diff --git a/cli/src/agent/backends/acp/AcpStdioTransport.ts b/cli/src/agent/backends/acp/AcpStdioTransport.ts
index 9f93b876..e74f7681 100644
--- a/cli/src/agent/backends/acp/AcpStdioTransport.ts
+++ b/cli/src/agent/backends/acp/AcpStdioTransport.ts
@@ -65,7 +65,11 @@ export class AcpStdioTransport {
 
         this.process.on('error', (error) => {
             logger.debug('[ACP] Process error', error);
-            this.rejectAllPending(error instanceof Error ? error : new Error(String(error)));
+            const message = error instanceof Error ? error.message : String(error);
+            this.rejectAllPending(new Error(
+                `Failed to spawn ${options.command}: ${message}. Is it installed and on PATH?`,
+                { cause: error }
+            ));
         });
     }
 
diff --git a/cli/src/codex/codexLocal.ts b/cli/src/codex/codexLocal.ts
index 24a51039..33fe8aa7 100644
--- a/cli/src/codex/codexLocal.ts
+++ b/cli/src/codex/codexLocal.ts
@@ -95,7 +95,8 @@ export async function codexLocal(opts: {
 
             child.on('error', (error) => {
                 cleanupAbortHandler();
-                reject(error);
+                const message = error instanceof Error ? error.message : String(error);
+                reject(new Error(`Failed to spawn codex: ${message}. Is Codex CLI installed and on PATH?`, { cause: error }));
             });
 
             child.on('exit', (code, signal) => {