DoneClaim: backup collision repair

What Changed

• Product commit: 656432d6e (fix(omo-config-core): avoid backup filename collisions)
• Push status: pushed to origin/code-yeongyu/senpi-task-w0-config-loader-writer.
  • Artifact: .omo/evidence/senpi-task/task-2-config-loader-writer/push-backup-collision-20260706.txt
• packages/omo-config-core/src/writer/writer.test.ts adds a frozen-clock regression test for two immediate updateOmoConfig calls against one existing commented project omo.jsonc.
• packages/omo-config-core/src/writer/writer.ts writes backups with exclusive file creation and appends a numeric suffix when the timestamped .bak.<ISO> candidate already exists.

What Was Tested

• RED: bun test packages/omo-config-core/src/writer/writer.test.ts --bail
  • Artifact: .omo/evidence/senpi-task/task-2-config-loader-writer/red-backup-collision-20260706.txt
• GREEN focused writer/security: bun test packages/omo-config-core/src/writer --bail
  • Artifact: .omo/evidence/senpi-task/task-2-config-loader-writer/focused-writer-tests-20260706.txt
• Full package: bun test packages/omo-config-core --bail
  • Artifact: .omo/evidence/senpi-task/task-2-config-loader-writer/bun-test-omo-config-core-20260706.txt
• Drift guard: bun test tests/omo-config-category-drift.test.ts --bail
  • Artifact: .omo/evidence/senpi-task/task-2-config-loader-writer/category-drift-20260706.txt
• Typecheck: bun run typecheck
  • Artifact: .omo/evidence/senpi-task/task-2-config-loader-writer/typecheck-20260706.txt
• Whitespace: git diff --check code-yeongyu/senpi-task-w0-config-schema...HEAD
  • Artifact: .omo/evidence/senpi-task/task-2-config-loader-writer/diff-check-20260706.txt
• Static scans for as any, TS suppressions, empty catch, and changed-file pure LOC.
  • Artifacts: .omo/evidence/senpi-task/task-2-config-loader-writer/static-scan-20260706.txt, .omo/evidence/senpi-task/task-2-config-loader-writer/loc-scan-20260706.txt

Manual QA

• Scenario: public updateOmoConfig called twice immediately against the same existing commented project omo.jsonc under a fixed timestamp.
• Invocation: bun --eval importing loadOmoConfig and updateOmoConfig from ./packages/omo-config-core/src/index.ts.
• Binary observable: first backup path is .bak.2026-07-06T00-00-00-000Z; second backup path is .bak.2026-07-06T00-00-00-000Z.1; both existed before fixture cleanup; current config preserved the comment and loaded default_concurrency: 3 plus wait.default_ms: 12000; cleanup removed the temp root.
• Artifact: .omo/evidence/senpi-task/task-2-config-loader-writer/manual-backup-collision-20260706.json

Cleanup And Scope

• Product diff/status proof:
  • .omo/evidence/senpi-task/task-2-config-loader-writer/product-diff-20260706.patch
  • .omo/evidence/senpi-task/task-2-config-loader-writer/status-before-commit-20260706.txt
• Touched product files are limited to packages/omo-config-core/src/writer/writer.ts and packages/omo-config-core/src/writer/writer.test.ts.
• Evidence is limited to .omo/evidence/senpi-task/task-2-config-loader-writer/.

Residual Risk

• Existing branch diff versus code-yeongyu/senpi-task-w0-config-schema already includes broader omo-config-core work; this repair only covers the backup collision lane.
• writer.test.ts is in the 200-250 pure LOC warning band at 212 LOC. No split was done because the request was a minimal repair.