refactor(core): split quic.rs (3.2k lines) into src/quic/ — pure move

Networking-audit deferred plan §3. One file per concern, zero logic edits:

  quic/mod.rs      MAGIC/CTL_MAGIC + re-exports (every crate::quic::X path
                   compiles unchanged across host + all clients)
  quic/msgs.rs     Hello/Welcome/Start, typed control msgs + type bytes,
                   resolve_codec, ColorInfo, window_loss_ppm, pairing msgs
  quic/pake.rs     the SPAKE2 pairing exchange
  quic/datagram.rs 0xC9–0xCF plane codecs (audio/rumble/mic/rich-input/
                   hidout/HdrMeta/HostTiming)
  quic/io.rs       length-prefixed stream IO
  quic/clock.rs    clock_offset_ns estimator, clock_sync, ClockResync
  quic/endpoint.rs quinn config, ALPN, pinning verifiers, keep-alive
  quic/tests.rs    the cross-cutting test module, unchanged

Mechanical deltas only: the nested `pub mod` wrappers became files (one
dedent), submodules import what they previously inherited from the parent
scope, and the three RichInput kind tags are pub(super) for the tests
(same-module before). Verified line-multiset-identical after normalizing
indentation. cargo check --workspace, core tests (quic), clippy, and
cargo ndk check all green.

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

crates/punktfunk-core/src/quic/clock.rs

@@ -0,0 +1,155 @@
+//! Wall-clock skew: the connect-time handshake ([`clock_sync`]), the NTP-style offset
+//! estimator ([`clock_offset_ns`]), and the mid-stream re-sync state machine
+//! ([`ClockResync`]).
+
+use super::{io, ClockEcho, ClockProbe};
+
+/// Estimate the host↔client clock offset (**host minus client**, ns) and RTT (ns) from skew-handshake
+/// samples `(t1, t2, t3, t4)` — NTP's formula, taking the **minimum-RTT** sample (least queuing
+/// noise; also discards the first round's host-setup latency). Offset is positive when the host
+/// clock is ahead of the client's; add it to a client timestamp to express it in the host clock.
+/// Returns `None` for an empty sample set.
+pub fn clock_offset_ns(samples: &[(u64, u64, u64, u64)]) -> Option<(i64, u64)> {
+    samples
+        .iter()
+        .map(|&(t1, t2, t3, t4)| {
+            let rtt = ((t4 as i128 - t1 as i128) - (t3 as i128 - t2 as i128)).max(0) as u64;
+            let offset = (((t2 as i128 - t1 as i128) + (t3 as i128 - t4 as i128)) / 2) as i64;
+            (offset, rtt)
+        })
+        .min_by_key(|&(_, rtt)| rtt)
+}
+
+/// One wall-clock skew-handshake outcome (see [`clock_sync`]).
+pub struct ClockSkew {
+    /// Host clock minus client clock, ns: add it to a client timestamp to express it in host time.
+    pub offset_ns: i64,
+    /// Round-trip time of the minimum-RTT sample, ns.
+    pub rtt_ns: u64,
+    /// How many probe rounds the host answered.
+    pub rounds: usize,
+}
+
+/// Run the wall-clock skew handshake from the client side over the (already-open) control stream:
+/// `ROUNDS` [`ClockProbe`]/[`ClockEcho`] round-trips, returning the host↔client offset from the
+/// minimum-RTT sample. `None` if the host never answers (an old host) — the caller then assumes a
+/// shared clock. Each read is bounded so a silent host can't wedge session start. Shared by the
+/// reference client and the embeddable connector; uses the realtime clock the host stamps `pts_ns`
+/// with, so the offset aligns a client receive instant to the host's capture clock.
+pub async fn clock_sync(
+    send: &mut quinn::SendStream,
+    recv: &mut quinn::RecvStream,
+) -> Option<ClockSkew> {
+    use std::time::Duration;
+    const ROUNDS: usize = 8;
+    let read_timeout = Duration::from_secs(2);
+    let mut samples: Vec<(u64, u64, u64, u64)> = Vec::with_capacity(ROUNDS);
+    for _ in 0..ROUNDS {
+        let t1 = wall_clock_ns();
+        let probe = ClockProbe { t1_ns: t1 }.encode();
+        if io::write_msg(send, &probe).await.is_err() {
+            break;
+        }
+        let read = tokio::time::timeout(read_timeout, io::read_msg(recv)).await;
+        let echo = match read {
+            Ok(Ok(b)) => match ClockEcho::decode(&b) {
+                Ok(e) => e,
+                Err(_) => break,
+            },
+            _ => break, // timeout or stream error -> old host / no skew support
+        };
+        samples.push((echo.t1_ns, echo.t2_ns, echo.t3_ns, wall_clock_ns()));
+    }
+    clock_offset_ns(&samples).map(|(offset_ns, rtt_ns)| ClockSkew {
+        offset_ns,
+        rtt_ns,
+        rounds: samples.len(),
+    })
+}
+
+/// Wall-clock now (ns since the Unix epoch) — the clock the skew handshake stamps and the host
+/// stamps AU `pts_ns` with (CLOCK_REALTIME basis, deliberately NOT monotonic: steps/slew are
+/// exactly what the handshake measures across machines).
+pub fn wall_clock_ns() -> u64 {
+    std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .map(|d| d.as_nanos() as u64)
+        .unwrap_or(0)
+}
+
+/// What [`ClockResync::on_echo`] asks the driver to do next.
+#[derive(Debug, PartialEq, Eq)]
+pub enum ResyncStep {
+    /// Nothing — the echo was stale (a previous batch) or no batch is in flight.
+    Idle,
+    /// Send this next-round probe and keep feeding echoes.
+    Probe(ClockProbe),
+    /// The batch is complete: the min-RTT estimate over its rounds, per [`clock_offset_ns`].
