docs(09): capture phase context

Phase 9: Extended Scenarios
- Vision and goals documented
- Four core scenarios: conflict hand-back, multi-agent, recovery, question/answer
- CI deferred - focus on test coverage

.planning/phases/09-extended-scenarios/09-CONTEXT.md

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+# Phase 9: Extended Scenarios - Context
+
+**Gathered:** 2026-01-31
+**Status:** Ready for planning
+
+<vision>
+## How This Should Work
+
+This phase proves the system handles real-world complexity — not just happy paths, but the messy scenarios that happen when multiple agents work in parallel, things go wrong, and the system needs to recover.
+
+Four core scenarios to validate:
+
+1. **Conflict hand-back** — When a merge fails, the agent receives the conflict and resolves it. The full round-trip works.
+
+2. **Multi-agent parallel work** — Multiple agents dispatched simultaneously, each working in their worktree, merging in correct dependency order.
+
+3. **Recovery/resume after interruption** — System can pick up where it left off after crash or interruption.
+
+4. **Agent question/answer resume** — When an agent asks a question (AskUserQuestion), the system pauses, receives the answer, and the agent continues from where it stopped.
+
+</vision>
+
+<essential>
+## What Must Be Nailed
+
+- **All four scenarios proven** — Each must have E2E test coverage demonstrating the flow works
+- **Conflict resolution round-trip** — Agent receives conflict, fixes it, merge succeeds
+- **Question/answer resume** — Agent pauses for input, receives response, continues execution
+
+</essential>
+
+<specifics>
+## Specific Ideas
+
+- Use MockAgentManager scenarios to simulate waiting_for_input and crash states
+- Use MockWorktreeManager to inject merge conflicts
+- Test multi-agent by pre-seeding multiple idle agents and dispatching parallel tasks
+- No CI pipeline needed — focus purely on test coverage
+
+</specifics>
+
+<notes>
+## Additional Context
+
+CI was explicitly deferred — not part of this phase scope. Phase goal is proving system resilience and coordination, not automation infrastructure.
+
+</notes>
+
+---
+
+*Phase: 09-extended-scenarios*
+*Context gathered: 2026-01-31*