fix(tui): handle session.error events in global sync

[OmarAlaaeldein]

Issue for this PR

Closes #48530

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

In the terminal TUI, when a session encounters an error and the server emits a session.error event, the global sync reducer in packages/tui ignored it. As a result:

1. session_status[sessionID] remained permanently stuck in busy mode with an unending progress spinner.
2. The last assistant message was never updated with an error marker or finish: "error".

This PR adds a session.error handler in packages/tui/src/context/sync.tsx (the terminal counterpart to #48534 for packages/app). When session.error is received:

• session_status[sessionID] is reset to { type: "idle" }.
• The last assistant message in the session is marked with the error payload and finish: "error".

How did you verify your code works?

• Added unit test in packages/tui/test/cli/cmd/tui/sync.test.tsx asserting that session.error resets the session status to idle and marks the assistant message error and finish state.
• Ran bun test test/cli/cmd/tui/sync.test.tsx (3/3 pass).
• Ran bun run --cwd packages/tui typecheck (tsgo --noEmit passes with 0 errors).

Screenshots / recordings

N/A (TUI state reconciliation)

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Related PR found:

• fix(app): handle session.error events in global sync #48534 - fix(app): handle session.error events in global sync
  • fix(app): handle session.error events in global sync #48534
  • Why related: This PR (48606) explicitly references fix(app): handle session.error events in global sync #48534 as its counterpart. While fix(app): handle session.error events in global sync #48534 adds the same session.error handling to packages/app, this PR adds it to packages/tui. They address the same issue (session.error events are ignored by global sync (stuck busy, no error shown) #48530) in parallel across different packages. This is intentional paired work, not a duplicate.