diff --git a/backend/__tests__/unit/middleware/logAgentInstallRefusal.test.js b/backend/__tests__/unit/middleware/logAgentInstallRefusal.test.js
new file mode 100644
index 0000000000..b08e247efc
--- /dev/null
+++ b/backend/__tests__/unit/middleware/logAgentInstallRefusal.test.js
@@ -0,0 +1,63 @@
+const { logAgentInstallRefusal } = require('../../../middleware/logAgentInstallRefusal');
+
+describe('agent install refusal logging', () => {
+  let warn;
+
+  beforeEach(() => { warn = jest.spyOn(console, 'warn').mockImplementation(() => {}); });
+  afterEach(() => { warn.mockRestore(); });
+
+  test('machine placement refusal records wrapper and omits credentials', () => {
+    const req = {
+      body: { agentName: 'my-agent', instanceId: 'default', machineId: 'machine-1', token: 'secret' },
+      user: { id: 'owner-1' },
+    };
+    const res = {
+      statusCode: 200,
+      locals: {},
+      json: jest.fn(),
+    };
+    const next = jest.fn();
+    logAgentInstallRefusal('/api/agent-binding/request', 'wrapper')(req, res, next);
+    expect(next).toHaveBeenCalledTimes(1);
+    res.statusCode = 404;
+    res.json({ message: 'Agent identity not found' });
+    expect(warn).toHaveBeenCalledTimes(1);
+    const line = JSON.parse(warn.mock.calls[0][1]);
+    expect(line).toEqual({
+      route: '/api/agent-binding/request',
+      agentName: 'my-agent',
+      instanceId: 'default',
+      runtimeType: 'wrapper',
+      reason: 'agent_identity_not_found',
+      userId: 'owner-1',
+    });
+    expect(warn.mock.calls[0].join(' ')).not.toContain('secret');
+    expect(warn.mock.calls[0].join(' ')).not.toContain('machine-1');
+  });
+
+  test('credential-shaped values in logged fields are redacted before serialization', () => {
+    const credential = 'cm_agent_example123';
+    const req = {
+      body: {
+        agentName: credential,
+        instanceId: credential,
+        config: { runtime: { runtimeType: credential } },
+      },
+      user: { id: 'owner-1' },
+    };
+    const res = { statusCode: 404, locals: {}, json: jest.fn() };
+    logAgentInstallRefusal('/api/registry/install')(req, res, () => {});
+    res.json({ error: 'Agent not found in registry' });
+    expect(warn).toHaveBeenCalledTimes(1);
+    const fullLine = warn.mock.calls[0].join(' ');
+    expect(fullLine).not.toContain(credential);
+    expect(JSON.parse(warn.mock.calls[0][1])).toEqual({
+      route: '/api/registry/install',
+      agentName: '[redacted]',
+      instanceId: '[redacted]',
+      runtimeType: 'unknown',
+      reason: 'agent_not_found_in_registry',
+      userId: 'owner-1',
+    });
+  });
+});
diff --git a/backend/__tests__/unit/routes/registry.install-reserved-names.test.js b/backend/__tests__/unit/routes/registry.install-reserved-names.test.js
index 4eaadc619c..e94a328a91 100644
--- a/backend/__tests__/unit/routes/registry.install-reserved-names.test.js
+++ b/backend/__tests__/unit/routes/registry.install-reserved-names.test.js
@@ -87,7 +87,12 @@ const buildSelectLeanChain = (result) => ({
   select: jest.fn().mockReturnValue({ lean: jest.fn().mockResolvedValue(result) }),
 });
 
-const makeRes = () => ({ status: jest.fn().mockReturnThis(), json: jest.fn() });
+const makeRes = () => ({
+  statusCode: 200,
+  locals: {},
+  status: jest.fn(function status(code) { this.statusCode = code; return this; }),
+  json: jest.fn(),
+});
 
 
 const officialRow = (agentName) => ({
@@ -99,7 +104,7 @@ const officialRow = (agentName) => ({
   manifest: { context: { required: [] }, runtime: { type: 'standalone' } },
 });
 
