docs(09-03): complete scenario C corridor efficiency TDD plan

Phase 9 complete: All three trip planner modes validated with TDD.

Summary of 09-03 accomplishments:
- Feature 1: Corridor game inclusion (5 tests, 1 fix)
  - Enhanced findDirectionalStadiums() to exclude beyond-endpoint games
- Feature 2: Anti-backtracking validation (7 tests, all passed)
  - Confirmed existing implementation validates monotonic progress

12 tests added, 3 commits (2 test, 1 feat).

State updates:
- Progress: 30% → 40%
- Phase 9: Complete (3/3 plans)
- Next: Phase 10 (Trip Builder Options TDD)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.planning/STATE.md

@@ -10,11 +10,11 @@ See: .planning/PROJECT.md (updated 2026-01-10)
 ## Current Position
 
 Phase: 9 of 12 (Trip Planner Modes TDD)
-Plan: 2 of 3 in current phase
-Status: In progress, executing plans
-Last activity: 2026-01-10 — Completed 09-02: Scenario B filler conflict TDD
+Plan: 3 of 3 in current phase
+Status: Phase complete
+Last activity: 2026-01-10 — Completed 09-03: Scenario C corridor efficiency TDD
 
-Progress: ███░░░░░░░ 30%
+Progress: ████░░░░░░ 40%
 
 ## Shipped Milestones
 
@@ -46,10 +46,11 @@ None.
 ### Roadmap Evolution
 
 - Milestone v1.1 TDD & Correctness created: Test-driven validation of trip planning engine, 5 phases (Phase 8-12)
+- Phase 9.1 inserted after Phase 9: Fix flaky test when ran in parallel (URGENT) - 5 tests fail in parallel but pass individually due to Swift Testing state pollution
 
 ## Session Continuity
 
 Last session: 2026-01-10
-Stopped at: Plan 09-02 complete (filler conflict TDD)
+Stopped at: Phase 9 complete (trip planner modes TDD)
 Resume file: None
-Next action: /gsd:execute-plan .planning/phases/09-trip-planner-modes-tdd/09-03-PLAN.md
+Next action: /gsd:execute-plan .planning/phases/10-trip-builder-options-tdd/10-01-PLAN.md