
 	mock := &github.MockClient{
-		CreateStackFn: func([]int) (int, error) {
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
 			createCalled = true
-			return 42, nil
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
-		UpdateStackFn: func(string, []int) error {
+		AddToStackFn: func(int, []int) (*github.RemoteStack, error) {
 			updateCalled = true
-			return nil
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -1255,9 +1286,9 @@ func TestSyncStack_IncludesMergedBranches(t *testing.T) {
 
 	var gotNumbers []int
 	mock := &github.MockClient{
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			gotNumbers = prNumbers
-			return 42, nil
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -1280,9 +1311,9 @@ func TestSyncStack_SkipsBranchesWithoutPR(t *testing.T) {
 
 	var gotNumbers []int
 	mock := &github.MockClient{
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			gotNumbers = prNumbers
-			return 42, nil
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -1343,8 +1374,8 @@ func TestSubmit_UpdatesBaseBranch(t *testing.T) {
 			}{number, base})
 			return nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
-			return 42, nil
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -1370,8 +1401,9 @@ func TestSubmit_UpdatesBaseBranch(t *testing.T) {
 func TestSubmit_SkipsBaseUpdateWhenStacked(t *testing.T) {
 	// Stack already exists (s.ID is set), so base updates should be skipped.
 	s := stack.Stack{
-		ID:    "99",
-		Trunk: stack.BranchRef{Branch: "main"},
+		ID:     "99",
+		Number: 99,
+		Trunk:  stack.BranchRef{Branch: "main"},
 		Branches: []stack.BranchRef{
 			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 10}},
 			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 11}},
@@ -1410,8 +1442,11 @@ func TestSubmit_SkipsBaseUpdateWhenStacked(t *testing.T) {
 			updateCalled = true
 			return nil
 		},
-		UpdateStackFn: func(stackID string, prNumbers []int) error {
-			return nil
+		GetStackFn: func(int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 99, Number: 99, PullRequests: []int{10, 11}}, nil
+		},
+		AddToStackFn: func(int, []int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 99, Number: 99, PullRequests: []int{10, 11}}, nil
 		},
 	}
 
@@ -1494,8 +1529,8 @@ func TestSubmit_CreatesMissingPRsAndUpdatesExisting(t *testing.T) {
 			}{number, base})
 			return nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
-			return 42, nil
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -1555,9 +1590,7 @@ func TestSubmit_PreflightCheck_404_BailsOut(t *testing.T) {
 		},
 	}
 
-	// Use an OAuth token so the PAT pre-flight check passes and we
-	// exercise the ListStacks 404 path.
-	setTestTokenForHost(cfg, "gho_test_oauth_token")
+	setTestRepo(cfg)
 
 	cmd := SubmitCmd(cfg)
 	cmd.SetArgs([]string{"--auto"})
@@ -1610,9 +1643,7 @@ func TestSubmit_PreflightCheck_404_Interactive_UserDeclinesAborts(t *testing.T)
 		},
 	}
 
-	// Use an OAuth token so the PAT pre-flight check passes and we
-	// exercise the ListStacks 404 path.
-	setTestTokenForHost(cfg, "gho_test_oauth_token")
+	setTestRepo(cfg)
 
 	cmd := SubmitCmd(cfg)
 	cmd.SetArgs([]string{"--auto"})
@@ -1642,9 +1673,9 @@ func TestSyncStack_SkippedWhenStacksUnavailable(t *testing.T) {
 
 	createCalled := false
 	mock := &github.MockClient{
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			createCalled = true
-			return 42, nil
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -1699,7 +1730,7 @@ func TestSubmit_PreflightCheck_EmptyList_Proceeds(t *testing.T) {
 		CreatePRFn: func(base, head, title, body string, draft bool) (*github.PullRequest, error) {
 			return &github.PullRequest{Number: 1, ID: "PR_1", URL: "https://github.com/o/r/pull/1"}, nil
 		},
-		CreateStackFn: func([]int) (int, error) { return 99, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 99, Number: 99}, nil },
 	}
 
 	cmd := SubmitCmd(cfg)
@@ -1717,8 +1748,9 @@ func TestSubmit_PreflightCheck_EmptyList_Proceeds(t *testing.T) {
 
 func TestSubmit_PreflightCheck_SkippedWhenStackIDSet(t *testing.T) {
 	s := stack.Stack{
-		ID:    "42", // Existing stack — pre-flight check should be skipped.
-		Trunk: stack.BranchRef{Branch: "main"},
+		ID:     "42", // Existing stack — pre-flight check should be skipped.
+		Number: 42,
+		Trunk:  stack.BranchRef{Branch: "main"},
 		Branches: []stack.BranchRef{
 			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 10}},
 			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 11}},
@@ -1738,7 +1770,7 @@ func TestSubmit_PreflightCheck_SkippedWhenStackIDSet(t *testing.T) {
 	cfg.GitHubClientOverride = &github.MockClient{
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			listStacksCallCount++
-			return []github.RemoteStack{{ID: 42, PullRequests: []int{10, 11}}}, nil
+			return []github.RemoteStack{{ID: 42, Number: 42, PullRequests: []int{10, 11}}}, nil
 		},
 		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
 			switch number {
@@ -1752,7 +1784,12 @@ func TestSubmit_PreflightCheck_SkippedWhenStackIDSet(t *testing.T) {
 		FindPRForBranchFn: func(string) (*github.PullRequest, error) {
 			return &github.PullRequest{Number: 10, URL: "https://github.com/o/r/pull/10"}, nil
 		},
-		UpdateStackFn: func(string, []int) error { return nil },
+		GetStackFn: func(int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 42, Number: 42, PullRequests: []int{10}}, nil
+		},
+		AddToStackFn: func(int, []int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 42, Number: 42, PullRequests: []int{10, 11}}, nil
+		},
 	}
 
 	cmd := SubmitCmd(cfg)
@@ -1790,15 +1827,18 @@ func newPendingSubmitState(priorStackID string) *modify.StateFile {
 func TestHandlePendingModify_DeletesOldStack(t *testing.T) {
 	gitDir := t.TempDir()
 
-	saveModifyState(t, gitDir, newPendingSubmitState("stack-123"))
+	saveModifyState(t, gitDir, newPendingSubmitState("123"))
 
-	s := &stack.Stack{ID: "stack-123", Trunk: stack.BranchRef{Branch: "main"}}
+	s := &stack.Stack{ID: "123", Number: 42, Trunk: stack.BranchRef{Branch: "main"}}
 
-	var deletedStackID string
+	var unstackedNumber int
 	client := &github.MockClient{
-		DeleteStackFn: func(id string) error {
-			deletedStackID = id
-			return nil
+		ListStacksFn: func() ([]github.RemoteStack, error) {
+			return []github.RemoteStack{{ID: 123, Number: 42}}, nil
+		},
+		UnstackFn: func(number int) (*github.RemoteStack, bool, error) {
+			unstackedNumber = number
+			return nil, true, nil
 		},
 	}
 
@@ -1808,7 +1848,7 @@ func TestHandlePendingModify_DeletesOldStack(t *testing.T) {
 
 	err := handlePendingModify(cfg, client, s, gitDir)
 	require.NoError(t, err)
-	assert.Equal(t, "stack-123", deletedStackID)
+	assert.Equal(t, 42, unstackedNumber)
 	assert.Equal(t, "", s.ID)
 }
 
@@ -1820,9 +1860,9 @@ func TestHandlePendingModify_NoStateFile(t *testing.T) {
 
 	deleteCalled := false
 	client := &github.MockClient{
-		DeleteStackFn: func(id string) error {
+		UnstackFn: func(int) (*github.RemoteStack, bool, error) {
 			deleteCalled = true
-			return nil
+			return nil, true, nil
 		},
 	}
 
@@ -1832,7 +1872,7 @@ func TestHandlePendingModify_NoStateFile(t *testing.T) {
 
 	err := handlePendingModify(cfg, client, s, gitDir)
 	assert.NoError(t, err)
-	assert.False(t, deleteCalled, "DeleteStack should not be called when no state file exists")
+	assert.False(t, deleteCalled, "Unstack should not be called when no state file exists")
 	assert.Equal(t, "stack-123", s.ID, "stack ID should remain unchanged")
 }
 
@@ -1850,9 +1890,9 @@ func TestHandlePendingModify_WrongPhase(t *testing.T) {
 
 	deleteCalled := false
 	client := &github.MockClient{
-		DeleteStackFn: func(id string) error {
+		UnstackFn: func(int) (*github.RemoteStack, bool, error) {
 			deleteCalled = true
-			return nil
+			return nil, true, nil
 		},
 	}
 
@@ -1862,20 +1902,23 @@ func TestHandlePendingModify_WrongPhase(t *testing.T) {
 
 	err := handlePendingModify(cfg, client, s, gitDir)
 	assert.NoError(t, err)
-	assert.False(t, deleteCalled, "DeleteStack should not be called for non-pending_submit phase")
+	assert.False(t, deleteCalled, "Unstack should not be called for non-pending_submit phase")
 	assert.Equal(t, "stack-99", s.ID, "stack ID should remain unchanged")
 }
 
 func TestHandlePendingModify_DeleteFails(t *testing.T) {
 	gitDir := t.TempDir()
 
-	saveModifyState(t, gitDir, newPendingSubmitState("stack-456"))
+	saveModifyState(t, gitDir, newPendingSubmitState("456"))
 
-	s := &stack.Stack{ID: "stack-456", Trunk: stack.BranchRef{Branch: "main"}}
+	s := &stack.Stack{ID: "456", Number: 43, Trunk: stack.BranchRef{Branch: "main"}}
 
 	client := &github.MockClient{
-		DeleteStackFn: func(id string) error {
-			return fmt.Errorf("server error")
+		ListStacksFn: func() ([]github.RemoteStack, error) {
+			return []github.RemoteStack{{ID: 456, Number: 43}}, nil
+		},
+		UnstackFn: func(int) (*github.RemoteStack, bool, error) {
+			return nil, false, fmt.Errorf("server error")
 		},
 	}
 
@@ -1885,22 +1928,25 @@ func TestHandlePendingModify_DeleteFails(t *testing.T) {
 
 	err := handlePendingModify(cfg, client, s, gitDir)
 	assert.Error(t, err)
-	assert.Equal(t, "stack-456", s.ID, "stack ID should NOT be cleared on delete failure")
+	assert.Equal(t, "456", s.ID, "stack ID should NOT be cleared on delete failure")
 }
 
 func TestHandlePendingModify_Delete404(t *testing.T) {
 	gitDir := t.TempDir()
 
-	saveModifyState(t, gitDir, newPendingSubmitState("stack-gone"))
+	saveModifyState(t, gitDir, newPendingSubmitState("404"))
 
