fix(menubar): draw the pulse on CALayer to end 60% idle CPU

[Gnonymous]

What

The menu-bar glyph animated through SwiftUI. A running SwiftUI animation inside an NSStatusItem re-evaluates the body every frame, and each of those frames dragged the whole item through Auto Layout and -[NSStatusItem _updateReplicants] (which mirrors the item onto every screen and the Control Center), re-resolving both Text runs on the way.

Sampled at 3086 / 5623 main-thread samples — a permanent 60% of a core with nothing on screen changing size.

It was not the curve

Two fixes that looked obvious did nothing, and ruling them out is what located the real cost:

Attempt	Result
sin(phase) opacity → two constant endpoints	65%
Gate NSHostingView.invalidateIntrinsicContentSize	62%
Disable the animation outright	0%

The chain is driven by redraw, not by size invalidation, so nothing on the SwiftUI side reaches it. The cost is the hosting, not the animation curve.

Fix

PulseLayerView (new, AppKit) strokes PulseGlyph into a CAShapeLayer and breathes via CABasicAnimation — Core Animation interpolates on the render server, so the app submits once and burns nothing per frame. The readout stays SwiftUI as a sibling view, so only a text change can resize the item, and that happens on the 30s refresh. PulseIcon keeps the identical mark as a still frame for the offscreen renderer.

Measured

Release build, same machine and workload:

	CPU median	_updateReplicants samples
before	60%, sustained	3086
after	0.0%	0

The 30s aggregation is now the only CPU event, showing as a brief spike between long stretches of silence.

Two real bugs fixed along the way

• Every active flip stacked another repeatForever without cancelling the last, so idle cost grew with uptime — 198% after three weeks.
• Tempo never followed throughput: period read throughput but the animation only restarted when active flipped. Now bucketed, so a busy agent visibly pulses faster without restarting on every refresh.

Verification

• swift build clean
• --self-test 24/24 pass
• --render-menubar output pixel-identical to before
• Live status item confirmed by hand: animation smooth, layout and alignment unchanged

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