feat(client): motion and self-dismissal for the InfoBar stack (UI/UX v3 P6d)

[mizu-jun]

Problem

The stack shipped in P6a–P6c already declared a Timed entrance, an Option<Timed> exit and an expires_at deadline — and nothing read any of them. infobar.rs carried a file-level #![allow(dead_code)] saying exactly that. So the three banners were still the only overlays in the product that pop in and out on a frame boundary, and the roadmap's word "auto-dismissing" described none of them.

Solution

• Motion is per bar, not per stack. apply_surface_fade is called inside the builder's loop, so one bar can fade out while the one under it is still arriving. InfoBar::visibility() is one expression (1 - exit.progress, else entrance.progress), and the exit resumes from what is on screen via Timed::resuming_at — a bar dismissed mid-entrance does not jump to opaque first.
• Dismissal is not deletion. ClientState::dismiss_info_bar starts the exit, retire_info_bars drops the bar once it has finished drawing out, and expire_info_bars applies the info severity's 20 s INFO_BAR_TTL (D3 — the warning and error severities never expire). Both run from the tick in lifecycle.rs, next to the existing retire calls.
• Esc, Enter and a successful connect all dismiss. Slot replacement stays abrupt: the replacing bar is drawn in the same place on the same frame, and cross-fading would only smear the two messages together.
• A dismissed bar is out of everything but the renderer at once — it takes no key, holds no slot against a repeat of the same message, and leaves the AccessKit tree and the tree hash immediately rather than announcing a bar the user just closed.
• infobar::top_live / top_dismissible replace StackLayout::top, so the keyboard path stops re-deriving the stack's order itself.

push_info_bar and apply_server_message now take &AnimationsConfig: the entrance duration is the user's setting, not a constant.

Gates

• G-idle — has_active_animation gains one clause and goes quiet once every bar settles. A bar merely counting down its 20 s deadline asks for no frames; covered by only_a_moving_bar_asks_for_frames.
• Reduced motion — with animations off every Timed is born finished, so a bar appears and leaves without a single extra frame (motion_off_makes_a_bar_appear_and_leave_without_a_single_extra_frame).
• G-a11y / G-hash — still exhaustive over the enum; a new test pins that a dismissed bar leaves both the nodes and the hash before its exit finishes.
• G-single, G-cap, G-order, G-i18n unchanged from P6a–P6c.

Verification

• cargo fmt --check — clean
• cargo clippy --workspace --all-targets -- -D warnings — no warnings
• cargo test --workspace — 28 suites pass (1111 in nexterm-client-gpu), 10 new tests
• Not covered: appearance. Per the spec's §7 this joins the P4/P5 on-device backlog; the thing worth looking at is three bars stacked in a small window, where the cap and the count suffix are all that stand between the stack and the terminal content.

Closes P6 (P6a #92, P6b #93, P6c #94, P6d here).

🤖 Generated with Claude Code

[github-actions]

Coverage report

Generated by cargo llvm-cov (workspace minus nexterm-client-gpu and nexterm-i18n).