refactor(windows-host): §2.5 step 1 — delete the dead/write-only monitor-lifecycle code

Removes the cruft the §2.5 ownership-model rewrite would otherwise carry forward, and corrects a
false invariant the docs described:

  * CURRENT_MON_GEN (sudovda) — the "current monitor generation" global was WRITE-ONLY. It was
    stored on every mgr_acquire (both backends) but its only reader, idd_push's `my_gen`, was set
    and NEVER read. The "session capturer re-checks the monitor gen each frame and bails on a
    reconnect" behaviour the doc describes was never wired — per-frame staleness is the SEPARATE
    ring FrameToken.generation / IDD_GENERATION mechanism (which works and is untouched). So the
    monitor-gen-via-WinCaptureTarget carry the design proposed is unnecessary. Deleted the static,
    its stores in both backends, the pf_vdisplay import, and idd_push's dead `my_gen` field/read.
    (MON_GEN — the lease-generation counter behind the stale-lease no-op — is REAL and kept.)

  * IDD_PERSIST + open_or_reuse + IddReuseHandle (idd_push) — a persistent-capturer reuse path
    from an early prototype, defined but with ZERO callers across the crate. Deleted, plus the now
    -orphaned `use std::sync::Mutex` and the now-dead `set_client_10bit` setter.

Windows-only; grep confirms no remaining references to any deleted symbol. Box build to follow.
First of the incremental §2.5 steps (user-approved OnceLock VirtualDisplayManager design).

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

crates/punktfunk-host/src/vdisplay/windows/pf_vdisplay.rs

@@ -38,9 +38,9 @@ use pf_vdisplay_proto::control;
 
 use super::{Mode, VirtualDisplay, VirtualOutput};
 // Backend-NEUTRAL CCD/DXGI helpers reused from the SudoVDA backend (a pf-vdisplay monitor's target_id
-// is a real OS target id, so these operate identically). The shared MON_GEN/CURRENT_MON_GEN generation
-// counter is reused too, so the IDD-push stale-ring bail works regardless of which backend is active.
-use super::sudovda::{CURRENT_MON_GEN, MON_GEN};
+// is a real OS target id, so these operate identically). The shared MON_GEN lease-generation counter is
+// reused too, so a stale preempted lease can't tear down the live monitor regardless of which backend is active.
+use super::sudovda::MON_GEN;
 use crate::win_adapter::resolve_render_adapter_luid;
 use crate::win_display::{
     isolate_displays_ccd, resolve_gdi_name, restore_displays_ccd, set_active_mode, SavedConfig,
@@ -554,7 +554,6 @@ fn mgr_acquire(mode: Mode) -> Result<VirtualOutput> {
         let pm = Some((mon.mode.width, mon.mode.height, mon.mode.refresh_hz));
         let target = mon.target();
         let gen = mon.gen;
-        CURRENT_MON_GEN.store(gen, Ordering::Relaxed);
         return Ok(VirtualOutput {
             node_id: 0,
             preferred_mode: pm,
@@ -581,7 +580,6 @@ fn mgr_acquire(mode: Mode) -> Result<VirtualOutput> {
     let pm = Some((mon.mode.width, mon.mode.height, mon.mode.refresh_hz));
     let target = mon.target();
     let gen = mon.gen;
-    CURRENT_MON_GEN.store(gen, Ordering::Relaxed);
     g.state = MgrState::Active { mon, refs: 1 };
     Ok(VirtualOutput {
         node_id: 0,

crates/punktfunk-host/src/vdisplay/windows/sudovda.rs

@@ -19,12 +19,6 @@ use std::sync::{Arc, Mutex, Once};
 // backends keeps the idd_push stale-ring bail working regardless of which backend is active).
 pub(crate) static MON_GEN: AtomicU64 = AtomicU64::new(1);
 
-/// The gen of the CURRENTLY-active monitor. A session capturer captures this at open and re-checks it
-/// each frame; when it changes (a reconnect preempted + recreated the monitor), the old session bails
-/// IMMEDIATELY instead of lingering on the dead ring's 20s frame deadline — which would otherwise hold
-/// its NVENC encoder open and exhaust the GPU's encode-session limit under rapid reconnects.
-pub(crate) static CURRENT_MON_GEN: AtomicU64 = AtomicU64::new(0);
-
 /// IDD-push mode: a new client connection preempts + recreates the monitor (single-client reconnect),
 /// because a REUSED IddCx monitor's swap-chain is dead. Off → monitors are shared across sessions.
 fn idd_push_mode() -> bool {
@@ -590,7 +584,6 @@ fn mgr_acquire(mode: Mode) -> Result<VirtualOutput> {
         let pm = Some((mon.mode.width, mon.mode.height, mon.mode.refresh_hz));
         let target = mon.target();
         let gen = mon.gen;
-        CURRENT_MON_GEN.store(gen, Ordering::Relaxed);
         return Ok(VirtualOutput {
             node_id: 0,
             preferred_mode: pm,
@@ -617,7 +610,6 @@ fn mgr_acquire(mode: Mode) -> Result<VirtualOutput> {
     let pm = Some((mon.mode.width, mon.mode.height, mon.mode.refresh_hz));
     let target = mon.target();
     let gen = mon.gen;
-    CURRENT_MON_GEN.store(gen, Ordering::Relaxed);
     g.state = MgrState::Active { mon, refs: 1 };
     Ok(VirtualOutput {
         node_id: 0,