refactor(tests+frontend): one http_sink helper for the hook tests; apiErrorMessage replaces ten hand-rolled error-body parses; type X, import specifiers are not definitions (#2904, milestone 299 step 6)

tests/helpers.http_sink replaces three module-local _Sink handlers (the
write-path tests and the after-write test). ProjectView + SettingsView
parsed `(e as {body?:{error?}}).body?.error || fallback` by hand ten times
beside the apiErrorMessage canon (#2853) - all ten now call it. The
extractor (server + the hook awk mirror) no longer reads `import { type Foo }`
as a definition of Foo - that was the last "identical body" sym family.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/helpers.py

@@ -6,6 +6,7 @@ them; a module imports what it needs with ``from tests.helpers import ...``.
 """
 from __future__ import annotations
 
+from contextlib import contextmanager
 from datetime import datetime, timezone
 from types import SimpleNamespace
 from unittest.mock import AsyncMock, MagicMock
@@ -182,3 +183,39 @@ def design_token_stub(name, value_by_mode, group_name=None, purpose=None,
         name=name, value_by_mode=value_by_mode, group_name=group_name,
         purpose=purpose, order_index=order_index, supersedes=supersedes or [],
     )
+
+
+@contextmanager
+def http_sink(reply: bytes = b'{"context":"","note_ids":[]}'):
+    """A throwaway local HTTP listener for hook end-to-end tests: yields
+    ``(port, seen)`` where ``seen`` collects every GET's parsed query string
+    (one dict per request, in order). Lets the shell be tested end to end —
+    the extraction, the encoding, the URL — without a Scribe instance.
+
+    Three test modules each carried their own ``_Sink`` handler before #2904
+    consolidated them here; pass ``reply`` for the body the hook should see.
+    """
+    import http.server
+    import threading
+    import urllib.parse
+
+    seen: list[dict] = []
+
+    class _Sink(http.server.BaseHTTPRequestHandler):
+        def do_GET(self):
+            seen.append(urllib.parse.parse_qs(urllib.parse.urlparse(self.path).query))
+            self.send_response(200)
+            self.send_header("Content-Type", "application/json")
+            self.end_headers()
+            self.wfile.write(reply)
+
+        def log_message(self, *a):
+            pass
+
+    server = http.server.HTTPServer(("127.0.0.1", 0), _Sink)
+    threading.Thread(target=server.serve_forever, daemon=True).start()
+    try:
+        yield server.server_port, seen
+    finally:
+        server.shutdown()
+        server.server_close()