fix(gastown): fix eviction test assertions and replace as casts with Zod validation

- Replace incorrect test that asserted touchAgentHeartbeat() clears drain
  flag (it doesn't) with tests for acknowledgeContainerReady() which is
  the actual mechanism that clears drain state
- Add test for nonce mismatch case (wrong nonce keeps draining=true)
- Add test verifying touchAgentHeartbeat returns drainNonce but doesn't
  clear draining flag, and only acknowledgeContainerReady clears it
- Replace manual 'as' casts in handleContainerReady with Zod schema
  validation per project conventions

Author: jrf0110

cloudflare-gastown/src/handlers/town-eviction.handler.ts

@@ -1,4 +1,5 @@
 import type { Context } from 'hono';
+import { z } from 'zod';
 import { extractBearerToken } from '@kilocode/worker-utils';
 import type { GastownEnv } from '../gastown.worker';
 import { getTownDOStub } from '../dos/Town.do';
@@ -125,24 +126,13 @@ export async function handleContainerReady(
     return c.json(resError('Cross-town access denied'), 403);
   }
 
-  let nonce: string | undefined;
-  try {
-    const body: unknown = await c.req.json();
-    if (
-      body &&
-      typeof body === 'object' &&
-      'nonce' in body &&
-      typeof (body as { nonce: unknown }).nonce === 'string'
-    ) {
-      nonce = (body as { nonce: string }).nonce;
-    }
-  } catch {
-    // No body or invalid JSON
-  }
+  const ContainerReadyBody = z.object({ nonce: z.string() });
 
-  if (!nonce) {
+  const parsed = ContainerReadyBody.safeParse(await c.req.json().catch(() => null));
+  if (!parsed.success) {
     return c.json(resError('Missing required field: nonce'), 400);
   }
+  const { nonce } = parsed.data;
 
   const town = getTownDOStub(c.env, params.townId);
   const cleared = await town.acknowledgeContainerReady(nonce);

cloudflare-gastown/test/integration/town-container.test.ts

@@ -137,23 +137,57 @@ describe('Town DO — container eviction draining lifecycle', () => {
     expect(await town.isDraining()).toBe(true);
   });
 
-  it('touchAgentHeartbeat() clears draining flag after eviction', async () => {
+  it('acknowledgeContainerReady() clears draining flag with correct nonce', async () => {
+    const id = `town-${crypto.randomUUID()}`;
+    const town = env.TOWN.get(env.TOWN.idFromName(id));
+
+    // Set draining flag and capture the nonce
+    const drainNonce = await town.recordContainerEviction();
+    expect(await town.isDraining()).toBe(true);
+
+    // Acknowledge with the correct nonce clears the drain flag
+    const cleared = await town.acknowledgeContainerReady(drainNonce);
+    expect(cleared).toBe(true);
+    expect(await town.isDraining()).toBe(false);
+  });
+
+  it('acknowledgeContainerReady() rejects wrong nonce and stays draining', async () => {
+    const id = `town-${crypto.randomUUID()}`;
+    const town = env.TOWN.get(env.TOWN.idFromName(id));
+
+    // Set draining flag
+    await town.recordContainerEviction();
+    expect(await town.isDraining()).toBe(true);
+
+    // Wrong nonce should not clear the drain flag
+    const cleared = await town.acknowledgeContainerReady('wrong-nonce');
+    expect(cleared).toBe(false);
+    expect(await town.isDraining()).toBe(true);
+  });
+
+  it('touchAgentHeartbeat() returns drainNonce during eviction', async () => {
     const id = `town-${crypto.randomUUID()}`;
     const town = env.TOWN.get(env.TOWN.idFromName(id));
 
     // Register an agent so heartbeat has a valid target
     const agent = await town.registerAgent({
       role: 'polecat',
-      name: 'drain-clear-test',
-      identity: `drain-clear-${id}`,
+      name: 'drain-nonce-test',
+      identity: `drain-nonce-${id}`,
     });
 
     // Set draining flag
-    await town.recordContainerEviction();
+    const drainNonce = await town.recordContainerEviction();
     expect(await town.isDraining()).toBe(true);
 
-    // Heartbeat should clear draining flag
-    await town.touchAgentHeartbeat(agent.id);
+    // Heartbeat returns the drainNonce (but does NOT clear draining)
+    const heartbeatResult = await town.touchAgentHeartbeat(agent.id);
+    expect(heartbeatResult.drainNonce).toBe(drainNonce);
+    expect(await town.isDraining()).toBe(true);
+
+    // Only acknowledgeContainerReady with the nonce clears it
+    const cleared = await town.acknowledgeContainerReady(drainNonce);
+    expect(cleared).toBe(true);
     expect(await town.isDraining()).toBe(false);
   });