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/StreamHUDView.swift

@@ -65,7 +65,9 @@ struct StreamHUDView: View {
     private var compactLine: String {
         var parts = ["\(model.fps) fps"]
         if model.endToEndValid {
-            parts.append(String(format: "%.1f ms", model.endToEndP50Ms))
+            // Floor-shaved (design/apple-presentation-rebuild.md): the OS present pipeline's
+            // fixed depth is excluded, so the headline describes Punktfunk's own latency.
+            parts.append(String(format: "%.1f ms", model.endToEndAdjP50Ms))
         } else if model.hostNetworkValid {
             parts.append(String(format: "%.1f ms", model.hostNetworkP50Ms))
         }
@@ -86,24 +88,36 @@ struct StreamHUDView: View {
             }
             if model.endToEndValid {
                 // Stage-2: the end-to-end headline (capture→on-glass, measured directly, skew-
-                // corrected) — "(same-host clock)" when the host didn't answer the skew handshake.
-                Text("end-to-end \(model.endToEndP50Ms, specifier: "%.1f") ms p50 · \(model.endToEndP95Ms, specifier: "%.1f") p95 · capture→on-glass\(model.endToEndSkewCorrected ? "" : " (same-host clock)")")
+                // corrected) — "(same-host clock)" when the host didn't answer the skew
+                // handshake. FLOOR-SHAVED (design/apple-presentation-rebuild.md): the OS present
+                // pipeline's fixed depth is excluded so the number describes Punktfunk's own
+                // latency; the detailed tier shows the excluded floor as its own line, and the
+                // stats log keeps the raw values.
+                Text("end-to-end \(model.endToEndAdjP50Ms, specifier: "%.1f") ms p50 · \(model.endToEndAdjP95Ms, specifier: "%.1f") p95 · capture→on-glass\(model.endToEndSkewCorrected ? "" : " (same-host clock)")")
                     .font(.system(.caption2, design: .monospaced))
                     .foregroundStyle(.secondary)
                 // The equation (detailed tier only): the stages tiling the headline interval
                 // (per-window p50s — they only approximately sum to the directly-measured
                 // total). With a host that reports per-AU timings (0xCF) the first term splits
-                // into host + network (phase 2); an old host keeps the combined term.
+                // into host + network (phase 2); an old host keeps the combined term. The
+                // display term is floor-shaved like the headline, so the equation still sums.
                 if verbosity == .detailed && model.hostNetworkValid && model.decodeValid && model.displayValid {
                     if model.splitValid {
-                        Text("= host \(model.hostP50Ms, specifier: "%.1f") + network \(model.networkP50Ms, specifier: "%.1f") + decode \(model.decodeP50Ms, specifier: "%.1f") + display \(model.displayP50Ms, specifier: "%.1f")")
+                        Text("= host \(model.hostP50Ms, specifier: "%.1f") + network \(model.networkP50Ms, specifier: "%.1f") + decode \(model.decodeP50Ms, specifier: "%.1f") + display \(model.displayAdjP50Ms, specifier: "%.1f")")
                             .font(.system(.caption2, design: .monospaced))
                             .foregroundStyle(.secondary)
                     } else {
-                        Text("= host+network \(model.hostNetworkP50Ms, specifier: "%.1f") + decode \(model.decodeP50Ms, specifier: "%.1f") + display \(model.displayP50Ms, specifier: "%.1f")")
+                        Text("= host+network \(model.hostNetworkP50Ms, specifier: "%.1f") + decode \(model.decodeP50Ms, specifier: "%.1f") + display \(model.displayAdjP50Ms, specifier: "%.1f")")
                             .font(.system(.caption2, design: .monospaced))
                             .foregroundStyle(.secondary)
                     }
+                    if model.osFloorValid {
+                        // The excluded OS term, kept visible for honesty: display-pipeline
+                        // minimum no client can pace under (~2 refresh intervals composited).
+                        Text("os present +\(model.osFloorP50Ms, specifier: "%.1f") excluded (display pipeline minimum)")
+                            .font(.system(.caption2, design: .monospaced))
+                            .foregroundStyle(.tertiary)
+                    }
                 }
             } else if model.hostNetworkValid {
                 // Stage-1 fallback presenter: the layer decodes + presents internally with no