Fix validate_errors.cjs to handle missing logs folder gracefully

[Copilot]

Problem

The validate_errors.cjs script was throwing an error when the logs folder doesn't exist, causing workflow failures:

Error: Log path not found: /tmp/gh-aw/.copilot/logs/
    at main (eval at callAsyncFunction (/home/runner/work/_actions/actions/github-script/v8/dist/index.js:36187:16), <anonymous>:15:13)

This occurred because:

1. The Copilot engine sets GITHUB_AW_AGENT_OUTPUT to /tmp/gh-aw/.copilot/logs/ (a directory)
2. The validation step runs unconditionally with if: always()
3. If no logs were generated or the directory doesn't exist yet, the script would fail

Solution

Modified the error handling in validate_errors.cjs to gracefully handle missing log paths by logging an informational message and returning early, rather than throwing an error:

Before:

if (!fs.existsSync(logPath)) {
  throw new Error(`Log path not found: ${logPath}`);
}

After:

if (!fs.existsSync(logPath)) {
  core.info(`Log path not found: ${logPath}`);
  core.info("No logs to validate - skipping error validation");
  return;
}

This approach:

• Matches the behavior of parse_copilot_log.cjs, which handles the same scenario gracefully
• Allows the validation step to complete successfully when there are no logs to validate
• Provides clear informational messages about why validation was skipped
• Prevents workflow failures when the logs directory legitimately doesn't exist

Testing

• ✅ All JavaScript tests pass (31 tests in validate_errors.test.cjs)
• ✅ All Go unit tests pass
• ✅ make agent-finish validation completed successfully

Fixes the error reported in the issue where the validation step was failing due to a missing logs folder.

Original prompt

In the step that validates agent logs, make sure that the logs folder exists.

Run actions/github-script@v8
Error: Log path not found: /tmp/gh-aw/.copilot/logs/
    at main (eval at callAsyncFunction (/home/runner/work/_actions/actions/github-script/v8/dist/index.js:36187:16), <anonymous>:15:13)
    at eval (eval at callAsyncFunction (/home/runner/work/_actions/actions/github-script/v8/dist/index.js:36187:16), <anonymous>:185:3)
    at callAsyncFunction (/home/runner/work/_actions/actions/github-script/v8/dist/index.js:36188:12)
    at main (/home/runner/work/_actions/actions/github-script/v8/dist/index.js:36285:26)
    at /home/runner/work/_actions/actions/github-script/v8/dist/index.js:36260:1
    at /home/runner/work/_actions/actions/github-script/v8/dist/index.js:36317:3
    at Object.<anonymous> (/home/runner/work/_actions/actions/github-script/v8/dist/index.js:36320:12)
    at Module._compile (node:internal/modules/cjs/loader:1760:14)
    at Object..js (node:internal/modules/cjs/loader:1893:10)
    at Module.load (node:internal/modules/cjs/loader:1480:32)
Error: Error validating log: Log path not found: /tmp/gh-aw/.copilot/logs/

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