diff --git a/apps/web/src/lib/agent-harness/model-gateway-security.test.ts b/apps/web/src/lib/agent-harness/model-gateway-security.test.ts
new file mode 100644
index 0000000000..c49e92faa6
--- /dev/null
+++ b/apps/web/src/lib/agent-harness/model-gateway-security.test.ts
@@ -0,0 +1,279 @@
+import { beforeEach, expect, it, jest } from '@jest/globals';
+import jwt from 'jsonwebtoken';
+import * as fixtures from './operation-test-fixture';
+import { harnessInputDigest } from './authorization';
+import type * as Gateway from './model-gateway';
+import type * as Route from '@/app/api/internal/agent-harness/model/route';
+
+const { authority, conversationId, operationId, originalTime, primary, runId } = fixtures;
+jest.mock('@/lib/constants', () => ({
+  APP_URL: 'https://app.example',
+  ORGANIZATION_ID_HEADER: 'x-kilocode-organizationid',
+}));
+jest.mock('@/lib/utils.server', () => ({ warnExceptInTest: jest.fn() }));
+const { harnessModelScope } = jest.requireActual<typeof Gateway>('./model-gateway');
+const { POST } = jest.requireActual<typeof Route>('@/app/api/internal/agent-harness/model/route');
+const completion = {
+  model: 'paid/model',
+  messages: [{ role: 'user' as const, content: 'Hello' }],
+  stream: true,
+  max_tokens: 128,
+};
+const chunk = {
+  id: 'generation-1',
+  model: completion.model,
+  created: 1,
+  choices: [{ index: 0, delta: { content: 'Hello' }, finish_reason: 'stop' }],
+  usage: { prompt_tokens: 3, completion_tokens: 2, total_tokens: 5, cost: 0.002 },
+};
+const outputHeaders = {
+  'content-type': 'text/event-stream',
+  'request-id': 'request-1',
+  authorization: 'upstream-secret',
+};
+const sse = (data = `data: ${JSON.stringify(chunk)}\n\ndata: [DONE]\n\n`) =>
+  new Response(data, { headers: outputHeaders });
+const requests: Request[] = [];
+let gateway: () => Response;
+function capability(
+  body: unknown,
+  context: unknown = authority,
+  scopePatch: Record<string, unknown> = {}
+) {
+  const input = { conversationId, operationId, runId, completion: body };
+  const scope = {
+    ...harnessModelScope({ ...input, completion }),
+    inputDigest: harnessInputDigest(input),
+    ...scopePatch,
+  };
+  return jwt.sign({ grantId: runId, authority: context, scope }, 'test-signing-key', {
+    issuer: 'agent-harness',
+    audience: scope.audience,
+    expiresIn: 60,
+  });
+}
+function invoke(
+  body: unknown = completion,
+  token = capability(completion),
+  init: RequestInit = {}
+) {
+  const request = new Request('https://app.example/api/internal/agent-harness/model', {
+    method: 'POST',
+    body: JSON.stringify(body),
+    ...init,
+    headers: {
+      'content-type': 'application/json',
+      'x-internal-api-key': 'test-service-key',
+      authorization: `Bearer ${token}`,
+      'x-agent-harness-conversation-id': conversationId,
+      'x-agent-harness-operation-id': operationId,
+      'x-agent-harness-run-id': runId,
+      'x-kilocode-organizationid': 'forged-org',
+      'x-kilocode-feature': 'forged-feature',
+      ...init.headers,
+    },
+  });
+  return POST(request);
+}
+beforeEach(() => {
+  requests.length = 0;
+  gateway = () => sse();
+  const user = { id: authority.userId, blocked_reason: null, api_token_pepper: 'current-pepper' };
+  jest.spyOn(primary.query.kilocode_users, 'findFirst').mockResolvedValue(user);
+  jest.spyOn(globalThis, 'fetch').mockImplementation(async (url, init) => {
+    requests.push(new Request(url, init));
+    return gateway();
+  });
+});
+
+it.each([
+  'capability header',
+  'grant revocation',
+  'generation',
+  'blocked user',
+  'messages',
+  'conversation',
+  'operation',
+])('blocks %s before inference', async reason => {
+  const token = capability(completion);
+  if (reason === 'grant revocation') {