+    Done { offset_ns: i64, rtt_ns: u64 },
+}
+
+/// Mid-stream wall-clock re-sync (networking-audit deferred plan §2): the same 8-round
+/// probe/echo estimate as the connect-time [`clock_sync`], restructured as a state machine so
+/// the client's control task can drive it from its `select!` loop without blocking the stream —
+/// echoes interleave with other control traffic; rounds are matched by the echoed `t1`.
+///
+/// A step or slow drift of either wall clock after connect silently corrupts the clock-based
+/// jump-to-live signal, the ABR one-way-delay signal, and every latency stat. Re-syncing
+/// restores them; the disarm heuristic stays as the final backstop.
+pub struct ClockResync {
+    /// `t1_ns` of the probe in flight; `None` = no batch active. An echo whose `t1` doesn't
+    /// match is stale (an abandoned batch) and ignored.
+    pending_t1: Option<u64>,
+    samples: Vec<(u64, u64, u64, u64)>,
+}
+
+impl ClockResync {
+    /// Rounds per batch — matches the connect-time [`clock_sync`].
+    pub const ROUNDS: usize = 8;
+
+    pub fn new() -> ClockResync {
+        ClockResync {
+            pending_t1: None,
+            samples: Vec::with_capacity(Self::ROUNDS),
+        }
+    }
+
+    /// Start a (new) batch, abandoning any batch still in flight — its late echoes won't match
+    /// `pending_t1` and get ignored. Returns the first probe to send, stamped `now_ns`.
+    pub fn begin(&mut self, now_ns: u64) -> ClockProbe {
+        self.samples.clear();
+        self.pending_t1 = Some(now_ns);
+        ClockProbe { t1_ns: now_ns }
+    }
+
+    /// Feed an inbound [`ClockEcho`] received at `now_ns` (the round's `t4`).
+    pub fn on_echo(&mut self, echo: &ClockEcho, now_ns: u64) -> ResyncStep {
+        if self.pending_t1 != Some(echo.t1_ns) {
+            return ResyncStep::Idle; // stale (abandoned batch) or unsolicited
+        }
+        self.samples.push((echo.t1_ns, echo.t2_ns, echo.t3_ns, now_ns));
+        if self.samples.len() < Self::ROUNDS {
+            self.pending_t1 = Some(now_ns);
+            return ResyncStep::Probe(ClockProbe { t1_ns: now_ns });
+        }
+        self.pending_t1 = None;
+        match clock_offset_ns(&self.samples) {
+            Some((offset_ns, rtt_ns)) => ResyncStep::Done { offset_ns, rtt_ns },
+            None => ResyncStep::Idle, // unreachable: ROUNDS > 0 samples were just collected
+        }
+    }
+}
+
+impl Default for ClockResync {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+/// Acceptance guard for a re-sync batch: apply the new offset only when its min RTT is
+/// comparable to the connect-time RTT — `≤ max(2 ms, 1.5 × connect RTT)`. A congested window
+/// biases the offset by its queueing delay, and frames already read late exactly then; better
+/// to keep the old estimate and let the next batch try again.
+pub fn accept_resync(batch_rtt_ns: u64, connect_rtt_ns: u64) -> bool {
+    batch_rtt_ns <= (connect_rtt_ns + connect_rtt_ns / 2).max(2_000_000)
+}

crates/punktfunk-core/src/quic/datagram.rs

@@ -0,0 +1,418 @@
+//! The QUIC-datagram side planes, demultiplexed by their first byte (0xC9–0xCF):
+//! audio, rumble, mic uplink, rich input, HID output, HDR metadata, host timing.
+
+/// Datagram wire tags. Video rides UDP; everything low-rate rides QUIC datagrams,
+/// demultiplexed by the first byte: input = [`crate::input::INPUT_MAGIC`] (0xC8, client→host),
+/// audio = [`AUDIO_MAGIC`] (0xC9, host→client), rumble = [`RUMBLE_MAGIC`] (0xCA, host→client),
+/// mic = [`MIC_MAGIC`] (0xCB, client→host), rich-input = [`RICH_INPUT_MAGIC`] (0xCC, client→host),
+/// HID-output = [`HIDOUT_MAGIC`] (0xCD, host→client), HDR metadata = [`HDR_META_MAGIC`]
+/// (0xCE, host→client).
+pub const AUDIO_MAGIC: u8 = 0xC9;
+pub const RUMBLE_MAGIC: u8 = 0xCA;
+/// Microphone uplink: the client's mic, Opus-encoded, client → host (the inverse of
+/// [`AUDIO_MAGIC`]). The host feeds it into a virtual PipeWire source so its apps can record it.
+pub const MIC_MAGIC: u8 = 0xCB;
+/// Rich client→host input: events too big for the fixed 18-byte [`InputEvent`]
+/// (crate::input::InputEvent) — the DualSense touchpad and motion sensors. Variable-length,
+/// kind-tagged (see [`RichInput`]).
+pub const RICH_INPUT_MAGIC: u8 = 0xCC;
+/// HID output, host → client: DualSense feedback a game wrote to the host's virtual controller
+/// (lightbar, player LEDs, adaptive triggers) — the rich analog of [`RUMBLE_MAGIC`]. See
+/// [`HidOutput`].
+pub const HIDOUT_MAGIC: u8 = 0xCD;
+
+/// Audio datagram, host → client: `[0xC9][u32 seq LE][u64 pts_ns LE][opus payload]`.
+/// One Opus frame per datagram (5 ms — well under any MTU); QUIC already encrypts.
+pub fn encode_audio_datagram(seq: u32, pts_ns: u64, opus: &[u8]) -> Vec<u8> {
+    let mut b = Vec::with_capacity(13 + opus.len());
+    b.push(AUDIO_MAGIC);
+    b.extend_from_slice(&seq.to_le_bytes());
+    b.extend_from_slice(&pts_ns.to_le_bytes());
+    b.extend_from_slice(opus);
+    b
+}
+
+/// Parse an audio datagram → `(seq, pts_ns, opus payload)`. `None` on bad tag/length.
