perf(metrics): Batch token counting IPC to reduce worker round-trip overhead

[yamadashy]

Batch token counting items into groups of 50 per worker task instead of sending individual files. This reduces worker thread IPC round-trips from ~991 to ~20 for a typical repository, significantly cutting thread creation and message-passing overhead.

Changes

• Add TokenCountBatchTask / MetricsWorkerTask / MetricsWorkerResult types and countTokensBatch handler to calculateMetricsWorker
• Introduce metricsWorkerRunner.ts with MetricsTaskRunner type alias and type-safe runTokenCount / runBatchTokenCount helpers — centralizes as casts in one place instead of scattering them across callers
• Update calculateSelectiveFileMetrics with METRICS_BATCH_SIZE=50 batching
• Update calculateOutputMetrics, calculateGitDiffMetrics, calculateGitLogMetrics to use runTokenCount helper
• Update unifiedWorker task inference to recognize batch metrics tasks (items + encoding)
• Update all related tests for new types and batch mode

Benchmark (from prior testing, repomix on itself, ~991 files)

• Before: ~2147ms
• After: ~1544ms
• Improvement: ~28%

Checklist

• Run npm run test
• Run npm run lint

---

[github-actions]

⚡ Performance Benchmark

Latest commit:	7f401d9 refactor(metrics): Use batchResults.flat() instead of manual loop
Status:	✅ Benchmark complete!
Ubuntu:	1.50s (±0.05s) → 1.49s (±0.02s) · -0.01s (-0.7%)
macOS:	0.91s (±0.07s) → 0.89s (±0.05s) · -0.02s (-2.2%)
Windows:	2.23s (±0.35s) → 2.05s (±0.30s) · -0.18s (-8.0%)

Details

• Packing the repomix repository with node bin/repomix.cjs
• Warmup: 2 runs (discarded), interleaved execution
• Measurement: 20 runs / 30 on macOS (median ± IQR)
• Workflow run

History

411ce28 refactor(metrics): Use batchResults.flat() instead of manual loop

Ubuntu:	1.48s (±0.03s) → 1.47s (±0.02s) · -0.01s (-0.8%)
macOS:	1.19s (±0.14s) → 1.19s (±0.16s) · -0.00s (-0.2%)
Windows:	1.84s (±0.06s) → 1.83s (±0.06s) · -0.01s (-0.7%)

1c6b5a8 perf(metrics): Batch token counting IPC to reduce worker round-trip overhead

Ubuntu:	1.48s (±0.02s) → 1.49s (±0.03s) · +0.01s (+0.6%)
macOS:	0.88s (±0.08s) → 0.87s (±0.03s) · -0.01s (-1.1%)
Windows:	2.36s (±0.07s) → 2.36s (±0.07s) · +0.00s (+0.0%)

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📝 Walkthrough

Walkthrough

This PR introduces a new MetricsTaskRunner type abstraction and helper functions to standardize metrics worker task execution. The metrics worker now supports batch token counting alongside single-item tasks. All calculate*Metrics functions are refactored to use the new abstraction, and SelectiveFileMetrics implements file batching (size 50).

Changes

Cohort / File(s)	Summary
Metrics Worker Type Abstraction src/core/metrics/metricsWorkerRunner.ts	New file introducing MetricsTaskRunner type, runTokenCount, and runBatchTokenCount helper functions for standardized metrics task execution.
Metrics Worker Batch Support src/core/metrics/workers/calculateMetricsWorker.ts	Worker now handles both TokenCountTask and TokenCountBatchTask, adding batch-mode processing with new countTokensBatch helper; branching logic routes to single or batch execution based on task shape.
Metrics Calculation Functions src/core/metrics/calculateGitDiffMetrics.ts, src/core/metrics/calculateGitLogMetrics.ts, src/core/metrics/calculateOutputMetrics.ts	Updated to depend on MetricsTaskRunner instead of generic TaskRunner<TokenCountTask, number>; token execution delegated to runTokenCount helper instead of direct runner invocation.
Selective File Metrics Batching src/core/metrics/calculateSelectiveFileMetrics.ts	Refactored to batch file processing in chunks of 50 using runBatchTokenCount; replaced per-file task runner calls with per-batch submission; progress reporting now tracks batch completion.
Metrics Orchestrator src/core/metrics/calculateMetrics.ts	Updated MetricsTaskRunnerWithWarmup interface and createMetricsTaskRunner to use explicit MetricsTaskRunner, MetricsWorkerTask, MetricsWorkerResult types; adjusted fallback initialization accordingly.
Worker Type Inference src/shared/unifiedWorker.ts	Expanded inferWorkerTypeFromTask for calculateMetrics to detect both single-mode (content + encoding) and batch-mode (items + encoding) task shapes.
Metrics Tests tests/core/metrics/calculateGitDiffMetrics.test.ts, tests/core/metrics/calculateGitLogMetrics.test.ts, tests/core/metrics/calculateOutputMetrics.test.ts, tests/core/metrics/calculateSelectiveFileMetrics.test.ts	Updated mock task runners to use MetricsTaskRunner and accept MetricsWorkerTask inputs; batch test mocks added branching logic to handle items property; type imports adjusted to match new abstraction.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• #1302 — Modifies metrics worker/task-runner surface in calculateMetrics and packager wiring, directly overlapping with this refactoring.
• #1380 — Converts per-file worker tasks to batched items-based tasks and updates worker inference logic, mirroring the batching pattern introduced here.
• #1374 — Modifies createMetricsTaskRunner and MetricsTaskRunnerWithWarmup types in the same metrics orchestrator file.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main performance optimization: batching token counting to reduce worker round-trip overhead, which is the primary focus of this changeset.
Description check	✅ Passed	The pull request description comprehensively covers the changes, provides a detailed Changes section with file-level modifications, includes performance benchmarks, and confirms both test and lint checklist items are complete.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch perf/batch-metrics-token-counting

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[codecov]

Codecov Report

❌ Patch coverage is 71.79487% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.26%. Comparing base (9d5b928) to head (7f401d9).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
src/core/metrics/workers/calculateMetricsWorker.ts	8.33%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1411      +/-   ##
==========================================
- Coverage   87.42%   87.26%   -0.17%     
==========================================
  Files         116      117       +1     
  Lines        4397     4420      +23     
  Branches     1020     1021       +1     
==========================================
+ Hits         3844     3857      +13     
- Misses        553      563      +10     

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[cloudflare-workers-and-pages]

Deploying repomix with    Cloudflare Pages

Latest commit:	7f401d9
Status:	✅  Deploy successful!
Preview URL:	https://a66133f0.repomix.pages.dev
Branch Preview URL:	https://perf-batch-metrics-token-cou.repomix.pages.dev

View logs

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 4 additional findings.