refactor(host/W6.2): extract virtual-display orchestration into the pf-vdisplay crate

vdisplay.rs + vdisplay/* (the per-compositor Linux backends — KWin zkde-screencast,
wlroots swaymsg, Mutter RemoteDesktop, Hyprland — and the Windows IddCx/pf-vdisplay
driver backend, behind one VirtualDisplay trait; the mode-conflict admission
registry, the display policy/identity/custom-preset state, and the session-env /
gamescope routing) move into crates/pf-vdisplay (plan §W6). The DDC/CI panel-power
control (used only here) and the KWin zkde protocol XML move with it. This
completes the host-crate decomposition: capture, encode, inject, and vdisplay are
now four subsystem crates over the shared leaves, and punktfunk-host is the
orchestrator (serve/supervisor + native + gamestream + mgmt).

Coupling breaks (all down-only, cargo-tree acyclic):
- capture::dxgi identity -> pf_frame::dxgi; win_display/monitor_devnode/
  console_session_mismatch -> pf-win-display leaf; can_open_another_session ->
  pf-encode (the NVENC session-budget admission gate — acyclic peer edge).
- The registry's DisplayCreated/DisplayReleased emits into the host SSE event bus
  invert to a leaf hook: pf-vdisplay emits a neutral DisplayEvent to a
  host-registered DISPLAY_EVENT_SINK, so it never reaches the orchestrator's
  events module.
- The IddCx driver module is renamed pf_vdisplay -> driver (its old name collided
  with the crate name through the host's `mod vdisplay` shim glob).

The host keeps `mod vdisplay { pub use pf_vdisplay::* }` so every crate::vdisplay::*
path (serve/mgmt/native/the capture FrameChannelSender seam) is unchanged; the
heavy deps (wayland/ashpd/tokio + the zkde protocol) moved with the crate.
Co-authored: a fail-closed IOCTL-reply-length security fix (reject short/zeroed
pf-vdisplay driver replies before trusting protocol_version/target_id/wudf_pid/luid,
security-review 2026-07-17) rides this commit in the moved driver module.

Verified: Linux clippy -D warnings (pf-vdisplay + host nvenc,vulkan-encode,pyrowave
--all-targets) + pf-vdisplay 63/63 + host 167/167 tests; Windows clippy -D warnings
(pf-vdisplay --all-targets + host nvenc,amf-qsv --all-targets) Finished exit 0.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/pf-vdisplay/src/vdisplay/layout.rs