+pub fn decode_audio_datagram(b: &[u8]) -> Option<(u32, u64, &[u8])> {
+    if b.len() < 13 || b[0] != AUDIO_MAGIC {
+        return None;
+    }
+    let seq = u32::from_le_bytes(b[1..5].try_into().unwrap());
+    let pts_ns = u64::from_le_bytes(b[5..13].try_into().unwrap());
+    Some((seq, pts_ns, &b[13..]))
+}
+
+/// Rumble datagram, host → client: `[0xCA][u16 pad LE][u16 low LE][u16 high LE]`.
+/// Force-feedback state for pad `pad` (0xFFFF amplitudes, 0/0 = stop).
+pub fn encode_rumble_datagram(pad: u16, low: u16, high: u16) -> [u8; 7] {
+    let mut b = [0u8; 7];
+    b[0] = RUMBLE_MAGIC;
+    b[1..3].copy_from_slice(&pad.to_le_bytes());
+    b[3..5].copy_from_slice(&low.to_le_bytes());
+    b[5..7].copy_from_slice(&high.to_le_bytes());
+    b
+}
+
+/// Parse a rumble datagram → `(pad, low, high)`. `None` on bad tag/length.
+pub fn decode_rumble_datagram(b: &[u8]) -> Option<(u16, u16, u16)> {
+    if b.len() < 7 || b[0] != RUMBLE_MAGIC {
+        return None;
+    }
+    let u16at = |o: usize| u16::from_le_bytes([b[o], b[o + 1]]);
+    Some((u16at(1), u16at(3), u16at(5)))
+}
+
+/// Mic datagram, client → host: `[0xCB][u32 seq LE][u64 pts_ns LE][opus payload]` — the same
+/// layout as [`encode_audio_datagram`] with [`MIC_MAGIC`], one Opus frame per datagram.
+pub fn encode_mic_datagram(seq: u32, pts_ns: u64, opus: &[u8]) -> Vec<u8> {
+    let mut b = Vec::with_capacity(13 + opus.len());
+    b.push(MIC_MAGIC);
+    b.extend_from_slice(&seq.to_le_bytes());
+    b.extend_from_slice(&pts_ns.to_le_bytes());
+    b.extend_from_slice(opus);
+    b
+}
+
+/// Parse a mic datagram → `(seq, pts_ns, opus payload)`. `None` on bad tag/length.
+pub fn decode_mic_datagram(b: &[u8]) -> Option<(u32, u64, &[u8])> {
+    if b.len() < 13 || b[0] != MIC_MAGIC {
+        return None;
+    }
+    let seq = u32::from_le_bytes(b[1..5].try_into().unwrap());
+    let pts_ns = u64::from_le_bytes(b[5..13].try_into().unwrap());
+    Some((seq, pts_ns, &b[13..]))
+}
+
+pub(super) const RICH_TOUCHPAD: u8 = 0x01;
+pub(super) const RICH_MOTION: u8 = 0x02;
+pub(super) const RICH_TOUCHPAD_EX: u8 = 0x03;
+
+/// A rich client→host controller input beyond the fixed [`InputEvent`](crate::input::InputEvent):
+/// the DualSense touchpad and motion sensors. `pad` is the gamepad index. Wire form is
+/// `[0xCC][kind][fields…]` — variable-length and kind-tagged (forward-compatible: an unknown
+/// kind decodes to `None` and is dropped).
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum RichInput {
+    /// One touchpad contact. `x`/`y` are normalized `0..=65535` in SCREEN convention —
+    /// origin top-left, +y DOWN, exactly what SDL/Windows/Android capture APIs produce
+    /// (the host scales to the DualSense touchpad resolution); `active = false` lifts
+    /// the finger.
+    Touchpad {
+        pad: u8,
+        finger: u8,
+        active: bool,
+        x: u16,
+        y: u16,
+    },
+    /// Motion sensors: `gyro` (pitch/yaw/roll) + `accel`, raw signed-16 in the sensor's own
+    /// units — passed straight into the DualSense report.
+    Motion {
+        pad: u8,
+        gyro: [i16; 3],
+        accel: [i16; 3],
+    },
+    /// A richer trackpad contact that also identifies *which* physical pad (Steam Controller / Deck
+    /// have two), carries a separate click vs touch state, and a pressure reading. `surface`:
+    /// `0` = the single / DualSense touchpad, `1` = the Steam left pad, `2` = the Steam right pad.
+    /// Coordinates are **signed** (centred at 0) in SCREEN convention — +x right, +y DOWN,
+    /// what every client capture API produces. Device-raw quirks are the HOST applier's job
+    /// (the Deck report is +y up: `steam_proto` flips it — the first live session shipped
+    /// clients that sent screen-y straight through, so the wire meaning is fixed as screen-y
+    /// and hosts translate). `pressure` is `0` for a surface with no force sensor. New clients
+    /// send this for every touch surface; the host decodes both `Touchpad` (`0x01`) and
+    /// `TouchpadEx` (`0x03`) indefinitely.
