#19286 cmux-next: thread minimap current turn as a longer accent tick (cx-f7c)

Summary

The thread minimap's current turn is now a longer tick in the accent color (cx-f7c, taken over from hq-5c with Leo's spec).

• The turn being read rests at 14 px instead of the 6 px of the others, in --agent-accent at full opacity. The reader sees where they are in the thread at a glance.
• While hovering, the fisheye still grows the ticks near the pointer, and the current turn keeps at least its 14 px.
• Every turn on screen is still lit together at 54 %, as before.

Background: the minimap from feat-hq5c-thread-minimap is already fully in feat-cmux-next, so this builds on base.

• It already has one tick per turn, a hover card with the bold prompt, the first lines of the reply and a bookmark, and click to jump.
• Gallery receipts: #19081 and #19083.
• Prev/next turn keys are a separate PR next, because they add app actions and shortcuts.

Testing

• webviews/test/thread-minimap-current.test.tsx renders VirtualTranscript over 12 turns in a 1040 × 600 viewport:
  • At the latest message, only the last tick is current: aria-current, data-current (the accent), and a 14 px bar.
  • Every other tick is 6 px with no accent.
  • Scrolled to the top, the first tick is the current one.
  • Red: CI web dispatched on the test commit (run 38122928866). The result is in a comment below.
  • Green: this PR's hosted web / react-apps-check and Agent Session web tests on the head.
• vp check passes locally, and check-layers.py is ok.
• Gallery: agent-pane.thread-minimap / long-chat shows the accent tick.

Changelog

Changed: The agent chat's thread minimap shows the turn you are reading as a longer accent tick

🤖 Generated with Claude Code

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Summary by cubic

The thread minimap now draws the turn you're reading as a longer tick in the accent color, so you can see where you are in the thread at a glance.

• The current turn rests at 14 px instead of the 6 px used for other ticks, filled with --agent-accent at full opacity.
• Hover fisheye growth still applies, and the current tick keeps at least its 14 px.
• Adds a test over 12 turns that finds the current tick by its aria-current marker (at the latest message the last prompt sits low in the viewport) and checks its data-current and width, after opening and after scrolling to the top.

Showcase

Open the live gallery