* fix: simplify conversation storage — atomic assistant rows with tool_calls JSON
Replace the denormalized storage model (separate rows for assistant
content, tool_call, tool_result) with atomic assistant rows carrying
tool_calls as a JSON column. Eliminates the 100-line heuristic
reconstruct_messages function and its cross-turn merge bug.
Schema: add tool_calls TEXT column to conversations (migration 013).
Migration backfills existing data — merges tool_call rows into their
parent assistant row as JSON, renames tool_result to tool, deletes
consumed tool_call rows.
Session save path: assistant content + tool_calls saved in one
save_message call before tool execution (crash resilient). Tool
results saved as role="tool".
Extract shared storage utilities to _utils.py: row_to_dict, mutable
field frozensets, reconstruct_messages. Both backends import from
_utils — PostgreSQL no longer depends on _sqlite.py.
Includes denied/blocked tool call badge fix on resume: _build_history
detects denied results and propagates flag to parent assistant entry.
Frontend uses flag for correct badge-denied rendering. Denied tools
visually muted. role="status" on badges for accessibility.
Net -45 lines. 8 new tests for reconstruction, all 1914 tests pass.
* fix: migration 013 uses parameterized deletes and ordered downgrade
- DELETE of consumed tool_call rows now uses parameterized batches
(chunks of 500) instead of string interpolation
- Downgrade rebuilds via temp table to preserve chronological id
ordering when re-inserting tool_call rows
Patrick Buckley