T-130: MCP server over HTTP+SSE for /ide integration

Seventh slice of T-99. clide now advertises itself to Claude Code's
/ide command and serves a working MCP endpoint over HTTP+SSE per
D-73 (the Q-33 transport decision, locked in this commit).

What lands:
* D-73 — MCP transport for /ide is SSE over HTTP. Resolves Q-33;
  references D-68 + D-72.
* lib/src/ipc/mcp_server.dart — McpServer class. localhost HTTP
  listener on a random port; GET /sse opens a long-lived SSE stream
  with an initial endpoint event carrying the session id; POST
  /messages?sessionId=... accepts JSON-RPC requests and replies via
  the matching SSE stream. JSON-RPC handlers for initialize,
  tools/list, tools/call.
* Discovery file at $HOME/.claude/ide/<pid>.lock with the workspace
  + url so `/ide` can find us. Removed on stop.
* The two /ide minimum tools (mcp__ide__getDiagnostics,
  mcp__ide__executeCode) ship as stubs — real implementations need
  the analyzer integration / a clide eval surface, both follow-ups.
* main.dart starts the MCP server alongside the unix IPC server on
  daemonClientFactory and project switch. Failure non-fatal — the
  UI runs without MCP.
* 12 server tests cover lifecycle (start/stop, lock file), unknown
  paths, full JSON-RPC round-trip for all four methods, error
  responses, and edge cases (unknown session, malformed JSON,
  notification without id).

The "Claude Code's /ide discovers and connects" smoke is deferred to
T-131 wrap-up since it needs a real Claude Code session against the
running app — out of scope for unit/widget tests.

Co-Authored-By: Claude <noreply@anthropic.com>

governance/decisions/architecture.md

@@ -279,4 +279,12 @@ Core, rendering, IPC, kernel, panel manager.
 - **Cross-reference:** [D-56](#d-56-dissolve-daemon-process-flutter-app-hosts-ipc-server), [D-70](#d-70-ipc-socket-path-is-per-workspace-deterministic), `lib/src/pty/native_pty.dart` (per-handler isolate offload example), `lib/kernel/src/scheduler.dart` (same pattern).
 - **Raised by:** 2026-05-18 — T-99 design pass; user explicitly considered worker-isolate-per-connection and confirmed serial dispatch on main is the right shape given the shared-state architecture.
 
+### D-73: MCP transport for /ide is SSE over HTTP
+- **Date:** 2026-05-19
+- **Decision:** The `/ide`-compatible MCP server clide ships per [D-68](#d-68-dual-integration-surface--bash-cli-primary-mcp-secondary) uses **HTTP + Server-Sent Events** as its transport. The Flutter app binds an HTTP server on a random localhost port at startup, advertises itself via a discovery file at `$HOME/.claude/ide/<pid>.lock` (the format Claude Code's `/ide` command discovers), and serves: a `GET /sse` endpoint that opens a long-lived SSE stream for server-to-client JSON-RPC responses + events, and a `POST /messages` endpoint that accepts client-to-server JSON-RPC requests. Closes Q-33.
+- **Rationale:** clide's Flutter app is always-running and user-launched — the agent connects to it, not the other way around. That rules out stdio (which assumes the agent spawns the server as a subprocess). Between SSE and WebSocket, SSE wins on three counts: (a) Claude Code's existing `/ide` discovery already uses HTTP servers advertised via lock files, (b) SSE is trivially implementable on `dart:io`'s `HttpServer` (long-lived response + `data: <json>\n\n` per message — no upgrade dance, no framing), (c) JSON-RPC is fundamentally client-pushes-requests / server-pushes-responses-and-events, which maps cleanly to "POST in / SSE out." WebSocket buys bidirectional symmetry we don't need. Per [D-72](#d-72-ipc-server-is-multi-connection-with-serial-dispatch-on-the-main-isolate) the MCP layer is just another transport that wraps the same `DaemonDispatcher` — no second source of truth.
+- **Cost:** SSE requires a long-lived HTTP response. Browsers cap concurrent SSE connections per origin at 6, but the consumers here are Claude Code instances (not browsers) and one-per-workspace is the expected fan-out. Adds an HTTP listener alongside the unix socket — a small surface increase, but the alternatives are worse. Each running clide grabs a random localhost port; no contention.
+- **Cross-reference:** [D-68](#d-68-dual-integration-surface--bash-cli-primary-mcp-secondary), [D-72](#d-72-ipc-server-is-multi-connection-with-serial-dispatch-on-the-main-isolate), `lib/src/ipc/mcp_server.dart` (this transport's implementation lands in T-130).
+- **Raised by:** 2026-05-19 — T-130 design pass; user picked SSE over HTTP after weighing against WebSocket and stdio.
+
 ---