fix: write execution file in finally block so rate limit errors are parseable

[hashwnath]

Fixes #1040

Problem

When the Claude Code SDK throws (e.g. rate limit, crash), the execution file is never written because the catch block in run-claude-sdk.ts re-throws immediately, making the writeFile call on the subsequent lines unreachable.

This means workflows using continue-on-error: true cannot inspect the collected messages to distinguish rate limits from other failures — both surface as exit code 1 with a generic SDK stack trace, and the execution_file output is empty.

Solution

Instead of re-throwing immediately in the catch block, the SDK error is stored in a variable. The execution file write proceeds (guarded by messages.length > 0 to avoid writing empty files), and only then is the error re-thrown.

This ensures:

• The execution_file output is always populated when messages were collected, regardless of whether the SDK completed successfully
• Callers can parse the execution file to detect rate_limit_event messages vs other failures
• The error is still propagated with the same message format
• No behavioral change for the success path

Changes

• base-action/src/run-claude-sdk.ts: Store SDK error instead of immediately re-throwing; write execution file before propagating the error

Testing

• All 653 existing tests pass
• TypeScript type checking passes
• Prettier formatting passes