# Milestone v1.2: Session Attachments

**Status:** SHIPPED 2026-02-07
**Phases:** 12-16
**Total Plans:** 11

## Overview

Add file attachment capability to music sessions, allowing users to upload files from their computer and view them in the chat window with real-time synchronization across all session participants.

## Phases

### Phase 12: Attachment Research & Backend Validation
**Goal**: Validate existing backend infrastructure and understand legacy attachment patterns
**Depends on**: Phase 11 (previous milestone complete)
**Research**: Likely (exploring legacy attachment implementation and backend API)
**Research topics**: Legacy AttachmentStore patterns, MusicNotation model and API, S3 upload flow, file type/size validation, attachment-chat integration
**Requirements**: None (research phase)
**Plans**: 2 plans

**Success Criteria:**
1. Backend API contract documented (endpoints, payloads, responses)
2. MusicNotation model capabilities validated (no code changes needed)
3. S3 upload flow understood (signed URLs, multipart form data)
4. Legacy file validation patterns documented (type whitelist, 10 MB limit)
5. Integration points identified (chat window, WebSocket, Redux)

Plans:
- [x] 12-01-PLAN.md — Document legacy AttachmentStore and backend API contract
- [x] 12-02-PLAN.md — Validate backend infrastructure and design React integration strategy

### Phase 13: File Upload Infrastructure
**Goal**: Users can select files from OS dialog and upload to S3 with validation and progress feedback
**Depends on**: Phase 12
**Research**: Unlikely (following established patterns from research phase)
**Requirements**: REQ-1.1, REQ-1.2, REQ-1.3, REQ-1.4, REQ-6.1, REQ-6.2, REQ-6.3, REQ-7.1
**Plans**: 3 plans

**Success Criteria:**
1. User clicks Attach button in session toolbar → OS file dialog opens
2. File selection validates type (.pdf, .xml, .mxl, .txt, .png, .jpg, .jpeg, .gif, .mp3, .wav) and size (≤ 10 MB)
3. Invalid files show immediate error toast (type or size) without starting upload
4. Valid files upload to S3 via MusicNotation API with multipart form data
5. Upload progress indicator displays in chat window (percentage or spinner)
6. Upload completes → API returns attachment metadata (id, file_name, file_url, size)
7. Correct attachment_type set (notation/audio) based on file extension
8. Attachment associated with correct music_session_id
9. User can continue using app while upload is in progress (non-blocking)

Plans:
- [x] 13-01-PLAN.md — TDD: Attachment validation service (validateFileSize, validateFileType, getAttachmentType)
- [x] 13-02-PLAN.md — TDD: Redux upload state and REST helpers (uploadAttachment thunk, uploadMusicNotation)
- [x] 13-03-PLAN.md — Attach button integration (JKChatAttachButton + JKChatComposer integration)

### Phase 14: Chat Integration & Display
**Goal**: Attachments display as messages in chat window with metadata and clickable links
**Depends on**: Phase 13
**Research**: Unlikely (extending existing chat message display)
**Requirements**: REQ-2.1, REQ-2.2, REQ-2.3, REQ-2.4, REQ-2.5, REQ-4.1, REQ-4.2, REQ-7.2, REQ-7.3
**Plans**: 3 plans

**Success Criteria:**
1. Attachment appears in chat as message: "[UserName] attached [FileName]"
2. Attachment message includes metadata: filename, file size (KB/MB), uploader, timestamp
3. Attachment has visual indicator (icon, styling) to distinguish from text messages
4. Filename is clickable link that opens file in new browser tab (target="_blank")
5. Browser handles view/download based on file type (PDF viewer, image display, audio player, XML download)
6. Attachment messages sort chronologically with regular chat messages
7. Chat auto-scrolls when new attachment appears (reuses existing logic)
8. Chat history includes attachments (persist across page refresh, visible when joining session)
9. Attachment messages display correctly at different window sizes (responsive layout, long filename truncation)

Plans:
- [x] 14-01-PLAN.md — Attachment message display with metadata and styling
- [x] 14-02-PLAN.md — Clickable links and responsive layout
- [x] 14-03-PLAN.md — Gap closure: REST API attachment transformation (fixes REQ-2.5)

### Phase 15: Real-time Synchronization
**Goal**: New attachments broadcast to all session participants in real-time via WebSocket
**Depends on**: Phase 14
**Research**: Unlikely (extending existing WebSocket handlers)
**Requirements**: REQ-3.1, REQ-3.2
**Plans**: 1 plan

**Success Criteria:**
1. User uploads file → WebSocket message broadcasts to all session participants
2. Attachment appears immediately in all users' chat windows (no manual refresh)
3. WebSocket message includes: music_session_id, file_name, file_url, user_name, size, timestamp
4. Optimistic update prevents duplicate messages for uploader (deduplication by msg_id)
5. Multiple users in same session all see attachment in real-time
6. User joining session after upload sees attachment in chat history

Plans:
- [x] 15-01-PLAN.md — Verify real-time sync and create integration tests

### Phase 16: Attachment Finalization
**Goal**: Complete attachment feature with comprehensive error handling, edge cases, and UAT validation
**Depends on**: Phase 15
**Research**: Unlikely (error handling and validation of established code)
**Requirements**: REQ-5.1, REQ-5.2, REQ-5.3, REQ-5.4, REQ-5.5
**Plans**: 2 plans

**Success Criteria:**
1. File size exceeded (>10 MB) → toast "File size exceeds 10 MB limit", upload blocked
2. Invalid file type → toast with allowed types list, upload blocked
3. Network error during upload → toast "Upload failed. Please try again.", optimistic message removed, retry possible
4. Upload success → toast "File uploaded successfully" (auto-dismiss), attachment in chat
5. Missing/deleted file on S3 → browser 404 page (no app crash)
6. All edge cases handled: rapid clicks, disconnection, empty states, long filenames
7. Comprehensive UAT checklist validates all 26 requirements

Plans:
- [x] 16-01-PLAN.md — Error handling, success toast, and S3 404 handling
- [x] 16-02-PLAN.md — UAT checklist and final integration testing

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## Milestone Summary

**Key Decisions:**
- Use existing MusicNotation backend API (no backend changes needed)
- Eager fetch chat history on session join (for unread badge persistence)
- Triple-location deduplication for attachment messages (WebSocket, REST, upload fulfilled)
- File validation on client side before upload (type whitelist, 10 MB limit)

**Issues Resolved:**
- Attachment message deduplication race condition (fixed in Phase 16 UAT)
- Unread count not persisting across page reloads (fixed in Phase 16 UAT)
- REST API attachment transformation for chat history (fixed in Phase 14-03)

**Issues Deferred:**
- None

**Technical Debt Incurred:**
- None

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*For current project status, see .planning/ROADMAP.md*
