fix(session): mark recovered assistant turns as aborted

[dzianisv]

Summary

When the server restarts during an in-flight session turn, Session.recover() already converts running tool parts into server restarted errors and force-completes unfinished assistant messages. The missing piece was that those assistant messages were still stored as successful completions with error: null.

This patch marks recovered orphaned assistant messages as MessageAbortedError so the UI renders the turn as interrupted instead of looking like a silent dead-end or stuck session.

Closes #24

Changes

• load assistant message data during startup recovery
• mark recovered orphaned assistant messages as MessageAbortedError if they do not already carry an error
• preserve the recovered time.completed behavior
• add a regression test covering orphaned assistant + running tool recovery

Testing

• bun test test/session/session.test.ts
• bun typecheck
• browser-visible isolated E2E with a seeded orphaned session on a patched local server: page renders Interrupted plus the server restarted tool error and no stale active session state

[github-actions]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• PR description is missing required template sections. Please use the PR template.

Please edit this PR description to address the above within 2 hours, or it will be automatically closed.

If you believe this was flagged incorrectly, please let a maintainer know.

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

This pull request has been automatically closed because it was not updated to meet our contributing guidelines within the 2-hour window.

Feel free to open a new pull request that follows our guidelines.