fix(bluebird): make the thread panel collapse stick when opening a task

[k11kirky]

Problem

In the Channels (project-bluebird) space, the thread panel docked on the right of a task has a collapse button, but collapsing it never stuck: opening any task called openThread, which unconditionally reset collapsed: false, overriding the persisted preference. The panel sprang open on every task open.

Changes

• threadPanelStore.openThread now takes an expand option; the channel task route opens the thread with expand: false so the user's collapse preference is kept. Explicitly opening a thread from a feed card still force-expands.
• Dropped the redundant store write in WebsiteChannelHome.handleOpenTask — the task route's mount effect already points the panel at the task.
• Instrumented the collapse/expand toggle with Channel action events (collapse_thread / expand_thread, surface thread_panel).

How did you test this?

• pnpm --filter @posthog/shared --filter @posthog/ui typecheck
• Biome check on the touched files

Automatic notifications

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

Why

Requested in the project-bluebird channel: the thread right panel should be collapsible when opening a task, and the choice should persist.

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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 e92cec1.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix(bluebird): respect thread panel coll..." | Re-trigger Greptile}