stats --json also prints the human table, so the output is not machine readable

[royalpinto007]

Problem

agentrace stats --json writes both a human table and the JSON to stdout:

console.print(table)

if args.json:
    print(json.dumps({...}))

So the actual output is a Rich-rendered table followed by a JSON object, on the same stream. agentrace stats --json | jq . fails. The CI smoke test does not catch this because it runs the command without piping it anywhere.

The wider version of the problem: --json exists only on stats. list, check, and show have no machine readable output at all. That is awkward for a tool whose README pitches check --strict as a CI gate, because the exit code is all a CI job can consume. You cannot post findings to a PR comment, write them to a report artifact, or filter them with jq.

Suggested approach

1. Fix stats --json first: when --json is passed, either suppress the table entirely or send it to stderr. Suppressing is the more conventional choice for a data flag. Decide, and say which in --help.
2. Promote --json to a top level flag on the parser rather than a per subcommand one, so agentrace --json check works uniformly.
3. Define the JSON shape for each command and document it in the README, because once someone scripts against it, it is an interface:
   • list: an array of runs with id, description, duration, char counts, background, error.
   • check: an array of {run_id, description, findings: [{check, severity, message, evidence}]} plus a summary object. Finding is already a dataclass, so dataclasses.asdict covers most of it.
   • show: one run object including full prompt and result.
4. Add a schema version field, for example "schema": 1, so the shape can change later without silently breaking whoever scripted against it.
5. Add tests that each command's --json output parses cleanly with nothing else on stdout. That case is exactly what is broken today.

Done when

• agentrace stats --json | jq . works.
• Every command supports --json with a documented shape.
• The README documents the schema.
• Tests assert stdout is valid JSON and nothing else.

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