fix(httpapi): return mcp server not found errors (#28817)

packages/opencode/test/server/httpapi-mcp.test.ts

@@ -192,4 +192,36 @@ describe("mcp HttpApi", () => {
       },
     },
   )
+
+  it.instance(
+    "returns typed not found errors for missing MCP servers",
+    () =>
+      Effect.gen(function* () {
+        const tmp = yield* TestInstance
+        const handler = yield* handlerScoped
+
+        for (const input of [
+          { method: "POST", route: "/mcp/missing/auth" },
+          { method: "POST", route: "/mcp/missing/auth/authenticate" },
+          { method: "POST", route: "/mcp/missing/auth/callback", body: JSON.stringify({ code: "code" }) },
+          { method: "DELETE", route: "/mcp/missing/auth" },
+          { method: "POST", route: "/mcp/missing/connect" },
+          { method: "POST", route: "/mcp/missing/disconnect" },
+        ]) {
+          const response = yield* request(handler, input.route, tmp.directory, {
+            method: input.method,
+            headers: input.body ? { "content-type": "application/json" } : undefined,
+            body: input.body,
+          })
+
+          expect(response.status).toBe(404)
+          expect(yield* json(response)).toEqual({
+            _tag: "McpServerNotFoundError",
+            name: "missing",
+            message: "MCP server not found: missing",
+          })
+        }
+      }),
+    { config: { mcp: {} } },
+  )
 })