diff --git a/src/cliOutput.ts b/src/cliOutput.ts
index 862de8b5b..0d029337c 100644
--- a/src/cliOutput.ts
+++ b/src/cliOutput.ts
@@ -36,7 +36,8 @@ export const validateCliOutputArguments = (
   let tokenWindow = false;
   for (let index = 0; index < arguments_.length; index += 1) {
     const argument = arguments_[index];
-    if (argument === "--") break;
+    // Incur scans builtins across `--` and accepts only the spaced --format form.
+    // Mirror its effective format so malformed requests still emit complete JSON.
     if (argument === "--json") {
       format = "json";
       continue;
@@ -49,10 +50,6 @@ export const validateCliOutputArguments = (
       }
       continue;
     }
-    if (argument?.startsWith("--format=")) {
-      format = argument.slice("--format=".length);
-      continue;
-    }
     if (argument === "--token-limit" || argument === "--token-offset") {
       if (arguments_[index + 1] !== undefined) {
         tokenWindow = true;
diff --git a/tests/boundary/cli/cliOutput.test.ts b/tests/boundary/cli/cliOutput.test.ts
index 771cd34db..4ca3d913d 100644
--- a/tests/boundary/cli/cliOutput.test.ts
+++ b/tests/boundary/cli/cliOutput.test.ts
@@ -57,6 +57,25 @@ describe("CLI output argument and sanitization boundary", () => {
     ).toEqual({ ok: true });
   });
 
+  workspaceCliTest(
+    "preserves complete JSON errors when native builtin flags follow unusual arguments",
+    async ({ cli }) => {
+      for (const arguments_ of [
+        ["providers", "--", "--json", "--token-limit", "5"],
+        ["providers", "--json", "--format=toon", "--token-limit", "5"],
+      ]) {
+        const result = await cli.run({ arguments: arguments_ });
+        expect(result.exitCode).toBe(1);
+        expect(result.stdout).not.toContain("[truncated:");
+        expect(JSON.parse(result.stdout)).toMatchObject({
+          ok: false,
+          error: { code: "UNSUPPORTED_OUTPUT_COMBINATION" },
+        });
+      }
+    },
+    CLI_INTEGRATION_TIMEOUT_MS,
+  );
+
   workspaceCliTest(
     "fails before emitting a truncated JSON document",
     async ({ cli }) => {