fix: recognize Cursor session-not-found error format

src/acp-error-shapes.ts

@@ -89,6 +89,10 @@ export function formatUnknownErrorMessage(error: unknown): string {
   return String(error);
 }
 
+// Matches "session" followed by optional ID (quoted or unquoted) followed by "not found"
+// Examples: "Session \"abc\" not found", "Session abc-123 not found"
+const SESSION_NOT_FOUND_PATTERN = /session\s+["'\w\-]+\s+not found/i;
+
 function isSessionNotFoundText(value: unknown): boolean {
   if (typeof value !== "string") {
     return false;
@@ -100,7 +104,8 @@ function isSessionNotFoundText(value: unknown): boolean {
     normalized.includes("resource not found") ||
     normalized.includes("session not found") ||
     normalized.includes("unknown session") ||
-    normalized.includes("invalid session identifier")
+    normalized.includes("invalid session identifier") ||
+    SESSION_NOT_FOUND_PATTERN.test(value)
   );
 }
 

test/error-normalization.test.ts

@@ -57,6 +57,19 @@ test("isAcpResourceNotFoundError recognizes session-not-found hints in nested er
     true,
   );
 });
+
+test("isAcpResourceNotFoundError recognizes Cursor session-not-found format", () => {
+  // Cursor returns: {"code":-32602,"message":"Invalid params","data":{"message":"Session \"xxx\" not found"}}
+  const cursorError = {
+    code: -32602,
+    message: "Invalid params",
+    data: {
+      message: 'Session "nonexistent-session-id" not found',
+    },
+  };
+
+  assert.equal(isAcpResourceNotFoundError(cursorError), true);
+});
 test("isAcpQueryClosedBeforeResponseError matches typed ACP payload", () => {
   const error = {
     code: -32603,