Implements wave 1 of the media retention spec: retention config, service, and CLI commands. Three composable modes (keep, days, processed) with per-stream overrides and retroactive purge. Safety invariant: never deletes raw media from incomplete segments. Completion checks verify all processing is done before any deletion. New files: - think/retention.py — core retention service - tests/test_retention.py — 34 tests covering all retention logic CLI commands: - sol call journal retention purge --older-than 30d [--stream] [--dry-run] - sol call journal storage-summary [--json] Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>