fix(mcp): stamp last_seen_at on /speak too + tighten path predicate

POST /speak is a REST wrapper around voicebox.speak for agents that
don't talk MCP (shell scripts, ACP, A2A). It reads X-Voicebox-Client-Id
and uses it for the same per-client profile resolution + default
personality lookup the MCP tool does (speak.py:39-64), so its callers
are first-class clients — but the ClientIdMiddleware only stamped
last_seen_at on /mcp* paths. REST speak callers showed up as "never
seen" in Settings → MCP despite actively acting on their bindings.

Widen the stamp predicate to an explicit ("/mcp", "/speak") prefix
list, and require a path boundary on match so future routes named
/mcpfoo or /speakers don't silently inherit the stamp via the prefix.
New test_client_id_middleware.py pins the scope with 17 parametrised
cases (both the allowed set and the overlap cases that must not match).

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

backend/tests/test_client_id_middleware.py

@@ -0,0 +1,49 @@
+"""Unit tests for the ClientIdMiddleware path predicate.
+
+Locks down which endpoints advance ``last_seen_at`` on the
+``MCPClientBinding`` row. Getting this wrong is silent: the Settings UI
+just shows a stale "last heard from" timestamp and bindings never get
+auto-created for new REST callers.
+"""
+
+import pytest
+
+from backend.mcp_server.context import _is_stamped_path
+
+
+@pytest.mark.parametrize(
+    "path",
+    [
+        "/mcp",
+        "/mcp/",
+        "/mcp/tools/call",
+        "/mcp/bindings",  # admin REST; benign — frontend never sets the header
+        "/speak",
+        "/speak/",
+    ],
+)
+def test_mcp_semantic_paths_are_stamped(path: str) -> None:
+    assert _is_stamped_path(path) is True
+
+
+@pytest.mark.parametrize(
+    "path",
+    [
+        "/",
+        "/health",
+        "/generate",
+        "/captures",
+        "/profiles",
+        "/profiles/abc/compose",
+        "/events/speak",
+        "/tasks/active",
+        "/llm/generate",
+        # Prefix overlap should not match — /speakers is a hypothetical
+        # future endpoint that shouldn't leak the stamp.
+        "/speakers",
+        # Same for anything starting with /mcpfoo.
+        "/mcpfoo",
+    ],
+)
+def test_other_paths_are_not_stamped(path: str) -> None:
+    assert _is_stamped_path(path) is False