Stabilize OpenCode pending approval/question compatibility

[StatPan]

Goal

Make pending permission/question discovery and reply handling reliable across /api/tree, /api/agent/tree, approval routes, SSE state, and OpenCode 1.3.

Derived from #14 Phase 6 dirty branch handoff.

Scope

• Decide the canonical pending-state source: direct OpenCode REST, SSE broadcaster memory, or a documented merge of both.
• Validate /permission, /question, and /question/:requestID/reply request/response shapes against OpenCode 1.3.
• Update adapter interfaces and route tests together.
• Preserve read-only session state except explicit approval/question replies.

Out of Scope

• Do not change final UI interaction design in this issue.
• Do not push the broad dirty worktree into PR fix: Phase 6 review follow-up — shared util, GET side-effect, dead branch, test gap #13.
• Do not mutate GitHub/Gira state from Agentree runtime.

Acceptance Criteria

Functional:

• GET /api/tree and GET /api/agent/tree expose pending permissions/questions consistently.
• Pending status overrides are deterministic when permission and question are both present.
• Question replies use the OpenCode-compatible payload shape.
• Freeform and option answers have regression tests.
• SSE cleanup after reply/reject is covered by tests or explicitly documented as eventual-consistency behavior.

Code/product quality:

• Adapter boundaries are clear and route mocks match the updated interface.
• Error handling is explicit for missing OpenCode endpoints or malformed pending payloads.
• The route behavior remains read-only except explicit approval/question replies.

Verification

• ./node_modules/.bin/vitest run src/server/routes/agent.test.ts src/server/routes/approval.test.ts src/server/sse/broadcaster.test.ts
• ./node_modules/.bin/tsc -p tsconfig.json --noEmit
• git diff --check
• Optional/manual: run against a live OpenCode 1.3 server with one permission request and one question request.

Notes

Current dirty-branch evidence from #14: route tests fail because agent.ts now calls opencodeAdapter.listPendingPermissions, but the existing test mock does not provide that method. approval.test.ts and broadcaster.test.ts passed in the handoff run.