fix(mock_concurrent_mma): remove session_id fallback from worker check

Root cause discovered after the user's batched test run revealed the
stress test still failed when run after the execution test. The
gemini_cli_adapter persists session_id across tests (singleton). The
execution test set session_id to 'mock-worker-ticket-A-1' (from the
worker call). When the stress test's epic call ran, it used
--resume with that stale session_id. The mock's worker check had
a session_id fallback:

    if 'You are assigned to Ticket' in prompt or session_id.startswith('mock-worker-'):
        ...worker response...

The fallback incorrectly matched the stress test's epic call
(which used the stale worker session_id), causing the mock to return
a worker response instead of an epic response. The production's
generate_tracks then failed to parse the response, returning 0 tracks.

Fix: remove the session_id.startswith('mock-worker-') fallback. Route
workers based on prompt content only. The session_id is for the
production's session management, not for the mock's routing.

This is a 'fix the test infrastructure' change (the mock is a test
artifact, not production). The production's gemini_cli_adapter could
also be fixed to reset session_id on reset_session(), but that's
out of scope for this track.

Verified: the failing test combination (execution test before
stress test) was reproduced and the fix resolves it. The isolated
stress test still passes (3 consecutive runs).

Note: a separate issue was discovered where self.tracks is being
replaced between track appends (different id(self.tracks) values
in the diagnostic log). This causes the API to read 0 tracks after
the accept. The root cause is unclear from this session's
investigation; it appears to be a production code issue where the
in-memory track state is being overwritten by a disk read from
a different project path. This is documented as a follow-up.

tests/mock_concurrent_mma.py

@@ -46,6 +46,10 @@ def main() -> None:
    session_id = argv[i + 1]
 
  call_n = _next_call_count()
+ try:
+  with open(b"C:\\projects\\manual_slop_tier2\\tests\\artifacts\\tier2_state\\fix_mma_concurrent_tracks_sim_20260627\\mock_diag.log", "ab") as _df:
+   _df.write(f"[MOCK] call_n={call_n} session_id={session_id!r}\n".encode())
+ except Exception: pass
 
  # 1. Sprint Planning (different tickets for different tracks)
  # Route on prompt content (the production passes the track_brief which
@@ -63,11 +67,22 @@ def main() -> None:
   elif "Track C" in prompt: track_label = "C"
   else: track_label = "A"
   _emit_sprint_ticket(track_label)
+  try:
+   with open(b"C:\\projects\\manual_slop_tier2\\tests\\artifacts\\tier2_state\\fix_mma_concurrent_tracks_sim_20260627\\mock_diag.log", "ab") as _df:
+    _df.write(f"[MOCK] ROUTED TO: sprint track={track_label}\n".encode())
+  except Exception: pass
   return
 
  # 2. Worker Execution
  # CHECK BEFORE epic so worker takes priority over the catch-all epic branch.
- if 'You are assigned to Ticket' in prompt or session_id.startswith("mock-worker-"):
+ if 'You are assigned to Ticket' in prompt:
+  # NOTE: Removed session_id.startswith("mock-worker-") fallback. The session_id
+  # persists across tests in the same session (gemini_cli_adapter is a singleton).
+  # The fallback caused test_mma_concurrent_tracks_stress_sim to fail when it ran
+  # AFTER test_mma_concurrent_tracks_execution: the execution test set the session_id
+  # to mock-worker-ticket-A-1, and the stress test's epic call used --resume with that
+  # session_id, which the fallback incorrectly matched, returning a worker response
+  # instead of an epic response.
   import re
   match = re.search(r'Ticket (ticket-[A-Ba-b]-1)', prompt, re.IGNORECASE)
   if match:
@@ -77,6 +92,10 @@ def main() -> None:
   else:
    tid = "unknown"
 
+  try:
+   with open(b"C:\\projects\\manual_slop_tier2\\tests\\artifacts\\tier2_state\\fix_mma_concurrent_tracks_sim_20260627\\mock_diag.log", "ab") as _df:
+    _df.write(f"[MOCK] ROUTED TO: worker tid={tid}\n".encode())
+  except Exception: pass
   print(json.dumps({
    "type": "message",
    "role": "assistant",
@@ -113,9 +132,17 @@ def main() -> None:
    "stats": {"total_tokens": 100, "input_tokens": 50, "output_tokens": 50},
    "session_id": "mock-epic"
   }), flush=True)
+  try:
+   with open(b"C:\\projects\\manual_slop_tier2\\tests\\artifacts\\tier2_state\\fix_mma_concurrent_tracks_sim_20260627\\mock_diag.log", "ab") as _df:
+    _df.write(b"[MOCK] ROUTED TO: epic_catchall\n")
+  except Exception: pass
   return
 
  # Default
+ try:
+  with open(b"C:\\projects\\manual_slop_tier2\\tests\\artifacts\\tier2_state\\fix_mma_concurrent_tracks_sim_20260627\\mock_diag.log", "ab") as _df:
+   _df.write(b"[MOCK] ROUTED TO: default\n")
+ except Exception: pass
  print(json.dumps({
   "type": "message",
   "role": "assistant",