[huacnlee]

Follow-up to #3781, fixing the P3 from this review, which was still open when #3781 merged.

Problem. On macOS, a trackpad swipe that leads sideways for GESTURE_GAP (250 ms) or longer stops flat at an edge instead of stretching. touch_phase ignored sideways Moved packets, so the first vertical packet saw a pause, started a new gesture and cleared touched. The swipe then counted as a wheel.

Fix. touch_phase now calls follow for every packet, so any sideways packet keeps the stream alive. Only Started/Ended set touched.

Behaviour change on all platforms. touch_phase is not macOS-gated, so on every platform a continuous sideways stream now prevents a new gesture from starting. That includes not resetting spent. This has no test of its own.

Tested on Linux

• cargo test -p gpui-base --features test-support --lib: 1580 passed. The macOS-gated tests do not compile here.
• cargo clippy -p gpui-base --features test-support --all-targets -- --deny warnings and cargo fmt -p gpui-base --check: clean.
• With the macOS cfg forced on: all 17 Overscroll tests pass, including the new a_swipe_that_leads_sideways_past_the_gap_still_bounces. With the fix reverted, only the new test fails.

Not tested. Real macOS and trackpad hardware, and end-to-end ScrollBounce/Input.

@insd47 this touches your code from #3781, so your review is welcome.

🤖 Noop (reviewer) · AI agent acting for @huacnlee

[insd47]

Checked on macOS: the change is the same one I had locally (e8c9a970), so this replaces it.

• cargo test -p gpui-base --features test-support --lib overscroll: 17 passed, with the macOS-only tests compiled in, including a_swipe_that_leads_sideways_past_the_gap_still_bounces.
• My probe of 1,392 simulated scenarios against the base before scroll: Stop a smooth-scrolling wheel at the edge on macOS #3781 (child and wheel ScrollBounce, bounce on and off, four parents, three offsets, 29 gestures, including 320 ms sideways leads that turn into an edge): only the 8 intended wheel scenarios differ, and the long-lead trackpad swipes stretch as they did before scroll: Stop a smooth-scrolling wheel at the edge on macOS #3781.

On the untested cross-platform change: the probe ran on macOS only, and none of its gestures hits an edge, leads sideways past the gap, then hits the edge again in one stream, which is the case where spent now carries over. I'd expect that to match a stream with no pause anyway.