fix: reject ambiguous show run ids

[Rayan-and-beyond]

Summary

• reject ambiguous short IDs in agentrace show instead of silently selecting the first run
• prefer an exact full-ID match when another run shares the same suffix
• list matching full IDs and safe descriptions so the user can retry precisely

Closes #9

Validation

• .venv/bin/pytest -q — 57 passed
• .venv/bin/ruff check . — passed
• focused show regressions — 2 passed
• mutation proof: restoring the old match[0] behavior makes the ambiguity regression fail
• git diff --check — passed

[github-actions]

This is in, @Rayan-and-beyond. Really appreciate it.

Agentrace gets better every time someone outside the repo digs in like this.

If you find Agentrace useful, consider dropping a star. It helps more people find it.

Happy to see more from you whenever you have the time.