-	s := &stack.Stack{ID: "stack-gone", Trunk: stack.BranchRef{Branch: "main"}}
+	s := &stack.Stack{ID: "404", Number: 44, Trunk: stack.BranchRef{Branch: "main"}}
 
 	client := &github.MockClient{
-		DeleteStackFn: func(id string) error {
-			return &api.HTTPError{
+		ListStacksFn: func() ([]github.RemoteStack, error) {
+			return []github.RemoteStack{{ID: 404, Number: 44}}, nil
+		},
+		UnstackFn: func(int) (*github.RemoteStack, bool, error) {
+			return nil, false, &api.HTTPError{
 				StatusCode: 404,
 				Message:    "Not Found",
-				RequestURL: &url.URL{Path: "/repos/o/r/cli_internal/pulls/stacks/stack-gone"},
+				RequestURL: &url.URL{Path: "/repos/o/r/stacks/44"},
 			}
 		},
 	}
@@ -1943,8 +1989,9 @@ func TestClearPendingModifyState_NoFile(t *testing.T) {
 
 func TestSubmit_WithPendingModify_SequentialPush(t *testing.T) {
 	s := stack.Stack{
-		ID:    "old-stack-42",
-		Trunk: stack.BranchRef{Branch: "main"},
+		ID:     "42",
+		Number: 7,
+		Trunk:  stack.BranchRef{Branch: "main"},
 		Branches: []stack.BranchRef{
 			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 10}},
 			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 11}},
@@ -1954,7 +2001,7 @@ func TestSubmit_WithPendingModify_SequentialPush(t *testing.T) {
 
 	tmpDir := t.TempDir()
 	writeStackFile(t, tmpDir, s)
-	saveModifyState(t, tmpDir, newPendingSubmitState("old-stack-42"))
+	saveModifyState(t, tmpDir, newPendingSubmitState("42"))
 
 	// Track call ordering
 	var callOrder []string
@@ -1970,15 +2017,17 @@ func TestSubmit_WithPendingModify_SequentialPush(t *testing.T) {
 	restore := git.SetOps(mock)
 	defer restore()
 
-	var deletedStackID string
+	var unstackedNumber int
 	var createdStackPRs []int
+	unstacked := false
 
 	cfg, _, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		DeleteStackFn: func(id string) error {
-			deletedStackID = id
-			callOrder = append(callOrder, "delete:"+id)
-			return nil
+		UnstackFn: func(number int) (*github.RemoteStack, bool, error) {
+			unstackedNumber = number
+			unstacked = true
+			callOrder = append(callOrder, fmt.Sprintf("unstack:%d", number))
+			return nil, true, nil
 		},
 		FindPRForBranchFn: func(branch string) (*github.PullRequest, error) {
 			switch branch {
@@ -2006,13 +2055,17 @@ func TestSubmit_WithPendingModify_SequentialPush(t *testing.T) {
 			}
 			return nil, nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			createdStackPRs = prNumbers
 			callOrder = append(callOrder, "create_stack")
-			return 99, nil
+			return &github.RemoteStack{ID: 99, Number: 99}, nil
 		},
 		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{}, nil
+			// The old stack exists until it is unstacked, then it is gone.
+			if unstacked {
+				return []github.RemoteStack{}, nil
+			}
+			return []github.RemoteStack{{ID: 42, Number: 7, PullRequests: []int{10, 11, 12}}}, nil
 		},
 	}
 
@@ -2027,8 +2080,8 @@ func TestSubmit_WithPendingModify_SequentialPush(t *testing.T) {
 
 	assert.NoError(t, err)
 
-	// DeleteStack called with old stack ID
-	assert.Equal(t, "old-stack-42", deletedStackID)
+	// Unstack called with old stack number
+	assert.Equal(t, 7, unstackedNumber)
 
 	// Push called per-branch (3 separate calls, not 1 atomic call)
 	require.Len(t, pushCalls, 3, "should push each branch individually")
@@ -2042,13 +2095,13 @@ func TestSubmit_WithPendingModify_SequentialPush(t *testing.T) {
 	// CreateStack called with all 3 PRs
 	assert.Equal(t, []int{10, 11, 12}, createdStackPRs)
 
-	// Verify ordering: delete before push, push before create_stack
+	// Verify ordering: unstack before push, push before create_stack
 	assert.True(t, len(callOrder) >= 5, "expected at least 5 calls, got %d: %v", len(callOrder), callOrder)
 	deleteIdx := -1
 	firstPushIdx := -1
 	createIdx := -1
 	for i, c := range callOrder {
-		if c == "delete:old-stack-42" && deleteIdx == -1 {
+		if c == "unstack:7" && deleteIdx == -1 {
 			deleteIdx = i
 		}
 		if c == "push:b1" && firstPushIdx == -1 {
@@ -2109,8 +2162,8 @@ func TestSubmit_FetchesBeforePush(t *testing.T) {
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{}, nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
-			return 42, nil
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -2168,7 +2221,7 @@ func TestSubmit_UsesPRTemplate(t *testing.T) {
 			capturedBody = body
 			return &github.PullRequest{Number: 1, ID: "PR_1", URL: "https://github.com/o/r/pull/1"}, nil
 		},
-		CreateStackFn: func([]int) (int, error) { return 1, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 1, Number: 1}, nil },
 	}
 
 	cmd := SubmitCmd(cfg)
@@ -2228,7 +2281,7 @@ func TestSubmit_IgnoresSymlinkedPRTemplate(t *testing.T) {
 			capturedBody = body
 			return &github.PullRequest{Number: 1, ID: "PR_1", URL: "https://github.com/o/r/pull/1"}, nil
 		},
-		CreateStackFn: func([]int) (int, error) { return 1, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 1, Number: 1}, nil },
 	}
 
 	cmd := SubmitCmd(cfg)
@@ -2274,7 +2327,7 @@ func TestSubmit_NoTemplate_UsesFooter(t *testing.T) {
 			capturedBody = body
 			return &github.PullRequest{Number: 1, ID: "PR_1", URL: "https://github.com/o/r/pull/1"}, nil
 		},
-		CreateStackFn: func([]int) (int, error) { return 1, nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { return &github.RemoteStack{ID: 1, Number: 1}, nil },
 	}
 
 	cmd := SubmitCmd(cfg)
@@ -2288,91 +2341,6 @@ func TestSubmit_NoTemplate_UsesFooter(t *testing.T) {
 	assert.Contains(t, capturedBody, feedbackURL)
 }
 
-func TestSubmit_PreflightCheck_PAT_BailsOut(t *testing.T) {
-	s := stack.Stack{
-		Trunk: stack.BranchRef{Branch: "main"},
-		Branches: []stack.BranchRef{
-			{Branch: "b1"},
-			{Branch: "b2"},
-		},
-	}
-
-	tmpDir := t.TempDir()
-	writeStackFile(t, tmpDir, s)
-
-	pushed := false
-	mock := newSubmitMock(tmpDir, "b1")
-	mock.PushFn = func(string, []string, bool, bool) error {
-		pushed = true
-		return nil
-	}
-	restore := git.SetOps(mock)
-	defer restore()
-
-	listStacksCalled := false
-	cfg, _, errR := config.NewTestConfig()
-	cfg.GitHubClientOverride = &github.MockClient{
-		ListStacksFn: func() ([]github.RemoteStack, error) {
-			listStacksCalled = true
-			return nil, nil
-		},
-	}
-
-	// Simulate a classic PAT — the pre-flight check should abort.
-	setTestTokenForHost(cfg, "ghp_classic_pat_token")
-
-	cmd := SubmitCmd(cfg)
-	cmd.SetArgs([]string{"--auto"})
-	cmd.SetOut(io.Discard)
-	cmd.SetErr(io.Discard)
-	err := cmd.Execute()
-
-	cfg.Err.Close()
-	errOut, _ := io.ReadAll(errR)
-	output := string(errOut)
-
-	assert.ErrorIs(t, err, ErrStacksUnavailable)
-	assert.Contains(t, output, "Personal access tokens are not supported by gh stack")
-	assert.Contains(t, output, "gh auth login")
-	assert.False(t, pushed, "should not push when using a PAT")
-	assert.False(t, listStacksCalled, "should not call ListStacks when PAT detected")
-}
-
-func TestSubmit_PreflightCheck_FinegrainedPAT_BailsOut(t *testing.T) {
-	s := stack.Stack{
-		Trunk: stack.BranchRef{Branch: "main"},
-		Branches: []stack.BranchRef{
-			{Branch: "b1"},
-			{Branch: "b2"},
-		},
-	}
-
-	tmpDir := t.TempDir()
-	writeStackFile(t, tmpDir, s)
-
-	mock := newSubmitMock(tmpDir, "b1")
-	restore := git.SetOps(mock)
-	defer restore()
-
-	cfg, _, errR := config.NewTestConfig()
-	cfg.GitHubClientOverride = &github.MockClient{}
-
-	setTestTokenForHost(cfg, "github_pat_11AABBCC_xxxx")
-
-	cmd := SubmitCmd(cfg)
-	cmd.SetArgs([]string{"--auto"})
-	cmd.SetOut(io.Discard)
-	cmd.SetErr(io.Discard)
-	err := cmd.Execute()
-
-	cfg.Err.Close()
-	errOut, _ := io.ReadAll(errR)
-	output := string(errOut)
-
-	assert.ErrorIs(t, err, ErrStacksUnavailable)
-	assert.Contains(t, output, "Personal access tokens are not supported by gh stack")
-}
-
 func TestSubmit_DisablesAutoMergeOnExistingPR(t *testing.T) {
 	s := stack.Stack{
 		Trunk: stack.BranchRef{Branch: "main"},
@@ -2418,8 +2386,8 @@ func TestSubmit_DisablesAutoMergeOnExistingPR(t *testing.T) {
 			disabledAutoMergePRIDs = append(disabledAutoMergePRIDs, prID)
 			return nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
-			return 42, nil
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -2470,8 +2438,8 @@ func TestSubmit_DisableAutoMergeFailure_ContinuesWithWarning(t *testing.T) {
 		DisableAutoMergeFn: func(prID string) error {
 			return fmt.Errorf("permission denied")
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
-			return 42, nil
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 
@@ -2522,8 +2490,8 @@ func TestSubmit_NoAutoMerge_SkipsDisable(t *testing.T) {
 			t.Fatal("DisableAutoMerge should not be called when auto-merge is not enabled")
 			return nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
-			return 42, nil
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 42, Number: 42}, nil
 		},
 	}
 

cmd/sync_test.go

@@ -1757,13 +1757,13 @@ func TestSync_CreatesRemoteStackWhenPRsExist(t *testing.T) {
 			listCalls++
 			return nil, nil
 		},
-		CreateStackFn: func(prNumbers []int) (int, error) {
+		CreateStackFn: func(prNumbers []int) (*github.RemoteStack, error) {
 			createdWith = prNumbers
-			return 7, nil
+			return &github.RemoteStack{ID: 7, Number: 7}, nil
 		},
-		UpdateStackFn: func(string, []int) error {
-			t.Fatal("UpdateStack should not be called when no remote stack exists")
-			return nil
+		AddToStackFn: func(int, []int) (*github.RemoteStack, error) {
+			t.Fatal("AddToStack should not be called when no remote stack exists")
+			return nil, nil
 		},
 	}
 
@@ -1796,15 +1796,15 @@ func TestSync_AdoptsExistingEqualRemoteStack(t *testing.T) {
 	ghMock := &github.MockClient{
 		FindPRForBranchFn: openPRFinder(map[string]int{"b1": 101, "b2": 102}),
 		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{{ID: 9, PullRequests: []int{101, 102}}}, nil
+			return []github.RemoteStack{{ID: 9, Number: 9, PullRequests: []int{101, 102}}}, nil
 		},
-		CreateStackFn: func([]int) (int, error) {
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
 			t.Fatal("CreateStack should not be called when the remote stack matches")
-			return 0, nil
+			return nil, nil
 		},
-		UpdateStackFn: func(string, []int) error {
-			t.Fatal("UpdateStack should not be called when the remote stack matches")
-			return nil
+		AddToStackFn: func(int, []int) (*github.RemoteStack, error) {
+			t.Fatal("AddToStack should not be called when the remote stack matches")
+			return nil, nil
 		},
 	}
 
