[wingleeio]

This replaces #1034's ten-tick rail and hover prompt list. The rail goes back to how it was, one tick per prompt, and a conversation too long for it now scrolls the rail, the way Codex's prompt rail does.

Back to the old rail

• Every prompt has its own tick at the natural 8px spacing.
• Hovering a tick widens it and its neighbours and shows a preview card with the prompt and the opening of its reply. Clicking a tick glides the transcript to that prompt.

Scrolling, like Codex

• Once the ticks don't fit, the rail shows a window onto them: 70% of the space between the titlebar and the composer, at most 640px. Codex uses min(70vh, 40rem).
• Scroll over the rail to move through the ticks. There's no visible scrollbar, as in Codex. A wheel over the rail never scrolls the transcript behind it, even at the rail's ends.
• The rail's ends fade while there are more ticks beyond them.
• The rail follows the prompts on screen: when they change, from reading or jumping, it moves just enough to keep their ticks clear of the fades. It only moves when what's lit changes, so a rail you've scrolled by hand stays put.

Kept from #1034

• The rail centres between the titlebar and the composer.
• While the transcript is pinned to the bottom, every prompt on screen lights its tick, not just the one being read.

Screenshots below are offscreen renders from the new rail-fixture example. The conversation has 150 prompts and is pinned to the bottom.

The rail at rest, scrolled to the latest prompts, with the ones on screen lit:

Hovering a tick:

After scrolling over the rail (the transcript didn't move):

After clicking a tick: the transcript jumped and the rail kept the lit prompts in view:

Light theme:

An eight-prompt chat looks exactly like the old rail:

Not ported from Codex: dragging along the rail to scrub through prompts.

Testing

• cargo test -p zeron-ui --lib rail::tests passes (15), with new tests for the window height and for how far the rail follows.
• cargo run -p zeron-ui --example rail-fixture --features appshots-fixture -- --capture <dir> renders the screenshots. ZERON_RAIL_PROMPTS sets the length and ZERON_PALETTE_LIGHT=1 switches to the light theme.

🤖 Generated with Claude Code

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