Defer server file changes until guarded restart activation

Persist beta, promotion, drift, and rollback payloads until occupancy and restart-capacity checks pass. Preserve rollback snapshots and campaign ordering, and allow held rollback campaigns to resume safely.

Fixes #28

Validation: 805 tests passed, Svelte checks clean, production build passed.

tests/unit/beta-plans.test.ts

@@ -84,9 +84,11 @@ describe('durable beta test plans', () => {
         await tick(); await tick();
         expect(existsSync(scriptPath(names[1]))).toBe(false);
         for (let i = 0; i < 4; i++) await tick();
-        expect(existsSync(scriptPath(names[1]))).toBe(true);
+        expect(existsSync(scriptPath(names[1]))).toBe(false);
         expect(getBeta(id)?.state).toBe('running');
         expect(listBetaServers(id)[1].stage).toBe('awaiting-empty');
+        await tick();
+        expect(existsSync(scriptPath(names[1]))).toBe(true);
         for (let i = 0; i < 6; i++) await tick();
         expect(getBeta(id)?.state).toBe('ready-promote');
     });
@@ -120,6 +122,9 @@ describe('durable beta test plans', () => {
         expect(testView(id)?.servers[0].progress[0].current).toBe(25);
         expect(testView(id)?.evidence.filter(e => e.kind === 'round_change')).toHaveLength(1);
         await tick();
+        expect(existsSync(scriptPath(names[1]))).toBe(false);
+        await postTelemetry(gameEvent('heartbeat', 99, 0, names[1]));
+        await tick();
         expect(existsSync(scriptPath(names[1]))).toBe(true);
     });
 
@@ -170,9 +175,12 @@ describe('durable beta test plans', () => {
         const { getBeta } = await import('../../src/lib/server/fleet/beta.js');
         const { db } = await import('../../src/lib/server/db/index.js');
         expect(getBeta(id)?.state).toBe('rolled-back');
-        expect(await readFile(scriptPath(names[0]), 'utf8')).toBe('original');
+        expect(await readFile(scriptPath(names[0]), 'utf8')).toBe('main() {}');
         expect(existsSync(scriptPath(names[1]))).toBe(false);
         expect(db().prepare("SELECT server, restart_state FROM deployment_servers").all()).toEqual([{ server: names[0], restart_state: 'pending' }]);
+        const { sweep } = await import('../helpers/provisioning.js');
+        await sweep();
+        expect(await readFile(scriptPath(names[0]), 'utf8')).toBe('original');
     });
 
     it('keeps snapshots and holds after a paused failure, without deploying subsequent waves', async () => {