mac: the workspace moves on §4's springs

[stupart]

Tyler: "the js version was much better / smoother." This is the "smoother" half — §4, which I had never read.

ConchMotion already held §4's exact values — morph bounce 0.12 / response 0.46, pop 0.34 / 0.36, with resolved(reduceMotion:) built in. The workspace simply never used them, animating with hand-rolled .easeOut(duration: 0.18) instead. The overlay has used the real springs for months (control-bar-source.test.ts pins them); this applies the same convention to the window.

§4 says	was	now
⌘B collapse → morph	.easeOut(0.18)	ConchMotion.morph
side by side / deliverable fill → morph	did not animate at all	ConchMotion.morph
switching sessions → fade in over 0.12 s, no slide	instant swap	0.12 s opacity fade
Reduce Motion → drops the bounce, keeps the timing	nil — killed the animation outright	resolved(reduceMotion:)

That last row is a behaviour fix, not a value: passing nil made Reduce Motion mean "no animation", where §4 means "no bounce".

The fade is declarative, on purpose

mac-phase1-source forbids imperative animation blocks in the transcript — one that restarts on every streamed token never settles the viewport. My first attempt used one and tripped that guard, which was right to fire. The fade now rides .animation(_:value:) with the value flipped on the next runloop turn, so it cannot touch the scroll path at all.

(My own comment then tripped the same guard by containing the forbidden word. Reworded — the guard is a plain substring check and was correct both times.)

Mutation battery

mutation	result
⌘B drifts back to a hand-rolled easing that nils out under Reduce Motion	1 fail
the stage stops moving between its pages	1 fail
the switch fade loses its animation modifier	1 fail
the fade is set in the same frame, so nothing animates	1 fail

Gate

bun test 2303/0 exit 0 · tsc --noEmit exit 0 · swift test exit 0 · Mac xcodebuild BUILD SUCCEEDED · iOS xcodebuild BUILD SUCCEEDED — re-run after rebasing onto #297, since both slices edited DashboardView.swift and the same test file.

A still frame cannot verify this one. conch shot captures a moment; springs are the thing between moments. It builds, it is guarded, and the values are yours from the lab — but judging whether it feels right is on the live window.

🤖 Generated with Claude Code

https://claude.ai/code/session_01SfEX6bfwCGXtThk1JRNmsE