#25641 cmux NEXT Session Info: the toggle reads as pressed, and the panel runs full length

Leo's words (2026-10-26)

"the session rail session info thing, like, you literally didn't do. I mean, why is the button not toggled? Why is the button area still, like, just garbage? What is this? There's still that line of that box with the background that just always is there, and, like, you still haven't done the full-length thing. It's still just this constrained height for, like, no reason at all. At all. And, like, it's still somehow not merged."

This PR covers "why is the button not toggled?" and "the full-length thing". The line and box behind the tools is a separate PR (rail-opus/tools-box helper).

What changed

• Toggled button: the Session Info toggle (the list icon, PanelToggle) takes a soft fill on its 24px square while the panel is open, a step up on hover. Before, the open state only switched the glyph to the text's ink, which did not read as toggled. No other header icon draws a fill; at rest and on hover the icons stay plain (Leo, 2026-10-25).
• Full length: the floating card's ceiling is now the room under the header less its 8px inset at the foot. The 560px and 80%-of-the-room caps are gone, so a busy chat's card runs the full height before its body scrolls. It still floats (design/session-info.md): it is not a sidebar or a column, it ends right after its content when there's little to show, it never pushes the chat except when both fit, and it starts below the header, so it never covers the top-right buttons.

Gallery

• agent-pane.header-tools: panel-open (chosen: soft fill), panel-open-ink (before), panel-open-accent, panel-open-dot. Only the fill reads as toggled at a glance; the accent look is the same as ink under the default text-colored accent.
• agent-pane.chat-inspector: ceiling (chosen: full room), ceiling-capped (before: 560px / 80%), ceiling-most (90%, leaves a band), fits-content (little to show: ends at content).

Tests

• chat-inspector-overlay-toggle.test.ts: the busy-card test now checks the card reaches the room's foot (less the inset) and then scrolls; the fits-content test keeps "below the ceiling".
• Still red locally, being fixed: two cases of "the toggle is above the open overlay and a click on it closes the Inspector" (chromium, header and tab row). 44 of 46 inspector tests pass.

Risk

Low: CSS on one toggle and one max-height, plus gallery variants. Before/after: the gallery variants above (panel-open-ink / ceiling-capped are the before).

Agent session: agent session

🤖 Generated with Claude Code

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