@@ -1829,28 +1829,32 @@ func TestSync_UpdatesPartialRemoteStack(t *testing.T) {
 	tmpDir := t.TempDir()
 	writeStackFile(t, tmpDir, s)
 
-	var updatedID string
-	var updatedWith []int
+	var updatedNumber int
+	var addedWith []int
 	ghMock := &github.MockClient{
 		FindPRForBranchFn: openPRFinder(map[string]int{"b1": 101, "b2": 102, "b3": 103}),
 		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{{ID: 9, PullRequests: []int{101, 102}}}, nil
+			return []github.RemoteStack{{ID: 9, Number: 9, PullRequests: []int{101, 102}}}, nil
 		},
-		CreateStackFn: func([]int) (int, error) {
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
 			t.Fatal("CreateStack should not be called when a matching stack exists")
-			return 0, nil
+			return nil, nil
 		},
-		UpdateStackFn: func(stackID string, prNumbers []int) error {
-			updatedID = stackID
-			updatedWith = prNumbers
-			return nil
+		GetStackFn: func(stackNumber int) (*github.RemoteStack, error) {
+			assert.Equal(t, 9, stackNumber)
+			return &github.RemoteStack{ID: 9, Number: 9, PullRequests: []int{101, 102}}, nil
+		},
+		AddToStackFn: func(stackNumber int, prNumbers []int) (*github.RemoteStack, error) {
+			updatedNumber = stackNumber
+			addedWith = prNumbers
+			return &github.RemoteStack{ID: 9, Number: 9, PullRequests: []int{101, 102, 103}}, nil
 		},
 	}
 
 	output := runSyncWithGitHub(t, newSyncMockNoRebase(tmpDir, "b1"), ghMock)
 
-	assert.Equal(t, "9", updatedID)
-	assert.Equal(t, []int{101, 102, 103}, updatedWith)
+	assert.Equal(t, 9, updatedNumber)
+	assert.Equal(t, []int{103}, addedWith)
 	assert.Contains(t, output, "Stack updated on GitHub with 3 PRs")
 	assert.Contains(t, output, "Stack synced")
 	assert.NotContains(t, output, "Branches synced")
@@ -1878,9 +1882,9 @@ func TestSync_FewerThanTwoPRs_BranchesSynced(t *testing.T) {
 			listCalled = true
 			return nil, nil
 		},
-		CreateStackFn: func([]int) (int, error) {
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
 			createCalled = true
-			return 0, nil
+			return &github.RemoteStack{}, nil
 		},
 	}
 
@@ -1905,8 +1909,8 @@ func TestSync_StacksUnavailable_BranchesSynced(t *testing.T) {
 	ghMock := &github.MockClient{
 		FindPRForBranchFn: openPRFinder(map[string]int{"b1": 101, "b2": 102}),
 		ListStacksFn:      func() ([]github.RemoteStack, error) { return nil, nil },
-		CreateStackFn: func([]int) (int, error) {
-			return 0, &api.HTTPError{StatusCode: 404, Message: "Not Found"}
+		CreateStackFn: func([]int) (*github.RemoteStack, error) {
+			return nil, &api.HTTPError{StatusCode: 404, Message: "Not Found"}
 		},
 	}
 
@@ -1932,18 +1936,18 @@ func TestSync_PRsSpanMultipleStacks_BranchesSynced(t *testing.T) {
 		FindPRForBranchFn: openPRFinder(map[string]int{"b1": 101, "b2": 102}),
 		ListStacksFn: func() ([]github.RemoteStack, error) {
 			return []github.RemoteStack{
-				{ID: 9, PullRequests: []int{101}},
-				{ID: 10, PullRequests: []int{102}},
+				{ID: 9, Number: 9, PullRequests: []int{101}},
+				{ID: 10, Number: 10, PullRequests: []int{102}},
 			}, nil
 		},
-		CreateStackFn: func([]int) (int, error) { createCalled = true; return 0, nil },
-		UpdateStackFn: func(string, []int) error { updateCalled = true; return nil },
+		CreateStackFn: func([]int) (*github.RemoteStack, error) { createCalled = true; return nil, nil },
+		AddToStackFn:  func(int, []int) (*github.RemoteStack, error) { updateCalled = true; return nil, nil },
 	}
 
 	output := runSyncWithGitHub(t, newSyncMockNoRebase(tmpDir, "b1"), ghMock)
 
 	assert.False(t, createCalled, "CreateStack should not be called on divergence")
-	assert.False(t, updateCalled, "UpdateStack should not be called on divergence")
+	assert.False(t, updateCalled, "AddToStack should not be called on divergence")
 	assert.Contains(t, output, "multiple stacks")
 	assert.NotContains(t, output, "submitting", "divergence guidance should be command-neutral, not submit-specific")
 	assert.Contains(t, output, "Branches synced")
@@ -2041,7 +2045,11 @@ func TestSync_RemoteAhead_PullsNewBranches(t *testing.T) {
 
 	ghMock := &github.MockClient{
 		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{{ID: 9, PullRequests: []int{101, 102, 103, 104, 105}}}, nil
+			return []github.RemoteStack{{ID: 9, Number: 9, PullRequests: []int{101, 102, 103, 104, 105}}}, nil
+		},
+		GetStackFn: func(stackNumber int) (*github.RemoteStack, error) {
+			assert.Equal(t, 9, stackNumber)
+			return &github.RemoteStack{ID: 9, Number: 9, PullRequests: []int{101, 102, 103, 104, 105}}, nil
 		},
 		FindPRByNumberFn: prByNumberFinder(map[int]string{101: "b1", 102: "b2", 103: "b3", 104: "b4", 105: "b5"}),
 	}
@@ -2089,7 +2097,11 @@ func TestSync_RemoteAhead_QueuedBranchNotPushed(t *testing.T) {
 
 	ghMock := &github.MockClient{
 		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{{ID: 9, PullRequests: []int{101, 102, 103}}}, nil
+			return []github.RemoteStack{{ID: 9, Number: 9, PullRequests: []int{101, 102, 103}}}, nil
+		},
+		GetStackFn: func(stackNumber int) (*github.RemoteStack, error) {
+			assert.Equal(t, 9, stackNumber)
+			return &github.RemoteStack{ID: 9, Number: 9, PullRequests: []int{101, 102, 103}}, nil
 		},
 		FindPRByNumberFn: func(n int) (*github.PullRequest, error) {
 			branch := map[int]string{101: "b1", 102: "b2", 103: "b3"}[n]
@@ -2143,7 +2155,7 @@ func TestSync_RemoteAhead_DuplicateBranchAborts(t *testing.T) {
 
 	ghMock := &github.MockClient{
 		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{{ID: 9, PullRequests: []int{101, 102, 103}}}, nil
+			return []github.RemoteStack{{ID: 9, Number: 9, PullRequests: []int{101, 102, 103}}}, nil
 		},
 		FindPRByNumberFn: prByNumberFinder(map[int]string{101: "b1", 102: "b2", 103: "b3"}),
 	}
@@ -2207,7 +2219,11 @@ func TestSync_RemoteInSync_NoPull(t *testing.T) {
 
 	ghMock := &github.MockClient{
 		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{{ID: 9, PullRequests: []int{101, 102}}}, nil
+			return []github.RemoteStack{{ID: 9, Number: 9, PullRequests: []int{101, 102}}}, nil
+		},
+		GetStackFn: func(stackNumber int) (*github.RemoteStack, error) {
+			assert.Equal(t, 9, stackNumber)
+			return &github.RemoteStack{ID: 9, Number: 9, PullRequests: []int{101, 102}}, nil
 		},
 		FindPRByNumberFn: prByNumberFinder(map[int]string{101: "b1", 102: "b2"}),
 	}
@@ -2240,7 +2256,10 @@ func divergentStack(t *testing.T, tmpDir string) {
 func divergentRemoteMock() *github.MockClient {
 	return &github.MockClient{
 		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{{ID: 9, PullRequests: []int{101, 102, 104}}}, nil
+			return []github.RemoteStack{{ID: 9, Number: 9, PullRequests: []int{101, 102, 104}}}, nil
+		},
+		GetStackFn: func(stackNumber int) (*github.RemoteStack, error) {
+			return &github.RemoteStack{ID: 9, Number: 9, PullRequests: []int{101, 102, 104}}, nil
 		},
 		FindPRByNumberFn: prByNumberFinder(map[int]string{101: "b1", 102: "b2", 103: "b3", 104: "b4"}),
 	}
@@ -2260,9 +2279,18 @@ func TestSync_Divergent_NonInteractive_Aborts(t *testing.T) {
 	mock := newSyncMockNoRebase(tmpDir, "b1")
 	mock.CreateBranchFn = func(name, base string) error { created = append(created, name); return nil }
 	mock.PushFn = func(string, []string, bool, bool) error { pushed = true; return nil }
-	ghMock.CreateStackFn = func([]int) (int, error) { t.Fatal("CreateStack must not be called"); return 0, nil }
-	ghMock.UpdateStackFn = func(string, []int) error { t.Fatal("UpdateStack must not be called"); return nil }
-	ghMock.DeleteStackFn = func(string) error { t.Fatal("DeleteStack must not be called"); return nil }
+	ghMock.CreateStackFn = func([]int) (*github.RemoteStack, error) {
+		t.Fatal("CreateStack must not be called")
+		return nil, nil
+	}
+	ghMock.AddToStackFn = func(int, []int) (*github.RemoteStack, error) {
+		t.Fatal("AddToStack must not be called")
+		return nil, nil
+	}
+	ghMock.UnstackFn = func(int) (*github.RemoteStack, bool, error) {
+		t.Fatal("Unstack must not be called")
+		return nil, false, nil
+	}
 
 	output, err := runSyncCfg(t, mock, func(cfg *config.Config) { cfg.GitHubClientOverride = ghMock })
 	require.NoError(t, err)
@@ -2407,12 +2435,22 @@ func TestSync_Divergent_DeleteRemote(t *testing.T) {
 	divergentStack(t, tmpDir)
 
 	deleted := false
-	var deletedID string
+	var deletedNumber int
 	var pushed bool
 	ghMock := divergentRemoteMock()
-	ghMock.DeleteStackFn = func(id string) error { deleted = true; deletedID = id; return nil }
-	ghMock.CreateStackFn = func([]int) (int, error) { t.Fatal("CreateStack must not be called"); return 0, nil }
-	ghMock.UpdateStackFn = func(string, []int) error { t.Fatal("UpdateStack must not be called"); return nil }
+	ghMock.UnstackFn = func(number int) (*github.RemoteStack, bool, error) {
+		deleted = true
+		deletedNumber = number
+		return nil, true, nil
+	}
+	ghMock.CreateStackFn = func([]int) (*github.RemoteStack, error) {
+		t.Fatal("CreateStack must not be called")
+		return nil, nil
+	}
+	ghMock.AddToStackFn = func(int, []int) (*github.RemoteStack, error) {
+		t.Fatal("AddToStack must not be called")
+		return nil, nil
+	}
 	mock := newSyncMockNoRebase(tmpDir, "b1")
 	mock.PushFn = func(string, []string, bool, bool) error { pushed = true; return nil }
 
