diff --git a/.changeset/app-default-agent-platform-binding.md b/.changeset/app-default-agent-platform-binding.md
new file mode 100644
index 00000000..4ff69726
--- /dev/null
+++ b/.changeset/app-default-agent-platform-binding.md
@@ -0,0 +1,17 @@
+---
+'hotcrm': patch
+---
+
+Bind the CRM app's ambient chat to the platform `ask` agent. `crm_enterprise`
+still declared `defaultAgent: 'sales_copilot'`, an app-authored agent retired in
+#512 — per ADR-0063 §1/§2 the key is a surface binding whose only resolvable
+values are the two platform agents (`ask` for data surfaces, `build` for
+authoring surfaces), so the runtime's `loadAgent()` refused the record and the
+floating chatbot resolved to nothing. Nothing caught it: `defaultAgent` accepts
+any well-formed snake_case name, and the platform's agent lint only walks
+authored agents. HotCRM's six shipped skills already attach to `ask` by
+`surface` affinity, so the assistant now answers with its full skill set.
+Adds a guard to `test/metadata-references.test.ts` that pins every app's
+`defaultAgent` against the platform agent set read straight off the spec's
+`AgentSchema`, so the next dangling binding fails locally instead of in a demo.
+Refs #586.
diff --git a/src/apps/crm.app.ts b/src/apps/crm.app.ts
index 827ee53b..103fa428 100644
--- a/src/apps/crm.app.ts
+++ b/src/apps/crm.app.ts
@@ -15,7 +15,13 @@ export const CrmApp = App.create({
   name: 'crm_enterprise',
   label: 'HotCRM',
   icon: 'briefcase',
-  defaultAgent: 'sales_copilot',
+  // ADR-0063 §1/§2 — `defaultAgent` is a surface binding, not a custom-agent
+  // slot: the only resolvable values are the two PLATFORM agents, `ask` (data
+  // surface) and `build` (authoring surface). HotCRM is a data surface, so it
+  // binds `ask`; the app's own AI capability ships as skills (`src/skills/`),
+  // which attach to the platform agents by `surface` affinity. The app-authored
+  // agents this key used to name were retired in #512.
+  defaultAgent: 'ask',
   branding: {
     primaryColor: '#4169E1',
     logo: '/assets/crm-logo.png',
diff --git a/src/pages/account_detail.page.ts b/src/pages/account_detail.page.ts
index a9d6385d..677e4cf2 100644
--- a/src/pages/account_detail.page.ts
+++ b/src/pages/account_detail.page.ts
@@ -22,8 +22,8 @@ import type { Page } from '@objectstack/spec/ui';
  * Why not embed an inline chat panel? `ai:chat_window` was dropped
  * from objectui (see @object-ui/layout CHANGELOG 5.x). The supported
  * surface is the global floating chatbot mounted by app-shell, which
- * picks up `defaultAgent: 'sales_copilot'` from this app and is
- * launched from the FAB at the bottom-right.
+ * picks up `defaultAgent: 'ask'` from this app and is launched from
+ * the FAB at the bottom-right.
  */
 export const AccountDetailPage = {
   name: 'account_detail_page',
diff --git a/test/metadata-references.test.ts b/test/metadata-references.test.ts
index a749b96e..f6b910d0 100644
--- a/test/metadata-references.test.ts
+++ b/test/metadata-references.test.ts
@@ -2,6 +2,7 @@
 
 import { describe, it, expect } from 'vitest';
 import { isDateMacroToken } from '@objectstack/spec/data';
+import { AgentSchema } from '@objectstack/spec/ai';
 import stack from '../objectstack.config';
 
 /**
@@ -1283,3 +1284,69 @@ describe('form views do not declare a dead data provider', () => {
     expect(unresolved, `views whose object no longer resolves:\n  ${unresolved.join('\n  ')}`).toEqual([]);
   });
 });
+
+/**
+ * `App.defaultAgent` is a SURFACE BINDING, not a custom-agent slot.
+ *
+ * ADR-0063 §1/§2: the kernel ships exactly two agents — `ask` (the data
+ * surface, the implicit default) and `build` (authoring surfaces such as
+ * Studio). Tenant/app-package custom agents were withdrawn, and HotCRM's own
+ * app-authored agents were retired in #512; the app's AI capability now ships
+ * as skills, which attach to a platform agent by `surface` affinity.
+ *
+ * Nothing caught the dangling binding this replaces. `App.defaultAgent` is
+ * typed `SnakeCaseIdentifierSchema` — any well-formed snake_case name parses —
+ * so `os validate`, `pnpm build` and the platform's agent lint (which only
+ * walks `stack.agents`) all stayed green while `defaultAgent: 'sales_copilot'`
+ * pointed at an agent that had not existed for months. The failure is silent
+ * and late: `loadAgent()` refuses the non-platform record at chat time, so the
+ * only symptom is the ambient chatbot not answering in a demo.
+ *
+ * The platform set is READ FROM THE SPEC (`AgentSchema.shape.surface`), not
+ * transcribed here — the agent names and the surface names are the same two
+ * tokens, so this guard tracks the contract instead of drifting from it.
+ */
+describe('app AI bindings resolve to a platform agent', () => {
+  const apps: AnyRec[] = (stack as any).apps ?? [];
+
+  /** `['ask', 'build']` — straight off the spec's own surface enum. */
+  const PLATFORM_AGENTS: string[] = (() => {
+    const surface = (AgentSchema as AnyRec).shape.surface;
+    const enumSchema = typeof surface.removeDefault === 'function' ? surface.removeDefault() : surface;
+    return enumSchema.options as string[];
+  })();
+
+  it('the spec still exposes exactly the two platform agents', () => {
+    // Guard the guard: if this introspection ever returns [] the checks below
+    // would pass by asserting nothing (or fail for the wrong reason).
+    expect(PLATFORM_AGENTS).toEqual(['ask', 'build']);
+  });
+
+  it('every app defaultAgent names a platform agent', () => {
+    expect(apps.length, 'no apps found in the stack — the guard is vacuous').toBeGreaterThan(0);
+    const bad: string[] = [];
+    for (const app of apps) {
+      const agent = app.defaultAgent;
+      if (agent === undefined) continue; // omitting the key is legal — `ask` is implicit
+      if (!PLATFORM_AGENTS.includes(agent)) {
+        bad.push(
+          `${app.name}: defaultAgent "${agent}" is not a platform agent ` +
+            `(${PLATFORM_AGENTS.join(' | ')}) — it will not resolve at chat time`,
+        );
+      }
+    }
+    expect(bad, `dangling app agent bindings:\n  ${bad.join('\n  ')}`).toEqual([]);
+  });
+
+  it('the app authors no agents of its own — the surface is skills-only', () => {
+    // ADR-0063 §2. Re-introducing an app agent is what makes a name like
+    // `sales_copilot` look plausible in `defaultAgent` again; skills are the
+    // supported way to deepen an app's AI capability.
+    const agents: AnyRec[] = (stack as any).agents ?? [];
+    expect(
+      agents.map((a) => a.name),
+      'app-authored agents were retired in #512 — author skills instead (ADR-0063 §2)',
+    ).toEqual([]);
+    expect(((stack as any).skills ?? []).length, 'no skills registered').toBeGreaterThan(0);
+  });
+});