Reindex completed with errors

### Describe the bug

Runing `/chronicle reindex` shows:

> ● ⚠ Reindex completed with errors: 5 sessions indexed locally, 41 queued for backfill. Errors: 2 session(s) failed

with no explanation of what the errors are, where I can find more information or what I can do to remedy the situation.

### Affected version

GitHub Copilot CLI 1.0.62.

### Steps to reproduce the behavior

1. Type `/chronicle reindex`
2. Observe errors

### Expected behavior

An explanation of what the errors are, where I can find more information or what I can do to remedy the situation.

### Additional context

_No response_

Start by tracing the `/chronicle reindex` command entry point and its error-reporting path. Reproduce the command and inspect how failed sessions are handled. Done means the output explains the errors, points to more information, and indicates possible remedies.

Scritto dal modello di indicizzazione a partire dal testo della issue.