drm: address the phase-2 split review

1- do not depend on the libdrmtap-sys crate for the pin: its build.rs statically compiles the whole libdrmtap C tree and a CAP_SYS_ADMIN helper and links -ldrm/-lseccomp/-lcap, which defeats the runtime-dlopen model. keep drm a pure dlopen backend and pin the .so by the build.py DRMTAP_REF release tag, guarded by a strict vX.Y.Z regex. drops the now-moot Cargo.lock freshness CI checks. 2- render-node-less consumers no longer lose the stream: the --server signals need_cpu on DrmStart when it cannot open a convert context, and the --service streams the CPU-converted frame path for that connection instead of a dma-buf fd the consumer cannot detile (which used to fall through to a PipeWire path nobody can approve on an unattended seat). 3- mark PipeWire initialized only after every per-display capturer is created, so a partial failure retries instead of the flag falsely reporting a complete init. 4- reject a degenerate (zero width/height) or short CPU frame before it reaches PixelBuffer::new (which derives stride as data.len()/height, dividing by zero). 5- keep the export-ledger epoch at DRM_DISPLAY_GENERATION so a hotplug invalidates cached buffers (elision stays off until the recycled-fb_id inode case is handled). 6- validate the udev uevent source (kernel nl_pid, multicast) with recvmsg so a local process cannot unicast a spoofed drm-change event to the root listener.
2026-09-05 23:51:04 +03:00 · 2026-07-21 00:25:19 -03:00
parent 3b6914b1b2
commit 6cc426e9f5
7 changed files with 131 additions and 88 deletions
--- a/.github/workflows/flutter-build.yml
+++ b/.github/workflows/flutter-build.yml
@@ -1708,11 +1708,12 @@ jobs:
              export DRMTAP_REPO="https://github.com/rustdesk-org/libdrmtap"
              export DRMTAP_REF="v0.4.13"
              # Guard: refuse a loose/branch ref so a moving `main` can never silently
-              # regress the pin. Only a vX.Y.Z tag is accepted.
-              case "$DRMTAP_REF" in
-                v[0-9]*.[0-9]*.[0-9]*) ;;
-                *) echo "FATAL: DRMTAP_REF must be a pinned vX.Y.Z tag, got '$DRMTAP_REF'"; exit 1;;
-              esac
+              # regress the pin. Only an EXACT vX.Y.Z tag is accepted (a strict anchored
+              # match, so values like v0.4.13-ci or a branch that resolves under
+              # `git clone --branch` are rejected).
+              if ! printf '%s' "$DRMTAP_REF" | grep -qE '^v[0-9]+\.[0-9]+\.[0-9]+$'; then
+                echo "FATAL: DRMTAP_REF must be a pinned vX.Y.Z tag, got '$DRMTAP_REF'"; exit 1
+              fi
              git config --global --add safe.directory '*' || true
              rm -rf third_party/libdrmtap
              git clone --depth 1 --branch "$DRMTAP_REF" "$DRMTAP_REPO" third_party/libdrmtap
@@ -1731,16 +1732,9 @@ jobs:
              [ -n "$(find "$DRMTAP_PREBUILT_DIR" -name 'libdrmtap.so.0.*' -type f)" ] \
                || { echo "FATAL: prebuilt libdrmtap.so missing"; exit 1; }
              ls -l "$DRMTAP_PREBUILT_DIR"
-              # Lock-freshness guard, BEFORE the `--locked` build (which itself fails on a
-              # checksum mismatch): prove Cargo.lock is in sync with Cargo.toml and actually
-              # contains the pinned libdrmtap-sys (the integrator must have run
-              # `cargo update -p libdrmtap-sys --precise 0.4.13`). This turns a stale/loose lock
-              # into an explicit, readable failure instead of a confusing error deep in the build.
-              # The `=0.4.13` requirement in libs/scrap/Cargo.toml + `--locked` already force the
-              # exact resolved version + its checksum; this only confirms the lock was regenerated.
-              cargo update --locked --dry-run
-              cargo tree --locked --features drm -p libdrmtap-sys -i >/dev/null \
-                || { echo "FATAL: Cargo.lock does not contain the pinned libdrmtap-sys (run: cargo update -p libdrmtap-sys --precise 0.4.13)"; exit 1; }
+              # The drm backend is pure runtime-dlopen (no libdrmtap-sys crate dependency),
+              # so the pin is the DRMTAP_REF tag verified above plus the prebuilt .so; there
+              # is nothing to assert in Cargo.lock for it.
              cargo build --locked --lib $JOBS --features hwcodec,flutter,unix-file-copy-paste,drm --release
              python3 ./build.py --flutter --drm --skip-cargo
              for name in rustdesk-unattended-wayland*??.deb; do
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4485,16 +4485,6 @@ dependencies = [
 "pkg-config",
 ]