+    TouchpadEx {
+        pad: u8,
+        surface: u8,
+        finger: u8,
+        touch: bool,
+        click: bool,
+        x: i16,
+        y: i16,
+        pressure: u16,
+    },
+}
+
+impl RichInput {
+    pub fn encode(&self) -> Vec<u8> {
+        let mut out = vec![RICH_INPUT_MAGIC];
+        match *self {
+            RichInput::Touchpad {
+                pad,
+                finger,
+                active,
+                x,
+                y,
+            } => {
+                out.extend_from_slice(&[RICH_TOUCHPAD, pad, finger, active as u8]);
+                out.extend_from_slice(&x.to_le_bytes());
+                out.extend_from_slice(&y.to_le_bytes());
+            }
+            RichInput::Motion { pad, gyro, accel } => {
+                out.extend_from_slice(&[RICH_MOTION, pad]);
+                for v in gyro.iter().chain(accel.iter()) {
+                    out.extend_from_slice(&v.to_le_bytes());
+                }
+            }
+            RichInput::TouchpadEx {
+                pad,
+                surface,
+                finger,
+                touch,
+                click,
+                x,
+                y,
+                pressure,
+            } => {
+                let state = (touch as u8) | ((click as u8) << 1);
+                out.extend_from_slice(&[RICH_TOUCHPAD_EX, pad, surface, finger, state]);
+                out.extend_from_slice(&x.to_le_bytes());
+                out.extend_from_slice(&y.to_le_bytes());
+                out.extend_from_slice(&pressure.to_le_bytes());
+            }
+        }
+        out
+    }
+
+    pub fn decode(b: &[u8]) -> Option<RichInput> {
+        if b.first() != Some(&RICH_INPUT_MAGIC) {
+            return None;
+        }
+        match *b.get(1)? {
+            RICH_TOUCHPAD if b.len() >= 9 => Some(RichInput::Touchpad {
+                pad: b[2],
+                finger: b[3],
+                active: b[4] != 0,
+                x: u16::from_le_bytes([b[5], b[6]]),
+                y: u16::from_le_bytes([b[7], b[8]]),
+            }),
+            RICH_MOTION if b.len() >= 15 => {
+                let i16at = |o: usize| i16::from_le_bytes([b[o], b[o + 1]]);
+                Some(RichInput::Motion {
+                    pad: b[2],
+                    gyro: [i16at(3), i16at(5), i16at(7)],
+                    accel: [i16at(9), i16at(11), i16at(13)],
+                })
+            }
+            RICH_TOUCHPAD_EX if b.len() >= 12 => Some(RichInput::TouchpadEx {
+                pad: b[2],
+                surface: b[3],
+                finger: b[4],
+                touch: b[5] & 0x01 != 0,
+                click: b[5] & 0x02 != 0,
+                x: i16::from_le_bytes([b[6], b[7]]),
+                y: i16::from_le_bytes([b[8], b[9]]),
+                pressure: u16::from_le_bytes([b[10], b[11]]),
+            }),
+            _ => None,
+        }
+    }
+}
+
+const HIDOUT_LED: u8 = 0x01;
+const HIDOUT_PLAYER_LEDS: u8 = 0x02;
+const HIDOUT_TRIGGER: u8 = 0x03;
+const HIDOUT_TRACKPAD_HAPTIC: u8 = 0x04;
+
+/// DualSense feedback flowing host → client (what a game wrote to the host's virtual pad).
+/// Wire form `[0xCD][kind][pad][fields…]`. The rich analog of the fixed rumble datagram;
+/// rumble itself stays on [`RUMBLE_MAGIC`].
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum HidOutput {
+    /// Lightbar RGB.
+    Led { pad: u8, r: u8, g: u8, b: u8 },
+    /// Player-indicator LEDs (low 5 bits).
+    PlayerLeds { pad: u8, bits: u8 },
+    /// One adaptive-trigger effect: `which` 0 = L2, 1 = R2; `effect` is the raw DualSense
+    /// trigger parameter block (mode + params) for the client to replay on a real controller.
+    Trigger { pad: u8, which: u8, effect: Vec<u8> },
+    /// A trackpad haptic pulse for a Steam Controller's voice-coil actuators (its only "rumble").
+    /// `side` 0 = right pad, 1 = left pad; `amplitude` + `period` (µs off-time) + `count` (pulses)
+    /// synthesize a buzz. A client without trackpad coils drops it (or maps it to ordinary rumble).
+    TrackpadHaptic {
+        pad: u8,
+        side: u8,
+        amplitude: u16,
+        period: u16,
+        count: u16,
+    },
+}
+
+impl HidOutput {
+    pub fn encode(&self) -> Vec<u8> {
+        let mut out = vec![HIDOUT_MAGIC];
+        match self {
+            HidOutput::Led { pad, r, g, b } => {
+                out.extend_from_slice(&[HIDOUT_LED, *pad, *r, *g, *b])
+            }
+            HidOutput::PlayerLeds { pad, bits } => {
+                out.extend_from_slice(&[HIDOUT_PLAYER_LEDS, *pad, *bits])
+            }
+            HidOutput::Trigger { pad, which, effect } => {
+                out.extend_from_slice(&[HIDOUT_TRIGGER, *pad, *which]);
+                out.extend_from_slice(effect);
+            }
+            HidOutput::TrackpadHaptic {
+                pad,
+                side,
+                amplitude,
+                period,
+                count,
+            } => {
+                out.extend_from_slice(&[HIDOUT_TRACKPAD_HAPTIC, *pad, *side]);
+                out.extend_from_slice(&amplitude.to_le_bytes());
+                out.extend_from_slice(&period.to_le_bytes());
+                out.extend_from_slice(&count.to_le_bytes());
+            }
+        }
+        out
+    }
+
+    pub fn decode(b: &[u8]) -> Option<HidOutput> {
+        if b.first() != Some(&HIDOUT_MAGIC) {
+            return None;
+        }
+        match *b.get(1)? {
+            HIDOUT_LED if b.len() >= 6 => Some(HidOutput::Led {
+                pad: b[2],
+                r: b[3],
+                g: b[4],
+                b: b[5],
+            }),
+            HIDOUT_PLAYER_LEDS if b.len() >= 4 => Some(HidOutput::PlayerLeds {
+                pad: b[2],
+                bits: b[3],
+            }),
+            HIDOUT_TRIGGER if b.len() >= 4 => Some(HidOutput::Trigger {
+                pad: b[2],
+                which: b[3],
+                effect: b[4..].to_vec(),
+            }),
+            HIDOUT_TRACKPAD_HAPTIC if b.len() >= 10 => Some(HidOutput::TrackpadHaptic {
+                pad: b[2],
+                side: b[3],
+                amplitude: u16::from_le_bytes([b[4], b[5]]),
+                period: u16::from_le_bytes([b[6], b[7]]),
+                count: u16::from_le_bytes([b[8], b[9]]),
+            }),
+            _ => None,
+        }
+    }
+}
+
+/// Static HDR metadata, host → client: SMPTE ST.2086 mastering display colour volume + CEA-861.3
+/// content light level. Tag [`HDR_META_MAGIC`]. Carried on a datagram (not [`Welcome`]) because it
+/// is larger and can change mid-stream when the source's mastering intent changes; the host
+/// re-sends it on keyframes so a client that dropped the best-effort datagram converges. Omitted
+/// for HLG (scene-referred — no mastering metadata).
