feat(session): Skia console UI — overlay contract + stats OSD/capture HUD (phase 4a)

The §6.1 presenter↔console-UI contract lands: pf-presenter exposes its
device (SharedDevice) and composites at most one premultiplied-alpha
quad per frame (new overlay.frag + LOAD render pass over the swapchain;
zero cost while the overlay returns None). pf-console-ui implements it
with skia-safe on the shared VkDevice: DirectContext via the ash
dispatch chain, a ring of two offscreen render targets (one-frame-in-
flight safe), damage-driven redraws — the OSD re-renders at 1 Hz, the
hint on capture toggles, nothing per-frame. Skia never touches the
swapchain. The session binary carries it behind the default ui feature:
4.9 MB stripped without, 10 MB with (measured).

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

clients/linux-session/Cargo.toml

@@ -12,9 +12,17 @@ repository.workspace = true
 name = "punktfunk-session"
 path = "src/main.rs"
 
+[features]
+default = ["ui"]
+# The Skia console UI (stats OSD, capture HUD, later the gamepad library). Dropping it
+# (`--no-default-features`) is the ~15 MB-smaller power-user build: same streaming,
+# stats on stdout only.
+ui = ["dep:pf-console-ui"]
+
 # Same Linux gating as the rest of the client stack; elsewhere this is a stub binary.
 [target.'cfg(target_os = "linux")'.dependencies]
 pf-presenter = { path = "../../crates/pf-presenter" }
+pf-console-ui = { path = "../../crates/pf-console-ui", optional = true }
 pf-client-core = { path = "../../crates/pf-client-core" }
 punktfunk-core = { path = "../../crates/punktfunk-core", features = ["quic"] }
 anyhow = "1"

clients/linux-session/README.md

@@ -23,6 +23,11 @@ In-stream keys match the desktop client: click captures input (Ctrl+Alt+Shift+Q
 releases), Ctrl+Alt+Shift+D disconnects, F11 toggles fullscreen; the controller escape
 chord (L1+R1+Start+Select, hold to disconnect) works the same.
 
+The default build carries the Skia console UI (`ui` feature): the stats OSD and capture
+hint render in-window (Ctrl+Alt+Shift+S toggles both the OSD and the stdout mirror).
+`--no-default-features` is the ~5 MB power-user build — same streaming, stats on stdout
+only, no Skia anywhere in the dependency tree.
+
 Decode follows the Settings preference: VAAPI frames import zero-copy into Vulkan
 (per-plane dmabuf + the stream's CICP-driven CSC shader); boxes whose driver can't
 import (NVIDIA proprietary by design) fall back to software decode automatically.

clients/linux-session/src/main.rs

@@ -152,6 +152,12 @@ mod session_main {
                 // This host's card carries the accent bar in the desktop client now.
                 trust::touch_last_used(&trust::hex(&fingerprint));
             })),
+            // The Skia console UI (stats OSD, capture HUD) — compiled out of the
+            // power-user build (`--no-default-features` drops the `ui` feature).
+            #[cfg(feature = "ui")]
+            overlay: Some(Box::new(pf_console_ui::SkiaOverlay::new())),
+            #[cfg(not(feature = "ui"))]
+            overlay: None,
         };
 
         let outcome = pf_presenter::run_session(opts, move |gamepad, native, force_software| {