When a turn ends, the relay fetches its trace from GET /precision/trace and stores it with the turn in facts (capped, gone at 90 days) #547

The store half of #534. The arm's trace (417ad8b) and src/facts.ts (5f2aecf) are on main.

Done when:

• [ ] When a turn ends, the relay fetches GET /precision/trace?session=<id> for that turn's session once, with a short timeout, and stores it with the turn's row in facts. Each trace is capped in size, and it is dropped with the turn at 90 days.
• [ ] An arm without the route, or one that 404s, stores nothing and never delays the turn's row.
• [ ] facts exposes traceFor(turnId). Tests cover the round trip, the 404, and retention.
• [ ] bun --cwd Software/so101 test passes. No API or page change.

Brief: any builder.

Parked by the crew: the preview's deploy failed and the decider saw no point in another try (pull #552 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Parked by the crew: @smith's run ended without a pull: the pull landed

Parked twice since a person last spoke here, so it is the planner's now. Every reason:

1. the preview's deploy failed and the decider saw no point in another try (pull #552 closed)
2. @smith's run ended without a pull: the pull landed

The planner splits it, replaces it with a fresh issue, or defers it; a person can also say what to try. Nothing starts here until then, and the board lists it.

Already done on main in 27e9c27 (#553). When a turn ends, the relay fetches /precision/trace with a 2 s timeout and stores the trace with the turn (src/relay.ts), and facts.traceFor(turnId) is in src/facts.ts. Closing as done.

Dropped: the done close is refused for my scope, and nothing is left to build. The work is on main in 27e9c27 (#553). #548 no longer waits on it.