-const installAs = async ({ role = 'user', agentName, runtimeType }) => {
+const installAs = async ({ role = 'user', agentName, runtimeType, recordRefusal = false }) => {
   User.findById.mockReturnValue(buildSelectLeanChain({ username: 'installer', role, entitlements: { cloudAgents: true } }));
   const req = {
     body: {
@@ -113,6 +118,10 @@ const installAs = async ({ role = 'user', agentName, runtimeType }) => {
     userId: 'user-1',
   };
   const res = makeRes();
+  if (recordRefusal) {
+    const layer = installRouter.stack.find((entry) => entry.route?.path === '/install');
+    layer.route.stack[0].handle(req, res, () => {});
+  }
   await installHandler(req, res);
   return res;
 };
@@ -173,4 +182,25 @@ describe('registry install — built-in names are reserved for self-serve instal
     const res = await installAs({ agentName: 'standup-bot', runtimeType: 'webhook' });
     expect(reservedCalls(res)).toHaveLength(0);
   });
+
+  test('the registry 404 emits one structured refusal line without credentials', async () => {
+    const warn = jest.spyOn(console, 'warn').mockImplementation(() => {});
+    try {
+      AgentRegistry.getByName.mockResolvedValue(null);
+      const res = await installAs({ agentName: 'new-agent', runtimeType: 'unsupported', recordRefusal: true });
+      expect(res.statusCode).toBe(404);
+      const lines = warn.mock.calls.filter(([prefix]) => prefix === '[agent-install-refused]');
+      expect(lines).toHaveLength(1);
+      expect(JSON.parse(lines[0][1])).toEqual({
+        route: '/api/registry/install',
+        agentName: 'new-agent',
+        instanceId: 'default',
+        runtimeType: 'unknown',
+        reason: 'agent_not_found_in_registry',
+        userId: 'user-1',
+      });
+    } finally {
+      warn.mockRestore();
+    }
+  });
 });
diff --git a/backend/middleware/logAgentInstallRefusal.ts b/backend/middleware/logAgentInstallRefusal.ts
new file mode 100644
index 0000000000..0658eb7ba4
--- /dev/null
+++ b/backend/middleware/logAgentInstallRefusal.ts
@@ -0,0 +1,74 @@
+import { NextFunction, Request, Response } from 'express';
+
+type RefusalBody = { code?: unknown; error?: unknown; message?: unknown; msg?: unknown };
+
+// Only static response text is mapped. Unknown responses retain a bounded HTTP
+// code rather than turning user-supplied error text into a log dimension.
+const reasonByMessage: Record<string, string> = {
+  'Agent not found in registry': 'agent_not_found_in_registry',
+  'Agent identity not found': 'agent_identity_not_found',
+  'Machine not found': 'machine_not_found',
+  'Pod not found': 'pod_not_found',
+  Unauthorized: 'unauthorized',
+  'agentName required': 'agent_name_required',
+  'agentName must be a string': 'agent_name_invalid',
+  'machineId required (null to withdraw)': 'machine_id_required',
+};
+
+const runtimeTypes = new Set([
+  'webhook', 'wrapper', 'hosted', 'native', 'moltbot', 'internal',
+  'managed-agents', 'claude-code', 'codex',
+]);
+
+const credentialPrefix = /^(?:cm[_-]agent[_-]|gh[opurs][_-]|github[_-]pat[_-]|sk-|xox[abprs]-|bearer|eyj)/i;
+
+const logIdentity = (value: unknown, allowScopedName = false): string | null => {
+  if (typeof value !== 'string') return null;
+  const name = value.trim().toLowerCase();
+  const valid = allowScopedName
+    ? /^(@[a-z0-9-]+\/)?[a-z0-9-]+$/.test(name)
+    : /^[a-z0-9-]+$/.test(name);
+  // Refused requests can supply credentials in place of names. Never "clean"
+  // an invalid value into something that resembles a safe identity.
+  if (!valid || name.length > 64 || credentialPrefix.test(name)) return '[redacted]';
+  return name || null;
+};
+
+const logRuntimeType = (value: unknown): string | null => {
+  if (typeof value !== 'string') return null;
+  const runtimeType = value.trim().toLowerCase();
+  return runtimeTypes.has(runtimeType) ? runtimeType : 'unknown';
+};
+
+const reasonCode = (body: RefusalBody, status: number): string => {
+  if (typeof body.code === 'string'
+    && /^[a-z][a-z0-9_]{0,79}$/.test(body.code)
+    && !credentialPrefix.test(body.code)) return body.code;
+  const message = body.error || body.message || body.msg;
+  return typeof message === 'string' ? reasonByMessage[message] || `http_${status}` : `http_${status}`;
+};
+
+/** Record one structured line for each refused install or machine placement. */
+export const logAgentInstallRefusal = (route: string, defaultRuntimeType?: string) => (
+  req: Request & { user?: { id?: unknown } }, res: Response, next: NextFunction,
+): void => {
+  const originalJson = res.json.bind(res);
+  let logged = false;
+  res.json = ((body: RefusalBody) => {
+    if (!logged && res.statusCode >= 400) {
+      logged = true;
+      const requestBody = req.body && typeof req.body === 'object' ? req.body : {};
+      const runtime = requestBody.config?.runtime?.runtimeType || requestBody.runtimeType || defaultRuntimeType;
+      console.warn('[agent-install-refused]', JSON.stringify({
+        route,
+        agentName: logIdentity(requestBody.agentName, true),
+        instanceId: logIdentity(res.locals.agentInstallInstanceId || requestBody.instanceId) || 'default',
+        runtimeType: logRuntimeType(runtime),
+        reason: reasonCode(body && typeof body === 'object' ? body : {}, res.statusCode),
+        userId: req.user?.id == null ? null : String(req.user.id),
+      }));
+    }
+    return originalJson(body);
+  }) as Response['json'];
+  next();
+};
diff --git a/backend/routes/agentBinding.ts b/backend/routes/agentBinding.ts
index f7ecfa6aa0..9c5bbe08e8 100644
--- a/backend/routes/agentBinding.ts
+++ b/backend/routes/agentBinding.ts
@@ -20,6 +20,7 @@ import {
   seatEnvironmentKey,
 } from '../services/seatEnvironmentProjection';
 import { ownsRuntimeIdentity, OwnershipFailure } from '../services/runtimeIdentityOwnership';
+import { logAgentInstallRefusal } from '../middleware/logAgentInstallRefusal';
 
