diff --git a/src/local-agent-acp.test.ts b/src/local-agent-acp.test.ts
index 1aa2c077e..f20f02020 100644
--- a/src/local-agent-acp.test.ts
+++ b/src/local-agent-acp.test.ts
@@ -14,6 +14,7 @@ import {
   deliverAcpSessionUpdate,
   resolveAcpCommand,
   selectAcpPermissionOption,
+  matchAcpSelectValue,
 } from "./local-agent-acp.js";
 import { GrokPromptCompletionRegistry } from "./local-agent-grok.js";
 
@@ -822,3 +823,12 @@ test("a stop requested before the prompt is sent starts no provider work", async
   assert.equal(preAbortRequests.includes("session/prompt"), false);
   await preAbortRuntime.close();
 });
+
+test("an ACP select accepts a plain name when exactly one bracketed variant matches", () => {
+  const available = ["default[]", "composer-2.5[fast=true]", "grok-4.6[effort=high,fast=true]", "grok-4.6[effort=low]"];
+
+  assert.equal(matchAcpSelectValue(available, "composer-2.5[fast=true]"), "composer-2.5[fast=true]");
+  assert.equal(matchAcpSelectValue(available, "composer-2.5"), "composer-2.5[fast=true]");
+  assert.equal(matchAcpSelectValue(available, "grok-4.6"), undefined, "ambiguous names match nothing");
+  assert.equal(matchAcpSelectValue(available, "composer"), undefined);
+});
diff --git a/src/local-agent-acp.ts b/src/local-agent-acp.ts
index 784624a34..ec09ab03b 100644
--- a/src/local-agent-acp.ts
+++ b/src/local-agent-acp.ts
@@ -954,13 +954,26 @@ function resolveAcpSelectConfigUpdate(
 
   if (!configId) throw new Error(`${options.provider} ACP ${options.label} is missing an id.`);
   const available = flattenAcpSelectValues(config);
+  const value = matchAcpSelectValue(available, options.value);
 
-  if (!available.includes(options.value)) {
+  if (!value) {
     const suffix = available.length > 0 ? ` Available values: ${available.join(", ")}.` : "";
     throw new Error(`${options.provider} ACP ${options.label} does not support '${options.value}'.${suffix}`);
   }
 
-  return { sessionId, configId, value: options.value };
+  return { sessionId, configId, value };
+}
+
+/**
+ * Accepts an exact option value, or a plain name such as `composer-2.5` when exactly one option is that name plus
+ * bracketed settings (Cursor's `composer-2.5[fast=true]`). An ambiguous name matches nothing.
+ */
+export function matchAcpSelectValue(available: readonly string[], requested: string): string | undefined {
+  if (available.includes(requested)) return requested;
+
+  const variants = available.filter((value) => value.startsWith(`${requested}[`) && value.endsWith("]"));
+
+  return variants.length === 1 ? variants[0] : undefined;
 }
 
 export function flattenAcpSelectValues(option: JsonObject): string[] {