diff --git a/client/src/lib/api.ts b/client/src/lib/api.ts
index ad6c5844..592ab231 100644
--- a/client/src/lib/api.ts
+++ b/client/src/lib/api.ts
@@ -1700,25 +1700,37 @@ export const api = {
       requestCodexBackupsHelper(params),
     /**
      * GET /api/codex-config/mcp - configured MCP servers from the codex CLI.
+     * Coerces the CLI's JSON output (which may be an object) to an array.
      * @returns `{ mcp }` — {@link CodexMcpServer} items.
      */
-    mcp: () => request<{ mcp: CodexMcpServer[] }>("/codex-config/mcp"),
+    mcp: async () => {
+      const res = await request<{ mcp: unknown }>("/codex-config/mcp");
+      return { mcp: Array.isArray(res.mcp) ? res.mcp : [] };
+    },
     /**
      * GET /api/codex-config/plugins - installed plugins from the codex CLI.
+     * Coerces the CLI's JSON output (which may be an object) to an array.
      * @returns `{ plugins }` — {@link CodexPlugin} items.
      */
-    plugins: () => request<{ plugins: CodexPlugin[] }>("/codex-config/plugins"),
+    plugins: async () => {
+      const res = await request<{ plugins: unknown }>("/codex-config/plugins");
+      return { plugins: Array.isArray(res.plugins) ? res.plugins : [] };
+    },
     /**
      * GET /api/codex-config/marketplaces - registered marketplaces from the codex CLI.
+     * Coerces the CLI's JSON output (which may be an object) to an array.
      * @returns `{ marketplaces }` — {@link CodexMarketplace} items.
      */
-    marketplaces: () => request<{ marketplaces: CodexMarketplace[] }>("/codex-config/marketplaces"),
+    marketplaces: async () => {
+      const res = await request<{ marketplaces: unknown }>("/codex-config/marketplaces");
+      return { marketplaces: Array.isArray(res.marketplaces) ? res.marketplaces : [] };
+    },
     /**
      * POST /api/codex-config/mcp/add - add an MCP server via the `codex` CLI.
-     * @param args Arguments for `codex mcp add`.
+     * @param args {@link CodexMcpAddArgs} for `codex mcp add`.
      * @returns `{ ok, stdout, stderr }` — success and CLI output.
      */
-    mcpAdd: (args: unknown) =>
+    mcpAdd: (args: CodexMcpAddArgs) =>
       request<{ ok: true; stdout: string; stderr: string }>("/codex-config/mcp/add", {
         method: "POST",
         body: JSON.stringify(args),
@@ -1735,10 +1747,10 @@ export const api = {
       }),
     /**
      * POST /api/codex-config/plugins/action - add or remove a plugin via the `codex` CLI.
-     * @param args Arguments with `spec` and `action` fields.
+     * @param args {@link CodexPluginActionArgs} with `spec` and `action` fields.
      * @returns `{ ok, stdout, stderr }` — success and CLI output.
      */
-    pluginAction: (args: unknown) =>
+    pluginAction: (args: CodexPluginActionArgs) =>
       request<{ ok: true; stdout: string; stderr: string }>("/codex-config/plugins/action", {
         method: "POST",
         body: JSON.stringify(args),
@@ -1755,10 +1767,10 @@ export const api = {
       }),
     /**
      * POST /api/codex-config/marketplaces/action - update or remove a marketplace via the `codex` CLI.
-     * @param args Arguments with `name` and `action` fields.
+     * @param args {@link CodexMarketplaceActionArgs} with `name` and `action` fields.
      * @returns `{ ok, stdout, stderr }` — success and CLI output.
      */
-    marketplaceAction: (args: unknown) =>
+    marketplaceAction: (args: CodexMarketplaceActionArgs) =>
       request<{ ok: true; stdout: string; stderr: string }>("/codex-config/marketplaces/action", {
         method: "POST",
         body: JSON.stringify(args),
@@ -2994,6 +3006,28 @@ export interface CodexMarketplace {
   [key: string]: unknown;
 }
 
+/** Arguments for POST /api/codex-config/mcp/add. */
+export interface CodexMcpAddArgs {
+  name: string;
+  url?: string;
+  bearerTokenEnvVar?: string;
+  command?: string;
+  args?: string[];
+  env?: Record<string, string>;
+}
+
+/** Arguments for POST /api/codex-config/plugins/action. */
+export interface CodexPluginActionArgs {
+  spec: string;
+  action: "add" | "remove";
+}
+
+/** Arguments for POST /api/codex-config/marketplaces/action. */
+export interface CodexMarketplaceActionArgs {
+  name: string;
+  action: "remove";
+}
+
 // ─────────────────────────────────────────────────────────────────────────────
 // Run types — request/response shapes for the Run page's `claude` process
 // spawning/management. `RunMode`/`RunStatus`/`PermissionMode`/`EffortLevel`