fix: tighten input_schema per Volcengine Jimeng 3.0 Pro contract

- frames: enum [121, 241] (was minimum 1)
- prompt: maxLength 800 (was 2000)
- seed: minimum -1 (was unbounded)
- Add 9 schema validation rejection tests
- Add authoritative API reference link to PROVIDERS.md
- Document CVSync2Async* route choice and schema constraints

Fixes calesthio's second review feedback on PR #341.

docs/PROVIDERS.md

@@ -123,8 +123,17 @@ Authentication uses Volcengine IAM V4 signing (HMAC-SHA256), not a Bearer token.
 
 API flow: `POST ?Action=CVSync2AsyncSubmitTask` → poll `POST ?Action=CVSync2AsyncGetResult` → download `video_url`.
 
+The implementation uses the compatible generic `CVSync2Async*` route (API version `2022-08-31`) rather than the model-specific `2024-06-06` actions presented in the public API explorer. This is intentional — the generic route supports the same Jimeng 3.0 Pro model via `req_key` while remaining stable across model updates.
+
 The `req_key` for video is `jimeng_ti2v_v30_pro`. Success code is `10000`. Task statuses: `in_queue`, `generating`, `done`, `not_found`, `expired`.
 
+**Authoritative API reference:** [Jimeng TI2V V30 Pro SubmitTask](https://api.volcengine.com/api-docs/view?action=JimengTI2VV30PROSubmitTask&serviceCode=cv&version=2024-06-06)
+
+**Schema constraints** (enforced by `input_schema` to prevent paid-call failures):
+- `prompt`: max 800 characters
+- `frames`: must be exactly `121` (5s) or `241` (10s) at 24fps
+- `seed`: `-1` for random, or any non-negative integer
+
 #### Pricing
 
 | Model | Price |

tests/contracts/test_jimeng_video.py

@@ -318,3 +318,63 @@ class TestRegistryDiscovery:
         jimeng = [t for t in registry._tools.values() if t.name == "jimeng_video"]
         assert len(jimeng) == 1
         assert jimeng[0].provider == "volcengine"
+
+
+# ------------------------------------------------------------------
+# Schema validation — reject invalid inputs before paid API call
+# ------------------------------------------------------------------
+
+class TestSchemaValidation:
+
+    def test_frames_accepts_121(self):
+        schema = JimengVideo().input_schema
+        valid = schema["properties"]["frames"]
+        assert valid["enum"] == [121, 241]
+
+    def test_frames_rejects_non_enum(self):
+        import jsonschema
+        schema = JimengVideo().input_schema
+        for invalid in [1, 100, 200, 500, 0, -1]:
+            instance = {"prompt": "test", "frames": invalid}
+            with pytest.raises(jsonschema.ValidationError):
+                jsonschema.validate(instance, schema)
+
+    def test_prompt_max_length_800(self):
+        schema = JimengVideo().input_schema
+        assert schema["properties"]["prompt"]["maxLength"] == 800
+
+    def test_prompt_rejects_over_800_chars(self):
+        import jsonschema
+        schema = JimengVideo().input_schema
+        instance = {"prompt": "x" * 801}
+        with pytest.raises(jsonschema.ValidationError):
+            jsonschema.validate(instance, schema)
+
+    def test_prompt_accepts_800_chars(self):
+        import jsonschema
+        schema = JimengVideo().input_schema
+        instance = {"prompt": "x" * 800}
+        jsonschema.validate(instance, schema)
+
+    def test_seed_minimum_is_negative_one(self):
+        schema = JimengVideo().input_schema
+        assert schema["properties"]["seed"]["minimum"] == -1
+
+    def test_seed_rejects_below_negative_one(self):
+        import jsonschema
+        schema = JimengVideo().input_schema
+        for invalid in [-2, -10, -100]:
+            instance = {"prompt": "test", "seed": invalid}
+            with pytest.raises(jsonschema.ValidationError):
+                jsonschema.validate(instance, schema)
+
+    def test_seed_accepts_negative_one(self):
+        import jsonschema
+        schema = JimengVideo().input_schema
+        jsonschema.validate({"prompt": "test", "seed": -1}, schema)
+
+    def test_seed_accepts_zero_and_positive(self):
+        import jsonschema
+        schema = JimengVideo().input_schema
+        for valid in [0, 1, 42, 999999]:
+            jsonschema.validate({"prompt": "test", "seed": valid}, schema)

tools/video/jimeng_video.py

@@ -86,7 +86,8 @@ class JimengVideo(BaseTool):
         "properties": {
             "prompt": {
                 "type": "string",
-                "description": "Video description. Max 2000 chars. Supports Chinese.",
+                "maxLength": 800,
+                "description": "Video description. Max 800 chars. Supports Chinese.",
             },
             "operation": {
                 "type": "string",
@@ -102,7 +103,7 @@ class JimengVideo(BaseTool):
             },
             "frames": {
                 "type": "integer",
-                "minimum": 1,
+                "enum": [121, 241],
                 "default": 121,
                 "description": "Total frames. 121=5s, 241=10s at 24fps.",
             },
@@ -113,6 +114,7 @@ class JimengVideo(BaseTool):
             },
             "seed": {
                 "type": "integer",
+                "minimum": -1,
                 "default": -1,
                 "description": "Random seed. -1 for random.",
             },