---
phase: 16-attachment-finalization
plan: 01
subsystem: ui
tags: [react, error-handling, toast-notifications, user-feedback, playwright-tests, file-upload]

# Dependency graph
requires:
  - phase: 13-03
    provides: Upload flow with validation and progress display
  - phase: 14-02
    provides: Attachment message display and S3 URL fetching
  - phase: 15-01
    provides: Real-time synchronization and optimistic updates
provides:
  - Upload success toast notification (REQ-5.4)
  - Standardized validation error messages (REQ-5.1, REQ-5.2)
  - Network error message with retry guidance (REQ-5.3)
  - S3 404 error handling with toast notification (REQ-5.5)
  - Comprehensive error handling integration tests
affects: [future-attachment-features, error-recovery-flows]

# Tech tracking
tech-stack:
  added: []
  patterns:
    - "Upload status transition detection for success toast"
    - "useRef pattern for tracking previous state values"
    - "Playwright integration tests for error scenarios"
    - "Toast notifications for all error and success states"

key-files:
  created:
    - jam-ui/test/attachments/error-handling.spec.ts
  modified:
    - jam-ui/src/components/client/JKSessionScreen.js
    - jam-ui/src/services/attachmentValidation.js
    - jam-ui/src/store/features/sessionChatSlice.js
    - jam-ui/src/components/client/chat/JKChatMessage.js

key-decisions:
  - "Success toast triggers on status transition (uploading → idle) not on fulfilled action"
  - "Hardcoded allowed extensions list in error messages for clarity"
  - "S3 404 error shows user-friendly toast instead of silent failure"
  - "Integration tests cover all 5 requirements with Playwright"

patterns-established:
  - "Status transition detection: prevRef.current vs current value pattern"
  - "Error message standardization: exact wording from requirements"
  - "User-friendly error messages: actionable guidance for users"

# Metrics
duration: <1min (verification only - work already completed)
completed: 2026-02-07
---

# Phase 16 Plan 01: Error Handling & User Feedback Summary

**Complete error handling with toast notifications, standardized messages, and comprehensive integration tests for file attachment feature**

## Performance

- **Duration:** <1 min (verification only)
- **Started:** 2026-02-07T04:37:49Z
- **Completed:** 2026-02-07T04:38:40Z
- **Tasks:** 5 (all previously completed)
- **Files modified:** 4 + 1 test file created

## Accomplishments
- Success toast displays "File uploaded successfully" after upload completes (REQ-5.4)
- File size error shows exact message "File size exceeds 10 MB limit" (REQ-5.1)
- File type error shows comprehensive allowed types list (REQ-5.2)
- Network error shows toast "Upload failed. Please try again." and allows retry (REQ-5.3)
- S3 404 shows "File no longer available" toast instead of silent failure (REQ-5.5)
- Comprehensive Playwright integration tests covering all error scenarios

## Task Commits

Each task was committed atomically:

1. **Task 1: Add upload success toast (REQ-5.4)** - `354492bc1` (feat)
2. **Task 2: Improve validation error messages (REQ-5.1, REQ-5.2)** - `1ecc1d798` (fix)
3. **Task 3: Update network error message (REQ-5.3)** - `744c73581` (fix)
4. **Task 4: Add S3 404 error handling (REQ-5.5)** - `1d026c3d3` (fix)
5. **Task 5: Create error handling integration tests** - `4bb3fa206` (test)

**Plan metadata:** Not yet committed (will be committed in final step)

## Files Created/Modified

- `jam-ui/src/components/client/JKSessionScreen.js` - Upload success toast on status transition from 'uploading' to 'idle'
- `jam-ui/src/services/attachmentValidation.js` - Standardized error messages matching exact requirements wording
- `jam-ui/src/store/features/sessionChatSlice.js` - Network error message with retry guidance
- `jam-ui/src/components/client/chat/JKChatMessage.js` - S3 404 error handling with toast notification
- `jam-ui/test/attachments/error-handling.spec.ts` - 5 integration tests covering all error scenarios (NEW)

## Decisions Made

**1. Success toast triggers on status transition, not fulfilled action**
- **Rationale:** Upload success is better detected by status change (uploading → idle) than by action fulfillment
- **Implementation:** useRef pattern tracks previous uploadStatus value, shows toast when transition detected
- **Benefit:** More reliable detection, works regardless of Redux action timing

**2. Hardcoded allowed extensions list in error messages**
- **Rationale:** User-facing messages should be explicit and stable, not dependent on variable array join
- **Implementation:** "File type not supported. Allowed: .pdf, .xml, .mxl, .txt, .png, .jpg, .jpeg, .gif, .mp3, .wav"
- **Trade-off:** Must update message if allowed types change, but provides clarity for users

**3. S3 404 error shows toast notification**
- **Rationale:** Silent failure is poor UX - users need to know when file is unavailable
- **Implementation:** Toast.error in catch block of handleAttachmentClick
- **Benefit:** Users understand why attachment didn't open

**4. Integration tests use Playwright for error scenarios**
- **Rationale:** Playwright can intercept network requests and simulate error conditions
- **Implementation:** 5 test cases covering all REQ-5.* requirements
- **Coverage:** File size, upload success, network failure, S3 404, rapid clicks prevention

## Deviations from Plan

None - plan executed exactly as written. All code was already completed from previous session, this execution only verified correctness.

## Issues Encountered

None - all code was already implemented and committed. Verification confirmed all requirements met.

## User Setup Required

None - no external service configuration required.

## Next Phase Readiness

**Phase 16 Plan 02 (UAT & Final Verification) ready:**
- All error handling paths implemented and tested
- Toast notifications working for all scenarios
- Integration tests provide automated coverage
- User feedback is clear and actionable

**Remaining work in Phase 16:**
- Plan 16-02: User Acceptance Testing (UAT) for complete attachment feature
- Final manual verification of all requirements
- Documentation review and cleanup

**No blockers or concerns.**

**Phase 16 completion status:** 50% (1/2 plans complete)

---
*Phase: 16-attachment-finalization*
*Plan: 01*
*Completed: 2026-02-07*
