docs(track): update umbrella with sub-track 2 Phase 14 addendum (11/11 tiers PASS clean)

Added a Phase 14 Update section to the result_migration_20260616
umbrella spec.md documenting:

- The 2 fixes (Issue 1: GUI subprocess crash; Issue 2: xdist race)
- The final test pass count: 11/11 tiers PASS clean
- Sub-track 2 is now fully ready for merge with no documented issues
- Sub-track 3 (result_migration_app_controller) is unblocked

The Phase 14 update is positioned between section 7 (Commits) and
section 8 (See Also), preserving the existing section numbering.

conductor/tracks/result_migration_20260616/spec.md

@@ -437,6 +437,49 @@ Total: 1 + 5*5 = 26 commits across the 5 sub-tracks.
 
 ---
 
+
+## Phase 14 Update (2026-06-18): Live GUI Test Fixes
+
+Sub-track 2 (`result_migration_small_files_20260617`) shipped on
+2026-06-17 with **2 documented test infrastructure issues** that blocked
+full closure. The follow-up track `live_gui_test_fixes_20260618` was
+created and shipped on 2026-06-18 with both fixes applied.
+
+### The 2 fixes
+
+**Issue 1: `test_execution_sim_live` GUI subprocess crash (`tier-3-live_gui`)**
+- Symptom: GUI subprocess (port 8999) crashes mid-test with `0xC00000FD = STATUS_STACK_OVERFLOW`
+- Root cause: `imgui.set_window_focus("Response")` was called directly during the response panel render, exhausting the GUI main thread's 1.94 MB stack on Windows
+- Fix: defer the focus call to the next frame's idle phase via a new `_pending_focus_response` flag
+- Same root cause as `test_z_negative_flows.py` documented in `docs/reports/NEGATIVE_FLOWS_INVESTIGATION_20260617_REFINED.md`
+
+**Issue 2: `test_live_gui_workspace_exists` xdist race (`tier-1-unit-gui`)**
+- Symptom: xdist race where the owner worker's teardown removes the shared workspace path before a client worker's test can assert it exists
+- Root cause: `live_gui_workspace` fixture returned the path without ensuring it existed
+- Fix: call `workspace.mkdir(parents=True, exist_ok=True)` before returning
+- Pre-existing on parent commit `4ab7c732` (verified)
+
+### Final test pass count: 11/11 tiers PASS clean
+
+After both fixes, **all 11 test tiers pass clean** (~825s total). This
+is the final pass count for sub-track 2. The 4 Gemini 503 pre-existing
+skip markers remain (out of scope for the live_gui_test_fixes track;
+deferred to a follow-up track to mock the Gemini API in
+`summarize.summarise_file`).
+
+### Sub-track 2 status
+
+Sub-track 2 (`result_migration_small_files_20260617`) is now FULLY
+ready for merge with no documented issues from the live_gui_test_fixes
+track. Sub-track 3 (`result_migration_app_controller`) is unblocked.
+
+### References
+
+- `conductor/tracks/live_gui_test_fixes_20260618/spec.md` - the fix track spec
+- `conductor/tracks/live_gui_test_fixes_20260618/plan.md` - the fix track plan
+- `docs/reports/TRACK_COMPLETION_live_gui_test_fixes_20260618.md` - the fix track completion report
+- `tests/artifacts/PHASE14_TEST_RUN_RESULTS.log` - 11/11 tier verification
+
 ## 8. See Also
 
 - `conductor/code_styleguides/error_handling.md` — the canonical convention