fix(agent): retry oversized resume on a fresh session with summarized history

[tatoalo]

Problem

When a resumed session's transcript no longer fits the model's context window, the API rejects every request — including the SDK's own auto-compaction — so the resume continuation fails with Internal error: Prompt is too long. That is classified as a non-recoverable agent_error, the run dies before doing any work, and every subsequent resume of the task hits the same wall: the task is permanently stuck.

Follow-up to #3331 (which makes hydration unlikely to produce an oversized transcript in the first place); this adds the safety net for any remaining path to an oversized resume.

Changes

• When the resume continuation fails with a prompt-too-long error, start a fresh session (same session meta) and re-send the pending user message with the summarized conversation history that the non-native resume path already uses (capped at 50k estimated tokens), instead of failing the run.
• One retry per run, gated to the native-resume continuation turn; any other failure keeps the existing handleTurnFailure behavior.
• New isPromptTooLongError predicate in error-classification.ts.

[trunk-io]

Merging to main in this repository is managed by Trunk.

• To merge this pull request, check the box to the left or comment /trunk merge below.

After your PR is submitted to the merge queue, this comment will be automatically updated with its status. If the PR fails, failure details will also be posted here

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit df83f0d.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "refactor(agent): simplify oversized-resu..." | Re-trigger Greptile}

[github-actions]

No showstoppers. The retry mechanism is well-guarded with a one-shot flag, state is cleaned up in a finally block on both success and failure paths, and the previously raised concern about stale resume state on failed retries is demonstrably fixed in the current diff.