feat(sessions): Add clickable minimap of user messages

[thmsobrmlr]

TL;DR

Long chats are hard to move around in. This adds a row of small dots down the right edge of the chat — one per message you sent. Click a dot to jump to that message; hover to see what it said. The dot for the message you're reading right now is highlighted.

Problem

In long agent conversations there is no quick way to see where your own messages sit or to jump back to one. The Cmd/Ctrl+J picker and Alt+Up/Down exist, but nothing gives a spatial, always-visible overview of the thread.

Changes

• New ConversationMinimap: a vertical rail docked left of the scrollbar with one clickable marker per user message, hover tooltips with a one-line preview, and an accent on the message currently on screen. Hidden when the conversation has fewer than two user messages and in compact embeds (command center, canvas panel).
• Wired into both thread renderers behind the useNewChatThread setting: the new ChatThread uses the scroller engine's currentAnchorId and scrollToMessage; the legacy ConversationView reuses its jump-to-message path and tracks the current message through a new onFirstVisibleRowChange callback on VirtualizedList (fires only when the topmost row changes, so scrolling does not re-render the thread).

How did you test this?

• Added ConversationMinimap.test.tsx (6 tests: marker filtering/preview truncation, hidden under two messages, click-to-jump, aria-current on the active marker) — passing.
• pnpm --filter @posthog/ui test src/features/sessions (478 tests) and pnpm --filter @posthog/ui typecheck — both clean; Biome clean on changed files.
• Could not run the Electron app in this sandbox (no display), so no screenshot; the rail follows the same overlay conventions as the existing scroll-to-bottom button and sticky header.

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 3 issues in 3 files · 3 warnings.

3 warnings

src/features/sessions/components/ConversationMinimap.tsx

• ⚠️ src/features/sessions/components/ConversationMinimap.tsx:12 Non-component export in component file only-export-components

src/features/sessions/components/ConversationView.tsx

• ⚠️ src/features/sessions/components/ConversationView.tsx:125 Many related useState calls prefer-useReducer

src/features/sessions/components/VirtualizedList.tsx

• ⚠️ src/features/sessions/components/VirtualizedList.tsx:56 Large component is hard to read and change no-giant-component

_{Reviewed by React Doctor for commit f72a8c1.}

[github-actions]

This PR has had no activity for 7 days and has been marked stale. We are moving to the monorepo and tightening PR staleness in preparation, so it will be closed in 7 days if no further activity occurs.

[charlesvien]

Closing stale PRs ahead of Friday's monorepo migration. If this is a mistake, rebase and reopen for review.