diff --git a/apps/api/src/lib/setupGuard.ts b/apps/api/src/lib/setupGuard.ts
new file mode 100644
index 0000000..d927e1d
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+++ b/apps/api/src/lib/setupGuard.ts
@@ -0,0 +1,21 @@
+/**
+ * setupGuard.ts — Phase 12 setup-wizard lock gate.
+ *
+ * Exports: isSetupLocked() — returns true when the setup wizard has already been
+ * completed and no further calls to the /api/setup/* surface should be accepted.
+ *
+ * Key constraint (D-10): NEVER cache the result at module level.
+ * This function MUST be called fresh at the top of every /api/setup/* handler so
+ * that a concurrent POST /api/setup/complete (Pitfall 8 / SETUP-04) is reflected
+ * immediately on the next call — even if two requests arrive within the same
+ * event-loop tick. The per-call freshness pattern mirrors db.select() in health.ts.
+ *
+ * Wave-0 stub (Plan 01): returns false (setup always appears incomplete).
+ * Real implementation (Plan 02): reads app_config.setup_complete + checks
+ * member_credentials + VAPID env (effective-config branch, D-10).
+ */
+export async function isSetupLocked(): Promise<boolean> {
+  // STUB — Wave-0 placeholder. Real impl: Plan 02.
+  // Re-evaluated fresh on every call — NEVER cache at module level (D-10).
+  return false;
+}
diff --git a/apps/api/src/routes/setup.ts b/apps/api/src/routes/setup.ts
new file mode 100644
index 0000000..eb58669
--- /dev/null
+++ b/apps/api/src/routes/setup.ts
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+/**
+ * setup.ts — /api/setup/* route surface (Phase 12 initial-setup wizard).
+ *
+ * Mounted in index.ts: app.route('/api/setup', setupRouter)
+ * Mount position: BEFORE app.use('/api/*', devAuthBypass()) so the wizard
+ * is reachable pre-authentication — same pre-auth surface as /health (T-01-03).
+ *
+ * Wave-0 stub (Plan 01): empty router — all handlers are added in Plan 02.
+ * Plan 02 owns the index.ts mount as well, to keep file-ownership clean.
+ *
+ * Security note: every handler added in Plan 02 MUST call isSetupLocked() as
+ * its first statement and return 423 if locked (SETUP-04 / Pitfall 8 / D-10).
+ */
+
+import { Hono } from 'hono';
+
+export const setupRouter = new Hono();