---
issue: 127
issue_title: "refactor: extract SessionLogger interface to unify logging + notification"
---

# Retro: #127 — extract SessionLogger interface

## Final Retrospective (2026-05-08T01:10:00Z)

### Session summary

Extracted three separate `HandlerDeps` logging/notification fields (`writeDebugLog`, `writeReviewLog`, `notifyWarning`) into a `SessionLogger` interface with `debug`/`review`/`warn` methods.
Created `src/session-logger.ts` with the interface and `createSessionLogger()` factory, updated all handler source files and 6 test `makeDeps()` factories.
Shipped as v5.8.0 with zero behavioral change. 7 new unit tests; total suite 1252 tests across 56 files.

### Observations

#### What went well

- **Three-phase pipeline completed cleanly.**
  Plan → TDD (4 cycles) → ship in one session with no user corrections needed.
- **Plan-to-code translation was nearly 1:1.**
  The `SessionLogger` interface, `createSessionLogger()` factory, `HandlerDeps` change, and handler migration all matched the plan exactly.
  The mechanical find-and-replace nature of the change made the TDD steps predictable.
- **Test factory updates were trivially correct.**
  Replacing 3 fields with 1 nested object (`logger: { debug: vi.fn(), review: vi.fn(), warn: vi.fn() }`) worked identically across all 6 files.

#### What caused friction (agent side)

- `wrong-abstraction` — Plan listed `src/handlers/gates/runner.ts` as needing `deps.writeReviewLog` → `deps.logger.review` changes, but `runner.ts` uses `GateRunnerDeps` (a separate interface explicitly scoped as a non-goal), not `HandlerDeps`.
  The plan confused the parameter name `deps` (which appears in both `runGateCheck` and handler functions) with the `HandlerDeps` type.
  Self-identified during step 2 by reading the import at the top of `runner.ts` before editing.
  Impact: added friction but no rework — no incorrect edit was made.

- `missing-context` — Multi-block edit on `src/handlers/types.ts` accidentally introduced a `/** @deprecated Use logger.warn instead. */` comment above `logResolvedConfigPaths()`.
  The third edit block was intended to remove `notifyWarning` and its JSDoc, but the replacement text included a stray deprecation annotation that attached to the wrong field.
  Self-identified by re-reading the file immediately after the edit.
  Impact: one follow-up edit to remove the stray comment, ~30 seconds of rework, no incorrect commit landed.

#### What caused friction (user side)

- None observed.

### Changes made

1. Created `docs/retro/0127-extract-session-logger.md` (this file).