@@ -2424,7 +2462,7 @@ func TestSync_Divergent_DeleteRemote(t *testing.T) {
 	require.NoError(t, err)
 
 	assert.True(t, deleted, "remote stack should be deleted")
-	assert.Equal(t, "9", deletedID)
+	assert.Equal(t, 9, deletedNumber)
 	assert.False(t, pushed, "sync should stop after deleting the remote stack")
 	assert.Contains(t, output, "Deleted the stack on GitHub")
 	assert.Contains(t, output, "gh stack submit")
@@ -2443,9 +2481,18 @@ func TestSync_Divergent_Cancel(t *testing.T) {
 	divergentStack(t, tmpDir)
 
 	ghMock := divergentRemoteMock()
-	ghMock.DeleteStackFn = func(string) error { t.Fatal("DeleteStack must not be called"); return nil }
-	ghMock.CreateStackFn = func([]int) (int, error) { t.Fatal("CreateStack must not be called"); return 0, nil }
-	ghMock.UpdateStackFn = func(string, []int) error { t.Fatal("UpdateStack must not be called"); return nil }
+	ghMock.UnstackFn = func(int) (*github.RemoteStack, bool, error) {
+		t.Fatal("Unstack must not be called")
+		return nil, false, nil
+	}
+	ghMock.CreateStackFn = func([]int) (*github.RemoteStack, error) {
+		t.Fatal("CreateStack must not be called")
+		return nil, nil
+	}
+	ghMock.AddToStackFn = func(int, []int) (*github.RemoteStack, error) {
+		t.Fatal("AddToStack must not be called")
+		return nil, nil
+	}
 	var pushed bool
 	mock := newSyncMockNoRebase(tmpDir, "b1")
 	mock.PushFn = func(string, []string, bool, bool) error { pushed = true; return nil }
@@ -2490,7 +2537,11 @@ func TestSync_MergedBranchPruned_NoFalseDivergence(t *testing.T) {
 
 	ghMock := &github.MockClient{
 		ListStacksFn: func() ([]github.RemoteStack, error) {
-			return []github.RemoteStack{{ID: 9, PullRequests: []int{101, 102, 103}}}, nil
+			return []github.RemoteStack{{ID: 9, Number: 9, PullRequests: []int{101, 102, 103}}}, nil
+		},
+		GetStackFn: func(stackNumber int) (*github.RemoteStack, error) {
+			assert.Equal(t, 9, stackNumber)
+			return &github.RemoteStack{ID: 9, Number: 9, PullRequests: []int{101, 102, 103}}, nil
 		},
 		FindPRByNumberFn: func(n int) (*github.PullRequest, error) {
 			branch := map[int]string{101: "b1", 102: "b2", 103: "b3"}[n]

cmd/unstack.go

@@ -2,11 +2,9 @@ package cmd
 
 import (
 	"errors"
-	"fmt"
 
 	"github.com/cli/go-gh/v2/pkg/api"
 	"github.com/github/gh-stack/internal/config"
-	"github.com/github/gh-stack/internal/github"
 	"github.com/github/gh-stack/internal/modify"
 	"github.com/github/gh-stack/internal/stack"
 	"github.com/spf13/cobra"
@@ -55,11 +53,13 @@ func runUnstack(cfg *config.Config, opts *unstackOptions) error {
 	sf := result.StackFile
 	s := result.Stack
 
-	// Delete the stack on GitHub first (unless --local).
-	// Only proceed with local deletion after the remote operation succeeds.
+	// Unstack on GitHub first (unless --local). The server decides which PRs
+	// can be unstacked; PRs that are queued for merge or have auto-merge enabled
+	// are left in place and the stack is kept. Local tracking is only removed
+	// when the remote stack is fully dissolved.
 	if !opts.local {
-		if s.ID == "" {
-			cfg.Warningf("Stack has no remote ID — skipping server-side deletion")
+		if s.ID == "" && s.Number == 0 {
+			cfg.Warningf("Stack has no remote ID — skipping server-side unstack")
 		} else {
 			client, err := cfg.GitHubClient()
 			if err != nil {
@@ -67,36 +67,43 @@ func runUnstack(cfg *config.Config, opts *unstackOptions) error {
 				return ErrAPIFailure
 			}
 
-			blocked, err := shouldBlockUnstackDelete(client, s)
+			number, err := ensureStackNumber(client, s)
 			if err != nil {
-				cfg.Errorf("failed to check pull request states before unstack: %s", err)
+				cfg.Errorf("failed to look up stack on GitHub: %s", err)
 				return ErrAPIFailure
 			}
-			if blocked {
-				cfg.Errorf("Unstacking not allowed. Pull requests that are queued for merge, are merging, or are already merged will remain in the stack.")
-				return ErrInvalidArgs
-			}
 
-			if err := client.DeleteStack(s.ID); err != nil {
+			if number == 0 {
+				cfg.Warningf("Stack not found on GitHub — continuing with local unstack")
+			} else if _, dissolved, err := client.Unstack(number); err != nil {
 				var httpErr *api.HTTPError
 				if errors.As(err, &httpErr) {
 					switch httpErr.StatusCode {
 					case 404:
-						// Stack already deleted on GitHub — treat as success.
+						// Stack already gone on GitHub — treat as success.
 						cfg.Warningf("Stack not found on GitHub — continuing with local unstack")
 					case 422:
-						cfg.Errorf("Cannot delete stack on GitHub: %s", httpErr.Message)
-						return ErrAPIFailure
+						// The server refused: every PR is queued for merge or has
+						// auto-merge enabled, so nothing can be unstacked.
+						cfg.Errorf("Unstacking not allowed: %s", httpErr.Message)
+						return ErrInvalidArgs
 					default:
-						cfg.Errorf("Failed to delete stack on GitHub (HTTP %d): %s", httpErr.StatusCode, httpErr.Message)
+						cfg.Errorf("Failed to unstack on GitHub (HTTP %d): %s", httpErr.StatusCode, httpErr.Message)
 						return ErrAPIFailure
 					}
 				} else {
-					cfg.Errorf("Failed to delete stack on GitHub: %v", err)
+					cfg.Errorf("Failed to unstack on GitHub: %v", err)
 					return ErrAPIFailure
 				}
+			} else if !dissolved {
+				// Some PRs (queued for merge or with auto-merge enabled) remain
+				// stacked on GitHub, so the stack still exists. Keep local
+				// tracking so it continues to reflect the remote stack.
+				cfg.Warningf("Some pull requests are queued for merge or have auto-merge enabled and remain stacked on GitHub")
+				cfg.Printf("The stack was left in place — local tracking is unchanged")
+				return nil
 			} else {
-				cfg.Successf("Stack deleted on GitHub")
+				cfg.Successf("Stack removed on GitHub")
 			}
 		}
 	}
@@ -117,55 +124,3 @@ func runUnstack(cfg *config.Config, opts *unstackOptions) error {
 
 	return nil
 }
-
-func shouldBlockUnstackDelete(client github.ClientOps, s *stack.Stack) (bool, error) {
-	if s == nil || len(s.Branches) == 0 {
-		return false, nil
-	}
-
-	eligible := 0
-	ineligible := 0
-	for _, b := range s.Branches {
-		// Respect stored merged status when available in local stack metadata.
-		if b.PullRequest != nil && b.PullRequest.Merged {
-			ineligible++
-			continue
-		}
-
-		var (
-			pr  *github.PullRequest
-			err error
-		)
-
-		if b.PullRequest != nil && b.PullRequest.Number > 0 {
-			pr, err = client.FindPRByNumber(b.PullRequest.Number)
-			if err != nil {
-				return false, fmt.Errorf("checking PR #%d for branch %s: %w", b.PullRequest.Number, b.Branch, err)
-			}
-		} else {
-			pr, err = client.FindPRForBranch(b.Branch)
-			if err != nil {
-				return false, fmt.Errorf("checking PR for branch %s: %w", b.Branch, err)
-			}
-		}
-
-		// If the PR no longer exists (or branch has no open PR), do not block unstacking.
-		if pr == nil {
-			eligible++
-			continue
-		}
-
-		switch {
-		case pr.State == "MERGED":
-			ineligible++
-		case pr.IsQueued():
-			ineligible++
-		case pr.IsAutoMergeEnabled():
-			ineligible++
-		default:
-			eligible++
-		}
-	}
-
-	return ineligible > 0 && eligible == 0, nil
-}

cmd/unstack_test.go

@@ -37,6 +37,7 @@ func TestUnstack_RemovesStack(t *testing.T) {
 
 	s1 := stack.Stack{
 		ID:       "42",
+		Number:   42,
 		Trunk:    stack.BranchRef{Branch: "main"},
 		Branches: []stack.BranchRef{{Branch: "b1"}, {Branch: "b2"}},
 	}
@@ -46,12 +47,12 @@ func TestUnstack_RemovesStack(t *testing.T) {
 	}
 	writeTwoStacks(t, gitDir, s1, s2)
 
-	var deletedStackID string
+	var unstackedNumber int
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		DeleteStackFn: func(stackID string) error {
-			deletedStackID = stackID
-			return nil
+		UnstackFn: func(n int) (*github.RemoteStack, bool, error) {
+			unstackedNumber = n
+			return nil, true, nil // dissolved
 		},
 	}
 	err := runUnstack(cfg, &unstackOptions{})
@@ -59,8 +60,8 @@ func TestUnstack_RemovesStack(t *testing.T) {
 
 	require.NoError(t, err)
 	assert.Contains(t, output, "Stack removed from local tracking")
-	assert.Contains(t, output, "Stack deleted on GitHub")
-	assert.Equal(t, "42", deletedStackID)
+	assert.Contains(t, output, "Stack removed on GitHub")
+	assert.Equal(t, 42, unstackedNumber)
 
 	sf, err := stack.Load(gitDir)
 	require.NoError(t, err)
@@ -88,7 +89,7 @@ func TestUnstack_Local(t *testing.T) {
 	require.NoError(t, err)
 	assert.Contains(t, output, "Stack removed")
 	// With --local, the GitHub API should NOT be called.
-	assert.NotContains(t, output, "Stack deleted on GitHub")
+	assert.NotContains(t, output, "Stack removed on GitHub")
 
 	sf, err := stack.Load(gitDir)
 	require.NoError(t, err)
@@ -103,7 +104,7 @@ func TestUnstack_NoStackID_WarnsAndSkipsAPI(t *testing.T) {
 	})
 	defer restore()
 
