fix(tabs): keep the active tab in view when it changes state band on a phone

On phones and 600-767px tablets the header strip stays one horizontally
scrolling row. #538 (Tab Layout, default "by state") orders that row in one
flex `order` band per state, so when the ACTIVE session changes state (a
prompt sent: idle to working; a permission prompt: needs you) its chip
moves to another band while scrollLeft stays put, and the tab in use left
the screen (measured at 390px: x 165 to -870). #257's reveal rules only
covered a CHANGED active tab: _updateActiveTabImmediate reveals on a
switch, and _fullRenderSessionTabs restores scrollLeft and re-reveals only
when _lastRenderedActiveTabId changed, while a state change is an
incremental pass that never reveals at all.

_noteActiveTabBand() records the active tab's band (read off the element,
so it is what is on screen) and reports when it moved while the tab stayed
active. Both render paths reveal on that, in the single scrolling row only
(_isScrollingTabRow: not wrapping, not a vertical list). It is keyed on the
band, not the raw order value, because another tab entering or leaving the
active tab's band shifts that value by one and another tab's move must not
yank a strip the user is browsing. _updateActiveTabImmediate records too,
so the pass right after a switch still counts (viewing a waiting tab spends
its alert and drops it into the idle row). The incremental path reveals
after updateTabOverflowMode(), and only from the branch that reached
_syncTabTriageChrome(), so a pass that falls through to a full rebuild
mid-loop leaves the record for the rebuild to compare.

Tests in test/tab-triage.test.ts pin the reveal on both paths and after a
switch, and that another tab's band change, a wrapping strip, a vertical
list and an active web tab never scroll.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -331,7 +331,7 @@ Frontend JS modules have `@fileoverview` with `@dependency`/`@loadorder` tags. L
 
 **Entrance animations** (`entrance-animations.js`, all OFF by default): opt-in animations for tabs, terminal, windows and connection lines, chosen via `data-tab-anim` / `data-term-anim` / `data-win-anim` / `data-line-anim` on `<html>`; the default `legacy` theme short-circuits every hook. ⚠️ Tabs and lines are destroyed mid-animation on re-render, so re-apply to the fresh element by id with a negative `animation-delay` (resume, never restart). ⚠️ Terminal-pane styles may animate only transform / opacity / clip-path (anything else resizes the PTY via FitAddon); `blur` is the ONE sanctioned `filter` exception, do not generalise it. ⚠️ Line glow lives in `--line-glow` so blur keyframes interpolate. Persisted per-device in `codeman:*Anim` localStorage keys, never in `SettingsUpdateSchema`; lab at `?animlab=1`. Test: `test/entrance-animations.test.ts`. → [architecture-invariants#entrance-animations](docs/architecture-invariants.md#entrance-animations)
 
-**Mobile tab strip scrolling** (issue #257): under 768px the tab strip scrolls horizontally, so the active tab must be kept reachable. `_updateActiveTabImmediate()` reveals it via `computeTabScrollLeft()` (constants.js, rect math on the strip's own `scrollLeft`, never `scrollIntoView()`, which scrolls the document under the fixed header); `_fullRenderSessionTabs()` must restore `scrollLeft` across rebuilds and re-reveal only when the active tab changed (`_lastRenderedActiveTabId`). ⚠️ The phone-block `min-width` on `.session-tab.active .tab-name` keeps the tab's centre off the gear/close icons, sized for numberless tabs 10+ (floor 40px); do not shrink it. ⚠️ Never reintroduce hoisting the active session to the front of the strip. Test: `test/mobile-tab-tap-zones.test.ts`. → [architecture-invariants#mobile-tab-strip-scrolling](docs/architecture-invariants.md#mobile-tab-strip-scrolling)
+**Mobile tab strip scrolling** (issue #257): under 768px the tab strip scrolls horizontally, so the active tab must be kept reachable. `_updateActiveTabImmediate()` reveals it via `computeTabScrollLeft()` (constants.js, rect math on the strip's own `scrollLeft`, never `scrollIntoView()`, which scrolls the document under the fixed header); `_fullRenderSessionTabs()` must restore `scrollLeft` across rebuilds and re-reveal only when the active tab changed (`_lastRenderedActiveTabId`) or, grouped by state, the ACTIVE tab moved to another state band (`_noteActiveTabBand()`, both render paths, scrolling row only; another tab's move never scrolls). ⚠️ The phone-block `min-width` on `.session-tab.active .tab-name` keeps the tab's centre off the gear/close icons, sized for numberless tabs 10+ (floor 40px); do not shrink it. ⚠️ Never reintroduce hoisting the active session to the front of the strip. Tests: `test/mobile-tab-tap-zones.test.ts`, `test/tab-triage.test.ts`. → [architecture-invariants#mobile-tab-strip-scrolling](docs/architecture-invariants.md#mobile-tab-strip-scrolling)
 
 **Session list layout: header strip or left sidebar** (`sessionListLayout`, default `header`; per-device via `displayKeys`, also in `SettingsUpdateSchema`): the list can move into a collapsible `<aside>` (Alt+B, `toggleSessionSidebar`) or, via `tabOrientation`, a resizable vertical `#tabRail` (desktop/tablet only). ⚠️ There is ONE `#sessionTabs`, MOVED between hosts, never a second list: `applySessionListLayout()` runs first, then `applyTabOrientation()`, both BEFORE `applyTabWrapSettings()`, and both arm/disarm `_startSidebarRichClock()`. ⚠️ Axis decisions use `_isVerticalTabList()`, never `isSessionSidebarActive()` alone. ⚠️ Rich rows share one gate, `isRichTabRows()`; rich CSS pairs sidebar+rail with comma-grouped selectors, never `:is()`, and card rules stay rail-scoped. ⚠️ Rail sort (`tabRailSort`, default `activity`) is the flex `order` property only, never a DOM reorder; the arrow-key walk alone follows computed `order`. ⚠️ Leaving sidebar mode clears `_sidebarFilter`; the handheld overlay drawer is `inert` when closed, the docked rail never. → [architecture-invariants#session-list-layout-header-strip-vs-left-sidebar](docs/architecture-invariants.md#session-list-layout-header-strip-vs-left-sidebar)