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+# Refactor Plan: Duplication Reduction
+
+Date: 2026-02-15  
+Scope: Reduce high-impact code duplication in production and test-adjacent areas while preserving behavior.
+
+## Objectives
+
+- Eliminate high-risk duplication that can cause drift or inconsistent behavior.
+- Keep changes incremental and reviewable via phase-based PRs.
+- Follow strict TDD and repository requirements (`npm test` and `npm run build` green at each phase).
+
+## Working Rules (applies to every phase)
+
+1. Write failing tests first (Red).
+2. Implement minimal code to pass (Green).
+3. Refactor while staying green.
+4. Run full test suite: `npm test`.
+5. Run full build: `npm run build`.
+6. Do not change behavior unless explicitly planned in acceptance criteria.
+
+---
+
+## Phase 1 — Consolidate Electron API Contract (Highest ROI)
+
+### Problem
+`electronAPI` shape is duplicated across multiple files and can drift:
+- `src/main/preload.ts`
+- `src/renderer/types/electron.d.ts`
+- Overlapping app/store type surfaces in `src/renderer/store/appStore.ts`
+
+### Goal
+Create one canonical API contract and consume it from both preload and renderer type declarations.
+
+### Tasks
+- Add shared contract module (suggested: `src/shared/electronApi.ts`).
+- Move reusable API interfaces/types there.
+- Update `src/main/preload.ts` to use the shared type(s) where applicable.
+- Update `src/renderer/types/electron.d.ts` to reference the shared contract.
+- Remove duplicate preload-local `ElectronAPI` declarations if no longer needed.
+
+### Acceptance Criteria
+- Single source of truth for `electronAPI` contract shape.
+- No contract mismatch between preload and renderer types.
+- Typecheck/build pass with no API regressions.
+
+### Risks / Notes
+- Ambient type import patterns in `.d.ts` files can be tricky; keep changes minimal and explicit.
+
+---
+
+## Phase 2 — Extract Common Tag Mutation Workflow
+
+### Problem
+`TagEngine` repeats similar logic in:
+- `deleteTag`
+- `mergeTags`
+- `renameTag`
+
+Repeated steps include finding posts, parsing/updating tags JSON, syncing published files, and progress reporting.
+
+### Goal
+Refactor shared behavior into private helpers while preserving all task/event semantics.
+
+### Tasks
+- In `src/main/engine/TagEngine.ts`, add private helpers for:
+  - query posts containing a tag,
+  - transform tag arrays,
+  - persist post tag updates + file sync,
+  - shared progress calculation/reporting.
+- Update `deleteTag`, `mergeTags`, and `renameTag` to compose helpers.
+- Expand/adjust tests in `tests/engine/TagEngine.test.ts` to protect behavior.
+
+### Acceptance Criteria
+- Public method behavior and events unchanged.
+- Reduced duplicate blocks in `TagEngine`.
+- Existing and new tests pass.
+
+### Risks / Notes
+- Must preserve task progress percentages/messages expected by UI.
+
+---
+
+## Phase 3 — Unify Single/Batch Post-Media Operations
+
+### Problem
+`PostMediaEngine` duplicates linking/unlinking logic across single and batch methods:
+- `linkMediaToPost` vs `linkManyToPost`
+- `unlinkMediaFromPost` vs `unlinkManyFromPost`
+
+### Goal
+Create common primitives and make single/batch methods compose them.
+
+### Tasks
+- In `src/main/engine/PostMediaEngine.ts`, extract private primitives:
+  - create/delete relation rows,
+  - update media sidecar `linkedPostIds` (add/remove),
+  - shared sort-order handling where applicable.
+- Refactor single and batch methods to reuse primitives.
+- Add parity tests in `tests/engine/PostMediaEngine.test.ts`.
+
+### Acceptance Criteria
+- No behavior regressions in link/unlink semantics.
+- Event behavior preserved (`mediaLinked`/`mediaUnlinked` vs batch events).
+- Duplicate logic materially reduced.
+
+### Risks / Notes
+- Preserve ordering and skip logic for already-linked media.
+
+---
+
+## Phase 4 — Consolidate Project Mapping and Guard Clauses
+
+### Problem
+`ProjectEngine` repeats:
+- default-project delete protection checks,
+- DB row → `ProjectData` mapping in several methods.
+
+### Goal
+Centralize repetitive mapping and guard logic.
+
+### Tasks
+- In `src/main/engine/ProjectEngine.ts`, add:
+  - `assertDeletableProject(id)` (or equivalent guard helper),
+  - `mapDbProjectToProjectData(row)` mapper.
+- Replace repeated mapping/guard code in:
+  - `deleteProject`, `deleteProjectWithData`,
+  - `getProject`, `getAllProjects`, `getActiveProject`.
+- Validate with `tests/engine/ProjectEngine.test.ts`.
+
+### Acceptance Criteria
+- Same return shapes and delete behavior as before.
+- Less repeated mapping/guard logic.
+
+### Risks / Notes
+- Keep null/undefined normalization unchanged for optional fields.
+
+---
+
+## Phase 5 — Extract Metadata Sync Loop Scaffolding
+
+### Problem
+`MetadataDiffEngine` has near-identical loop scaffolding in:
+- `syncDbToFile`
+- `syncFileToDb`
+
+Includes progress reporting, success/failure accounting, and event-loop yielding.
+
+### Goal
+Abstract common iteration mechanics into one helper with operation-specific callbacks.
+
+### Tasks
+- In `src/main/engine/MetadataDiffEngine.ts`, add a generic internal iterator helper that handles:
+  - per-item execution,
+  - success/fail accounting,
+  - periodic progress updates,
+  - periodic `setImmediate` yielding.
+- Refactor both sync methods to use it.
+- Verify with `tests/engine/MetadataDiffEngine.test.ts`.
+
+### Acceptance Criteria
+- Same visible progress and final result semantics.
+- Reduced duplicated loop/control-flow code.
+
+### Risks / Notes
+- Progress message cadence should remain compatible with UI expectations.
+
+---
+
+## Phase 6 — Deduplicate Shared Color Utility in Renderer
+
+### Problem
+`getContrastColor` is duplicated in:
+- `src/renderer/components/TagInput/TagInput.tsx`
+- `src/renderer/components/TagsView/TagsView.tsx`
+
+### Goal
+Move color contrast logic into a shared renderer utility.
+
+### Tasks
+- Add utility module (suggested: `src/renderer/utils/color.ts`).
+- Replace local implementations in both components.
+- Add focused tests (suggested: `tests/renderer/utils/color.test.ts`).
+
+### Acceptance Criteria
+- No visual behavior change.
+- One implementation for contrast-color calculation.
+
+### Risks / Notes
+- Verify support for both 3-char and 6-char hex inputs.
+
+---
+
+## Suggested Delivery Sequence
+
+1. Phase 1 (API contract)
+2. Phase 2 (TagEngine)
+3. Phase 3 (PostMediaEngine)
+4. Phase 4 (ProjectEngine)
+5. Phase 5 (MetadataDiffEngine)
+6. Phase 6 (Renderer utility)
+
+Rationale: start with highest blast-radius drift risk, then engine-level duplication, then UI utility cleanup.
+
+---
+
+## Definition of Done (overall)
+
+- All phases merged with passing tests/build at each step.
+- No unresolved failing tests.
+- Clone report shows meaningful reduction in production hotspots.
+- Public behavior remains stable unless a change is explicitly approved.