+///
+/// All fields use the standard HDR10 SEI fixed-point units, so they pass straight to
+/// `DXGI_HDR_METADATA_HDR10` / Android `KEY_HDR_STATIC_INFO` / Apple `CAEDRMetadata` — the
+/// libavcodec `AVMasteringDisplayMetadata` side needs an `AVRational` conversion.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Default)]
+pub struct HdrMeta {
+    /// Display primaries G, B, R as (x, y) chromaticity in 1/50000 units (the ST.2086 RGB order
+    /// is G, B, R).
+    pub display_primaries: [[u16; 2]; 3],
+    /// White point (x, y) in 1/50000 units.
+    pub white_point: [u16; 2],
+    /// Max display mastering luminance, 0.0001 cd/m² units.
+    pub max_display_mastering_luminance: u32,
+    /// Min display mastering luminance, 0.0001 cd/m² units.
+    pub min_display_mastering_luminance: u32,
+    /// Maximum content light level (MaxCLL), nits. `0` = unknown.
+    pub max_cll: u16,
+    /// Maximum frame-average light level (MaxFALL), nits. `0` = unknown.
+    pub max_fall: u16,
+}
+
+/// HDR static-metadata datagram tag, host → client (the static analog of the per-frame VUI;
+/// see [`HdrMeta`]). Next tag after [`HIDOUT_MAGIC`].
+pub const HDR_META_MAGIC: u8 = 0xCE;
+
+/// Wire length of an [`HDR_META_MAGIC`] datagram: tag + 6×u16 primaries + 2×u16 white + 2×u32
+/// luminance + 2×u16 CLL/FALL = 29 bytes.
+const HDR_META_LEN: usize = 1 + 12 + 4 + 8 + 4;
+
+/// Encode an [`HdrMeta`] into a [`HDR_META_MAGIC`] datagram.
+pub fn encode_hdr_meta_datagram(m: &HdrMeta) -> Vec<u8> {
+    let mut b = Vec::with_capacity(HDR_META_LEN);
+    b.push(HDR_META_MAGIC);
+    for p in m.display_primaries.iter() {
+        b.extend_from_slice(&p[0].to_le_bytes());
+        b.extend_from_slice(&p[1].to_le_bytes());
+    }
+    b.extend_from_slice(&m.white_point[0].to_le_bytes());
+    b.extend_from_slice(&m.white_point[1].to_le_bytes());
+    b.extend_from_slice(&m.max_display_mastering_luminance.to_le_bytes());
+    b.extend_from_slice(&m.min_display_mastering_luminance.to_le_bytes());
+    b.extend_from_slice(&m.max_cll.to_le_bytes());
+    b.extend_from_slice(&m.max_fall.to_le_bytes());
+    b
+}
+
+/// Parse a [`HDR_META_MAGIC`] datagram → [`HdrMeta`]. `None` on bad tag or a short/truncated buffer
+/// (every attacker-controlled field is bounds-checked by the fixed length before any read).
+pub fn decode_hdr_meta_datagram(b: &[u8]) -> Option<HdrMeta> {
+    if b.len() < HDR_META_LEN || b[0] != HDR_META_MAGIC {
+        return None;
+    }
+    let u16at = |o: usize| u16::from_le_bytes([b[o], b[o + 1]]);
+    let u32at = |o: usize| u32::from_le_bytes([b[o], b[o + 1], b[o + 2], b[o + 3]]);
+    Some(HdrMeta {
+        display_primaries: [
+            [u16at(1), u16at(3)],
+            [u16at(5), u16at(7)],
+            [u16at(9), u16at(11)],
+        ],
+        white_point: [u16at(13), u16at(15)],
+        max_display_mastering_luminance: u32at(17),
+        min_display_mastering_luminance: u32at(21),
+        max_cll: u16at(25),
+        max_fall: u16at(27),
+    })
+}
+
+/// Per-AU host-timing datagram tag, host → client (see [`HostTiming`]). Next tag after
+/// [`HDR_META_MAGIC`]. Emitted once per access unit, right after its last packet left the host's
+/// socket, and only when the client advertised [`VIDEO_CAP_HOST_TIMING`].
+pub const HOST_TIMING_MAGIC: u8 = 0xCF;
+
+/// One access unit's host-side processing time: capture → fully sent (the whole host pipeline —
+/// capture read/convert, encode, FEC+seal, paced send). The client correlates it to the AU by
+/// `pts_ns` (the AU's capture stamp, unique per frame) and derives
+/// `network = (received + clock_offset − pts_ns) − host_us`, so the unified-stats equation's
+/// `host+network` stage splits into two per-frame-tiling terms. Best-effort like every side-plane
+/// datagram: a lost 0xCF just means that frame contributes no host/network sample.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct HostTiming {
+    /// The AU's capture stamp (host capture clock — matches the AU's `pts_ns` exactly).
+    pub pts_ns: u64,
+    /// Host capture→sent duration, µs (saturated at `u32::MAX` ≈ 71 min — far past the 10 s
+    /// client-side sanity clamp anyway).
+    pub host_us: u32,
+}
+
+/// Wire length of a [`HOST_TIMING_MAGIC`] datagram: tag + u64 pts + u32 µs = 13 bytes.