-[[package]]
-name = "libdrmtap-sys"
-version = "0.4.13"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e6c52136bd2bf94bb1071f3926eff327148faddc704338f3fca473e1d1974723"
-dependencies = [
- "cc",
- "pkg-config",
-]
-
 [[package]]
 name = "libgit2-sys"
 version = "0.14.2+1.5.1"
@@ -7620,7 +7610,6 @@ dependencies = [
 "hwcodec",
 "jni",
 "lazy_static",
- "libdrmtap-sys",
 "log",
 "ndk 0.7.0",
 "ndk-context",
--- a/build.py
+++ b/build.py
@@ -335,11 +335,11 @@ def ffi_bindgen_function_refactor():
 # libdrmtap is fetched at build time by cloning the rustdesk-org fork at a pinned
 # ref — the same way rustdesk sources its other native build deps (vcpkg,
 # flutter_rust_bridge, ...), rather than carrying a git submodule. The ref is an
-# EXACT release tag (vX.Y.Z), NOT a moving branch: the bundled runtime .so version must
-# match the `libdrmtap-sys = "=0.4.13"` crate pinned in libs/scrap/Cargo.toml (the dlopen
-# loader only checks ABI-major, so a minor skew between the two artifacts would go undetected).
-# Bump this tag and the crate pin together. Override the repo/ref via env (DRMTAP_REPO /
-# DRMTAP_REF) for local testing or another fork.
+# EXACT release tag (vX.Y.Z), NOT a moving branch, and it is the ONLY pin for the
+# drm backend: rustdesk dlopens this .so at runtime and does not depend on the
+# libdrmtap-sys crate (whose build.rs would statically link the C tree, a helper and
+# libdrm/seccomp/cap). Override the repo/ref via env (DRMTAP_REPO / DRMTAP_REF) for
+# local testing or another fork.
 LIBDRMTAP_REPO = os.environ.get('DRMTAP_REPO', 'https://github.com/rustdesk-org/libdrmtap')
 LIBDRMTAP_REF = os.environ.get('DRMTAP_REF', 'v0.4.13')

--- a/libs/scrap/Cargo.toml
+++ b/libs/scrap/Cargo.toml
@@ -11,11 +11,13 @@ edition = "2018"

