Fix sub-agent bootstrap from WebSocket messages

[threepointone]

Summary

• Prevent cross-DO native I/O during sub-agent facet startup by clearing native request/WebSocket/email context when crossing Agent instances and during facet bootstrap.
• Suppress protocol broadcasts only during facet bootstrap so startup cannot enumerate parent-owned WebSocket handles while normal post-bootstrap state sync to facet WebSocket clients still works.
• Add WebSocket regression coverage for spawning a sub-agent from onMessage and for state sync to clients connected directly to a sub-agent.
• Add a production repro fixture for issue Bug: _cf_initAsFacet throws "Cannot perform I/O on behalf of a different Durable Object" on first this.name read after the #1393 / 0.11.6 fix #1410.

Test plan

• npx vitest --project workers --run src/tests/sub-agent.test.ts
• npx oxfmt --check packages/agents/src/index.ts packages/agents/src/tests/sub-agent.test.ts packages/agents/src/tests/agents/sub-agent.ts wip/issue-1410-reporter-repro/src/index.ts wip/issue-1410-reporter-repro/wrangler.jsonc wip/issue-1410-reporter-repro/package.json wip/issue-1410-reporter-repro/tsconfig.json wip/issue-1410-reporter-repro/README.md .changeset/native-context-facet-bootstrap.md
• Deployed wip/issue-1410-reporter-repro and verified both /http-spawn and /ws return ok: true in production with scoped bootstrap suppression.

[changeset-bot]

🦋 Changeset detected

Latest commit: e8a8760

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
agents	Patch

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