+const HOST_TIMING_LEN: usize = 1 + 8 + 4;
+
+/// Encode a [`HostTiming`] into a [`HOST_TIMING_MAGIC`] datagram.
+pub fn encode_host_timing_datagram(t: &HostTiming) -> Vec<u8> {
+    let mut b = Vec::with_capacity(HOST_TIMING_LEN);
+    b.push(HOST_TIMING_MAGIC);
+    b.extend_from_slice(&t.pts_ns.to_le_bytes());
+    b.extend_from_slice(&t.host_us.to_le_bytes());
+    b
+}
+
+/// Parse a [`HOST_TIMING_MAGIC`] datagram → [`HostTiming`]. `None` on bad tag or a short buffer
+/// (the fixed length bounds every read before it happens).
+pub fn decode_host_timing_datagram(b: &[u8]) -> Option<HostTiming> {
+    if b.len() < HOST_TIMING_LEN || b[0] != HOST_TIMING_MAGIC {
+        return None;
+    }
+    Some(HostTiming {
+        pts_ns: u64::from_le_bytes(b[1..9].try_into().unwrap()),
+        host_us: u32::from_le_bytes(b[9..13].try_into().unwrap()),
+    })
+}

crates/punktfunk-core/src/quic/endpoint.rs

@@ -0,0 +1,370 @@
+use std::sync::{Arc, Mutex};
+
+/// Shared QUIC transport tuning for BOTH the host and client endpoints. Keep-alive is the
+/// load-bearing setting: with quinn's defaults it is OFF, so any quiet stretch on the
+/// connection (no input, audio muted or stalled, a capture hiccup, a mode change) lets the
+/// idle timer run out and quinn closes the session — surfacing to the embedder as
+/// `next_au` → Closed. The native equivalent of Moonlight's ENet keepalive: a small PING
+/// every `KEEP_ALIVE` keeps the path warm. The interval sits well under `MAX_IDLE` so
+/// several keepalives can be lost back-to-back (a wifi roam, a brief blip) without a false
+/// close, while a genuinely dead peer is still detected within `MAX_IDLE`.
+/// The default control-connection idle timeout (disconnect-detection latency). A vanished client
+/// is declared dead within this window — the Windows IDD-push path needs it short so a RECONNECT
+/// recreates a fresh virtual monitor instead of joining the still-lingering old session; the Linux
+/// path pairs it with the same-client reconnect preempt. Host-tunable via `server_with_identity_idle`.
+pub const DEFAULT_IDLE_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(8);
+
+fn stream_transport() -> Arc<quinn::TransportConfig> {
+    stream_transport_idle(DEFAULT_IDLE_TIMEOUT)
+}
+
+/// Transport config with a caller-chosen idle timeout (disconnect-detection latency). The
+/// keep-alive interval tracks it at half the idle window (capped at the default 4s), so a live
+/// path is PINGed at least twice per window and a single lost PING (wifi roam / brief blip) won't
+/// false-close. `idle` is clamped to a ≥1s floor so a misconfigured tiny value can't tear live
+/// sessions down. Active sessions are unaffected either way: video keeps the connection live and
+/// the keep-alive holds it open through quiet control periods.
+fn stream_transport_idle(idle: std::time::Duration) -> Arc<quinn::TransportConfig> {
+    use std::time::Duration;
+    let idle = idle.max(Duration::from_secs(1));
+    let keep_alive = (idle / 2).min(Duration::from_secs(4));
+    let mut t = quinn::TransportConfig::default();
+    t.max_idle_timeout(Some(
+        quinn::IdleTimeout::try_from(idle).expect("clamped idle timeout is a valid QUIC value"),
+    ));
+    t.keep_alive_interval(Some(keep_alive));
+    // The datagram planes (audio/rumble/hidout/host-timing host→client; mic/rich-input
+    // client→host) carry realtime state, not bulk data — but they are congestion-controlled,
+    // unlike video, which rides its own latest-wins UDP path. quinn's default 1 MiB datagram
+    // send buffer is a FIFO that only sheds oldest-first at the cap, so on a congested link
+    // (Wi-Fi under streaming load) it holds tens of seconds of Opus: audio and rumble build a
+    // standing delay that never drains while video stays live. Capping the buffer makes the
+    // plane latest-wins at the source — ~200 ms of stereo Opus (proportionally less at
+    // surround bitrates), so sustained congestion costs concealable drops, never lag.
+    t.datagram_send_buffer_size(4 * 1024);
+    Arc::new(t)
+}
+
+/// Server endpoint with a fresh self-signed certificate (tests/dev — production hosts
+/// persist an identity and use [`server_with_identity`] so clients can pin it).
+pub fn server(addr: std::net::SocketAddr) -> anyhow_result::Result<quinn::Endpoint> {
+    let cert = rcgen::generate_simple_self_signed(vec!["punktfunk".into()])
+        .map_err(|e| anyhow_result::Error::msg(format!("self-signed cert: {e}")))?;
+    let cert_der = rustls::pki_types::CertificateDer::from(cert.cert);
+    let key_der = rustls::pki_types::PrivatePkcs8KeyDer::from(cert.key_pair.serialize_der());
+    server_from_der(cert_der, key_der.into(), addr, DEFAULT_IDLE_TIMEOUT)
+}
+
+/// Server endpoint from a persisted PEM identity (certificate + PKCS#8 private key) —
+/// the host's long-lived self-signed cert, so the fingerprint clients pin is stable
+/// across restarts. Uses the [`DEFAULT_IDLE_TIMEOUT`]; see [`server_with_identity_idle`] to tune it.