+    const grants = primary.query.agent_harness_conversation_grants;
+    jest.spyOn(grants, 'findFirst').mockResolvedValue({
+      ...(await grants.findFirst()),
+      revoked_at: new Date(originalTime).toISOString(),
+    } as any);
+  }
+  if (reason === 'generation') {
+    const registry = primary.query.agent_harness_conversation_registry;
+    jest
+      .spyOn(registry, 'findFirst')
+      .mockResolvedValue({ ...(await registry.findFirst()), generation: 1 });
+  }
+  if (reason === 'blocked user')
+    jest.spyOn(primary.query.kilocode_users, 'findFirst').mockResolvedValue({
+      id: authority.userId,
+      blocked_reason: 'private-block-details',
+    } as any);
+  const headers: Record<string, string> = {};
+  if (reason === 'capability header') headers.authorization = '';
+  if (reason === 'conversation') headers['x-agent-harness-conversation-id'] = operationId;
+  if (reason === 'operation') headers['x-agent-harness-operation-id'] = runId;
+  const body =
+    reason === 'messages'
+      ? { ...completion, messages: [{ role: 'user', content: 'Forged' }] }
+      : completion;
+  const response = await invoke(body, token, { headers });
+  expect(response.status).toBe(
+    reason.includes('service') || reason === 'capability header' ? 401 : 403
+  );
+  expect(await response.json()).toMatchObject({
+    error: { type: 'access_revoked', retryable: false },
+  });
+  expect(response.headers.get('cache-control')).toBe('no-store');
+  expect(requests).toEqual([]);
+});
+it.each([
+  { audience: 'agent-harness:operations' },
+  { operation: 'read' },
+  { definitionVersion: '2' },
+  { dispatchId: runId },
+  { inputDigest: '0'.repeat(64) },
+  { target: { kind: 'client', clientId: operationId } },
+])('rejects a capability for a different scope %j', async scope => {
+  const response = await invoke(completion, capability(completion, authority, scope));
+  expect(response.status).toBe(403);
+  expect(await response.json()).toMatchObject({
+    error: { type: 'access_revoked', retryable: false },
+  });
+  expect(requests).toEqual([]);
+});
+it.each([{ model: ' ' }, { model: null }, { max_tokens: 0 }, { max_tokens: 1.5 }])(
+  'rejects invalid inference input %j',
+  async patch => {
+    const body = { ...completion, ...patch };
+    expect((await invoke(body, capability(body))).status).toBe(400);
+    expect(requests).toEqual([]);
+  }
+);
+it.each([
+  [400, 'invalid_input', false],
+  [401, 'access_revoked', false],
+  [402, 'limit_exceeded', false],
+  [403, 'access_revoked', false],
+  [404, 'invalid_input', false],
+  [408, 'storage_unavailable', true],
+  [429, 'storage_unavailable', true],
+  [503, 'storage_unavailable', true],
+] as const)('preserves HTTP and stream error %s', async (code, type, retryable) => {
+  for (const streaming of [false, true]) {
+    const error = JSON.stringify({
+      error: { code, message: 'upstream-secret', metadata: { authorization: 'credential' } },
+    });
+    gateway = () =>
+      streaming ? sse(`data: ${error}\n\ndata: [DONE]\n\n`) : new Response(error, { status: code });
+    const response = await invoke();
+    const text = await response.text();
+    expect(response.status).toBe(streaming ? 200 : code);
+    expect(text).toContain(`"code":${code}`);
+    expect(text).toContain(`"type":"${type}"`);
+    expect(text).toContain(`"retryable":${retryable}`);
+    expect(text).not.toMatch(/upstream-secret|credential|\[DONE\]/);
+  }
+  expect(requests).toHaveLength(2);
+});
+it.each([
+  [0, 'data: private-malformed\n\n', 422],
+  [1, 'data: {"choices":[{"delta":{"content":["private-malformed"]}}]}\n\n', 422],
+  [2, `data: ${'x'.repeat(1024 * 1024)}\n\n`, 413],
+] as const)('rejects malformed or oversized streams (case %s)', async (_case, data, code) => {
+  gateway = () => sse(data);
+  const text = await (await invoke()).text();