-	// Stack with no ID (never synced to GitHub)
+	// Stack with no ID/Number (never synced to GitHub)
 	writeStackFile(t, gitDir, stack.Stack{
 		Trunk:    stack.BranchRef{Branch: "main"},
 		Branches: []stack.BranchRef{{Branch: "b1"}, {Branch: "b2"}},
@@ -112,9 +113,9 @@ func TestUnstack_NoStackID_WarnsAndSkipsAPI(t *testing.T) {
 	apiCalled := false
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		DeleteStackFn: func(stackID string) error {
+		UnstackFn: func(int) (*github.RemoteStack, bool, error) {
 			apiCalled = true
-			return nil
+			return nil, true, nil
 		},
 	}
 	err := runUnstack(cfg, &unstackOptions{})
@@ -124,7 +125,49 @@ func TestUnstack_NoStackID_WarnsAndSkipsAPI(t *testing.T) {
 	assert.False(t, apiCalled, "API should not be called when stack has no ID")
 	assert.Contains(t, output, "no remote ID")
 	assert.Contains(t, output, "Stack removed from local tracking")
-	assert.NotContains(t, output, "Stack deleted on GitHub")
+	assert.NotContains(t, output, "Stack removed on GitHub")
+}
+
+func TestUnstack_ResolvesNumberFromID(t *testing.T) {
+	// A local stack that predates the Number field (only ID stored) resolves
+	// its stack number from the remote list before unstacking.
+	gitDir := t.TempDir()
+	restore := git.SetOps(&git.MockOps{
+		GitDirFn:        func() (string, error) { return gitDir, nil },
+		CurrentBranchFn: func() (string, error) { return "b1", nil },
+	})
+	defer restore()
+
+	writeStackFile(t, gitDir, stack.Stack{
+		ID:    "99",
+		Trunk: stack.BranchRef{Branch: "main"},
+		Branches: []stack.BranchRef{
+			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 101}},
+			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 102}},
+		},
+	})
+
+	var unstackedNumber int
+	cfg, outR, errR := config.NewTestConfig()
+	cfg.GitHubClientOverride = &github.MockClient{
+		ListStacksFn: func() ([]github.RemoteStack, error) {
+			return []github.RemoteStack{{ID: 99, Number: 7, PullRequests: []int{101, 102}}}, nil
+		},
+		UnstackFn: func(n int) (*github.RemoteStack, bool, error) {
+			unstackedNumber = n
+			return nil, true, nil
+		},
+	}
+	err := runUnstack(cfg, &unstackOptions{})
+	output := collectOutput(cfg, outR, errR)
+
+	require.NoError(t, err)
+	assert.Equal(t, 7, unstackedNumber, "should resolve the stack number from the internal ID")
+	assert.Contains(t, output, "Stack removed from local tracking")
+
+	sf, err := stack.Load(gitDir)
+	require.NoError(t, err)
+	assert.Empty(t, sf.Stacks)
 }
 
 func TestUnstack_API404_TreatedAsIdempotentSuccess(t *testing.T) {
@@ -136,8 +179,9 @@ func TestUnstack_API404_TreatedAsIdempotentSuccess(t *testing.T) {
 	defer restore()
 
 	writeStackFile(t, gitDir, stack.Stack{
-		ID:       "99",
-		Trunk:    stack.BranchRef{Branch: "main"},
+		ID:     "99",
+		Number: 99,
+		Trunk:  stack.BranchRef{Branch: "main"},
 		Branches: []stack.BranchRef{
 			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 101, Merged: true}},
 			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 102}},
@@ -146,14 +190,14 @@ func TestUnstack_API404_TreatedAsIdempotentSuccess(t *testing.T) {
 
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		DeleteStackFn: func(stackID string) error {
-			return &api.HTTPError{StatusCode: 404, Message: "Not Found"}
+		UnstackFn: func(int) (*github.RemoteStack, bool, error) {
+			return nil, false, &api.HTTPError{StatusCode: 404, Message: "Not Found"}
 		},
 	}
 	err := runUnstack(cfg, &unstackOptions{})
 	output := collectOutput(cfg, outR, errR)
 
-	// 404 means already deleted — should succeed and remove locally
+	// 404 means already gone — should succeed and remove locally
 	require.NoError(t, err)
 	assert.Contains(t, output, "continuing with local unstack")
 	assert.Contains(t, output, "Stack removed from local tracking")
@@ -163,7 +207,7 @@ func TestUnstack_API404_TreatedAsIdempotentSuccess(t *testing.T) {
 	assert.Empty(t, sf.Stacks)
 }
 
-func TestUnstack_API409_ShowsErrorAndStopsLocalDeletion(t *testing.T) {
+func TestUnstack_ServerError_StopsLocalDeletion(t *testing.T) {
 	gitDir := t.TempDir()
 	restore := git.SetOps(&git.MockOps{
 		GitDirFn:        func() (string, error) { return gitDir, nil },
@@ -172,8 +216,9 @@ func TestUnstack_API409_ShowsErrorAndStopsLocalDeletion(t *testing.T) {
 	defer restore()
 
 	writeStackFile(t, gitDir, stack.Stack{
-		ID:       "99",
-		Trunk:    stack.BranchRef{Branch: "main"},
+		ID:     "99",
+		Number: 99,
+		Trunk:  stack.BranchRef{Branch: "main"},
 		Branches: []stack.BranchRef{
 			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 101, Merged: true}},
 			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 102}},
@@ -182,15 +227,15 @@ func TestUnstack_API409_ShowsErrorAndStopsLocalDeletion(t *testing.T) {
 
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		DeleteStackFn: func(stackID string) error {
-			return &api.HTTPError{StatusCode: 409, Message: "Stack is currently being modified"}
+		UnstackFn: func(int) (*github.RemoteStack, bool, error) {
+			return nil, false, &api.HTTPError{StatusCode: 409, Message: "Stack is currently being modified"}
 		},
 	}
 	err := runUnstack(cfg, &unstackOptions{})
 	output := collectOutput(cfg, outR, errR)
 
 	assert.ErrorIs(t, err, ErrAPIFailure)
-	assert.Contains(t, output, "Failed to delete stack on GitHub (HTTP 409)")
+	assert.Contains(t, output, "Failed to unstack on GitHub (HTTP 409)")
 	// Should NOT remove locally when remote fails
 	assert.NotContains(t, output, "Stack removed from local tracking")
 
@@ -234,7 +279,10 @@ func TestUnstack_RemovesCorrectStackByPointer(t *testing.T) {
 	assert.Equal(t, []string{"b1", "b2"}, sf.Stacks[0].BranchNames(), "should keep the OTHER stack intact")
 }
 
-func TestUnstack_PreflightBlocksDelete_WhenAllPRsIneligible(t *testing.T) {
+func TestUnstack_AllLocked_ServerRejects(t *testing.T) {
+	// Every PR is queued for merge or has auto-merge enabled. The server
+	// (not the client) rejects the unstack with a 422; the command surfaces the
+	// error and leaves local tracking in place.
 	gitDir := t.TempDir()
 	restore := git.SetOps(&git.MockOps{
 		GitDirFn:        func() (string, error) { return gitDir, nil },
@@ -243,30 +291,21 @@ func TestUnstack_PreflightBlocksDelete_WhenAllPRsIneligible(t *testing.T) {
 	defer restore()
 
 	writeStackFile(t, gitDir, stack.Stack{
-		ID:       "99",
-		Trunk:    stack.BranchRef{Branch: "main"},
+		ID:     "99",
+		Number: 99,
+		Trunk:  stack.BranchRef{Branch: "main"},
 		Branches: []stack.BranchRef{
-			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 101, Merged: true}},
+			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 101}},
 			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 102}},
 		},
 	})
 
-	deleteCalled := false
+	unstackCalled := false
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
-			switch number {
-			case 101:
-				return &github.PullRequest{Number: 101, State: "MERGED"}, nil
-			case 102:
-				return &github.PullRequest{Number: 102, State: "OPEN", MergeQueueEntry: &github.MergeQueueEntry{ID: "MQE_1"}}, nil
-			default:
-				return nil, nil
-			}
-		},
-		DeleteStackFn: func(stackID string) error {
-			deleteCalled = true
-			return nil
+		UnstackFn: func(int) (*github.RemoteStack, bool, error) {
+			unstackCalled = true
+			return nil, false, &api.HTTPError{StatusCode: 422, Message: "all pull requests are queued for merge or have auto-merge enabled"}
 		},
 	}
 
@@ -274,7 +313,7 @@ func TestUnstack_PreflightBlocksDelete_WhenAllPRsIneligible(t *testing.T) {
 	output := collectOutput(cfg, outR, errR)
 
 	assert.ErrorIs(t, err, ErrInvalidArgs)
-	assert.False(t, deleteCalled, "DeleteStack should not be called when all PRs are ineligible")
+	assert.True(t, unstackCalled, "the server decides eligibility, so Unstack is called")
 	assert.Contains(t, output, "Unstacking not allowed")
 	assert.NotContains(t, output, "Stack removed from local tracking")
 
@@ -283,7 +322,9 @@ func TestUnstack_PreflightBlocksDelete_WhenAllPRsIneligible(t *testing.T) {
 	require.Len(t, sf.Stacks, 1)
 }
 
-func TestUnstack_PreflightAllowsDelete_WhenMixedEligibility(t *testing.T) {
+func TestUnstack_PartialUnstack_KeepsLocalTracking(t *testing.T) {
+	// Some PRs (queued for merge / auto-merge) remain stacked, so the server
+	// returns the surviving stack (dissolved=false). Local tracking is kept.
 	gitDir := t.TempDir()
 	restore := git.SetOps(&git.MockOps{
 		GitDirFn:        func() (string, error) { return gitDir, nil },
@@ -292,30 +333,19 @@ func TestUnstack_PreflightAllowsDelete_WhenMixedEligibility(t *testing.T) {
 	defer restore()
 
 	writeStackFile(t, gitDir, stack.Stack{
-		ID:       "99",
-		Trunk:    stack.BranchRef{Branch: "main"},
+		ID:     "99",
+		Number: 99,
+		Trunk:  stack.BranchRef{Branch: "main"},
 		Branches: []stack.BranchRef{
 			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 101}},
 			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 102}},
 		},
 	})
 
-	deleteCalled := false
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
-			switch number {
-			case 101:
-				return &github.PullRequest{Number: 101, State: "MERGED"}, nil
-			case 102:
-				return &github.PullRequest{Number: 102, State: "OPEN"}, nil
-			default:
-				return nil, nil
-			}
-		},
-		DeleteStackFn: func(stackID string) error {
-			deleteCalled = true
-			return nil
+		UnstackFn: func(int) (*github.RemoteStack, bool, error) {
+			return &github.RemoteStack{ID: 99, Number: 99, PullRequests: []int{102}}, false, nil
 		},
 	}
 
@@ -323,16 +353,19 @@ func TestUnstack_PreflightAllowsDelete_WhenMixedEligibility(t *testing.T) {
 	output := collectOutput(cfg, outR, errR)
 
 	require.NoError(t, err)
-	assert.True(t, deleteCalled, "DeleteStack should be called when at least one PR is eligible")
-	assert.Contains(t, output, "Stack deleted on GitHub")
-	assert.Contains(t, output, "Stack removed from local tracking")
+	assert.Contains(t, output, "remain stacked on GitHub")
+	assert.Contains(t, output, "local tracking is unchanged")
+	assert.NotContains(t, output, "Stack removed from local tracking")
 
+	// The stack still exists remotely, so local tracking is preserved.
 	sf, loadErr := stack.Load(gitDir)
 	require.NoError(t, loadErr)
-	assert.Empty(t, sf.Stacks)
+	require.Len(t, sf.Stacks, 1)
 }
 
-func TestUnstack_PreflightLookupFailure_StopsDeletion(t *testing.T) {
+func TestUnstack_NumberLookupFailure_StopsDeletion(t *testing.T) {
+	// Resolving the stack number from its ID fails (list API error), so the
+	// command aborts without touching local tracking.
 	gitDir := t.TempDir()
 	restore := git.SetOps(&git.MockOps{
 		GitDirFn:        func() (string, error) { return gitDir, nil },
@@ -346,15 +379,15 @@ func TestUnstack_PreflightLookupFailure_StopsDeletion(t *testing.T) {
 		Branches: []stack.BranchRef{{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 101}}},
 	})
 
-	deleteCalled := false
+	unstackCalled := false
 	cfg, outR, errR := config.NewTestConfig()
 	cfg.GitHubClientOverride = &github.MockClient{
-		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
-			return nil, errors.New("graphql timeout")
+		ListStacksFn: func() ([]github.RemoteStack, error) {
+			return nil, errors.New("network error")
 		},
-		DeleteStackFn: func(stackID string) error {
-			deleteCalled = true
-			return nil
+		UnstackFn: func(int) (*github.RemoteStack, bool, error) {
+			unstackCalled = true
+			return nil, true, nil
 		},
 	}
 
