docs(13): create phase plan

Phase 13: Fix Duplicate Generations
- 1 plan created
- 2 tasks defined
- Ready for execution

.planning/phases/13-fix-duplicate-generations/13-01-PLAN.md

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+---
+phase: 13-fix-duplicate-generations
+plan: 01
+type: execute
+---
+
+<objective>
+Add content-based deduplication to the auto-save generations flow.
+
+Purpose: Prevent duplicate images/videos in the generations folder when the same content is generated multiple times. Currently every generation is saved regardless of whether identical content already exists.
+
+Output: Modified save-generation API that checks content hash before writing, returns existing file if duplicate found.
+</objective>
+
+<execution_context>
+@~/.claude/get-shit-done/workflows/execute-phase.md
+@~/.claude/get-shit-done/templates/summary.md
+</execution_context>
+
+<context>
+@.planning/PROJECT.md
+@.planning/ROADMAP.md
+@.planning/STATE.md
+
+**Key source files:**
+@src/app/api/save-generation/route.ts - Current save logic (no deduplication)
+@src/utils/imageStorage.ts - Existing hash logic for workflow images (lines 206-211)
+
+**Current behavior:**
+- `workflowStore.ts` calls `/api/save-generation` with `imageId = Date.now()` for every generation
+- `/api/save-generation` saves to `{directoryPath}/{imageId}.{ext}` unconditionally
+- No content hash check - identical images get duplicate files
+
+**Target behavior:**
+- Hash image/video content on server before saving
+- Check if file with same hash already exists in generations folder
+- If duplicate: return existing file path, don't create new file
+- If unique: save file with hash-based filename, return new path
+
+**Prior art:**
+- `imageStorage.ts:saveImageAndGetId` uses client-side hash of substring samples (lines 206-211)
+- Server-side crypto hash is more reliable and works for URL-fetched content
+</context>
+
+<tasks>
+
+<task type="auto">
+  <name>Task 1: Add content hashing to save-generation API</name>
+  <files>src/app/api/save-generation/route.ts</files>
+  <action>
+    Add server-side content hashing using Node.js crypto:
+
+    1. Import `crypto` module at top
+    2. After buffer is created (line ~95-108), compute content hash:
+       ```typescript
+       const contentHash = crypto.createHash('md5').update(buffer).digest('hex');
+       ```
+    3. Check if file with this hash already exists in directory:
+       - List files in directoryPath
+       - Check if any filename starts with the hash
+       - If found, return early with existing file info
+    4. Use hash-prefixed filename instead of timestamp-based:
+       - Change filename format to: `{hash}_{promptSnippet}.{extension}`
+       - Keep prompt snippet for human readability
+       - Hash ensures uniqueness without timestamp
+
+    Why MD5: Fast for binary data, collision resistance not critical for dedup (worst case: rare false duplicate). SHA256 is overkill for local file dedup.
+
+    Why hash in filename: Enables O(1) duplicate check via glob/fs.existsSync pattern match instead of reading all files.
+  </action>
+  <verify>
+    Build passes: `npm run build` succeeds without errors.
+    Manual test: Generate same image twice, second generation should return existing file path without creating duplicate.
+  </verify>
+  <done>
+    - MD5 hash computed from buffer content
+    - Filename uses hash prefix: `{hash}_{prompt}.{ext}`
+    - Duplicate check finds existing files by hash prefix
+    - Returns existing file info if duplicate found
+    - New files saved with hash-prefixed name
+  </done>
+</task>
+
+<task type="auto">
+  <name>Task 2: Add duplicate detection response handling</name>
+  <files>src/app/api/save-generation/route.ts</files>
+  <action>
+    Enhance response to indicate whether file was deduplicated:
+
+    1. Add `isDuplicate: boolean` field to response JSON
+    2. When returning existing file (duplicate found):
+       - Set `isDuplicate: true`
+       - Return existing `filePath` and `filename`
+       - Log deduplication event for observability
+    3. When saving new file:
+       - Set `isDuplicate: false`
+       - Return new `filePath` and `filename` as before
+
+    This allows callers (workflowStore) to know if deduplication occurred, useful for debugging and future UI feedback.
+  </action>
+  <verify>
+    Test duplicate scenario: Generate same content twice, second call returns `{ success: true, isDuplicate: true, filePath: existing }`.
+    Test unique scenario: Generate new content, returns `{ success: true, isDuplicate: false, filePath: new }`.
+  </verify>
+  <done>
+    - Response includes `isDuplicate` boolean field
+    - Duplicate files logged: "Generation deduplicated: existing file found"
+    - Unique files logged: "Generation saved" (existing log)
+  </done>
+</task>
+
+</tasks>
+
+<verification>
+Before declaring phase complete:
+- [ ] `npm run build` succeeds without errors
+- [ ] Generate same prompt twice → second returns existing file (no new file created)
+- [ ] Generate different prompt → new file created with hash prefix
+- [ ] Response includes `isDuplicate` field
+- [ ] Existing generations folder functionality preserved
+</verification>
+
+<success_criteria>
+- All tasks completed
+- All verification checks pass
+- No duplicate files created for identical content
+- Backward compatible: existing generations still accessible
+- Hash-based filenames enable fast duplicate lookup
+</success_criteria>
+
+<output>
+After completion, create `.planning/phases/13-fix-duplicate-generations/13-01-SUMMARY.md`
+</output>