@@ -0,0 +1,142 @@
+//! Pure display-**arrangement** engine (design: `design/display-management.md` §6.2). Given a
+//! group's members (in acquire order) and the `layout` policy, compute each member's top-left
+//! origin in the desktop coordinate space. No I/O, no OS types — the registry (for the
+//! `/display/state` readout) and the per-backend position apply both consume it, so the auto-row /
+//! manual math is defined and tested in exactly one place (the `pick_gamescope_mode` / `wiring_plan`
+//! discipline).
+//!
+//! * **auto-row** — left-to-right in acquire order, top-aligned: member *i* sits at
+//!   `x = Σ widths[0..i]`, `y = 0`. This is what compositors mostly do by default, made
+//!   deterministic.
+//! * **manual** — per-identity-slot offsets from [`Layout::positions`] (console-arranged): a member
+//!   whose stable identity slot has a stored position sits there; a member with no pin (no stored
+//!   position, or a shared/anonymous identity that has no slot) falls back to its auto-row origin, so
+//!   a half-arranged group never collapses everything onto the origin.
+//!
+//! Group membership + acquire order live in the registry ([`super::registry`]); this file only turns
+//! that ordered member list into positions.
+
+use super::policy::{Layout, LayoutMode};
+
+/// One display in a group, as the arranger sees it (given in acquire order).
+#[derive(Clone, Copy, Debug)]
+pub struct Member {
+    /// Stable per-client identity slot — the manual-layout key. `None` for a shared/anonymous
+    /// identity (no per-client slot), which can't carry a manual pin and therefore always auto-rows.
+    pub identity_slot: Option<u32>,
+    /// Pixel width, for auto-row `x` accumulation. Clamped at 0 (a bogus negative never shifts a
+    /// sibling left).
+    pub width: i32,
+}
+
+/// A member's resolved desktop-space top-left origin.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct Placement {
+    pub x: i32,
+    pub y: i32,
+}
+
+/// The auto-row origin of member `i`: the summed width of every prior member, top-aligned.
+fn auto_row_x(members: &[Member], i: usize) -> i32 {
+    members[..i].iter().map(|m| m.width.max(0)).sum()
+}
+
+/// Arrange `members` (in acquire order) per `layout`, returning one [`Placement`] per member in the
+/// same order. Pure — the single source of truth for auto-row / manual placement, shared by the
+/// state readout and (KWin) the per-backend position apply.
+pub fn arrange(members: &[Member], layout: &Layout) -> Vec<Placement> {
+    members
+        .iter()
+        .enumerate()
+        .map(|(i, m)| {
+            let auto = Placement {
+                x: auto_row_x(members, i),
+                y: 0,
+            };
+            match layout.mode {
+                LayoutMode::AutoRow => auto,
+                // A pinned member sits at its stored offset; an unpinned one falls back to auto-row.
+                LayoutMode::Manual => m
+                    .identity_slot
+                    .and_then(|slot| layout.positions.get(&slot.to_string()))
+                    .map(|p| Placement { x: p.x, y: p.y })
+                    .unwrap_or(auto),
+            }
+        })
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::policy::Position;
+    use std::collections::BTreeMap;
+
+    fn m(slot: Option<u32>, width: i32) -> Member {
+        Member {
+            identity_slot: slot,
+            width,
+        }
+    }
+
+    fn manual(pairs: &[(&str, i32, i32)]) -> Layout {
+        let mut positions = BTreeMap::new();
+        for (k, x, y) in pairs {
+            positions.insert(k.to_string(), Position { x: *x, y: *y });
+        }
+        Layout {
+            mode: LayoutMode::Manual,
+            positions,
+        }
+    }
+
+    #[test]
+    fn auto_row_accumulates_widths_top_aligned() {
+        let members = [m(Some(1), 2560), m(Some(2), 1920), m(None, 1280)];
+        let out = arrange(&members, &Layout::default()); // default = AutoRow
+        assert_eq!(
+            out,
+            vec![
+                Placement { x: 0, y: 0 },
+                Placement { x: 2560, y: 0 },
+                Placement { x: 4480, y: 0 },
+            ]
+        );
+    }
+
+    #[test]
+    fn manual_honors_pins_by_identity_slot() {
+        let members = [m(Some(1), 2560), m(Some(7), 1920)];
+        // Client 7 arranged to the LEFT of client 1 (crossing order reversed vs auto-row).
+        let layout = manual(&[("1", 1920, 0), ("7", 0, 0)]);
+        let out = arrange(&members, &layout);
+        assert_eq!(out[0], Placement { x: 1920, y: 0 });
+        assert_eq!(out[1], Placement { x: 0, y: 0 });
+    }
+
+    #[test]
+    fn manual_unpinned_and_slotless_fall_back_to_auto_row() {
+        let members = [m(Some(1), 2560), m(Some(9), 1920), m(None, 1280)];
+        // Only slot 1 is pinned; slot 9 has no stored pin; the third has no slot at all.
+        let layout = manual(&[("1", 100, 50)]);
+        let out = arrange(&members, &layout);
+        assert_eq!(out[0], Placement { x: 100, y: 50 }, "pinned");
+        assert_eq!(out[1], Placement { x: 2560, y: 0 }, "unpinned → auto-row");
+        assert_eq!(out[2], Placement { x: 4480, y: 0 }, "slotless → auto-row");
+    }
+
+    #[test]
+    fn empty_group_is_empty() {
+        assert!(arrange(&[], &Layout::default()).is_empty());
+        assert!(arrange(&[], &manual(&[("1", 0, 0)])).is_empty());
+    }
+
+    #[test]
+    fn negative_width_never_shifts_siblings_left() {
+        let members = [m(Some(1), -100), m(Some(2), 1920)];
+        let out = arrange(&members, &Layout::default());
+        let origin = Placement { x: 0, y: 0 };
+        assert_eq!(out[0], origin);
+        assert_eq!(out[1], origin, "clamped width contributes 0");
+    }
+}