@@ -362,47 +395,8 @@ func TestUnstack_PreflightLookupFailure_StopsDeletion(t *testing.T) {
 	output := collectOutput(cfg, outR, errR)
 
 	assert.ErrorIs(t, err, ErrAPIFailure)
-	assert.False(t, deleteCalled, "DeleteStack should not be called if preflight fails")
-	assert.Contains(t, output, "failed to check pull request states before unstack")
-	assert.NotContains(t, output, "Stack removed from local tracking")
-
-	sf, loadErr := stack.Load(gitDir)
-	require.NoError(t, loadErr)
-	require.Len(t, sf.Stacks, 1)
-}
-
-func TestUnstack_API422_ShowsInformativeErrorAndStopsLocalDeletion(t *testing.T) {
-	gitDir := t.TempDir()
-	restore := git.SetOps(&git.MockOps{
-		GitDirFn:        func() (string, error) { return gitDir, nil },
-		CurrentBranchFn: func() (string, error) { return "b1", nil },
-	})
-	defer restore()
-
-	writeStackFile(t, gitDir, stack.Stack{
-		ID:       "99",
-		Trunk:    stack.BranchRef{Branch: "main"},
-		Branches: []stack.BranchRef{
-			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 101}},
-			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 102}},
-		},
-	})
-
-	cfg, outR, errR := config.NewTestConfig()
-	cfg.GitHubClientOverride = &github.MockClient{
-		FindPRByNumberFn: func(number int) (*github.PullRequest, error) {
-			return &github.PullRequest{Number: number, State: "OPEN"}, nil
-		},
-		DeleteStackFn: func(stackID string) error {
-			return &api.HTTPError{StatusCode: 422, Message: "some pull requests cannot be removed from stack"}
-		},
-	}
-	err := runUnstack(cfg, &unstackOptions{})
-	output := collectOutput(cfg, outR, errR)
-
-	assert.ErrorIs(t, err, ErrAPIFailure)
-	assert.Contains(t, output, "Cannot delete stack on GitHub")
-	assert.Contains(t, output, "cannot be removed")
+	assert.False(t, unstackCalled, "Unstack should not be called if number lookup fails")
+	assert.Contains(t, output, "failed to look up stack on GitHub")
 	assert.NotContains(t, output, "Stack removed from local tracking")
 
 	sf, loadErr := stack.Load(gitDir)

cmd/utils.go

@@ -72,16 +72,49 @@ func printInterrupt(cfg *config.Config) {
 	cfg.Infof("Received interrupt, aborting operation")
 }
 
-// warnStacksUnavailableOrPAT prints an appropriate warning when a stacks API
-// call returns 404. If the token is a PAT the message focuses on the auth
-// issue; otherwise it falls back to the generic "not enabled" message.
-func warnStacksUnavailableOrPAT(cfg *config.Config) {
-	if cfg.WarnIfPAT() {
-		return
-	}
+// warnStacksUnavailable prints a warning when a stacks API call returns 404,
+// indicating stacked PRs are not enabled for the repository.
+func warnStacksUnavailable(cfg *config.Config) {
 	cfg.Warningf("Stacked PRs are not enabled for this repository")
 }
 
+// stackNumberByID resolves an internal stack ID (as stored in the local stack
+// file) to its human-facing stack number by consulting the remote stack list.
+// Returns ok=false when no remote stack matches the ID (e.g. it was deleted).
+func stackNumberByID(client github.ClientOps, id string) (number int, ok bool, err error) {
+	if id == "" {
+		return 0, false, nil
+	}
+	stacks, err := client.ListStacks()
+	if err != nil {
+		return 0, false, err
+	}
+	for _, rs := range stacks {
+		if strconv.Itoa(rs.ID) == id {
+			return rs.Number, true, nil
+		}
+	}
+	return 0, false, nil
+}
+
+// ensureStackNumber returns the stack number for s, resolving and caching it
+// from the remote stack list by internal ID when the local model predates the
+// Number field (older stack files stored only the ID). Returns 0 when the stack
+// number can't be determined.
+func ensureStackNumber(client github.ClientOps, s *stack.Stack) (int, error) {
+	if s.Number != 0 {
+		return s.Number, nil
+	}
+	number, found, err := stackNumberByID(client, s.ID)
+	if err != nil {
+		return 0, err
+	}
+	if found {
+		s.Number = number
+	}
+	return number, nil
+}
+
 // inputWithPrefill prompts the user for text input with the given prefill
 // already editable in the input field. Unlike survey.Input's Default (which
 // shows in parentheses), this places the prefill text directly in the
@@ -531,7 +564,7 @@ func syncStackPRsFromRemote(client github.ClientOps, s *stack.Stack) (map[string
 	var remotePRNumbers []int
 	for _, rs := range stacks {
 		if strconv.Itoa(rs.ID) == s.ID {
-			remotePRNumbers = rs.PullRequests
+			remotePRNumbers = rs.PRNumbers()
 			break
 		}
 	}
@@ -1248,7 +1281,7 @@ func reconcileRemoteStack(cfg *config.Config, sf *stack.StackFile, s *stack.Stac
 	found := false
 	for _, rs := range stacks {
 		if strconv.Itoa(rs.ID) == s.ID {
-			remotePRNumbers = rs.PullRequests
+			remotePRNumbers = rs.PRNumbers()
 			found = true
 			break
 		}
@@ -1506,6 +1539,7 @@ func resolveDivergenceUseRemote(cfg *config.Config, sf *stack.StackFile, s *stac
 
 	trunk := s.Trunk.Branch
 	remoteStackID := s.ID
+	remoteStackNumber := s.Number
 	oldBranches := s.BranchNames()
 
 	removeLocalStack(sf, s)
@@ -1520,7 +1554,7 @@ func resolveDivergenceUseRemote(cfg *config.Config, sf *stack.StackFile, s *stac
 		}
 	}
 
-	newStack, err := importRemoteStack(cfg, sf, gitDir, remote, trunk, prs, remoteStackID)
+	newStack, err := importRemoteStack(cfg, sf, gitDir, remote, trunk, prs, remoteStackID, remoteStackNumber)
 	if err != nil {
 		return res, err
 	}
@@ -1584,19 +1618,25 @@ func nearestBranchAfterReplace(oldBranches []string, currentBranch string, newSt
 func resolveDivergenceDeleteRemote(cfg *config.Config, client github.ClientOps, sf *stack.StackFile, s *stack.Stack, gitDir string) (remoteReconcileResult, error) {
 	res := remoteReconcileResult{stop: true}
 
-	if err := client.DeleteStack(s.ID); err != nil {
+	number, err := ensureStackNumber(client, s)
+	if err != nil || number == 0 {
+		cfg.Warningf("Remote stack already deleted")
+	} else if _, dissolved, unstackErr := client.Unstack(number); unstackErr != nil {
 		var httpErr *api.HTTPError
-		if errors.As(err, &httpErr) && httpErr.StatusCode == 404 {
+		if errors.As(unstackErr, &httpErr) && httpErr.StatusCode == 404 {
 			cfg.Warningf("Remote stack already deleted")
 		} else {
-			cfg.Errorf("failed to delete remote stack: %v", err)
+			cfg.Errorf("failed to delete remote stack: %v", unstackErr)
 			return res, ErrAPIFailure
 		}
-	} else {
+	} else if dissolved {
 		cfg.Successf("Deleted the stack on GitHub")
+	} else {
+		cfg.Warningf("Some pull requests could not be unstacked and remain on GitHub")
 	}
 
 	s.ID = ""
+	s.Number = 0
 	if err := stack.Save(gitDir, sf); err != nil {
 		return res, handleSaveError(cfg, err)
 	}

cmd/utils_test.go

@@ -691,39 +691,21 @@ func TestStackNeedsRebase_SkipsMergedBranches(t *testing.T) {
 	assert.False(t, stackNeedsRebase(s), "should skip merged branches and find stack up to date")
 }
 
-// setTestTokenForHost sets cfg.TokenForHostFn to return the given token for
-// any host. Also sets RepoOverride so tests don't depend on real git context.
-func setTestTokenForHost(cfg *config.Config, token string) {
-	cfg.TokenForHostFn = func(string) (string, string) { return token, "test" }
+// setTestRepo sets RepoOverride so tests don't depend on real git context.
+func setTestRepo(cfg *config.Config) {
 	cfg.RepoOverride = &repository.Repository{Host: "github.com", Owner: "o", Name: "r"}
 }
 
-func TestWarnStacksUnavailableOrPAT_ShowsPATMessage(t *testing.T) {
+func TestWarnStacksUnavailable_ShowsNotEnabled(t *testing.T) {
 	cfg, _, errR := config.NewTestConfig()
-	setTestTokenForHost(cfg, "github_pat_fine_grained")
 
-	warnStacksUnavailableOrPAT(cfg)
-
-	cfg.Err.Close()
-	errOut, _ := io.ReadAll(errR)
-	output := string(errOut)
-
-	assert.Contains(t, output, "Personal access tokens are not supported by gh stack")
-	assert.NotContains(t, output, "Stacked PRs are not enabled")
-}
-
-func TestWarnStacksUnavailableOrPAT_ShowsNotEnabledForOAuth(t *testing.T) {
-	cfg, _, errR := config.NewTestConfig()
-	setTestTokenForHost(cfg, "gho_oauth_token")
-
-	warnStacksUnavailableOrPAT(cfg)
+	warnStacksUnavailable(cfg)
 
 	cfg.Err.Close()
 	errOut, _ := io.ReadAll(errR)
 	output := string(errOut)
 
 	assert.Contains(t, output, "Stacked PRs are not enabled for this repository")
-	assert.NotContains(t, output, "Personal access tokens")
 }
 
 func TestEnsureLocalTrunk_AlreadyExists(t *testing.T) {

internal/config/auth.go

@@ -1,65 +0,0 @@
-package config
-
-import (
-	"strings"
-
-	"github.com/cli/go-gh/v2/pkg/auth"
-)
-
-// tokenForHost returns the auth token for the given host, using the
-// test override if set or falling back to the real auth.TokenForHost.
-func (cfg *Config) tokenForHost(host string) (string, string) {
-	if cfg.TokenForHostFn != nil {
-		return cfg.TokenForHostFn(host)
-	}
-	return auth.TokenForHost(host)
-}
-
-// IsPersonalAccessToken reports whether the active token for the current
-// repository's host is a personal access token (classic or fine-grained)
-// rather than an OAuth token from `gh auth login`.
-//
-// Token prefix conventions:
-//
-//	gho_        → OAuth token (supported)
-//	ghs_        → GitHub App installation token (supported)
-//	ghp_        → Classic personal access token (NOT supported)
-//	github_pat_ → Fine-grained personal access token (NOT supported)
-func (cfg *Config) IsPersonalAccessToken() bool {
-	host := cfg.RepoHost()
-	if host == "" {
-		return false
-	}
-	return cfg.isPersonalAccessTokenForHost(host)
-}
-
-// isPersonalAccessTokenForHost checks the token prefix for the given host.
-func (cfg *Config) isPersonalAccessTokenForHost(host string) bool {
-	token, _ := cfg.tokenForHost(host)
-	if token == "" {
-		return false
-	}
-	return strings.HasPrefix(token, "ghp_") || strings.HasPrefix(token, "github_pat_")
-}
-
-// RepoHost returns the GitHub host for the current repository, or an empty
-// string if it cannot be determined (e.g. not inside a git repo).
-func (cfg *Config) RepoHost() string {
-	repo, err := cfg.Repo()
-	if err != nil {
-		return ""
-	}
-	return repo.Host
-}
-
-// WarnIfPAT checks whether the active token is a personal access token and,
-// if so, prints a warning explaining that PATs are not supported by gh stack.
-// Returns true when a PAT is detected.
-func (cfg *Config) WarnIfPAT() bool {
-	if !cfg.IsPersonalAccessToken() {
-		return false
-	}
-	cfg.Warningf("Personal access tokens are not supported by gh stack during private preview")
-	cfg.Printf("  Run %s to authenticate with OAuth instead.", cfg.ColorCyan("gh auth login"))
-	return true
-}

