fix: refactor action log path resolution to a pure configuration helper

[cdsap]

Summary

Problem

src/index_with_backend.ts:16-33 mixes GitHub Action I/O, filesystem setup, default log-file collision handling, workspace-relative path resolution, and runtime orchestration in the run() entrypoint. The project already separates remote monitoring feature decisions into the pure resolveMonitoringFeatureFlags helper in src/monitoring_features.ts:20-56, but the local logging path rules remain embedded in the side-effect-heavy adapter.

Why this matters

The log path rules affect cleanup, artifact discovery, and local-vs-workspace behavior. Keeping them inline makes small behavior changes harder to test without exercising the full action entrypoint and increases the chance of breaking default artifact naming or custom log_file handling.

Proposed change

Introduce a small pure helper, for example resolveActionLogFileTarget, that accepts logFileInput, runId, workspaceDir, runnerTempRoot, and a boolean indicating whether the default log path already exists. Return runnerTempDir, logFilePath, defaultLogFile, and whether the collision fallback was used. Keep fs.mkdirSync, fs.existsSync, and core.info in src/index_with_backend.ts, but move the path decision itself into the helper with focused Jest coverage.

Notes

Clean architecture lens: this keeps the GitHub Action entrypoint as an infrastructure adapter and moves deterministic configuration policy into a small core helper, matching the existing resolveMonitoringFeatureFlags pattern without changing runtime behavior.

Fixes #163

Changes

• __tests__/action-config.test.ts
• __tests__/index-with-backend-flags.test.ts
• src/action_config.ts
• src/index_with_backend.ts
• src/monitoring_features.ts

Verification

• npm test -- --runInBand

[cdsap]

@cdsap PR Judge blocked this PR for manual review.

State: BLOCKED_DANGEROUS_DIFF
Reason: test removals: tests/index-with-backend-flags.test.ts

The judge will not auto-merge this PR until the risky diff is reviewed manually.