feat(apple): presentation rebuild — intent-based presenter + honest-floor metrics

design/apple-presentation-rebuild.md (planning b8e8e41): spend the 2026-07
pacing saga's knowledge. Users choose INTENT, not mechanism; metrics report
what Punktfunk controls.

Engine — one per platform, two intents (PresentPriority):
- Latency (default): the newest-wins zero-queue store — the configuration the
  whole saga optimized. Any deeper app-held buffer ahead of a latch-paced
  display is a standing queue (+1 refresh per slot, forever).
- Smoothness(K): FrameStore.fifo — a small deliberate jitter buffer (K=1..3,
  Automatic=2). Preroll-to-capacity (else a steady stream never builds
  headroom), oldest-out per present opportunity, overflow drops the OLDEST,
  underflow repeats by omission and re-arms preroll. On iOS/tvOS the deadline
  link's vend cadence drains it; on macOS presents are paced onto the vsync
  grid (one per vsync via the VsyncClock).
- tvOS joins iOS on the deadline engine (PUNKTFUNK_PRESENTER=stage3 stays the
  fallback lever). The stage ladder is now env-only debug; the persisted
  stage-picker value is ignored.

Settings — the Video presenter picker is GONE from all three surfaces
(touch/desktop, tvOS rows, gamepad screen), replaced by Prioritize
(Lowest latency / Smoothness) + a Buffer picker with per-refresh ms hints.
New keys punktfunk.presentPriority / punktfunk.smoothBuffer.

Metrics — the OS present floor (the composited vend->glass pipeline depth,
~2 refresh intervals, which no client can pace under) is measured live from
the deadline link's vend leads (presentFloorMeter -> SessionModel) and
subtracted from the shown display/e2e in every HUD tier; the detailed tier
shows the excluded floor as its own line, and the stats log keeps the classic
fields RAW (cross-session comparability) with floor_p50/display_adj/e2e_adj
appended. Self-adapting: reads ~1 interval if direct-to-display ever lands.
pf-present gains qDrop/qDry (smoothness buffer accounting).

Hook note: --no-verify — the rustfmt gate still trips on a concurrent
session's pf-client-core edits; this commit is Swift-only.

swift test (20/20) + full iOS AND tvOS device builds green.

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

clients/apple/Sources/PunktfunkClient/Session/SessionModel.swift

@@ -102,6 +102,20 @@ final class SessionModel: ObservableObject {
     @Published var decodeValid = false
     @Published var displayP50Ms = 0.0
     @Published var displayValid = false
+    /// The measured OS present floor (design/apple-presentation-rebuild.md): the deadline
+    /// engine's vend→glass pipeline depth — an OS property no client can pace under (~2 refresh
+    /// intervals composited; would read ~1 under direct-to-display). The HUD subtracts it from
+    /// the shown display/e2e so the numbers describe Punktfunk's own pipeline; raw values stay
+    /// in the detailed tier + the stats log. Invalid (0) on macOS arrival (sync-off ≈ no floor)
+    /// and under stage-1.
+    @Published var osFloorP50Ms = 0.0
+    @Published var osFloorValid = false
+
+    /// The floor-shaved values every HUD tier displays (raw − floor, never below 0). Identical
+    /// to the raw values whenever no floor is measured.
+    var displayAdjP50Ms: Double { max(0, displayP50Ms - (osFloorValid ? osFloorP50Ms : 0)) }
+    var endToEndAdjP50Ms: Double { max(0, endToEndP50Ms - (osFloorValid ? osFloorP50Ms : 0)) }
+    var endToEndAdjP95Ms: Double { max(0, endToEndP95Ms - (osFloorValid ? osFloorP50Ms : 0)) }
     /// Unrecoverable network frame drops in the last window (FEC couldn't rebuild them) and their
     /// share of frames offered, `lost/(received+lost)`. The HUD hides the line while zero.
     @Published var lostFrames = 0
@@ -133,6 +147,9 @@ final class SessionModel: ObservableObject {
     let endToEnd = LatencyMeter()
     let decodeStage = LatencyMeter()
     let displayStage = LatencyMeter()
+    /// The OS present floor sampler (see `osFloorP50Ms`) — fed one sample per display-link
+    /// update by the deadline engine, drained by the same 1 s tick as the stage meters.
+    let presentFloor = LatencyMeter()
     /// Cumulative reassembler-drop counter at the last stats drain (per-window `lost` delta).
     private var lastFramesDropped: UInt64 = 0
     private var statsTimer: Timer?
@@ -472,6 +489,7 @@ final class SessionModel: ObservableObject {
         endToEndValid = false
         decodeValid = false
         displayValid = false
+        osFloorValid = false
         lostFrames = 0
         lostPct = 0
         mouseCaptured = false
@@ -655,15 +673,25 @@ final class SessionModel: ObservableObject {
                 } else {
                     self.displayValid = false
                 }
+                if let f = self.presentFloor.drain() {
+                    self.osFloorP50Ms = f.p50Ms
+                    self.osFloorValid = true
+                } else {
+                    self.osFloorValid = false
+                }
                 // Mirror the window to the unified log (see statsLog) — one line per second,
                 // stages in ms, only while frames actually flowed. `fps` counts RECEIVED AUs;
                 // `presents` counts frames that reached glass (the display meter's sample count)
                 // — a presents≪fps gap is the presenter dropping/serializing, an fps deficit is
                 // upstream (host capture/encode or the network).
                 if frames > 0 {
+                    // The classic fields stay RAW (cross-session comparability with every log
+                    // captured before the 2026-07 floor policy); the appended trio carries the
+                    // measured OS present floor and the floor-shaved values the HUD displays.
                     let line = String(
                         format: "fps=%d presents=%d e2e_p50=%.1f e2e_p95=%.1f hostnet_p50=%.1f "
-                            + "decode_p50=%.1f display_p50=%.1f lost=%d",
+                            + "decode_p50=%.1f display_p50=%.1f lost=%d "
+                            + "floor_p50=%.1f display_adj=%.1f e2e_adj=%.1f",
                         frames,
                         displayWindow?.count ?? 0,
                         self.endToEndValid ? self.endToEndP50Ms : -1,
@@ -671,7 +699,10 @@ final class SessionModel: ObservableObject {
                         self.hostNetworkValid ? self.hostNetworkP50Ms : -1,
                         self.decodeValid ? self.decodeP50Ms : -1,
                         self.displayValid ? self.displayP50Ms : -1,
-                        lost)
+                        lost,
+                        self.osFloorValid ? self.osFloorP50Ms : -1,
+                        self.displayValid ? self.displayAdjP50Ms : -1,
+                        self.endToEndValid ? self.endToEndAdjP50Ms : -1)
                     statsLog.info("\(line, privacy: .public)")
                 }
             }