 [features]
 wayland = ["gstreamer", "gstreamer-app", "gstreamer-video", "dbus", "tracing", "zbus"]
-# `drm` pulls in the exact-pinned `libdrmtap-sys` crate (see the Linux target table below). rustdesk
-# still dlopen's `libdrmtap.so.0` at runtime (`drmtap_dl.rs`) rather than link-time linking it, so the
-# graceful PipeWire fallback when the .so/EGL is absent is preserved; the crate is pinned purely so its
-# committed Cargo.lock checksum supply-chain-pins the vendored source that build.py bundles.
-drm = ["dep:libdrmtap-sys"]
+# `drm` is a pure runtime-dlopen backend: rustdesk loads `libdrmtap.so.0` at runtime (`drmtap_dl.rs`)
+# and NEVER link-time links it, so the graceful PipeWire fallback when the .so or EGL is absent is
+# preserved and the drm build pulls in no libdrm/seccomp/cap/EGL link-time deps. The .so is version
+# pinned by build.py's `DRMTAP_REF = v0.4.13` (an exact release tag, not `main`). We deliberately do
+# NOT depend on the `libdrmtap-sys` crate: its build.rs statically compiles the whole libdrmtap C tree
+# and a CAP_SYS_ADMIN helper and emits `-ldrm -lseccomp -lcap`, which would defeat the dlopen model.
+drm = []
 mediacodec = ["ndk"]
 linux-pkg-config = ["dep:pkg-config"]
 hwcodec = ["dep:hwcodec"]
@@ -63,16 +65,6 @@ gstreamer = { version = "0.16", optional = true }
 gstreamer-app = { version = "0.16", features = ["v1_10"], optional = true }
 gstreamer-video = { version = "0.16", optional = true }
 zbus = { version = "3.15", optional = true }
-# libdrmtap ABI, pinned EXACTLY (the leading `=` blocks ^0.4.x semver drift). This is the ONLY
-# supply-chain pin for libdrmtap: the committed Cargo.lock `checksum` for this exact version pins the
-# bytes, so `cargo build --locked` refuses a tampered/republished 0.4.13. It must move in lockstep
-# with build.py's `DRMTAP_REF = v0.4.13` (the bundled runtime .so) — the loader only checks ABI-major.
-# NOTE for the integrator: after this edit the lockfile MUST be regenerated + committed with
-#   cargo update -p libdrmtap-sys --precise 0.4.13
-# so Cargo.lock gains the `[[package]] libdrmtap-sys 0.4.13 checksum=<sha256>` block (this stage does
-# not run cargo). `=0.4.13` alone is a version requirement, not a byte pin — the checksum is the pin.
-libdrmtap-sys = { version = "=0.4.13", optional = true }
-
 [dependencies.hwcodec]
 git = "https://github.com/rustdesk-org/hwcodec"
 optional = true
--- a/src/ipc.rs
+++ b/src/ipc.rs
@@ -494,7 +494,11 @@ pub enum Data {
    // the same `DrmConn` send (see `DrmConn::send_msg`), so it has NO trailing `send_raw()` body.
    /// Client -> service: begin streaming the chosen display.
    #[cfg(all(target_os = "linux", feature = "drm"))]
-    DrmStart { display: i32 },
+    // `need_cpu` is set by an unprivileged consumer that could not open a render-node convert context
+    // (drmtap_open_render failed, or an old .so lacks the split symbols). The service then streams the
+    // CPU-converted `DrmFrame` path for this connection instead of a dma-buf fd the consumer cannot
+    // detile, so a render-node-less seat still captures instead of losing the stream.
+    DrmStart { display: i32, need_cpu: bool },
    /// Service -> client: the enumerated DRM displays (sent once, before frames).
    #[cfg(all(target_os = "linux", feature = "drm"))]
    DrmDisplayList(Vec<DrmDisplayInfo>),
@@ -1651,8 +1655,12 @@ impl Drop for DrmStopGuard {
 /// and modifier; eliding then would serve a stale EGLImage. libdrmtap's own import cache keys on
 /// `fb_id + dma-buf inode` and can re-import ONLY when it is handed a real fd. Because always sending
 /// the fd is cheap (the converter still imports once per `fb_id` and closes the surplus fd) and is
-/// strictly safe, `DRM_FD_ELISION` defaults to `false` for v1 (always send). The ledger is fully
-/// wired so flipping the const on enables elision once the recycled-fb_id case is validated.
+/// strictly safe, `DRM_FD_ELISION` defaults to `false` for v1 (always send). The ledger's `epoch`
+/// tracks `DRM_DISPLAY_GENERATION` (bumped by the udev listener on a connector-topology change), so a
+/// hotplug/modeset invalidates every cached buffer and forces a real fd; but the ledger still cannot
+/// see the dma-buf inode, so a recycled fb_id within the SAME generation (identical geometry +
+/// modifier) would elide onto a stale EGLImage. Enabling elision needs that inode case validated
+/// first.
 #[cfg(all(target_os = "linux", feature = "drm"))]
 const DRM_FD_ELISION: bool = false;

@@ -1660,14 +1668,14 @@ const DRM_FD_ELISION: bool = false;
 struct SeenBuf {
    modifier: u64,
    dims: (u32, u32),
-    epoch: u32,
+    epoch: u64,
 }

 #[cfg(all(target_os = "linux", feature = "drm"))]
 struct ExportLedger {
    seen: HashMap<u32, SeenBuf>,
    order: std::collections::VecDeque<u32>, // insertion order, for evict-oldest
-    epoch: u32,
+    epoch: u64,
 }

