macOS: app appears "still open" after quitting — orphaned fullscreen Space in Mission Control

On macOS, a GUI app that was running in fullscreen appears to still be open after being quit or force-quit: Mission Control keeps showing a tile for it in the Spaces bar at the top, often rendered as a solid black thumbnail with the app's name under it. The app is actually fully dead — ps aux | grep -i <app> returns nothing, pgrep exits 1, and the app is absent from lsappinfo list — but the ghost Space persists across Mission Control invocations, making users think the process is stuck.

First prove the process is actually gone, then treat the leftover as a window-manager artifact, not a stuck process.

Step 1 — confirm the app is not running:
ps aux | grep -i <app> | grep -v grep
pgrep -ifl <app>
lsappinfo list | grep -E '^[0-9]+\) '
launchctl list | grep -i <app>

Step 2 — confirm the Space is orphaned. Fullscreen Spaces are type = 4 in the Spaces config and normally carry a pid field naming the owning process. An orphaned one has no pid:
defaults read com.apple.spaces SpacesDisplayConfiguration | grep -E 'id64|pid|type'
A type = 4 block with no pid above it is a ghost Space. (type = 0 is a normal desktop, type = 5/6 are its child window/backing entries.)

Step 3 — clear it, least invasive first:
1. Open Mission Control, hover the ghost tile, click the small close (X) badge in its corner.
2. If it will not dismiss: killall Dock. The Dock process owns Mission Control and the Spaces bar; it relaunches automatically in about a second, closes no applications, and loses no work. This reliably rebuilds the Spaces list and drops orphaned entries.
3. Only if still stuck: log out and back in.

Do NOT delete or hand-edit ~/Library/Preferences/com.apple.spaces.plist — that wipes the entire Space arrangement across all displays for a problem killall Dock already solves.

Correlate the timing: check ~/Library/Logs/DiagnosticReports/ for an .ips report matching the app. A bug_type of 309 is a hang/spin report and 109 is a crash. An app that hung or crashed while fullscreen is the usual way this artifact gets created.

macOS treats each fullscreen window as its own managed Space, and the Dock/WindowServer tears that Space down when the owning application exits cleanly. If the app hangs and is force-killed (or crashes) while fullscreen, it never completes the normal exit handshake, so the Space entry survives in the Dock's in-memory Spaces list and in com.apple.spaces with a dangling or absent owning pid. Mission Control then renders a Space that has no windows left to composite, which is why the thumbnail is black rather than missing. Restarting the Dock forces it to rebuild that list from live processes, dropping any Space whose owner no longer exists.

Diagnosing a user report that an application is "still open" after they closed it, when process-level checks show nothing running. Especially common with browsers and other apps people routinely run fullscreen on a dedicated Space.