PR #23796 - manaflow-ai/cmux

Leo-ask: ask-541000e7b0

Leo, on the Chief chat: "why is there a top banner? this is so ugly. iMessage dissipates that, and we don't even need this in the first place."

What changes for the person

The Chief chat has no header now: no avatar, no "Chief ›" pill, no glass band pinned over the transcript. Text never runs under anything.
The oldest message rests 16 pt under the pane's top (was 88 pt under the header).
As messages scroll up they fade out over the top 16 pt, like the scroll edge in Messages: a soft dissolve on the rows only, no band and no fill.
Clicks and scrolls at the top of the pane reach the messages (the hidden header no longer takes them).
Chief settings still open from the pane's tools, the command palette (Toggle Chief Settings) and the pet's menu.
Debug Settings > Home > Avatar and name over the chat brings back the old header (conversations opened after a change follow it).

How

HostView.useBareTop() (HeaderGlass.swift) hides the pane header and backdrop; placeNativeViews hands the window view a 16 pt rows inset and a 16 pt top fade; the scroll view starts at 0.
Vendored WindowView/HostHooks read the rows' top inset from rowsTopInset (default Messages' 80 + 8) instead of the constant, and the transcript clip's mask is a CAGradientLayer that ramps in over topFade points (solid when 0, as before). Patches regenerated against the pin (reverse-applied and round-tripped).
The top-right panel toggles from #22702 stay: with no header, PaneHeaderView.bare hides the avatar and pill, puts the toggles 8 pt from the top right, and lets clicks through everywhere else. The rows rest under the toggles (HostView.bareRowsTop: 44 pt with them, 16 pt without), and the first-run panel follows when the toggles come or go.
HomeTunables.chatHeader (default off) picks bare top or the old setHeaderGlass().

Changelog

Changed: the Chief chat has no header over its messages; they fade out at the top as they scroll.

Tests

Fleet runs (Xcode 26.6) at daa16abd and again at the head 655580c7: HomeBareTopTests, HomeHeaderGlassTests, HomeKeyboardTests pass. Follow-up commit (review notes): VoiceOver, older-page paging, the scroll knob and the flight recorder read the visible top (visibleTop) instead of 80 pt; the test allows half a point for the pixel-snapped offset.

HomeBareTopTests: no avatar/pill/band, the hidden header takes no click near the top, the scroll view reaches the top, the oldest row rests at 16 pt, the mask is ~0 at the top edge, ~0.5 mid-fade and full from 16 pt down; the header pane keeps Messages' geometry (88 pt, no fade); theTopRightTogglesStayWithNoHeader: the toggles sit top right, take their clicks, and the rows rest under them.

HomeBareTopFirstRunTests (CmuxNext): toggles that arrive after the first layout move the first-run panel under them. It was committed test-first at 6b4840a9; the fix is 5b5f6961, after review of the base merge 00957c00. The red and green fleet runs are in progress and will be posted as a comment. cmux-ci compile-check --ref 5b5f696110c70d0a1aeaa236b10b14b9e9b4bfdc --app --package CmuxMessagesLab: passed.

Observed / Not run

Observed: the fleet runs and compile above, and the real-app captures below. Not run: a capture showing the toggles. The capture's debug fixture page never adds them, so the 00957c00 capture shows the same bare top as 655580c7.

Before / after

Before (base 0ba602a4): the avatar and "Chief ›" pill on a blurred band over the messages.

Light	Dark

After: no header; the top row dissolves at the edge.

Capture steps-85ecd27cd2 at 00957c004293 (fleet build, capture mini, text checked for private data)

Light	Dark

Agent session: cosmic-gray

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