Replay a trace against local code

A fast iteration loop on a single production trace: take a trace whose output a developer didn't like, optionally change the code, re-run it against their LOCAL code, and show a concise diff of old vs new output — repeating until they're happy. Assumes nothing about the project's layout.

Invoked from the developer's coding agent: /agent-observability-replay-trace <trace-id> [<changes to test>]. With no modification, do the replay + diff only (a reproduce/regression check), then offer to enter the loop.

This file is the workflow spine — terse on purpose. The depth lives in references/details.md (trace backend + pup flags, the runner contract, export mode, polling, the trace-link scoping fix) and references/local-setup.md (making a deployed-only app locally runnable). Read details.md before you touch pup or generate the runner.

Writing code — keep comments minimal to none. Everything you generate or edit (the annotation, the runner's ENTRYPOINTS entries, a local harness, iteration edits) should match the surrounding code and carry no unnecessary comments — don't narrate what the code plainly does; add a comment only for a genuinely non-obvious why.