feat(cli): surface the MCP endpoint in the server-ready banner (#3167)

The MCP server (/api/v1/mcp) is a default-on core capability, but nothing in
the os dev / os serve boot output pointed to it — a developer had to already
know it was there to connect an AI client. This is the dev-loop discoverability
gap #3167 set out to close: the platform's "let an AI operate the running app"
channel was live but invisible.

printServerReady now prints the MCP URL and the SKILL.md pointer whenever the
surface is enabled — gated on isMcpServerEnabled(), the SAME switch that
auto-loads the plugin and gates the route, so the banner can never advertise an
endpoint that isn't served. Hidden when OS_MCP_SERVER_ENABLED=false.

Runtime-verified: the line renders with the URL + skill pointer when enabled and
is absent when disabled. CLI builds clean; lint clean. Closes the last
(optional, DX) item on #3167 — the admission story itself landed in #3202/#3225.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pbmw3pMqNJfPbkvwh9Fkjs

Author: claude

.changeset/mcp-dev-connect-hint.md

@@ -0,0 +1,13 @@
+---
+'@objectstack/cli': patch
+---
+
+feat(cli): surface the MCP endpoint in the server-ready banner (#3167)
+
+The MCP server (`/api/v1/mcp`) is a default-on core capability, but nothing in
+the `os dev` / `os serve` boot output pointed to it — a developer had to already
+know it was there to connect an AI client. The server-ready banner now prints
+the MCP URL and the `SKILL.md` pointer whenever the surface is enabled
+(`isMcpServerEnabled()`, the same switch that auto-loads the plugin and gates
+the route), so an agent can operate the running app straight from the dev loop.
+Hidden when `OS_MCP_SERVER_ENABLED=false`.

packages/cli/src/commands/serve.ts

@@ -2455,6 +2455,11 @@ export default class Serve extends Command {
         multiTenant: resolveMultiOrgEnabled(),
         seededAdmin,
         automation: automationSummary,
+        // #3167 — surface the default-on MCP endpoint in the dev loop, where an
+        // AI client can connect to operate the running app. Same decision point
+        // that auto-loads the plugin + gates the route, so the banner never
+        // advertises an endpoint that isn't served.
+        mcpEnabled: isMcpServerEnabled(),
       });
 
       // ── Publish the actually-bound port ────────────────────────────

packages/cli/src/utils/format.ts

@@ -203,6 +203,14 @@ export interface ServerReadyOptions {
    * armed. Collected from the live engine after runtime.start().
    */
   automation?: AutomationReadySummary;
+  /**
+   * Whether the MCP server surface (`/api/v1/mcp`) is on (#3167). Default-on
+   * core capability, but nothing in the dev loop surfaces it — an AI client
+   * (Claude Code, Cursor, …) can operate the running app the instant a
+   * developer knows the endpoint is there. The banner is where they look, so
+   * print the URL + the SKILL.md pointer when it's live.
+   */
+  mcpEnabled?: boolean;
 }
 
 export interface AutomationReadySummary {
@@ -233,6 +241,10 @@ export function printServerReady(opts: ServerReadyOptions) {
   if (opts.uiEnabled && opts.consolePath) {
     console.log(chalk.cyan('  ➜') + chalk.bold('  Console:   ') + chalk.cyan(base + opts.consolePath + '/'));
   }
+  if (opts.mcpEnabled) {
+    console.log(chalk.cyan('  ➜') + chalk.bold('  MCP:       ') + chalk.cyan(base + '/api/v1/mcp'));
+    console.log(chalk.dim(`      connect an AI client (Claude Code, Cursor, …) · skill: ${base}/api/v1/mcp/skill`));
+  }
   if (opts.seededAdmin) {
     console.log('');
     console.log(