test(#149): Add comprehensive rejection loop integration tests

Add integration tests validating rejection loop behavior:
- Agent claims done with failing tests → rejection + forced continuation
- Agent claims done with linting errors → rejection + forced continuation
- Agent claims done with low coverage → rejection + forced continuation
- Agent claims done with build errors → rejection + forced continuation
- All gates passing → completion allowed
- Multiple simultaneous failures → comprehensive rejection
- Continuation prompts are non-negotiable and directive
- Agents cannot bypass quality gates
- Remediation steps included in prompts

All 9 tests pass.
Build gate: passes
Lint gate: passes
Test gate: passes (100% pass rate)
Coverage: quality_orchestrator.py at 85%, forced_continuation.py at 100%

Refs #149

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

docs/scratchpads/149-test-rejection-loop.md

@@ -0,0 +1,41 @@
+# Issue #149: [COORD-009] Test rejection loop
+
+## Objective
+
+Validate quality gates prevent premature completion through simulated rejection scenarios.
+
+## Approach
+
+1. Create comprehensive integration tests for rejection loop scenarios
+2. Test each gate failure type triggers proper rejection
+3. Verify forced continuation prompts are generated correctly
+4. Ensure agents cannot bypass gates
+5. Validate loop continues until all gates pass
+
+## Test Scenarios
+
+- [ ] Agent claims done with failing tests
+- [ ] Agent claims done with linting errors
+- [ ] Agent claims done with low coverage
+- [ ] Agent claims done with build errors
+- [ ] All gates passing allows completion
+- [ ] Multiple simultaneous gate failures handled correctly
+- [ ] Forced continuation prompts are non-negotiable and actionable
+
+## Progress
+
+- [x] Read existing QualityOrchestrator and ForcedContinuationService code
+- [x] Write comprehensive integration tests (TDD)
+- [x] Run tests - all 9 tests pass
+- [x] Fix linting issues
+- [x] Run type checking - passes
+- [x] All quality gates pass
+- [ ] Commit changes
+
+## Testing
+
+Test file: `apps/coordinator/tests/test_rejection_loop.py`
+
+## Notes
+
+The services already exist from Issue 148, so this is primarily testing the rejection loop behavior through integration tests that simulate agent completion scenarios.