feat(ux): determinate restore rail, and a shutdown board that is actually visible

[AThraen]

Implements the two treatments chosen from the Waiting States options: Quiet Rail for startup, Restore Board for shutdown.

Startup — restore rail

A 25-session restore runs ~131s, with per-session launch cost swinging 12× (0.6s–10.9s, from crash.log). There's no steady rate to extrapolate from, so an indeterminate spinner reads identically at session 2 and session 22.

RestoreRail (2px, under the toolbar) + a 7 / 25 restoring pill give the aggregate; per-session state stays on the placeholder sidebar rows that already exist.

Deliberately non-blocking. Restore doesn't actually block you — placeholder rows let you click into a session the moment it lands — so nothing modal goes in front of it.

The counter advances after the try/catch, not inside it: a session that fails to restore still moves the rail, otherwise one bad session strands it short of full and reads as the exact hang it's meant to rule out.

Shutdown — the overlay was invisible, and that's the real bug

Reported as "more like 1 line - thats hard to see. no spinner or anything."

The markup looked fine — a Grid sibling with Panel.ZIndex="100" and a Storyboard-rotated arc dead centre.

WebView2 is an HwndHost. A native child window is composited by the OS on top of everything WPF renders, and Panel.ZIndex does not enter into it. The overlay was being drawn behind every terminal pane. What reached the user was scrim leaking through the few-pixel gaps between panes — hence a stray line and no spinner, since the spinner sat centred over a pane.

The codebase documents HwndHost for input in three places (#108). Nobody had written down the output half, which is the more expensive one to rediscover because the code looks correct.

Fix: collapse TerminalGrid before showing the overlay. Safe — every pane is about to be disposed, and a frozen terminal is worth nothing mid-shutdown.

Once visible, it earns being more than a spinner:

• every session named and ticked off — · pending, ◐ closing, ✓ clean, ⨯ force-disposed
• elapsed time per session, an overall k / N bar
• a budget bar against ClaudeShutdownBudgetMs, green → peach → pink
• force-disposed sessions are marked, not hidden — the case you most want to see, and it used to happen completely silently
• ShutdownHint escalates with elapsed time to explain why the wait is long

The hint is explanatory rather than jokey. It has to read well on the four-hundredth shutdown, which is the argument against the "be patient" copy in the original sketch.

Also here

• Board list scrollbar restyled (scoped to that ScrollViewer). Any setup past ~14 sessions scrolls, so the stock system-coloured bar was on screen for most shutdowns.
• Board skipped at zero sessions, so --clean runs don't flash a full-window "0 / 0".
• Corrected a stale comment claiming the adaptive config gate is "still used at SHUTDOWN" — fix(shutdown): flat post-exit pause and a budget sized from measurement #117 removed it from both paths.
• CLAUDE.md: the airspace rule written down, cross-linked from the existing input-side note.

Verification

Layout rendered offscreen via RenderTargetBitmap against the real markup extracted from MainWindow.xaml (not a copy), at 9 rows and 27 rows, to confirm the card caps at MaxHeight and the list scrolls with header/footer pinned.

304/304 tests pass, 0 warnings.

The airspace fix itself needs a live run — it's about OS compositing and can't be proven headlessly. That's the one thing to eyeball on merge.

🤖 Generated with Claude Code

https://claude.ai/code/session_01NDsEfog5kVkT5NmX1Ya5be