todo: give plans their own table and recover them after a crash ...

Todo already survived restarts inside the generic session_store KV row, but
the plan there was opaque JSON with no timestamp: after a server crash the
agent resumed a step marked in_progress with no way to tell whether it had
ever been done.

session_todos (user_id, session_id, tasks JSONB, revision, updated_at) now
holds the plan. Existing rows are migrated on first use and the KV source is
deleted in the same step, so clearing a plan is not undone by the next
process start.

Each step gains provenance fields (source, step_id, protocol_run_id) for the
protocol work, and insert_steps() splices a block after the step the agent
has already reached instead of making it re-issue the whole plan.

get_progress_message() now flags a plan whose in_progress step predates this
process once per (session, revision): re-check the real result before
marking it done.

The todo op "clear" now uses the same user scope as load/save; it used to
prefer ctx.user_id and could delete a different row than the one written.

Extract single shared Database pool, eliminate 4 duplicated pool creations ...

- Create navi/db.py::Database managing one asyncpg pool
- KvStore, PgSessionStore, MemoryStore, RecallScheduler now accept pool in constructor
- AppContainer holds Database, shutdown closes one pool instead of 4
- create_container creates one pool and passes it to all stores
- All tests updated to set _initialized=True on fakes to skip DDL

392 passed, 1 skipped

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Extract ContextCompressor, fix STL viewer, expand test suite, add architecture audit docs ...

- Extract ContextCompressor from agent.py (Step 1 of god-object refactor)
- Add retry + hard-truncate fallback logic to ContextCompressor
- Add unit tests: agent loop (14), compressor (18), KV store (8),
  auth encrypt (3), auth deps (13), todo/scratchpad/image_view/memory
- Fix WebGL STL viewer: allow-same-origin sandbox + graceful fallback
- Add CompressionStarted event and client-side compression notice
- Add docs/architecture_weak_spots.md and plan_01_god_object_agent.md
- Update test_events.py and test_agent_context_size.py for new logic

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>