---
phase: 21-book-mcp-apps-refresh
plan: 02
subsystem: docs
tags: [book, mcp-apps, adapter-pattern, chess, map, dataviz, chatgpt-adapter, multi-platform]

# Dependency graph
requires:
  - phase: 21-book-mcp-apps-refresh (plan 01)
    provides: Ch 12.5 first half with WidgetDir, bridge API, developer workflow
  - phase: 14-19 (v1.3 MCP Apps Developer Experience)
    provides: UIAdapter trait, ChatGptAdapter, McpAppsAdapter, McpUiAdapter, examples
provides:
  - Complete Ch 12.5 with adapter pattern, example walkthroughs, best practices, summary
affects: [22-23 (course chapters may reference Ch 12.5)]

# Tech tracking
tech-stack:
  added: []
  patterns: [UIAdapter trait pattern, MultiPlatformResource multi-host serving, stateless widget architecture, common 4-step MCP Apps server pattern]

key-files:
  created: []
  modified:
    - pmcp-book/src/ch12-5-mcp-apps.md

key-decisions:
  - "Documented all three adapter bridge APIs in table format extracted from actual inject_bridge() JavaScript source"
  - "Organized example walkthroughs to highlight unique patterns: stateless state (chess), context-aware queries (map), SQL injection prevention (dataviz)"
  - "Distilled common 4-step architecture pattern shared by all three examples into a reusable template"

patterns-established:
  - "Example walkthrough structure: architecture overview, tools table, key types/code, widget description, running instructions"
  - "Adapter comparison table format: Adapter | Host | MIME Type | Bridge API | Best For"

requirements-completed: [BKAP-03, BKAP-04]

# Metrics
duration: 4min
completed: 2026-02-28
---

# Phase 21 Plan 02: Adapter Pattern and Example Walkthroughs Summary

**Completed Ch 12.5 with UIAdapter trait documentation, three adapter bridge API tables, chess/map/dataviz architecture walkthroughs, and common 4-step server pattern**

## Performance

- **Duration:** 4 min
- **Started:** 2026-02-28T02:25:56Z
- **Completed:** 2026-02-28T02:30:08Z
- **Tasks:** 2
- **Files modified:** 1

## Accomplishments
- Documented UIAdapter trait with all five methods, TransformedResource struct, HostType and ExtendedUIMimeType enums
- Documented ChatGptAdapter bridge with 20+ methods/properties in categorized table (Core, State, Context, Communication, Files, Display, Environment)
- Documented McpAppsAdapter (4 methods) and McpUiAdapter (6 methods, 3 output formats) bridges
- Wrote chess example walkthrough: stateless GameState pattern, tool registration, StreamableHttpServer config
- Wrote map example walkthrough: Haversine distance, MapState context-aware queries, Leaflet.js
- Wrote dataviz example walkthrough: rusqlite SQL tools, table name validation, Chart.js dashboard
- Distilled common 4-step architecture pattern shared by all examples
- Added 8 best practices and comprehensive summary with forward references to Ch 13/14/15
- Chapter complete at 1294 lines, mdbook builds successfully

## Task Commits

Each task was committed atomically:

1. **Task 1: Write multi-platform adapter pattern section** - `1df9e24` (feat)
2. **Task 2: Write example walkthroughs and chapter conclusion** - `ef39496` (feat)

## Files Created/Modified
- `pmcp-book/src/ch12-5-mcp-apps.md` - Complete chapter: adapter pattern (UIAdapter, ChatGpt/McpApps/McpUi adapters, MultiPlatformResource), example walkthroughs (chess, map, dataviz), common pattern, best practices, summary

## Decisions Made
- Documented all bridge APIs in table format extracted directly from the inject_bridge() JavaScript source code, ensuring accuracy
- Highlighted unique architectural patterns per example rather than repeating the common structure
- Included focused code excerpts (10-30 lines) with file references rather than full source dumps
- Used the actual adapter.rs architecture diagram text in the overview section

## Deviations from Plan

None - plan executed exactly as written.

## Issues Encountered
None

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

## Next Phase Readiness
- Ch 12.5 is complete as a comprehensive, production-quality chapter (1294 lines)
- All four BKAP requirements completed (BKAP-01/02 in plan 01, BKAP-03/04 in plan 02)
- Phase 21 is complete, ready for Phase 22-23 (course chapters)

## Self-Check: PASSED

- FOUND: pmcp-book/src/ch12-5-mcp-apps.md
- FOUND: .planning/phases/21-book-mcp-apps-refresh/21-02-SUMMARY.md
- FOUND: commit 1df9e24
- FOUND: commit ef39496

---
*Phase: 21-book-mcp-apps-refresh*
*Completed: 2026-02-28*
