chore(m2b): TEMP cursor-meta probe — DROP BEFORE MERGE

Rate-limited journal logging of SPA_META_Cursor arrival/absence, reported
id/position/bitmap offset, and bitmap acceptance — the Linux cursor
pipeline is otherwise blind end-to-end during Mutter RecordVirtual
metadata bring-up on .21.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/pf-capture/src/linux/mod.rs

@@ -1362,8 +1362,19 @@ mod pipewire {
         // that SIGSEGVs inside the PipeWire `.process` callback (a segfault `catch_unwind` cannot
         // catch). Every offset below is validated against `region_size` with checked arithmetic,
         // mirroring the fd-length guard the main frame path already applies to xdg-desktop-portal-wlr.
+        // TEMP M2b on-glass probe (DROP BEFORE MERGE): the journal must show whether the
+        // compositor delivers SPA_META_Cursor at all, what it reports, and whether a bitmap is
+        // ever accepted — the cursor pipeline is otherwise blind end-to-end. Statics are fine for
+        // the single bring-up stream; every log is rate-limited or edge-triggered.
+        use std::sync::atomic::{AtomicU64, Ordering as ProbeOrd};
+        static PROBE_NULL: AtomicU64 = AtomicU64::new(0);
+        static PROBE_META: AtomicU64 = AtomicU64::new(0);
         let meta = unsafe { spa::sys::spa_buffer_find_meta(spa_buf, spa::sys::SPA_META_Cursor) };
         if meta.is_null() {
+            let n = PROBE_NULL.fetch_add(1, ProbeOrd::Relaxed) + 1;
+            if n.is_power_of_two() {
+                tracing::info!(n, "cursor meta probe: buffer carries NO SPA_META_Cursor");
+            }
             return;
         }
         // SAFETY: `meta` is non-null and points into the held buffer's metadata array.
@@ -1383,6 +1394,21 @@ mod pipewire {
                 (*cur).bitmap_offset,
             )
         };
+        // TEMP M2b probe (see above): what the meta reports, every 64th + the first few.
+        let n = PROBE_META.fetch_add(1, ProbeOrd::Relaxed) + 1;
+        if n <= 4 || n % 64 == 1 {
+            tracing::info!(
+                n,
+                id,
+                pos_x,
+                pos_y,
+                hot_x,
+                hot_y,
+                bmp_off,
+                region_size,
+                "cursor meta probe: SPA_META_Cursor arrived"
+            );
+        }
         if id == 0 {
             // Compositor reports no visible pointer (e.g. a game grabbed/hid it).
             cursor.visible = false;
@@ -1461,6 +1487,14 @@ mod pipewire {
         cursor.bw = bw;
         cursor.bh = bh;
         cursor.serial = cursor.serial.wrapping_add(1);
+        // TEMP M2b probe (see above): bitmap accepted — once per shape change by construction.
+        tracing::info!(
+            bw,
+            bh,
+            vfmt,
+            serial = cursor.serial,
+            "cursor meta probe: bitmap cached"
+        );
     }
 
     /// Destination channel byte offsets (R,G,B) and bytes-per-pixel for a packed-RGB `PixelFormat`,