diff --git a/.changeset/adr-0048-namespace-prefix-lint.md b/.changeset/adr-0048-namespace-prefix-lint.md
new file mode 100644
index 0000000000..1756691dfd
--- /dev/null
+++ b/.changeset/adr-0048-namespace-prefix-lint.md
@@ -0,0 +1,7 @@
+---
+"@objectstack/cli": minor
+---
+
+ADR-0048 follow-up: `os lint` now emits a `naming/namespace-prefix` **warning** when a bare-named UI/automation item is not namespace-prefixed. This shifts the cross-package collision detection (ADR-0048, runtime `MetadataCollisionError`) left to authoring time — a soft nudge to prefix `app`/`page`/`dashboard`/`flow`/`action`/`report`/`dataset` names with the package namespace, so a clash with another package is unlikely to ever reach install.
+
+Warning-only and never fatal (only errors fail the lint). An app named after the namespace (ADR-0019 single-app convention, e.g. `crm`) and `sys_`-reserved names are exempt; objects (already prefix-enforced as an error) and object-derived views are untouched.
diff --git a/docs/adr/0048-cross-package-metadata-collision.md b/docs/adr/0048-cross-package-metadata-collision.md
index 98a6104340..a939071cf4 100644
--- a/docs/adr/0048-cross-package-metadata-collision.md
+++ b/docs/adr/0048-cross-package-metadata-collision.md
@@ -199,9 +199,13 @@ detect.**
   an error; the fix (rename with a namespace prefix, or `warn` during
   migration) is in the message.
 - No change to the key shape, the overlay model, or object/nav paths.
-- Follow-ups (not in this ADR): a CLI lint that flags non-prefixed
-  bare-named metadata as a warning; prefix-strict spec validation for the
-  next net-new bare-named type.
+- Follow-ups: a CLI lint that flags non-prefixed bare-named metadata as a
+  warning — **implemented** as the `naming/namespace-prefix` rule in
+  `os lint` (covers `app`/`page`/`dashboard`/`flow`/`action`/`report`/
+  `dataset`; exempts an app named after the namespace per ADR-0019 and
+  `sys_` names; warning-only, never fatal). This shifts detection left from
+  the registration-time guard to authoring time. Still open: prefix-strict
+  spec validation for the next net-new bare-named type.
 
 ## 5. Implementation notes
 
diff --git a/packages/cli/src/commands/lint.ts b/packages/cli/src/commands/lint.ts
index c5838cde7e..5b099b09c2 100644
--- a/packages/cli/src/commands/lint.ts
+++ b/packages/cli/src/commands/lint.ts
@@ -216,6 +216,51 @@ export function lintConfig(config: any): LintIssue[] {
     }
   }
 
