#30881 cmux NEXT: incognito windows leave nothing in banners, quit files or space bars

Problem

An incognito window left traces outside itself (spaces-incognito-audit leaks 5, 6 and 9). Leo asked for incognito spaces on 2026-10-31. The spec (leo-workspace design/spaces.md, "Incognito") says: "Normal and incognito content never mix", and nothing of the window is kept.

• Leak 5: macOS banners carried the workspace name, tab, agent state and message into Notification Center history.
• Leak 6: At quit, the app wrote incognito agent chats' composers (chips and shell command) and page screenshots for the next launch.
• Leak 9: Every normal window's space bar listed the Incognito space, so the normal windows' sidebar snapshots recorded it.

Change

• Banners: DesktopNotifier.post(incognito:) replaces an incognito workspace's banner with a generic one. The title is "Incognito" and the body is "A tab in an incognito window needs you." It carries no subtitle, status badge or Allow/Deny. posted records what is shown. A click still opens the tab.
• Quit: the new AgentQuitFiles filters incognito tabs out of the composers and page images that QuitCoordinator saves.
• Space bar: the new IncognitoSpaceMarks records each incognito space. New Incognito Space marks it before the daemon mirrors it, so no frame lists it. SidebarSpaceBar.profiles(_:window:windows:) hides every marked space except the window's own incognito space.
• Localization: both new strings are added to NotificationsPanel.xcstrings in all 21 of its locales, which include the 9 app locales.

God types are net zero: WindowManager gains one stored property and merges one doc comment, and the other god files change only lines in place.

Tests

• Commit 1 adds failing tests only (IncognitoSurfacesTests).
• Commit 2 adds the fix.
• The fleet package suite runs red at the test commit and green at the head, together with the nearby notification, relaunch-wake and space suites.

Not covered (residual)

• An open incognito chat's unsent draft is still kept in agent-unsent-drafts.json while the window is open.
• Feed and iPhone push items are not filtered here.
• Mobile (leak 3) is a separate PR.

🤖 Generated with Claude Code

Agent session: agent session

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Summary by cubic

Stops incognito windows from leaving traces outside themselves—in Notification Center history, in the files the quit writes for the next launch, and in normal windows' space bars.

• Banners from an incognito window—agent, passkey, or sandboxed Run—now show a generic "Incognito" title and body with no subtitle, status badge, attachment, or Allow/Deny; clicking still opens the tab. A passkey request whose tab closed while waiting also shows the generic banner.
• Runs and hand-offs from incognito chats are never saved for the next launch or opened outside their window; a Run whose tab is already gone counts as incognito.
• The quit no longer saves incognito chats' composers or page images. It collects the incognito tabs before the window step closes the incognito workspaces, since a removed tab would no longer read as incognito.
• Normal windows' space bars no longer list an incognito space (so their sidebar snapshots don't record it); an incognito window still shows its own space.
• Both new banner strings are translated in all 21 NotificationsPanel locales.