Move per-use field derivation out of the listing path and into the writer that already opens the same file once at use-completion. The day-index entry is now a complete summary; api_talents_day reads it directly with no per-completed-use file opens. Same on-the-wire JSON shape. Same lode also fixes legacy day indexes (agent_id schema) which previously returned empty. - think/cortex.py: _append_day_index now writes thinking_count, tool_count, cost, error_message, output_file, prompt alongside the existing 10 fields. Single forward pass over the completed file. - apps/sol/routes.py: _get_uses_for_day reads the day index directly, with a single dual-key fallback for legacy agent_id entries. _parse_use_file deleted; get_use_end_state no longer called from the listing path. New _parse_active_use_file handles the bounded active glob. - tests/test_app_sol.py: covers index-only sufficiency, legacy agent_id schema, and tolerated blanks for pre-existing entries. Pre-existing entries that lack the new fields render as null. No retroactive bulk migration; no lazy upgrade path. Founder-pulled older days will gain rich data only when those uses run again. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>