Add Agent Island for Active Agents

[onevcat]

Summary

Continues #753 from @SunChJ on a fork-owned branch. This branch contains every commit from the original PR, so merging it with a merge commit also marks #753 as merged and keeps the author's history and attribution intact.

Agent Island is an opt-in, notch-aware projection of the Active Agents roster at the top of a selected display. It adds no agent state or acknowledgement model: Working stays a compact carousel, Blocked and unviewed Done entries surface as a compact attention collection, and the expanded roster composes the same row presentation and context menu as the sidebar. See docs/components/agent-island.md and docs-ai/066-agent-island/ for the design record.

Changes on top of #753

• Reset isIslandHovered when the roster empties. Hovering pauses the carousel timer; when the last entry left, the compact island unmounted without a hover-exit, so the stale flag kept later Working pairs from rotating. Covered by a TestClock regression. Closes the remaining blocker from the Add Agent Island for Active Agents #753 review.
• Match the Display picker by display UUID. Tags compared the full .display(id:name:) value, but name comes from NSScreen.localizedName and changes with the system language or a rename, leaving the picker with no matching tag. AgentIslandDisplaySelection is an id-only picker identity mapped back to the stored preference with the catalog's current name. Covered by unit tests.
• Revert unrelated line wrapping. The island commits were formatted by a bare swift-format run, which does not discover .swift-format.json and defaults to 100 columns. AppFeature.swift carried 78 lines of pure reflow next to 12 lines of real change; every whitespace-only hunk is restored so hot files diff by their functional changes alone.
• Align the compact bar with the notch. The notched bar was max(40, cutout + 8)pt tall and hung 8pt below the menu bar; it now uses the measured cutout height (which already follows the display scaling mode) with a 28pt floor for the icon cluster.
• Tune the notched bar. 12pt bottom corners and 20pt icons in a 24pt cluster; the floating pill keeps 21pt.
• Stop the icon cluster from springing back after panel resizes. The hosting view centers content vertically and the panel is resized only after layout, so when an attention cell appeared or disappeared the cluster (the one subtree with an .animation keyed on every entry refresh) interpolated from the transient offset and looked like it vanished and dropped in from above. The root is now pinned to the top and the cluster animation is keyed on membership/order only. The floating pill also no longer tears the cluster down on each carousel rotation.
• Fold island actions into one wrapper. island(Action) replaces three parallel cases and a context-menu router; the reducer forwards the wrapped sidebar action and collapses only when it presents Prowl UI, AppFeature surfaces the window in one place. Island navigation tests move out of the quit test file.
• Create the panel only while the setting is on. The controller observes agentIslandEnabled and starts or stops the panel, so a disabled island costs nothing at launch.
• Tidy structure. The live display catalog moves from Models/ to BusinessLogic/; the unused rootWidth is gone.
• Drop clipped shadows and match the roster width. The panel is content-sized so every shadow was cut at the window edge; the roster now takes the bar width (425pt on a 14-inch notch instead of a fixed 420pt).
• Per-state counts instead of a name carousel. Both the notched wing and the floating pill show blocked / done / working / idle counts as state-colored SF Symbols (omitting empty states) instead of "N Agents" or a rotating Working name. With no consumer left, the carousel reducer state, four-second clock effect, hover tracking, and their tests are removed.
• Roster rows show "pane title · branch". The island roster has the width for both, so it no longer follows the sidebar's either/or setting; a live Workflow badge still takes the line.
• Highlight the roster from the terminal manager's focus. The island dimmed rows against the reducer's focusedSurfaceID, a keyboard anchor fed by per-worktree deduplicated focus events that goes stale when a worktree is re-selected; it now uses the same source as the sidebar overlay. The display catalog is resolved on first use so a disabled island installs nothing at launch, and the lifecycle test now goes through the real observation instead of calling refreshLifecycle() itself. (Adversarial review, 2026-09-03.)
• Consolidate the design record. The nine working-note amendments under docs-ai/066-agent-island/ (four marked superseded by the next) are folded into 000-plan.md and 001-action.md; docs/components/agent-island.md now describes current behavior only.

Known limitation

On a notched display the bar sits on top of the menu bar, so while agents are running the ~120pt wing on each side of the cutout covers that part of the menu bar band; a menu title or status item under a wing is not clickable until the island disappears. Documented in docs/components/agent-island.md; narrowing the wings or offering floating placement on notched displays is an open product decision.

Testing

• ActiveAgentsFeatureTests, AgentIslandScreenTests, SettingsFeatureTests, SettingsFilePersistenceTests, BaguaWorkingIndicatorTests, AppFeatureQuitTests, AppFeatureSettingsChangedTests, AgentIslandIsolationTests, AppFeatureAgentIslandTests, AgentIslandStateSummaryTests, AgentIslandRosterContentTests, AgentIslandIconClusterTests: 152 tests pass on the latest head; make build-app zero warnings
• make check passes
• CI on the original head (c4606b06) was green

https://claude.ai/code/session_01PuwHwiuyozSN88w7EgTPAL