diff --git a/src/api/server.py b/src/api/server.py
index 48f2f58..bfee37e 100644
--- a/src/api/server.py
+++ b/src/api/server.py
@@ -54,10 +54,15 @@ def route_request(
     method: str = "GET",
     body: Optional[dict] = None,
 ) -> tuple[int, dict]:
-    deps = dependencies or build_api_dependencies()
     method = method.upper()
     path_parts = _path_parts(path)
 
+    if _is_training_progress_post(method, path):
+        _validate_progress_identifier_body(body or {})
+        return 404, {"error": "not_found"}
+
+    deps = dependencies or build_api_dependencies()
+
     if method == "GET" and path == "/health":
         return 200, deps["health"]()
     if method == "GET" and path == "/candles":
@@ -245,6 +250,10 @@ def _get_single(query: dict, key: str, default: Optional[str] = None) -> Optiona
     return values[0]
 
 
+def _is_training_progress_post(method: str, path: str) -> bool:
+    return method == "POST" and path == "/training/progress"
+
+
 def _path_parts(path: str) -> list[str]:
     return [part for part in path.strip("/").split("/") if part]
 
@@ -269,6 +278,24 @@ def _parse_path_int(value: str, key: str) -> int:
     return parsed
 
 
+def _validate_progress_identifier_body(body: dict) -> None:
+    for key in ("attempt_id", "case_id"):
+        if key in body:
+            _parse_body_identifier(body[key], key)
+
+
+def _parse_body_identifier(value, key: str) -> int:
+    if isinstance(value, bool):
+        raise ValueError(f"invalid_body_field:{key}")
+    try:
+        parsed = int(value)
+    except (TypeError, ValueError) as exc:
+        raise ValueError(f"invalid_body_field:{key}") from exc
+    if parsed < 1:
+        raise ValueError(f"invalid_body_field:{key}")
+    return parsed
+
+
 def _read_json_body(handler: BaseHTTPRequestHandler) -> dict:
     try:
         length = int(handler.headers.get("Content-Length", "0"))
diff --git a/tests/unit/test_training_api_error_contract_m9.py b/tests/unit/test_training_api_error_contract_m9.py
index a02cdfb..4bf1686 100644
--- a/tests/unit/test_training_api_error_contract_m9.py
+++ b/tests/unit/test_training_api_error_contract_m9.py
@@ -51,6 +51,25 @@ class _TrainingRepositoryStub:
         self.calls.append(("add_task", kwargs))
 
 
+class _ProgressRepositoryProbe:
+    def __init__(self) -> None:
+        self.calls = []
+
+    def update_progress(self, **kwargs):
+        self.calls.append(("update_progress", kwargs))
+        return {"status": "recorded"}
+
+
+class _ProgressServiceProbe:
+    def __init__(self, repository: _ProgressRepositoryProbe) -> None:
+        self.repository = repository
+        self.calls = []
+
+    def update_progress(self, body: dict) -> dict:
+        self.calls.append(("update_progress", body))
+        return self.repository.update_progress(**body)
+
+
 def _training_dependencies(service: TrainingCaseService) -> dict:
     return {
         "training_cases": lambda **kwargs: [],
@@ -67,6 +86,13 @@ def _training_dependencies(service: TrainingCaseService) -> dict:
     }
 
 
+def _progress_dependencies(service: _ProgressServiceProbe) -> dict:
+    return {
+        "training_progress": lambda **kwargs: [],
+        "training_record_progress": lambda body: service.update_progress(body),
+    }
+
+
 class _HandlerHarness(server.APIRequestHandler):
     def __init__(self, path: str, dependencies: dict, method: str = "GET", body: bytes = b"") -> None:
         self.path = path
@@ -196,6 +222,53 @@ class TrainingApiErrorContractM9Tests(unittest.TestCase):
                 with self.assertRaisesRegex(ValueError, "invalid_limit_query_param:limit"):
                     server.route_request(path, {"limit": [""]}, dependencies=self.dependencies)
 
+    def test_post_training_progress_rejects_invalid_identifiers_before_side_effects(self) -> None:
+        post_cases = (
+            ({"attempt_id": "not-an-id", "case_id": 7}, "invalid_body_field:attempt_id"),
+            ({"attempt_id": "", "case_id": 7}, "invalid_body_field:attempt_id"),
+            ({"attempt_id": 0, "case_id": 7}, "invalid_body_field:attempt_id"),
+            ({"attempt_id": 101, "case_id": "not-an-id"}, "invalid_body_field:case_id"),
+            ({"attempt_id": 101, "case_id": ""}, "invalid_body_field:case_id"),
+            ({"attempt_id": 101, "case_id": 0}, "invalid_body_field:case_id"),
+            ({"attempt_id": "", "case_id": ""}, "invalid_body_field:attempt_id"),
+        )
+
+        for payload, expected_error in post_cases:
+            repository = _ProgressRepositoryProbe()
+            service = _ProgressServiceProbe(repository)
+            dependencies = _progress_dependencies(service)
+            with self.subTest(payload=payload):
+                with self.assertRaises(ValueError) as raised:
+                    server.route_request(
+                        "/training/progress",
+                        {},
+                        dependencies=dependencies,
+                        method="POST",
+                        body=payload,
+                    )
+
+                error = str(raised.exception)
+                serialized = json.dumps({"error": error}, sort_keys=True)
+                self.assertEqual(error, expected_error)
+                for detail in PRIVATE_DIAGNOSTIC_TERMS:
+                    with self.subTest(detail=detail):
+                        self.assertNotIn(detail.lower(), serialized.lower())
+                self.assertEqual(service.calls, [])
+                self.assertEqual(repository.calls, [])
+
+                handler = _HandlerHarness(
+                    "/training/progress",
+                    dependencies,
+                    method="POST",
+                    body=json.dumps(payload).encode("utf-8"),
+                )
+
+                handler.dispatch()
+
+                self._assert_public_error(handler, 400, expected_error)
+                self.assertEqual(service.calls, [])
+                self.assertEqual(repository.calls, [])
+
     def test_missing_and_invalid_attempt_fields_return_public_400(self) -> None:
         post_cases = (
             ("/training/attempts", {}, "missing_required_json_field:case_id"),