+pub fn server_with_identity(
+    addr: std::net::SocketAddr,
+    cert_pem: &str,
+    key_pem: &str,
+) -> anyhow_result::Result<quinn::Endpoint> {
+    server_with_identity_idle(addr, cert_pem, key_pem, DEFAULT_IDLE_TIMEOUT)
+}
+
+/// Like [`server_with_identity`] but with a host-chosen control-connection idle timeout — the
+/// disconnect-detection latency (how long a vanished client takes to be declared dead). Shorter =
+/// faster teardown/linger of a dropped session; the value is clamped to a ≥1s floor and its
+/// keep-alive scales with it so a live session never false-closes.
+pub fn server_with_identity_idle(
+    addr: std::net::SocketAddr,
+    cert_pem: &str,
+    key_pem: &str,
+    idle: std::time::Duration,
+) -> anyhow_result::Result<quinn::Endpoint> {
+    use rustls::pki_types::pem::PemObject;
+    let cert_der = rustls::pki_types::CertificateDer::from_pem_slice(cert_pem.as_bytes())
+        .map_err(|e| anyhow_result::Error::msg(format!("cert pem: {e}")))?;
+    let key_der = rustls::pki_types::PrivateKeyDer::from_pem_slice(key_pem.as_bytes())
+        .map_err(|e| anyhow_result::Error::msg(format!("key pem: {e}")))?;
+    server_from_der(cert_der, key_der, addr, idle)
+}
+
+/// Fixed ALPN for the punktfunk/1 QUIC handshake. Pinning it rejects a cross-protocol peer at the
+/// TLS layer (defense-in-depth) and makes the wire protocol explicit. Both ends set the SAME value;
+/// a host with ALPN configured rejects a client that offers none, so client + host must be updated
+/// together (acceptable while the protocol/ABI is still evolving).
+const QUIC_ALPN: &[u8] = b"pkf1";
+
+fn server_from_der(
+    cert_der: rustls::pki_types::CertificateDer<'static>,
+    key_der: rustls::pki_types::PrivateKeyDer<'static>,
+    addr: std::net::SocketAddr,
+    idle: std::time::Duration,
+) -> anyhow_result::Result<quinn::Endpoint> {
+    let _ = rustls::crypto::ring::default_provider().install_default();
+    // Client auth is OFFERED but optional: a client that presents its self-signed
+    // identity is fingerprinted post-handshake (pairing / --require-pairing checks);
+    // one that presents none still connects (and is rejected at the app layer when
+    // pairing is required).
+    let mut rustls_cfg = rustls::ServerConfig::builder()
+        .with_client_cert_verifier(Arc::new(AcceptAnyClientCert))
+        .with_single_cert(vec![cert_der], key_der)
+        .map_err(|e| anyhow_result::Error::msg(format!("server config: {e}")))?;
+    rustls_cfg.alpn_protocols = vec![QUIC_ALPN.to_vec()];
+    let quic_cfg = quinn::crypto::rustls::QuicServerConfig::try_from(rustls_cfg)
+        .map_err(|e| anyhow_result::Error::msg(format!("quic server config: {e}")))?;
+    let mut server_config = quinn::ServerConfig::with_crypto(Arc::new(quic_cfg));
+    server_config.transport_config(stream_transport_idle(idle)); // keep-alive — see stream_transport_idle
+    Ok(quinn::Endpoint::server(server_config, addr)?)
+}
+
+/// Generate a fresh self-signed identity (certificate + PKCS#8 key, both PEM) — what a
+/// client persists once and presents on every connect so hosts can recognize it.
+pub fn generate_identity() -> anyhow_result::Result<(String, String)> {
+    let cert = rcgen::generate_simple_self_signed(vec!["punktfunk-client".into()])
+        .map_err(|e| anyhow_result::Error::msg(format!("self-signed cert: {e}")))?;
+    Ok((cert.cert.pem(), cert.key_pair.serialize_pem()))
+}
+
+/// Fingerprint of the client certificate a connection presented (host side), if any.
+pub fn peer_fingerprint(conn: &quinn::Connection) -> Option<[u8; 32]> {
+    let identity = conn.peer_identity()?;
+    let certs = identity
+        .downcast::<Vec<rustls::pki_types::CertificateDer<'static>>>()
+        .ok()?;
+    certs.first().map(|c| cert_fingerprint(c.as_ref()))
+}
+
+/// SHA-256 of a certificate's DER encoding — the fingerprint clients pin.
+pub fn cert_fingerprint(cert_der: &[u8]) -> [u8; 32] {
+    use sha2::Digest;
+    sha2::Sha256::digest(cert_der).into()
+}
+
+/// Fingerprint of a PEM-encoded certificate (what a host logs/shows for pairing UX —
+/// must match what the client's verifier computes from the DER on the wire).
+pub fn fingerprint_of_pem(cert_pem: &str) -> anyhow_result::Result<[u8; 32]> {
+    use rustls::pki_types::pem::PemObject;
+    let der = rustls::pki_types::CertificateDer::from_pem_slice(cert_pem.as_bytes())
+        .map_err(|e| anyhow_result::Error::msg(format!("cert pem: {e}")))?;
+    Ok(cert_fingerprint(der.as_ref()))
+}
+
+/// Client endpoint that skips certificate verification (TOFU bootstrap — read the
+/// observed fingerprint off the slot and pin it on the next connect).
+pub fn client_insecure() -> anyhow_result::Result<quinn::Endpoint> {
+    client_pinned(None).0
+}
+
+/// What [`client_pinned`] returns: the endpoint plus the slot the verifier writes the
+/// observed host fingerprint into during the handshake.
+pub type PinnedClient = (
+    anyhow_result::Result<quinn::Endpoint>,
+    Arc<Mutex<Option<[u8; 32]>>>,
+);
+
+/// Client endpoint that verifies the host by certificate fingerprint.
+///
+/// `pin = Some(sha256)` rejects any host whose leaf cert doesn't hash to `sha256`;
+/// `None` accepts any (trust-on-first-use). Either way the observed fingerprint is
+/// written to the returned slot during the handshake, so a TOFU caller can persist it.
