my-pi/pi-permission-system/docs/retro/0109-deduplicate-shared-helpers.md

issue, issue_title

issue	issue_title
109	refactor: deduplicate mergeFlatPermissions and path normalization helpers

Retro: #109 — deduplicate shared helpers

Final Retrospective (2026-05-07T13:35:00Z)

Session summary

Planned and executed a pure extraction refactoring that moved mergeFlatPermissions() into src/permission-merge.ts and normalizePathForComparison()/isPathWithinDirectory() into src/path-utils.ts. Both src/config-loader.ts and src/permission-manager.ts now import from the shared merge module; src/external-directory.ts barrel-re-exports the path helpers for backward compatibility. Released as v5.6.2 with zero behavioral change and 8 net-new unit tests for mergeFlatPermissions.

Observations

What went well

• TDD cycle was clean: 5 plan steps mapped to 4 commits with no unexpected breakage. The full 1224-test suite stayed green at every commit.
• Barrel re-export strategy worked: keeping export { ... } from "./path-utils" in external-directory.ts meant the 39 existing external-directory.test.ts tests passed without import changes, validating backward compatibility.
• New test coverage surfaced: mergeFlatPermissions() previously had zero direct unit tests. The extraction enabled 8 focused tests covering all merge branches (string×string, object×object, cross-type, empty inputs).

What caused friction (agent side)

• missing-context — In step 4, added import { isPathWithinDirectory, normalizePathForComparison } from "./path-utils" alongside export { ... } from "./path-utils" before removing the local function definitions in src/external-directory.ts. Biome flagged noRedeclare (local functions shadowed the imports) and noUnusedImports (the import was dead while locals existed). Impact: one extra edit cycle to remove the local definitions, then the import was needed again for internal callers. Self-identified via biome autoformat hook output.

What caused friction (user side)

• None observed — the user's involvement was the standard plan/TDD/ship command sequence with no corrections needed.