feat: add Tactility MCP Screen foundation

Apps/McpScreen/IMPLEMENTATION_PLAN.md

@@ -27,6 +27,47 @@ The original reference documents and implementations are:
 - Initial Tactility SDK: `0.7.0-dev`
 - Language: C/C++ with ESP-IDF, FreeRTOS, Tactility SDK, and LVGL
 
+## Current implementation status
+
+Phase 1 is implemented, builds successfully for ESP32-S3, and has been tested
+on a 320x240 Tactility device at runtime.
+
+Completed:
+
+- Tactility app lifecycle and app-owned drawing area
+- HTTP JSON-RPC endpoint on port 80
+- `tools/list`
+- `get_capabilities`
+- `clear_screen`
+- `draw_text`
+- request-size limits and JSON-RPC error responses
+- live `tools/list` and `get_capabilities` calls
+- live `clear_screen` and `draw_text` calls
+- live malformed-JSON error handling
+- crash-safe HTTP worker shutdown during app destruction
+- three forced stop/start cycles with the management and MCP endpoints still
+  responsive afterward
+
+Blocked by the current external-app ABI:
+
+- UDP discovery requires `lwip_recvfrom` and `lwip_sendto`, which the running
+  Tactility 0.7.0-dev firmware does not export to ELF apps. The existing bridge
+  falls back to HTTP subnet scanning, so MCP connectivity remains available.
+
+Pending verification:
+
+- verify service behavior while the app is genuinely hidden behind another
+  running application. A remote HelloWorld launch did not trigger `onHide`, so
+  this needs a manual launcher/device interaction test.
+
+### Shutdown implementation note
+
+Tactility unloads external-app ELF memory immediately after `onDestroy`
+returns. An app task blocked in `accept()` therefore cannot be allowed to
+survive destruction. The HTTP listener is non-blocking, client reads have
+short timeouts, and `onDestroy` closes sockets, waits for the worker to signal
+exit, then deletes the suspended worker task before returning.
+
 ## Design principles
 
 1. Preserve the existing MCP tool names and JSON-RPC contract wherever the
@@ -382,4 +423,3 @@ Implement Phase 1 as a minimal vertical slice:
 6. Add `get_capabilities`, `clear_screen`, and `draw_text`.
 7. Build.
 8. Run a host smoke test through the existing bridge.
-