v1.14.1-mcp-poc: single-server MCP client against Context7

Validates the MCP-client loop end-to-end against one real MCP server before
the full v1.15 port. New services/mcp-client.ts wraps @modelcontextprotocol/sdk
v1.29.0 with Streamable HTTP transport. On startup (when MCP_CONTEXT7_URL is
set), connects to Context7, discovers tools via tools/list, wraps each as a
ToolDef prefixed context7_<name>, and appends to ALL_TOOLS via appendMcpTools.

Read-only invariant guard rejects any tool with readOnlyHint: false. Tool
dispatch is transparent — executeToolCall routes MCP calls through the ToolDef
execute wrapper, which strips the prefix before calling the MCP server. Result
size capped at 5MB with truncation. Graceful degradation: server down at
startup → zero tools; server down mid-session → error result, model
self-corrects.

Adversarial review caught that a Zod .default() on the URL config made MCP
always-on instead of opt-in — fixed by removing the default. MCP_CONTEXT7_URL
must be explicitly set to enable.

ALL_TOOLS changed from ReadonlyArray to mutable to support late-registration.
appendMcpTools re-sorts and rebuilds TOOLS_BY_NAME after append.

348/348 server tests passing (16 new mcp-client tests). No schema changes,
no frontend changes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

pnpm-lock.yaml

@@ -57,6 +57,9 @@ importers:
       '@fastify/websocket':
         specifier: ^10.0.1
         version: 10.0.1
+      '@modelcontextprotocol/sdk':
+        specifier: ^1.29.0
+        version: 1.29.0(zod@3.25.76)
       ai:
         specifier: ^6.0.190
         version: 6.0.190(zod@3.25.76)
@@ -5774,7 +5777,7 @@ snapshots:
       bytes: 3.1.2
       content-type: 1.0.5
       debug: 4.4.3
-      http-errors: 2.0.0
+      http-errors: 2.0.1
       iconv-lite: 0.7.2
       on-finished: 2.4.1
       qs: 6.15.1
@@ -6151,7 +6154,7 @@ snapshots:
       etag: 1.8.1
       finalhandler: 2.1.1
       fresh: 2.0.0
-      http-errors: 2.0.0
+      http-errors: 2.0.1
       merge-descriptors: 2.0.0
       mime-types: 3.0.2
       on-finished: 2.4.1
@@ -6163,7 +6166,7 @@ snapshots:
       router: 2.2.0
       send: 1.2.1
       serve-static: 2.2.1
-      statuses: 2.0.1
+      statuses: 2.0.2
       type-is: 2.1.0
       vary: 1.1.2
     transitivePeerDependencies:
@@ -6262,7 +6265,7 @@ snapshots:
       escape-html: 1.0.3
       on-finished: 2.4.1
       parseurl: 1.3.3
-      statuses: 2.0.1
+      statuses: 2.0.2
     transitivePeerDependencies:
       - supports-color