fix: resume subagents lazily

[kermanx]

Related Issue

No linked issue; this addresses session resume work for persisted subagents.

Problem

Reopening a session eagerly replayed persisted subagents even when callers only needed the main agent. Several RPC and subagent paths also assumed referenced agents were already instantiated, which prevented persisted subagents from being restored only when they are accessed.

What changed

• Resume only the main agent when reopening a session, and lazily restore persisted subagents through a shared ensureAgentResumed path.
• Update session RPC, subagent host, subagent profile lookup, and resume result building to handle ready agents and in-flight resume entries correctly.
• Update tests for lazy subagent access, permission parent restoration, async tool execution metadata, and ready-agent accessors.

Verification

• pnpm --filter @moonshot-ai/agent-core typecheck
• pnpm --filter @moonshot-ai/agent-core exec vitest run test/session/subagent-host.test.ts test/session/init.test.ts test/tools/agent.test.ts test/harness/runtime.test.ts test/harness/skill-session.test.ts
• Read-only diff audit found no context-specific internal identifiers.

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue, or explained the problem above.
• I have added tests that prove my feature works.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update.

[changeset-bot]

🦋 Changeset detected

Latest commit: bd29df1

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

This PR includes changesets to release 2 packages

Name	Type
@moonshot-ai/agent-core	Patch
@moonshot-ai/kimi-code	Patch

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[pkg-pr-new]

pnpm dlx https://pkg.pr.new/@moonshot-ai/kimi-code@bd29df1

npx https://pkg.pr.new/@moonshot-ai/kimi-code@bd29df1

commit: bd29df1