 #[cfg(all(target_os = "linux", feature = "drm"))]
@@ -1852,7 +1860,22 @@ fn drm_udev_listener() {
    // datagram is truncated by `recv` and simply re-enumerates on the next matching event.
    let mut buf = [0u8; 8192];
    loop {
-        let n = unsafe { libc::recv(sock, buf.as_mut_ptr() as *mut libc::c_void, buf.len(), 0) };
+        // recvmsg (not recv) so the source address is available: bound to the kernel-uevent multicast
+        // group, a genuine uevent comes from the kernel (source nl_pid == 0) via a multicast group
+        // (nl_groups != 0). A local unprivileged process could otherwise UNICAST a spoofed
+        // "change@.../drm/..." datagram to this root listener and drive it to re-enumerate at will;
+        // dropping any non-kernel/non-multicast source closes that.
+        let mut src: libc::sockaddr_nl = unsafe { std::mem::zeroed() };
+        let mut iov = libc::iovec {
+            iov_base: buf.as_mut_ptr() as *mut libc::c_void,
+            iov_len: buf.len(),
+        };
+        let mut mhdr: libc::msghdr = unsafe { std::mem::zeroed() };
+        mhdr.msg_name = &mut src as *mut libc::sockaddr_nl as *mut libc::c_void;
+        mhdr.msg_namelen = std::mem::size_of::<libc::sockaddr_nl>() as libc::socklen_t;
+        mhdr.msg_iov = &mut iov;
+        mhdr.msg_iovlen = 1;
+        let n = unsafe { libc::recvmsg(sock, &mut mhdr, 0) };
        if n <= 0 {
            let err = std::io::Error::last_os_error();
            if n < 0 && err.kind() == std::io::ErrorKind::Interrupted {
@@ -1861,6 +1884,14 @@ fn drm_udev_listener() {
            log::info!("drm: udev uevent recv ended ({err}); hotplug refresh stopped");
            break;
        }
+        // Trust only a kernel-originated (nl_pid == 0), multicast-delivered (nl_groups != 0) datagram
+        // with a full source address; drop a unicast or user-spoofed message.
+        if (mhdr.msg_namelen as usize) < std::mem::size_of::<libc::sockaddr_nl>()
+            || src.nl_pid != 0
+            || src.nl_groups == 0
+        {
+            continue;
+        }
        if !uevent_is_drm_change(&buf[..n as usize]) {
            continue;
        }
@@ -2010,8 +2041,9 @@ async fn handle_drm_conn(stream: Connection) -> ResultType<()> {

    // worker -> task: display list, frames, cursor (bounded = backpressure).
    let (frame_tx, mut frame_rx) = tokio::sync::mpsc::channel::<DrmProducerMsg>(2);
-    // task -> worker: the chosen CRTC, sent once after the client's DrmStart.
-    let (crtc_tx, crtc_rx) = std::sync::mpsc::channel::<u32>();
+    // task -> worker: the chosen CRTC + whether the consumer needs the CPU path, sent once after the
+    // client's DrmStart.
+    let (crtc_tx, crtc_rx) = std::sync::mpsc::channel::<(u32, bool)>();
    let stop = Arc::new(AtomicBool::new(false));
    let _stop_guard = DrmStopGuard(stop.clone());
    let worker_stop = stop.clone();
@@ -2031,9 +2063,9 @@ async fn handle_drm_conn(stream: Connection) -> ResultType<()> {

    // Wait for the client to choose a display before streaming. `recv_msg_timeout2` gates only the
    // wait for the first byte, so a timeout leaves the stream at a clean frame boundary.
-    let display_idx = loop {
+    let (display_idx, need_cpu) = loop {
        match conn.recv_msg_timeout2(10_000).await {
-            Some(Ok((Data::DrmStart { display }, _fd))) => break display,
+            Some(Ok((Data::DrmStart { display, need_cpu }, _fd))) => break (display, need_cpu),
            Some(Ok((_, _fd))) => continue, // ignore unexpected messages; drop any stray fd
            Some(Err(e)) => return Err(e),
            None => return Ok(()), // timed out: client never chose a display
@@ -2057,8 +2089,9 @@ async fn handle_drm_conn(stream: Connection) -> ResultType<()> {
        );
        return Ok(());
    }
-    // Hand the CRTC to the worker; an error means it already gave up (reader vanished).
-    if crtc_tx.send(target_crtc).is_err() {
+    // Hand the CRTC + the consumer's CPU-path request to the worker; an error means it already gave up
+    // (reader vanished).
+    if crtc_tx.send((target_crtc, need_cpu)).is_err() {
        return Ok(());
    }