internal/config/auth_test.go

@@ -1,69 +0,0 @@
-package config
-
-import (
-	"io"
-	"testing"
-
-	"github.com/cli/go-gh/v2/pkg/repository"
-	"github.com/stretchr/testify/assert"
-)
-
-// testRepo is a fake repository used in tests to avoid depending on the
-// real git repo context (which may not exist in CI).
-var testRepo = &repository.Repository{Host: "github.com", Owner: "o", Name: "r"}
-
-func TestIsPersonalAccessToken(t *testing.T) {
-	tests := []struct {
-		name  string
-		token string
-		want  bool
-	}{
-		{"oauth token", "gho_abc123", false},
-		{"app installation token", "ghs_abc123", false},
-		{"classic PAT", "ghp_abc123", true},
-		{"fine-grained PAT", "github_pat_abc123", true},
-		{"empty token", "", false},
-		{"unknown prefix", "some_other_token", false},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			cfg := &Config{
-				TokenForHostFn: func(string) (string, string) { return tt.token, "test" },
-			}
-			got := cfg.isPersonalAccessTokenForHost("github.com")
-			assert.Equal(t, tt.want, got)
-		})
-	}
-}
-
-func TestWarnIfPAT_DetectsPAT(t *testing.T) {
-	cfg, _, errR := NewTestConfig()
-	cfg.RepoOverride = testRepo
-	cfg.TokenForHostFn = func(string) (string, string) { return "ghp_classic_pat_token", "test" }
-
-	result := cfg.WarnIfPAT()
-
-	cfg.Err.Close()
-	errOut, _ := io.ReadAll(errR)
-	output := string(errOut)
-
-	assert.True(t, result)
-	assert.Contains(t, output, "Personal access tokens are not supported by gh stack")
-	assert.Contains(t, output, "gh auth login")
-}
-
-func TestWarnIfPAT_IgnoresOAuth(t *testing.T) {
-	cfg, _, errR := NewTestConfig()
-	cfg.RepoOverride = testRepo
-	cfg.TokenForHostFn = func(string) (string, string) { return "gho_oauth_token", "test" }
-
-	result := cfg.WarnIfPAT()
-
-	cfg.Err.Close()
-	errOut, _ := io.ReadAll(errR)
-	output := string(errOut)
-
-	assert.False(t, result)
-	assert.Empty(t, output)
-}

internal/config/config.go

@@ -47,11 +47,6 @@ type Config struct {
 	// terminal. Used in tests to simulate text input prompts.
 	InputFn func(prompt, defaultValue string) (string, error)
 
-	// TokenForHostFn, when non-nil, is called instead of auth.TokenForHost
-	// to retrieve the auth token for a given GitHub host. Used in tests to
-	// simulate different token types (OAuth vs PAT).
-	TokenForHostFn func(host string) (string, string)
-
 	// RepoOverride, when non-nil, is returned by Repo() instead of
 	// calling repository.Current(). Used in tests to avoid depending on
 	// the real git repo context.

internal/github/client_interface.go

@@ -12,9 +12,11 @@ type ClientOps interface {
 	MarkPRReadyForReview(prID string) error
 	DisableAutoMerge(prID string) error
 	ListStacks() ([]RemoteStack, error)
-	CreateStack(prNumbers []int) (int, error)
-	UpdateStack(stackID string, prNumbers []int) error
-	DeleteStack(stackID string) error
+	FindStackForPR(prNumber int) (*RemoteStack, error)
+	GetStack(stackNumber int) (*RemoteStack, error)
+	CreateStack(prNumbers []int) (*RemoteStack, error)
+	AddToStack(stackNumber int, prNumbers []int) (*RemoteStack, error)
+	Unstack(stackNumber int) (*RemoteStack, bool, error)
 }
 
 // Compile-time check that Client satisfies ClientOps.

internal/github/github.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"math"
+	"net/http"
 
 	"github.com/cli/go-gh/v2/pkg/api"
 	graphql "github.com/cli/shurcooL-graphql"
@@ -399,16 +400,96 @@ func toGraphQLInt(n int) (graphql.Int, error) {
 	return graphql.Int(n), nil
 }
 
-type RemoteStack struct {
-	ID           int   `json:"id"`
-	PullRequests []int `json:"pull_requests"`
+// RemoteStackBase describes the base ref (and optionally SHA) of a stack.
+type RemoteStackBase struct {
+	Ref string `json:"ref"`
+	Sha string `json:"sha,omitempty"`
 }
 
-// ListStacks returns all stacks in the repository.
-// Returns an empty slice if no stacks exist.
-// A 404 response indicates stacked PRs are not enabled for this repository.
+// RemoteStackPRHead describes the head ref of a pull request in a stack.
+type RemoteStackPRHead struct {
+	Ref string `json:"ref"`
+	Sha string `json:"sha"`
+}
+
+// RemoteStackPR is a pull request entry within a remote stack, as returned by
+// the Stacks REST API list/detail endpoints.
+type RemoteStackPR struct {
+	Number   int               `json:"number"`
+	State    string            `json:"state"` // open, closed
+	Draft    bool              `json:"draft"`
+	MergedAt *string           `json:"merged_at"`
+	Head     RemoteStackPRHead `json:"head"`
+}
+
+// IsMerged reports whether the pull request has been merged.
+func (p RemoteStackPR) IsMerged() bool {
+	return p.MergedAt != nil && *p.MergedAt != ""
+}
+
+// RemoteStack represents a stack of pull requests as returned by the public
+// Stacks REST API (GET/POST /repos/{owner}/{repo}/stacks...). ID is the
+// internal identifier; Number is the human-facing stack number shown in the
+// github.com UI and used to address the stack in API paths.
+//
+// The API returns pull_requests as an array of objects; UnmarshalJSON flattens
+// them to the ordered PullRequests numbers (bottom to top) and preserves the
+// full entries in PRDetails for callers that need head refs or PR state.
+type RemoteStack struct {
+	ID           int             `json:"id"`
+	Number       int             `json:"number"`
+	NodeID       string          `json:"node_id"`
+	URL          string          `json:"url"`
+	Base         RemoteStackBase `json:"base"`
+	Open         bool            `json:"open"`
+	CreatedAt    string          `json:"created_at"`
+	PullRequests []int           `json:"-"`
+	PRDetails    []RemoteStackPR `json:"-"`
+}
+
+// UnmarshalJSON decodes the Stacks REST API representation, deriving the
+// ordered PullRequests numbers from the pull_requests objects.
+func (s *RemoteStack) UnmarshalJSON(data []byte) error {
+	type wire struct {
+		ID           int             `json:"id"`
+		Number       int             `json:"number"`
+		NodeID       string          `json:"node_id"`
+		URL          string          `json:"url"`
+		Base         RemoteStackBase `json:"base"`
+		Open         bool            `json:"open"`
+		CreatedAt    string          `json:"created_at"`
+		PullRequests []RemoteStackPR `json:"pull_requests"`
+	}
+	var w wire
+	if err := json.Unmarshal(data, &w); err != nil {
+		return err
+	}
+	s.ID = w.ID
+	s.Number = w.Number
+	s.NodeID = w.NodeID
+	s.URL = w.URL
+	s.Base = w.Base
+	s.Open = w.Open
+	s.CreatedAt = w.CreatedAt
+	s.PRDetails = w.PullRequests
+	s.PullRequests = make([]int, len(w.PullRequests))
+	for i, p := range w.PullRequests {
+		s.PullRequests[i] = p.Number
+	}
+	return nil
+}
+
+// PRNumbers returns the ordered pull request numbers in the stack, from bottom
+// to top.
+func (s *RemoteStack) PRNumbers() []int {
+	return s.PullRequests
+}
+
+// ListStacks returns all stacks in the repository, ordered by stack number
+// (descending). Returns an empty slice if no stacks exist. A 404 response
+// indicates stacked PRs are not enabled for this repository.
 func (c *Client) ListStacks() ([]RemoteStack, error) {
-	path := fmt.Sprintf("repos/%s/%s/cli_internal/pulls/stacks", c.owner, c.repo)
+	path := fmt.Sprintf("repos/%s/%s/stacks", c.owner, c.repo)
 	var stacks []RemoteStack
 	if err := c.rest.Get(path, &stacks); err != nil {
 		return nil, err
@@ -419,58 +500,92 @@ func (c *Client) ListStacks() ([]RemoteStack, error) {
 	return stacks, nil
 }
 
+// FindStackForPR returns the stack that contains the given pull request number,
+// using the list endpoint's server-side pull_request filter. Returns nil
+// (without error) when the PR is not part of any stack.
+func (c *Client) FindStackForPR(prNumber int) (*RemoteStack, error) {
+	path := fmt.Sprintf("repos/%s/%s/stacks?pull_request=%d", c.owner, c.repo, prNumber)
+	var stacks []RemoteStack
+	if err := c.rest.Get(path, &stacks); err != nil {
+		return nil, err
+	}
+	if len(stacks) == 0 {
+		return nil, nil
+	}
+	return &stacks[0], nil
+}
+
+// GetStack fetches a single stack by its stack number.
+func (c *Client) GetStack(stackNumber int) (*RemoteStack, error) {
+	path := fmt.Sprintf("repos/%s/%s/stacks/%d", c.owner, c.repo, stackNumber)
+	var rs RemoteStack
+	if err := c.rest.Get(path, &rs); err != nil {
+		return nil, err
+	}
+	return &rs, nil
+}
+
 // CreateStack creates a stack on GitHub from an ordered list of PR numbers.
-// The PR numbers must be ordered from bottom to top of the stack and must
-// form a valid base-to-head chain. Returns the server-assigned stack ID.
-func (c *Client) CreateStack(prNumbers []int) (int, error) {
+// The PR numbers must be ordered from bottom to top of the stack (at least two)
+// and must form a valid base-to-head chain. Returns the created stack.
+func (c *Client) CreateStack(prNumbers []int) (*RemoteStack, error) {
 	type createStackRequest struct {
-		PullRequestNumbers []int `json:"pull_request_numbers"`
+		PullRequests []int `json:"pull_requests"`
 	}
 
-	body, err := json.Marshal(createStackRequest{PullRequestNumbers: prNumbers})
+	body, err := json.Marshal(createStackRequest{PullRequests: prNumbers})
 	if err != nil {
-		return 0, fmt.Errorf("marshaling request: %w", err)
+		return nil, fmt.Errorf("marshaling request: %w", err)
 	}
 
-	path := fmt.Sprintf("repos/%s/%s/cli_internal/pulls/stacks", c.owner, c.repo)
-
-	var response struct {
-		ID int `json:"id"`
+	path := fmt.Sprintf("repos/%s/%s/stacks", c.owner, c.repo)
+	var rs RemoteStack
+	if err := c.rest.Post(path, bytes.NewReader(body), &rs); err != nil {
+		return nil, err
 	}
-
-	if err := c.rest.Post(path, bytes.NewReader(body), &response); err != nil {
-		return 0, err
-	}
-
-	return response.ID, nil
+	return &rs, nil
 }
 
