---
phase: 36-unify-uimimetype-and-extendeduimimetype-with-from-bridge
plan: 01
subsystem: ui
tags: [mime-type, type-conversion, from, try-from, mcp-apps]

requires:
  - phase: 34-fix-mcp-apps-chatgpt-compatibility
    provides: ExtendedUIMimeType and UIMimeType enum definitions
provides:
  - "From<UIMimeType> for ExtendedUIMimeType (infallible conversion)"
  - "TryFrom<ExtendedUIMimeType> for UIMimeType (fallible conversion with descriptive error)"
  - "Bidirectional bridge enabling Phase 37 TypedSyncTool with_ui"
affects: [37-add-with-ui-support-to-typedsynctool]

tech-stack:
  added: []
  patterns: [explicit-match-arms-no-wildcards, from-tryfrom-bridge-pattern]

key-files:
  created: []
  modified:
    - src/types/mcp_apps.rs
    - src/types/ui.rs

key-decisions:
  - "Used explicit match arms (no wildcards) for compile-time exhaustiveness when new variants are added"
  - "Error type is String to match existing FromStr error type on both enums"
  - "Used full crate::types::ui::UIMimeType path in impls to avoid ambiguity"

patterns-established:
  - "From/TryFrom bridge pattern: infallible narrowing via From, fallible widening via TryFrom with String error"

requirements-completed: [MIME-BRIDGE-01]

duration: 13min
completed: 2026-03-06
---

# Phase 36 Plan 01: Unify UIMimeType and ExtendedUIMimeType with From Bridge Summary

**Bidirectional From/TryFrom bridge between UIMimeType (3 variants) and ExtendedUIMimeType (7 variants) with explicit match arms for compile-time safety**

## Performance

- **Duration:** 13 min
- **Started:** 2026-03-06T21:28:17Z
- **Completed:** 2026-03-06T21:41:08Z
- **Tasks:** 2
- **Files modified:** 2

## Accomplishments
- From<UIMimeType> for ExtendedUIMimeType: infallible conversion for all 3 shared variants
- TryFrom<ExtendedUIMimeType> for UIMimeType: fallible conversion returning descriptive "extended-only variant" error for 4 extended-only variants
- Round-trip conversion verified: UIMimeType -> ExtendedUIMimeType -> UIMimeType preserves original value
- 4 comprehensive tests covering all conversion paths

## Task Commits

Each task was committed atomically:

1. **Task 1: Write failing tests for From and TryFrom bridge** - `8735351` (test)
2. **Task 2: Implement From and TryFrom bridge impls** - `dfae0cf` (feat)

_TDD: RED (test) followed by GREEN (feat)_

## Files Created/Modified
- `src/types/mcp_apps.rs` - Added From/TryFrom impls and 4 bridge tests
- `src/types/ui.rs` - Fixed pre-existing clippy useless_conversion warning

## Decisions Made
- Used explicit match arms (no wildcards) so the compiler flags missing arms when new variants are added to either enum
- Error type is String, consistent with existing FromStr::Err on both enums
- Used full crate::types::ui::UIMimeType path in impl blocks to avoid use-import ambiguity

## Deviations from Plan

### Auto-fixed Issues

**1. [Rule 3 - Blocking] Fixed pre-existing clippy useless_conversion in ui.rs**
- **Found during:** Task 2 (clippy verification)
- **Issue:** `map.extend(meta.into_iter())` triggers clippy::useless_conversion since `extend` accepts IntoIterator directly
- **Fix:** Changed to `map.extend(meta)` (removed redundant `.into_iter()`)
- **Files modified:** src/types/ui.rs
- **Verification:** `cargo clippy --features mcp-apps -p pmcp -- -D warnings` passes clean
- **Committed in:** dfae0cf (part of Task 2 commit)

---

**Total deviations:** 1 auto-fixed (1 blocking)
**Impact on plan:** Trivial one-line fix to unblock clippy verification. No scope creep.

## Issues Encountered
None

## User Setup Required
None - no external service configuration required.

## Next Phase Readiness
- From/TryFrom bridge is ready for Phase 37 (TypedSyncTool with_ui) to use
- All conversions are feature-gated under `mcp-apps`
- Non-mcp-apps build compiles cleanly (bridge impls are in mcp_apps.rs, gated by feature)

---
*Phase: 36-unify-uimimetype-and-extendeduimimetype-with-from-bridge*
*Completed: 2026-03-06*