@@ -2075,6 +2108,10 @@ async fn handle_drm_conn(stream: Connection) -> ResultType<()> {
    let mut seen_gen = DRM_DISPLAY_GENERATION.load(Ordering::Acquire);
    while let Some(msg) = frame_rx.recv().await {
        let gen = DRM_DISPLAY_GENERATION.load(Ordering::Acquire);
+        // Keep the ledger's epoch at the live generation so a hotplug/modeset (which may recycle an
+        // fb_id onto a new buffer) invalidates every cached buffer and forces a real fd on the next
+        // frame. Cheap (one field write) and only observable when DRM_FD_ELISION is enabled.
+        ledger.epoch = gen;
        if gen != seen_gen {
            seen_gen = gen;
            let fresh = DRM_DISPLAY_CACHE.lock().unwrap().clone();
@@ -2134,7 +2171,7 @@ async fn handle_drm_conn(stream: Connection) -> ResultType<()> {
 #[cfg(all(target_os = "linux", feature = "drm"))]
 fn drm_capture_worker(
    frame_tx: tokio::sync::mpsc::Sender<DrmProducerMsg>,
-    crtc_rx: std::sync::mpsc::Receiver<u32>,
+    crtc_rx: std::sync::mpsc::Receiver<(u32, bool)>,
    stop: std::sync::Arc<std::sync::atomic::AtomicBool>,
 ) {
    use std::sync::atomic::Ordering;
@@ -2170,8 +2207,9 @@ fn drm_capture_worker(
        return;
    }

-    // Wait for the task to relay the client's chosen CRTC (Err => the task gave up / disconnected).
-    let target_crtc = match crtc_rx.recv() {
+    // Wait for the task to relay the client's chosen CRTC + CPU-path request (Err => the task gave up
+    // / disconnected).
+    let (target_crtc, need_cpu) = match crtc_rx.recv() {
        Ok(c) => c,
        Err(_) => return,
    };
@@ -2199,10 +2237,12 @@ fn drm_capture_worker(
    static DRM_CONN_EPOCH: std::sync::atomic::AtomicU32 = std::sync::atomic::AtomicU32::new(0);
    let conn_epoch = DRM_CONN_EPOCH.fetch_add(1, Ordering::Relaxed);

-    // Prefer the zero-copy split export (root does NO EGL / convert / copy). If the loaded libdrmtap
-    // predates the split API, or grab_desc later reports ENOTSUP (no transferable dma-buf on this
-    // seat), fall back to the CPU-mapped path for this connection (pixels cross the wire).
-    let mut use_dmabuf = reader.supports_grab_desc();
+    // Prefer the zero-copy split export (root does NO EGL / convert / copy). Fall back to the
+    // CPU-mapped path for this connection (pixels cross the wire) when: the loaded libdrmtap predates
+    // the split API, grab_desc later reports ENOTSUP (no transferable dma-buf on this seat), OR the
+    // consumer asked for the CPU path because it has no render-node convert context (need_cpu) — in
+    // that last case the dma-buf fd would be useless to it and the stream would be lost.
+    let mut use_dmabuf = reader.supports_grab_desc() && !need_cpu;

    let mut last_cursor_id: u64 = 0;
    let mut stalled: u32 = 0;
--- a/src/server/drm_capturer.rs
+++ b/src/server/drm_capturer.rs
@@ -249,25 +249,30 @@ async fn recv_thread(
            return;
        }
    };
-    if let Err(err) = conn.send_msg(&Data::DrmStart { display }, None).await {
+    // Open the unprivileged render-node convert context ONCE, on THIS thread, BEFORE the handshake; it
+    // is dropped on this same thread when the loop exits (its EGL state + import-once cache are
+    // thread-local). `None` means no usable render node (a locked-down seat, or an old `.so` without
+    // the split symbols): we then ask the service for the CPU-converted `DrmFrame` path via
+    // `need_cpu`, so a render-node-less seat still captures instead of the service streaming a dma-buf
+    // fd we cannot detile (which would lose the stream and force a PipeWire fallback nobody may be
+    // present to approve on an unattended seat).
+    let mut converter = RenderConverter::open_render();
+    let need_cpu = converter.is_none();
+    if need_cpu {
+        log::info!(
+            "drm: no render-node convert context (drmtap_open_render failed or old .so); \
+             requesting the CPU-converted frame path for this stream"
+        );
+    }
+    if let Err(err) = conn
+        .send_msg(&Data::DrmStart { display, need_cpu }, None)
+        .await
+    {
        let _ = tx.send(Err(err));
        return;
    }
    let _ = tx.send(Ok(displays));