-// UpdateStack adds pull requests to an existing stack on GitHub.
-// The stack is identified by stackID. The full list of PR numbers in the
-// updated stack must be provided, including existing and new PRs, ordered
-// from bottom to top.
-func (c *Client) UpdateStack(stackID string, prNumbers []int) error {
-	type updateStackRequest struct {
-		PullRequestNumbers []int `json:"pull_request_numbers"`
+// AddToStack appends pull requests to the top of an existing stack. Only the
+// new PR numbers (the delta) should be provided, ordered from the current top
+// of the stack upward. Returns the updated stack.
+func (c *Client) AddToStack(stackNumber int, prNumbers []int) (*RemoteStack, error) {
+	type addToStackRequest struct {
+		PullRequests []int `json:"pull_requests"`
 	}
 
-	body, err := json.Marshal(updateStackRequest{PullRequestNumbers: prNumbers})
+	body, err := json.Marshal(addToStackRequest{PullRequests: prNumbers})
 	if err != nil {
-		return fmt.Errorf("marshaling request: %w", err)
+		return nil, fmt.Errorf("marshaling request: %w", err)
 	}
 
-	path := fmt.Sprintf("repos/%s/%s/cli_internal/pulls/stacks/%s", c.owner, c.repo, stackID)
+	path := fmt.Sprintf("repos/%s/%s/stacks/%d/add", c.owner, c.repo, stackNumber)
+	var rs RemoteStack
+	if err := c.rest.Post(path, bytes.NewReader(body), &rs); err != nil {
+		return nil, err
+	}
+	return &rs, nil
+}
 
-	var response struct {
-		ID int `json:"id"`
+// Unstack removes unlocked pull requests from a stack. The server leaves PRs
+// that cannot be unstacked (queued for merge or with auto-merge enabled) in
+// place. When PRs remain, the updated stack is returned with dissolved=false;
+// when none remain the stack is destroyed and dissolved=true (HTTP 204).
+func (c *Client) Unstack(stackNumber int) (rs *RemoteStack, dissolved bool, err error) {
+	path := fmt.Sprintf("repos/%s/%s/stacks/%d/unstack", c.owner, c.repo, stackNumber)
+	resp, err := c.rest.Request(http.MethodPost, path, nil)
+	if err != nil {
+		return nil, false, err
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode == http.StatusNoContent {
+		return nil, true, nil
 	}
 
-	return c.rest.Put(path, bytes.NewReader(body), &response)
-}
-
-// DeleteStack deletes a stack on GitHub.
-// The stack is identified by stackID. Returns nil on success (204).
-func (c *Client) DeleteStack(stackID string) error {
-	path := fmt.Sprintf("repos/%s/%s/cli_internal/pulls/stacks/%s", c.owner, c.repo, stackID)
-	return c.rest.Delete(path, nil)
+	var remaining RemoteStack
+	if decErr := json.NewDecoder(resp.Body).Decode(&remaining); decErr != nil {
+		return nil, false, fmt.Errorf("decoding unstack response: %w", decErr)
+	}
+	return &remaining, false, nil
 }

internal/github/github_test.go

@@ -1,10 +1,12 @@
 package github
 
 import (
+	"encoding/json"
 	"testing"
 
 	graphql "github.com/cli/shurcooL-graphql"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestPRURL(t *testing.T) {
@@ -80,3 +82,69 @@ func TestToGraphQLInt(t *testing.T) {
 		assert.Error(t, err)
 	})
 }
+
+// TestRemoteStack_UnmarshalJSON verifies the custom decoder that flattens the
+// Stacks REST API's pull_requests object array into ordered PullRequests
+// numbers while preserving the full entries in PRDetails. This is the only path
+// that populates those fields from the wire, so a shape regression here would
+// silently break every stack endpoint.
+func TestRemoteStack_UnmarshalJSON(t *testing.T) {
+	payload := `{
+		"id": 6154,
+		"number": 360,
+		"node_id": "S_kwABCD",
+		"url": "https://api.github.com/repos/o/r/stacks/360",
+		"base": {"ref": "main", "sha": "basesha"},
+		"open": true,
+		"created_at": "2026-01-01T00:00:00Z",
+		"pull_requests": [
+			{"number": 12, "state": "open", "draft": true, "merged_at": null, "head": {"ref": "feat-1", "sha": "sha1"}},
+			{"number": 15, "state": "closed", "draft": false, "merged_at": "2026-01-02T00:00:00Z", "head": {"ref": "feat-2", "sha": "sha2"}}
+		]
+	}`
+
+	var s RemoteStack
+	require.NoError(t, json.Unmarshal([]byte(payload), &s))
+
+	// Top-level metadata.
+	assert.Equal(t, 6154, s.ID)
+	assert.Equal(t, 360, s.Number)
+	assert.Equal(t, "S_kwABCD", s.NodeID)
+	assert.Equal(t, "https://api.github.com/repos/o/r/stacks/360", s.URL)
+	assert.Equal(t, "main", s.Base.Ref)
+	assert.Equal(t, "basesha", s.Base.Sha)
+	assert.True(t, s.Open)
+	assert.Equal(t, "2026-01-01T00:00:00Z", s.CreatedAt)
+
+	// Ordered PR numbers (bottom to top) derived from the object array.
+	assert.Equal(t, []int{12, 15}, s.PullRequests)
+	assert.Equal(t, []int{12, 15}, s.PRNumbers())
+
+	// Full PR entries preserved in PRDetails, including nullable merged_at.
+	require.Len(t, s.PRDetails, 2)
+	assert.Equal(t, 12, s.PRDetails[0].Number)
+	assert.Equal(t, "open", s.PRDetails[0].State)
+	assert.True(t, s.PRDetails[0].Draft)
+	assert.Nil(t, s.PRDetails[0].MergedAt)
+	assert.False(t, s.PRDetails[0].IsMerged())
+	assert.Equal(t, "feat-1", s.PRDetails[0].Head.Ref)
+	assert.Equal(t, "sha1", s.PRDetails[0].Head.Sha)
+
+	assert.Equal(t, 15, s.PRDetails[1].Number)
+	assert.Equal(t, "closed", s.PRDetails[1].State)
+	require.NotNil(t, s.PRDetails[1].MergedAt)
+	assert.Equal(t, "2026-01-02T00:00:00Z", *s.PRDetails[1].MergedAt)
+	assert.True(t, s.PRDetails[1].IsMerged())
+	assert.Equal(t, "feat-2", s.PRDetails[1].Head.Ref)
+}
+
+// TestRemoteStack_UnmarshalJSON_EmptyPRs ensures a stack with no pull_requests
+// decodes to empty (non-nil) slices rather than panicking.
+func TestRemoteStack_UnmarshalJSON_EmptyPRs(t *testing.T) {
+	var s RemoteStack
+	require.NoError(t, json.Unmarshal([]byte(`{"id": 1, "number": 2, "pull_requests": []}`), &s))
+	assert.Equal(t, 1, s.ID)
+	assert.Equal(t, 2, s.Number)
+	assert.Empty(t, s.PullRequests)
+	assert.Empty(t, s.PRDetails)
+}

internal/github/mock_client.go

@@ -12,9 +12,11 @@ type MockClient struct {
 	MarkPRReadyForReviewFn   func(string) error
 	DisableAutoMergeFn       func(string) error
 	ListStacksFn             func() ([]RemoteStack, error)
-	CreateStackFn            func([]int) (int, error)
-	UpdateStackFn            func(string, []int) error
-	DeleteStackFn            func(string) error
+	FindStackForPRFn         func(int) (*RemoteStack, error)
+	GetStackFn               func(int) (*RemoteStack, error)
+	CreateStackFn            func([]int) (*RemoteStack, error)
+	AddToStackFn             func(int, []int) (*RemoteStack, error)
+	UnstackFn                func(int) (*RemoteStack, bool, error)
 }
 
 // Compile-time check that MockClient satisfies ClientOps.
@@ -76,23 +78,37 @@ func (m *MockClient) ListStacks() ([]RemoteStack, error) {
 	return nil, nil
 }
 
-func (m *MockClient) CreateStack(prNumbers []int) (int, error) {
+func (m *MockClient) FindStackForPR(prNumber int) (*RemoteStack, error) {
+	if m.FindStackForPRFn != nil {
+		return m.FindStackForPRFn(prNumber)
+	}
+	return nil, nil
+}
+
+func (m *MockClient) GetStack(stackNumber int) (*RemoteStack, error) {
+	if m.GetStackFn != nil {
+		return m.GetStackFn(stackNumber)
+	}
+	return &RemoteStack{}, nil
+}
+
+func (m *MockClient) CreateStack(prNumbers []int) (*RemoteStack, error) {
 	if m.CreateStackFn != nil {
 		return m.CreateStackFn(prNumbers)
 	}
-	return 0, nil
+	return &RemoteStack{}, nil
 }
 
-func (m *MockClient) UpdateStack(stackID string, prNumbers []int) error {
-	if m.UpdateStackFn != nil {
-		return m.UpdateStackFn(stackID, prNumbers)
+func (m *MockClient) AddToStack(stackNumber int, prNumbers []int) (*RemoteStack, error) {
+	if m.AddToStackFn != nil {
+		return m.AddToStackFn(stackNumber, prNumbers)
 	}
-	return nil
+	return &RemoteStack{}, nil
 }
 
-func (m *MockClient) DeleteStack(stackID string) error {
-	if m.DeleteStackFn != nil {
-		return m.DeleteStackFn(stackID)
+func (m *MockClient) Unstack(stackNumber int) (*RemoteStack, bool, error) {
+	if m.UnstackFn != nil {
+		return m.UnstackFn(stackNumber)
 	}
-	return nil
+	return nil, false, nil
 }

internal/stack/schema.json

@@ -28,7 +28,11 @@
       "properties": {
         "id": {
           "type": "string",
-          "description": "Identifier for this stack, populated from the API when available."
+          "description": "Global identifier for this stack, populated from the API when available."
+        },
+        "number": {
+          "type": "integer",
+          "description": "Repo-scoped number identifying this stack, displayed in the GitHub UI. Used as the primary way to reference a stack."
         },
         "prefix": {
           "type": "string",

internal/stack/stack.go

@@ -43,6 +43,7 @@ type BranchRef struct {
 // Stack represents a single stack of branches.
 type Stack struct {
 	ID       string      `json:"id,omitempty"`
+	Number   int         `json:"number,omitempty"`
 	Prefix   string      `json:"prefix,omitempty"`
 	Numbered bool        `json:"numbered,omitempty"`
 	Trunk    BranchRef   `json:"trunk"`

internal/stack/stack_test.go

@@ -235,6 +235,7 @@ func TestLoad_Save_RoundTrip(t *testing.T) {
 			Stacks: []Stack{
 				{
 					ID:     "s1",
+					Number: 7,
 					Prefix: "feat",
 					Trunk:  BranchRef{Branch: "main", Head: "abc123"},
 					Branches: []BranchRef{
@@ -256,6 +257,7 @@ func TestLoad_Save_RoundTrip(t *testing.T) {
 
 		s := loaded.Stacks[0]
 		assert.Equal(t, "s1", s.ID)
+		assert.Equal(t, 7, s.Number)
 		assert.Equal(t, "feat", s.Prefix)
 		assert.Equal(t, "main", s.Trunk.Branch)
 		assert.Equal(t, "abc123", s.Trunk.Head)