+  expect(text).toContain(`"code":${code}`);
+  expect(text).not.toContain('private-malformed');
+});
+it('rejects wrong upstream media without forwarding its body', async () => {
+  gateway = () =>
+    new Response('<html>private</html>', { headers: { 'content-type': 'text/html' } });
+  const response = await invoke();
+  expect(response.status).toBe(422);
+  const text = await response.text();
+  expect(text).toContain('"retryable":false');
+  expect(text).not.toContain('private');
+});
+it.each([''])('preserves empty output %j', async data => {
+  gateway = () => sse(data);
+  const response = await invoke();
+  expect(response.status).toBe(200);
+  expect(await response.text()).toBe(data);
+});
+it('sanitizes a failed upstream read after progressive output', async () => {
+  const logs = (['log', 'info', 'debug', 'warn', 'error'] as const).map(method =>
+    jest.spyOn(console, method).mockImplementation(() => undefined)
+  );
+  let upstream!: ReadableStreamDefaultController<Uint8Array>;
+  gateway = () =>
+    new Response(
+      new ReadableStream({
+        start(controller) {
+          upstream = controller;
+          controller.enqueue(new TextEncoder().encode(`data: ${JSON.stringify(chunk)}\n\n`));
+        },
+      }),
+      { headers: outputHeaders }
+    );
+  const response = await invoke();
+  const reader = response.body!.getReader();
+  expect(new TextDecoder().decode((await reader.read()).value)).toContain('"content":"Hello"');
+  const token = requests[0].headers.get('authorization')!;
+  upstream.error(new TypeError(`private-read-error ${token}`));
+  const text = new TextDecoder().decode((await reader.read()).value);
+  expect(text).toContain('"code":503');
+  expect(text).toContain('"retryable":true');
+  expect(text).not.toContain(token);
+  expect(text).not.toMatch(/private-read-error|\[DONE\]/);
+  expect((await reader.read()).done).toBe(true);
+  expect(requests[0].signal.aborted).toBe(true);
+  expect(JSON.stringify(logs.flatMap(log => log.mock.calls))).not.toContain(token);
+});
+it('rejects oversized request bytes and empty bodies', async () => {
+  expect(
+    (await invoke(completion, capability(completion), { body: '界'.repeat(350000) })).status
+  ).toBe(413);
+  expect((await invoke(completion, capability(completion), { body: null })).status).toBe(400);
+  expect(requests).toEqual([]);
+});
+it.each([[0, 'private-malformed']] as const)(
+  'rejects malformed JSON and UTF-8 requests (case %s)',
+  async (_case, body) => {
+    const response = await invoke(completion, capability(completion), { body });
+    expect(response.status).toBe(400);
+    const text = await response.text();
+    expect(text).toContain('"retryable":false');
+    expect(text).not.toContain('private-malformed');
+    expect(requests).toEqual([]);
+  }
+);
+it.each([['deadline', 503]] as const)('cancels inference through the %s', async (target, code) => {
+  expect(
+    (await invoke(completion, capability(completion), { signal: AbortSignal.abort('private') }))
+      .status
+  ).toBe(499);
+  expect(requests).toEqual([]);
+  const cancelled = Promise.withResolvers<void>();
+  gateway = () =>
+    new Response(new ReadableStream({ cancel: () => cancelled.resolve() }), {
+      headers: outputHeaders,
+    });
+  const abort = new AbortController();
+  if (target === 'deadline') jest.spyOn(AbortSignal, 'timeout').mockReturnValue(abort.signal);
+  const response = await invoke(completion, capability(completion), {
+    signal: undefined,
+  });
+  const output = response.text();
+  abort.abort(new Error('private'));
+  const text = await output;
+  expect(text).toContain(`"code":${code}`);
+  expect(text).not.toMatch(/private|\[DONE\]/);
+  await cancelled.promise;
+  expect(requests[0].signal.aborted).toBe(true);
+});