-    // Open the unprivileged render-node convert context ONCE, on THIS thread; it is dropped on this
-    // same thread when the loop exits (its EGL state + import-once cache are thread-local). `None`
-    // means no usable render node (a locked-down seat, or an old `.so` without the split symbols): the
-    // CPU-fallback `DrmFrame` path still works, but a `DrmFrameDmabuf` we cannot convert ends the
-    // stream so the caller falls back (PipeWire per-display).
-    let mut converter = RenderConverter::open_render();
-    if converter.is_none() {
-        log::info!(
-            "drm: no render-node convert context (drmtap_open_render failed or old .so); \
-             only the CPU-fallback frame path will work on this stream"
-        );
-    }
-
    // Stream until stopped or the connection ends. Poll the header read with a short timeout (rather
    // than blocking indefinitely) so a dropped capturer re-checks `stop` and tears down promptly even
    // when the producer has stalled (no frames arriving). A dma-buf frame carries its fd inline on the
@@ -337,15 +342,33 @@ async fn recv_thread(
            }
            // CPU-fallback path (old `.so` / no transferable dma-buf): the producer packed BGRA and
            // sent it over the wire after the header. Store it as-is (BGRA); no convert needed.
-            Data::DrmFrame { width, height } => match conn.next_raw().await {
-                Ok(raw) => {
-                    let mut slot = shared.slot.lock().unwrap();
-                    slot.latest =
-                        Some((width as usize, height as usize, Pixfmt::BGRA, raw.to_vec()));
-                    shared.cv.notify_one();
+            Data::DrmFrame { width, height } => {
+                // Reject degenerate geometry before it reaches the slot: `frame()` hands this to
+                // PixelBuffer::new which derives the stride as `data.len() / height`, so height==0
+                // would divide by zero, and a zero width is meaningless. Require the body to hold at
+                // least width*height*4 BGRA bytes so a short body cannot misframe downstream.
+                if width == 0 || height == 0 {
+                    break format!("cpu frame: degenerate geometry {width}x{height}");
                }
-                Err(err) => break format!("frame body: {err}"),
-            },
+                let need = (width as usize)
+                    .saturating_mul(height as usize)
+                    .saturating_mul(4);
+                match conn.next_raw().await {
+                    Ok(raw) => {
+                        if raw.len() < need {
+                            break format!(
+                                "cpu frame: body {} bytes < {need} for {width}x{height}",
+                                raw.len()
+                            );
+                        }
+                        let mut slot = shared.slot.lock().unwrap();
+                        slot.latest =
+                            Some((width as usize, height as usize, Pixfmt::BGRA, raw.to_vec()));
+                        shared.cv.notify_one();
+                    }
+                    Err(err) => break format!("frame body: {err}"),
+                }
+            }
            Data::DrmCursor {
                id,
                width,
--- a/src/server/wayland.rs
+++ b/src/server/wayland.rs
@@ -228,7 +228,6 @@ pub(super) async fn check_init() -> ResultType<()> {
                }
                log::debug!("Attempting to fix logical size with try_fix_logical_size()");
                try_fix_logical_size(&mut all);
-                *PIPEWIRE_INITIALIZED.write().unwrap() = true;
                let num = all.len();
                let primary = super::display_service::get_primary_2(&all);
                let mut displays = super::display_service::update_sync_displays(&all);
@@ -269,6 +268,12 @@ pub(super) async fn check_init() -> ResultType<()> {

                    lock.insert(idx, cap_display_info as u64);
                }
+                // Mark PipeWire initialized only AFTER every per-display capturer was created and
+                // stored. Setting it earlier meant a partial failure above (a `Capturer::new` error
+                // propagated by `?`) returned Err with the flag already true, so the next check_init
+                // saw "initialized", skipped re-init, and left CAP_DISPLAY_INFO empty (no capture).
+                // This matters more now that the per-display DRM->PipeWire fallback funnels through here.
+                *PIPEWIRE_INITIALIZED.write().unwrap() = true;
            }
        }
    }