+  // ── Namespace-prefix advisory for bare-named metadata (ADR-0048 §3.3) ──
+  // Cross-package collision detection (ADR-0048) makes a clash between two
+  // packages' bare-named items (`page`/`flow`/`action`/…) a loud error at
+  // registration time. This shifts that left: a non-fatal nudge to prefix
+  // the name with the package namespace at authoring time, so the clash is
+  // unlikely to ever happen. Objects are already prefix-*enforced* (error)
+  // in defineStack; views are object-derived; `doc` has its own build lint
+  // — so they are excluded here. Warning only — prefix stays a recommended
+  // convention for legacy types, not a retroactive requirement.
+  const ns: string | undefined = config.manifest?.namespace;
+  if (ns) {
+    // A name is namespace-safe if it IS the namespace (ADR-0019: a package's
+    // single app is conventionally named after the namespace, e.g. `crm`),
+    // is prefixed with it (`crm_lead`), or is a platform-reserved `sys_` name.
+    const isNamespaceSafe = (name: string) =>
+      name === ns || name.startsWith(`${ns}_`) || name.startsWith('sys_');
+
+    // Bare-named UI/automation types subject to the cross-package collision
+    // (ADR-0048 §1.1). Data-driven so a new bare-named type is one line.
+    const PREFIXED_TYPES: Array<{ key: string; label: string }> = [
+      { key: 'apps', label: 'App' },
+      { key: 'pages', label: 'Page' },
+      { key: 'dashboards', label: 'Dashboard' },
+      { key: 'flows', label: 'Flow' },
+      { key: 'actions', label: 'Action' },
+      { key: 'reports', label: 'Report' },
+      { key: 'datasets', label: 'Dataset' },
+    ];
+
+    for (const { key, label } of PREFIXED_TYPES) {
+      const items: any[] = Array.isArray(config[key]) ? config[key] : [];
+      for (let i = 0; i < items.length; i++) {
+        const name = items[i]?.name;
+        if (typeof name !== 'string' || !name || isNamespaceSafe(name)) continue;
+        issues.push({
+          severity: 'warning',
+          rule: 'naming/namespace-prefix',
+          message: `${label} "${name}" is not namespace-prefixed. Two packages defining "${name}" collide on the registry key and fail at install (ADR-0048). Rename to "${ns}_${name}".`,
+          path: `${key}[${i}].name`,
+          fix: `${ns}_${name}`,
+        });
+      }
+    }
+  }
+
   // ── Data-model best practices (relationships / master-detail / roll-ups) ──
   // Cross-object rules that encode the conventions in ADR-0035 and the
   // objectstack-data/-ui skills. These double as the eval rubric (see score.ts).
diff --git a/packages/cli/test/lint-namespace-prefix.test.ts b/packages/cli/test/lint-namespace-prefix.test.ts
new file mode 100644
index 0000000000..10ccb7256e
--- /dev/null
+++ b/packages/cli/test/lint-namespace-prefix.test.ts
@@ -0,0 +1,69 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+import { describe, expect, it } from 'vitest';
+import { lintConfig } from '../src/commands/lint';
+
+const RULE = 'naming/namespace-prefix';
+const prefixIssues = (config: any) => lintConfig(config).filter((i) => i.rule === RULE);
+
+describe('lint — namespace-prefix advisory (ADR-0048 §3.3)', () => {
+  it('warns on a bare-named page without the namespace prefix', () => {
+    const issues = prefixIssues({
+      manifest: { namespace: 'crm' },
+      pages: [{ name: 'home', label: 'Home' }],
+    });
+    expect(issues).toHaveLength(1);
+    expect(issues[0].severity).toBe('warning');
+    expect(issues[0].path).toBe('pages[0].name');
+    expect(issues[0].fix).toBe('crm_home');
+    expect(issues[0].message).toContain('ADR-0048');
+  });
+
+  it('accepts a namespace-prefixed name', () => {
+    expect(
+      prefixIssues({ manifest: { namespace: 'crm' }, flows: [{ name: 'crm_onboarding' }] }),
+    ).toHaveLength(0);
+  });
+
+  it('exempts an app named after the namespace (ADR-0019 single-app convention)', () => {
+    // `defineApp({ name: 'crm' })` in namespace `crm` must NOT warn.
+    expect(
+      prefixIssues({ manifest: { namespace: 'crm' }, apps: [{ name: 'crm' }] }),
+    ).toHaveLength(0);
+  });
+
+  it('exempts platform-reserved sys_ names', () => {
+    expect(
+      prefixIssues({ manifest: { namespace: 'crm' }, pages: [{ name: 'sys_admin' }] }),
+    ).toHaveLength(0);
+  });
+
+  it('covers every bare-named UI/automation type', () => {
+    const issues = prefixIssues({
+      manifest: { namespace: 'crm' },
+      apps: [{ name: 'other' }],
+      pages: [{ name: 'home' }],
+      dashboards: [{ name: 'overview' }],
+      flows: [{ name: 'onboard' }],
+      actions: [{ name: 'send' }],
+      reports: [{ name: 'pipeline' }],
+      datasets: [{ name: 'sales' }],
+    });
+    expect(issues).toHaveLength(7);
+    expect(new Set(issues.map((i) => i.severity))).toEqual(new Set(['warning']));
+  });
+
+  it('is silent when the package declares no namespace', () => {
+    // No manifest.namespace → nothing to prefix against; stays quiet.
+    expect(prefixIssues({ pages: [{ name: 'home' }] })).toHaveLength(0);
+  });
+
+  it('does not touch objects (already prefix-enforced as an error) or views', () => {
+    const issues = prefixIssues({
+      manifest: { namespace: 'crm' },
+      objects: [{ name: 'lead', fields: { id: { type: 'text' } } }],
+      views: [{ name: 'lead.all' }],
+    });
+    expect(issues).toHaveLength(0);
+  });
+});