feat(chat-thread): user-message minimap in place of the jump pill + copy message next to timestamp

[adamleithp]

What

Replaces the floating "jump to your message" pill with a minimap of the user's turns, parked at the scroll container's top-right.

• Collapsed: one 2px tick per user message, width scaled by message length, current turn in accent. Capped at the last 12 ticks so the rail stays small; hidden below 2 user messages.
• Expanded: hover or keyboard focus opens the full list, anchored to the rail's own top-right corner (sideOffset = -anchor.height) so it expands in place, under the pointer, with no gap to cross. Opens scrolled to the current turn.
• Rows don't clip with an ellipsis — they fade at the right edge and ticker-scroll to the end on hover/focus (OverflowTickerText, same as sidebar items). Clicking scrolls the thread and leaves the list open for the next hop.
• Both bodies render it. The windowed body hands it its own onJump and anchorId, since the scroller engine only reaches mounted rows.

Built on quill's DropdownMenu (Base UI), so roving focus, typeahead, Escape and aria-haspopup/expanded come for free. The trigger carries aria-label="Jump to one of your N messages"; ticks are aria-hidden.

Gutter

The rail hugs the scroll container, not the message column, so the thread reserves CHAT_CONTENT_GUTTER on both sides of its scroll content (mirrored, so the column stays centred). Rows clear the rail at any panel width; turn rows drop their extra px now that the gutter provides it.

Removed

ThreadStickyHeader.tsx (both pill variants) and the offscreen flag on the virtualized anchor state, which only existed to time the pill's appearance.

Testing

pnpm --filter @posthog/ui typecheck and the full UI suite (2162 tests) pass. Driven in the running app over CDP: rail renders with the right tick count, hover opens the list, clicking a row scrolls the thread and keeps the list open, Escape closes it, and rows stay clear of the rail down to a 600px-wide panel. The windowed path was exercised by temporarily lowering the virtualization threshold — rail, list and anchor highlight all render there; the jump itself couldn't be observed because that session was mid-stream and auto-follow re-pins the viewport (same for the pill it replaces).

🤖 Generated with Claude Code

https://claude.ai/code/session_01BYPVPkN4Lm3gygchrpcoqr

[trunk-io]

😎 Merged successfully - details.

[github-actions]

React Doctor found 1 issue in 1 file · 1 warning.

1 warning

src/features/sessions/components/chat-thread/MessageMinimap.tsx

• ⚠️ src/features/sessions/components/chat-thread/MessageMinimap.tsx:168 Time or random value in JSX rendering-hydration-mismatch-time

_{Reviewed by React Doctor for commit fa0eafc.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "feat(chat-thread): user-message minimap ..." | Re-trigger Greptile}