fix(llmloop): record grace round requests

[Gongyl01]

Description

The grace round is the final LLM request sent after the main loop reaches its tool-request limit.

This change completes its request-level observability:

• create the main_task record before sending the request
• attach request identity using the record's RequestNo, allowing retry attempts to be correlated with the request
• record the response, token usage, and actual duration even when no tool call is returned
• record the request error and duration when the grace request fails
• emit the same LLM telemetry as regular main-task requests
• add tests for successful responses and suppressed request errors

Type of Change

• Bug fix (non-breaking change that fixes an issue)

How Has This Been Tested?

• make check
• make test
• make coverage - 91.4%
• Grace-round response and suppressed-error paths

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have added tests that prove the fix is effective
• New and existing unit tests pass locally

[github-actions]

✅ OpenCodeReview: Review complete: 0 finding(s) across 1 selected item(s).

[lizhengfeng101]

LGTM