fix(cloud-agent): make Kilo prompt JSON parsing explicit

Author: eshurakov

services/cloud-agent-next/src/kilo-facade/user-kilo-facade.test.ts

@@ -1915,6 +1915,51 @@ describe('handleKiloFacadeRequest', () => {
     expect(admitSubmittedMessage).not.toHaveBeenCalled();
   });
 
+  it('rejects malformed or oversized prompt_async bodies before balance or admission side effects', async () => {
+    const validatePromptBalance = vi.fn();
+    const admitPrompt = vi.fn();
+    const supportedPromptBody = JSON.stringify({ parts: [{ type: 'text', text: 'hello' }] });
+    for (const requestInit of [
+      { body: '{', headers: new Headers({ 'Content-Type': 'application/json' }) },
+      {
+        body: supportedPromptBody,
+        headers: new Headers({
+          'Content-Type': 'application/json',
+          'Content-Length': String(256 * 1024 + 1),
+        }),
+      },
+      {
+        body: supportedPromptBody.padEnd(256 * 1024 + 1, ' '),
+        headers: new Headers({ 'Content-Type': 'application/json' }),
+      },
+    ]) {
+      const response = await handleKiloFacadeRequest({
+        request: new Request(`http://worker.test/kilo/session/${kiloSessionId}/prompt_async`, {
+          method: 'POST',
+          ...requestInit,
+        }),
+        env: envStub(),
+        userId: 'usr_1',
+        authToken: 'validated-token',
+        deps: {
+          resolveRootSessionForKiloSession: vi.fn(async () => ({
+            cloudAgentSessionId: 'agent_cold',
+          })),
+          validatePromptBalance,
+          admitPrompt,
+        },
+      });
+
+      expect(response.status).toBe(400);
+      await expect(response.json()).resolves.toEqual({
+        error: 'KILO_BASIC_PROMPT_UNSUPPORTED',
+        message: 'Basic Kilo prompt body is not supported',
+      });
+    }
+    expect(validatePromptBalance).not.toHaveBeenCalled();
+    expect(admitPrompt).not.toHaveBeenCalled();
+  });
+
   it('rejects prompt_async attempts to bypass public balance validation after owner resolution', async () => {
     const env = envStub();
     const validatePromptBalance = vi.fn();

services/cloud-agent-next/src/kilo-facade/user-kilo-facade.ts

@@ -689,35 +689,48 @@ function promptPreflightError(error: unknown): Response {
   }
 }
 
-async function readRequestJson(request: Request): Promise<unknown> {
+type ReadRequestJsonResult =
+  | { success: true; value: unknown }
+  | { success: false; response: Response };
+
+async function readRequestJson(request: Request): Promise<ReadRequestJsonResult> {
   const declaredLength = request.headers.get('content-length');
   if (declaredLength !== null) {
     const bodyBytes = Number(declaredLength);
     if (!Number.isSafeInteger(bodyBytes) || bodyBytes > MAX_KILO_PROMPT_JSON_BYTES) {
-      return facadeError(
-        400,
-        'KILO_BASIC_PROMPT_UNSUPPORTED',
-        'Basic Kilo prompt body is not supported'
-      );
+      return {
+        success: false,
+        response: facadeError(
+          400,
+          'KILO_BASIC_PROMPT_UNSUPPORTED',
+          'Basic Kilo prompt body is not supported'
+        ),
+      };
     }
   }
   const response = new Response(request.body);
   const bytes = await readBoundedBody(response, MAX_KILO_PROMPT_JSON_BYTES);
   if (!bytes) {
-    return facadeError(
-      400,
-      'KILO_BASIC_PROMPT_UNSUPPORTED',
-      'Basic Kilo prompt body is not supported'
-    );
+    return {
+      success: false,
+      response: facadeError(
+        400,
+        'KILO_BASIC_PROMPT_UNSUPPORTED',
+        'Basic Kilo prompt body is not supported'
+      ),
+    };
   }
   try {
-    return JSON.parse(new TextDecoder().decode(bytes));
+    return { success: true, value: JSON.parse(new TextDecoder().decode(bytes)) };
   } catch {
-    return facadeError(
-      400,
-      'KILO_BASIC_PROMPT_UNSUPPORTED',
-      'Basic Kilo prompt body is not supported'
-    );
+    return {
+      success: false,
+      response: facadeError(
+        400,
+        'KILO_BASIC_PROMPT_UNSUPPORTED',
+        'Basic Kilo prompt body is not supported'
+      ),
+    };
   }
 }
 
@@ -755,11 +768,11 @@ async function admitBasicPrompt(params: {
   cloudAgentSessionId: string;
   deps?: KiloFacadeRequestDeps;
 }): Promise<SessionMessageAdmissionResult | Response> {
-  const value = await readRequestJson(params.request);
-  if (value instanceof Response) {
-    return value;
+  const body = await readRequestJson(params.request);
+  if (!body.success) {
+    return body.response;
   }
-  const parsed = parseBasicKiloPrompt(value);
+  const parsed = parseBasicKiloPrompt(body.value);
   if (!parsed.success) {
     return facadeError(
       400,