 // eslint-disable-next-line @typescript-eslint/no-require-imports
 const auth = require('../middleware/auth');
@@ -201,7 +202,7 @@ router.post('/adopt', bindingRateLimit, daemonAuth('agents:adopt'), async (req:
 // machine sees the request in /assigned and performs the adopt CAS itself,
 // so D3's "no adoption without a user choice" and "one binding writer" both
 // hold. machineId: null withdraws the request.
-router.post('/request', bindingRateLimit, auth, async (req: express.Request & { user?: { id?: string } }, res: express.Response) => {
+router.post('/request', logAgentInstallRefusal('/api/agent-binding/request', 'wrapper'), bindingRateLimit, auth, async (req: express.Request & { user?: { id?: string } }, res: express.Response) => {
   try {
     const agentName = normalize(req.body?.agentName);
     const instanceId = normalize(req.body?.instanceId) || 'default';
diff --git a/backend/routes/registry/install.ts b/backend/routes/registry/install.ts
index 401143250f..24c07439c3 100644
--- a/backend/routes/registry/install.ts
+++ b/backend/routes/registry/install.ts
@@ -49,6 +49,7 @@ const {
 const { validateEnvironmentMcpEntries } = require('../../utils/environmentSpecValidation');
 const { willSolelyInstallRuntimeIdentity, webhookUrlRefusal } = require('../../services/runtimeIdentityOwnership');
 const { personAgentWakeDefault } = require('../../services/wakeDefaultService');
+const { logAgentInstallRefusal } = require('../../middleware/logAgentInstallRefusal');
 const { assertAgentRuntimeMayJoinPod } = require('../../services/outsiderGrantAgentJoinPolicy');
 
 // Inlined per-route limiter. This comment used to attribute its clean CodeQL
@@ -151,7 +152,7 @@ const findExistingAgentInstance = async (agentName: any, instanceId: any) => {
  * POST /api/registry/install
  * Install an agent to a pod
  */
-installRouter.post('/install', installRateLimit, auth, async (req: any, res: any) => {
+installRouter.post('/install', logAgentInstallRefusal('/api/registry/install'), installRateLimit, auth, async (req: any, res: any) => {
   try {
     const {
       agentName, podId, version, config = {}, scopes = [], instanceId, displayName, gatewayId, description,
@@ -245,6 +246,7 @@ installRouter.post('/install', installRateLimit, auth, async (req: any, res: any
     } else {
       normalizedInstanceId = deriveInstanceId(displayName, agentName);
     }
+    if (res.locals) res.locals.agentInstallInstanceId = normalizedInstanceId;
 
     let agent = await AgentRegistry.getByName(agentName);