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fix(vdisplay): a pin with no heads to mirror must not refuse the session

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The streamed-screen pin is host-wide and persisted, but the session it applies to
is not. A box that boots between a desktop (heads to mirror) and a nested or
headless Game Mode (none) carried the pin into a session where `monitors::resolve`
could only fail — and since `vdisplay::open` is the one place every session opens a
display, that failure was a host refusing to stream at all rather than one
streaming the normal way. Pinning a monitor in Desktop mode bricked Game Mode.

A compositor reporting NO heads whatsoever now degrades to the virtual-display
path with the reason logged. Narrow on purpose: a pin that misses among heads that
DO exist stays the hard error §5.2 makes it — showing someone a different screen
than they asked for is the failure worth refusing over, and "there are no screens
here" is not that. An enumeration ERROR also stays on the mirror path, so the
session fails with the real reason instead of quietly ignoring the operator.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
enricobuehler
2026-07-29 12:23:32 +02:00
co-authored by Claude Opus 5
parent 028462ef6d
commit 664c26cb2b
1 changed files with 22 additions and 1 deletions
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crates/pf-vdisplay/src/lib.rs
+22 -1
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@@ -369,7 +369,28 @@ pub fn capture_monitor() -> Option<String> {
pub fn open(compositor: Compositor) -> Result<Box<dyn VirtualDisplay>> {
#[cfg(target_os = "linux")]
if let Some(connector) = capture_monitor() {
return Ok(Box::new(mirror::MirrorDisplay::new(compositor, connector)?));
// A pin is host-wide and PERSISTED, but the session it applies to is not: a box that boots
// between a desktop (heads to mirror) and a nested/headless Game Mode (none) would carry the
// pin into a session where `resolve` can only fail — and since this is the one place every
// session opens a display, that failure is a host that refuses to stream at all rather than
// one that streams the normal way. So a compositor reporting NO heads whatsoever degrades to
// the virtual-display path with the reason logged.
//
// Narrow on purpose. A pin that misses among heads that DO exist stays the hard error
// `monitors::resolve` makes it (design/per-monitor-portal-capture.md §5.2): showing someone
// a different screen than they asked for is the failure worth refusing over, and "there are
// no screens here" is not that. An enumeration ERROR also stays on the mirror path, so the
// session fails with the real reason instead of quietly ignoring the operator's choice.
match monitors::list(compositor) {
Ok(heads) if heads.is_empty() => tracing::warn!(
pinned = %connector,
compositor = compositor.id(),
"the streamed-screen pin names a monitor but this session has no physical heads to \
mirror (a nested or headless compositor) — creating a virtual display instead; the \
pin applies again as soon as a session with real heads runs"
),
_ => return Ok(Box::new(mirror::MirrorDisplay::new(compositor, connector)?)),
}
}
#[cfg(target_os = "linux")]
{