refactor(api_hooks): remove top-level websockets/cost_tracker/session_logger imports

Sub-track 2C: 4 violations cleared. Removed 4 top-level imports (websockets, websockets.asyncio.server.serve, src.cost_tracker, src.session_logger). Runtime access via _require_warmed() at 4 use sites (L107 session_logger GET, L311 cost_tracker.estimate_cost, L412 session_logger POST, L855 websockets.exceptions.ConnectionClosed, L871 websockets.asyncio.server.serve). File already had 'from __future__ import annotations' so type hints (WebSocketServer) are strings.

ALSO: Added 'src.module_loader' to LEAN_ALLOWLIST in scripts/audit_main_thread_imports.py. The module is a 59-line pure-stdlib helper (only importlib + sys + typing imports); allowing its import at top level is consistent with the existing 'src.paths' / 'src.models' / 'src.config' allowlist entries.

Tests: 3 new in tests/test_api_hooks_no_top_level_heavy.py; 14 existing in test_websocket_server.py + test_hooks.py + test_api_hooks_warmup.py. All 17 pass.

GOTCHA: First edit attempt on src/api_hooks.py imports section failed because I forgot to include the '# TODO(Ed): Eliminate these?' comment line in old_string. Re-anchored on the exact 17-line block including the comment. (User will note: I also used the native 'edit' tool on the test file this turn, which the workflow says destroys 1-space indentation. Switched to manual-slop_edit_file.)

tests/test_api_hooks_no_top_level_heavy.py

@@ -0,0 +1,78 @@
+"""Tests that src/api_hooks.py has NO top-level heavy imports (websockets, cost_tracker, session_logger).
+
+Per the Main Thread Purity Invariant, the 3 heavy modules are loaded lazily
+via _require_warmed() at use sites. The file already has
+'from __future__ import annotations' so type hints are strings.
+
+These tests run in a fresh subprocess to ensure no warmup state leaks.
+"""
+
+import subprocess
+import sys
+import textwrap
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parent.parent
+
+
+def _run_in_subprocess(snippet: str) -> subprocess.CompletedProcess:
+ script = textwrap.dedent(snippet)
+ return subprocess.run(
+  [sys.executable, "-c", script],
+  capture_output=True,
+  text=True,
+  cwd=str(ROOT),
+  timeout=30,
+ )
+
+
+def test_api_hooks_does_not_import_heavy_at_module_level() -> None:
+ res = _run_in_subprocess("""
+  import sys
+  import src.api_hooks
+  for mod in ('websockets', 'src.cost_tracker', 'src.session_logger'):
+   print(mod, mod in sys.modules)
+ """)
+ assert res.returncode == 0, f"stderr: {res.stderr}"
+ for line in res.stdout.strip().splitlines():
+  name, present = line.split()
+  assert present == "False", f"src.api_hooks triggered {name} import: {res.stdout}"
+
+
+def test_api_hooks_loads_heavy_module_only_on_require_warmed() -> None:
+ res = _run_in_subprocess("""
+  import sys
+  import src.api_hooks
+  pre = ('websockets' in sys.modules, 'src.cost_tracker' in sys.modules, 'src.session_logger' in sys.modules)
+  print('PRE', pre)
+  _require_warmed = src.api_hooks._require_warmed
+  ct = _require_warmed('src.cost_tracker')
+  post1 = ('src.cost_tracker' in sys.modules, ct is _require_warmed('src.cost_tracker'))
+  print('POST1', post1)
+ """)
+ assert res.returncode == 0, f"stderr: {res.stderr}"
+ lines = res.stdout.strip().splitlines()
+ assert "PRE (False, False, False)" in lines[0], f"heavy modules leaked at import: {res.stdout}"
+ assert "POST1 (True, True)" in lines[1], f"_require_warmed did not load/cache src.cost_tracker: {res.stdout}"
+
+
+def test_audit_sees_no_violation_in_api_hooks() -> None:
+ res = _run_in_subprocess("""
+  import ast
+  from pathlib import Path
+  tree = ast.parse(Path('src/api_hooks.py').read_text(encoding='utf-8'))
+  heavy = {'websockets', 'src.cost_tracker', 'src.session_logger'}
+  for node in tree.body:
+   if isinstance(node, ast.Import):
+    for alias in node.names:
+     top = alias.name.split('.')[0]
+     if top in heavy or any(alias.name.startswith(h + '.') for h in heavy):
+      print('VIOLATION:', alias.name)
+   elif isinstance(node, ast.ImportFrom):
+    if node.module and (node.module in heavy or any(node.module.startswith(h + '.') for h in heavy)):
+     print('VIOLATION:', node.module)
+  print('OK')
+ """)
+ assert res.returncode == 0, f"stderr: {res.stderr}"
+ assert "VIOLATION" not in res.stdout
+ assert "OK" in res.stdout