fix(tasks): expand latest plan after cloud resume

[puemos]

Problem

When a cloud task reconnects with a plan as its latest useful output, history replay marks the plan as historical and the UI folds it. Plan-mode inactivity cleanup can also close ACP before the pending plan prompt settles, persisting a misleading connection error in the thread.

Why: Resuming an interrupted task should preserve the result the user was last working from without surfacing an intentional shutdown as a task failure.

Changes

• Expand only the final historical plan during replay.
• Settle active plan prompts before closing ACP during session cleanup.

How did you test this?

• pnpm --filter @posthog/agent exec vitest run src/server/agent-server.test.ts
• pnpm --filter @posthog/agent typecheck
• pnpm exec biome check packages/agent/src/server/agent-server.ts packages/agent/src/server/agent-server.test.ts
• Existing plan replay tests and typechecks from the earlier commits.

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code

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[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 2d8b487.}