Review fixes: restore _build_sessions, fix flags, search filter, tests ...

- Restored _load_messages_map and _build_sessions helpers that were
  accidentally dropped in Phase 5 (list_all/list_page/search_list
  called them but they were missing, causing NameError at runtime)
- _build_sessions now filters messages by is_display so list methods
  return consistent display-only history like get()
- count_all/search_list EXISTS subquery now filters to is_display=true
  so search only matches visible chat messages
- Updated pg_session_store docstring to remove stale dual-write claim
- compressor summary_msg now defaults to is_display=False
- Added unit tests for message flags (agent, compressor, planning)

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

Phase 2: Dual-write with is_context/is_display flags on Message ...

- Message model gets is_context and is_display bools
- PgSessionStore.save() writes flags directly to session_messages
- Agent sets is_context=False on display-only messages, is_display=False on context-only
- Planning: plan context msg is_display=False, plan marker is_context=False
- Compression: summarized messages get is_context=False, summary added to messages with is_display=False
- Tests updated for extra user display+context messages per turn

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

Add subagent progress report on failure ...

When a subagent stops (timeout, max iterations, thinking stall, user stop),
it now returns a structured progress report built from its local message
context, so the parent agent knows what tools were called and what was
accomplished before the stop.

- Add _build_progress_report() to SubAgentRunner
- Report includes: turn number, assistant text, tool calls with results
- Prepended to result_text for every stop reason (completed also gets it)
- Updated test_run_ephemeral_complete to expect the report prefix

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

Fix token counting: show only completion tokens, not cumulative prompt+completion ...

The token_count displayed next to assistant messages was summing
prompt_tokens + completion_tokens across ALL tool-calling iterations,
giving hundreds of thousands of tokens for multi-turn conversations.

Now:
- token_count (coins icon) = only completion tokens generated by the model
- context_tokens (ContextBar) = only prompt tokens (context size sent to LLM)

This gives users a realistic measure of how much the model actually generated.

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>