+pub fn client_pinned(pin: Option<[u8; 32]>) -> PinnedClient {
+    client_pinned_with_identity(pin, None)
+}
+
+/// [`client_pinned`], additionally presenting a client identity (PEM cert + PKCS#8
+/// key) via TLS client auth — how a paired client identifies itself to the host.
+pub fn client_pinned_with_identity(
+    pin: Option<[u8; 32]>,
+    identity: Option<(&str, &str)>,
+) -> PinnedClient {
+    let observed = Arc::new(Mutex::new(None));
+    let ep = (|| {
+        let _ = rustls::crypto::ring::default_provider().install_default();
+        let builder = rustls::ClientConfig::builder()
+            .dangerous()
+            .with_custom_certificate_verifier(Arc::new(PinVerify {
+                pin,
+                observed: observed.clone(),
+            }));
+        let mut rustls_cfg = match identity {
+            None => builder.with_no_client_auth(),
+            Some((cert_pem, key_pem)) => {
+                use rustls::pki_types::pem::PemObject;
+                let cert =
+                    rustls::pki_types::CertificateDer::from_pem_slice(cert_pem.as_bytes())
+                        .map_err(|e| {
+                            anyhow_result::Error::msg(format!("client cert pem: {e}"))
+                        })?;
+                let key = rustls::pki_types::PrivateKeyDer::from_pem_slice(key_pem.as_bytes())
+                    .map_err(|e| anyhow_result::Error::msg(format!("client key pem: {e}")))?;
+                builder
+                    .with_client_auth_cert(vec![cert], key)
+                    .map_err(|e| anyhow_result::Error::msg(format!("client auth: {e}")))?
+            }
+        };
+        // Must match the server's ALPN ([`QUIC_ALPN`]) or the handshake is rejected.
+        rustls_cfg.alpn_protocols = vec![QUIC_ALPN.to_vec()];
+        let quic_cfg = quinn::crypto::rustls::QuicClientConfig::try_from(rustls_cfg)
+            .map_err(|e| anyhow_result::Error::msg(format!("quic client config: {e}")))?;
+        let mut client_cfg = quinn::ClientConfig::new(Arc::new(quic_cfg));
+        client_cfg.transport_config(stream_transport()); // keep-alive — see stream_transport
+        let mut ep = quinn::Endpoint::client("0.0.0.0:0".parse().unwrap())?;
+        ep.set_default_client_config(client_cfg);
+        Ok(ep)
+    })();
+    (ep, observed)
+}
+
+/// Minimal error plumbing without pulling anyhow into punktfunk-core's public API.
+pub mod anyhow_result {
+    pub type Result<T> = std::result::Result<T, Error>;
+    #[derive(Debug)]
+    pub struct Error(String);
+    impl Error {
+        pub fn msg(s: String) -> Self {
+            Error(s)
+        }
+    }
+    impl std::fmt::Display for Error {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            f.write_str(&self.0)
+        }
+    }
+    impl std::error::Error for Error {}
+    impl From<std::io::Error> for Error {
+        fn from(e: std::io::Error) -> Self {
+            Error(e.to_string())
+        }
+    }
+}
+
+/// Fingerprint-pinning verifier: trust is the SHA-256 of the host's (self-signed) leaf
+/// cert, not a CA chain. With no pin it accepts any cert (TOFU) but still records what
+/// it saw, so the embedder can persist the fingerprint and pin it from then on.
+/// Server-side client-cert verifier: accept any (self-signed) client certificate but
+/// verify the handshake signature for real — possession of the presented cert's key is
+/// what makes the post-handshake fingerprint ([`peer_fingerprint`]) meaningful.
+/// Authorization (is this fingerprint paired?) happens at the application layer.
+#[derive(Debug)]
+struct AcceptAnyClientCert;
+
+impl rustls::server::danger::ClientCertVerifier for AcceptAnyClientCert {
+    fn root_hint_subjects(&self) -> &[rustls::DistinguishedName] {
+        &[]
+    }
+
+    fn client_auth_mandatory(&self) -> bool {
+        false // unpaired/legacy clients still connect; gating is per-feature
+    }
+
+    fn verify_client_cert(
+        &self,
+        _end_entity: &rustls::pki_types::CertificateDer<'_>,
+        _intermediates: &[rustls::pki_types::CertificateDer<'_>],
+        _now: rustls::pki_types::UnixTime,
+    ) -> std::result::Result<rustls::server::danger::ClientCertVerified, rustls::Error>
+    {
+        Ok(rustls::server::danger::ClientCertVerified::assertion())
+    }
+
+    fn verify_tls12_signature(
+        &self,
+        message: &[u8],
+        cert: &rustls::pki_types::CertificateDer<'_>,
+        dss: &rustls::DigitallySignedStruct,
+    ) -> std::result::Result<rustls::client::danger::HandshakeSignatureValid, rustls::Error>
+    {
+        rustls::crypto::verify_tls12_signature(
+            message,
+            cert,
+            dss,
+            &rustls::crypto::ring::default_provider().signature_verification_algorithms,
+        )
+    }
+
+    fn verify_tls13_signature(
+        &self,
+        message: &[u8],
+        cert: &rustls::pki_types::CertificateDer<'_>,
+        dss: &rustls::DigitallySignedStruct,
+    ) -> std::result::Result<rustls::client::danger::HandshakeSignatureValid, rustls::Error>
+    {
+        rustls::crypto::verify_tls13_signature(
+            message,
+            cert,
+            dss,
+            &rustls::crypto::ring::default_provider().signature_verification_algorithms,
+        )
+    }
+
+    fn supported_verify_schemes(&self) -> Vec<rustls::SignatureScheme> {
+        rustls::crypto::ring::default_provider()
+            .signature_verification_algorithms
+            .supported_schemes()
+    }
+}
+
+#[derive(Debug)]
+struct PinVerify {
+    pin: Option<[u8; 32]>,
+    observed: Arc<Mutex<Option<[u8; 32]>>>,
+}
+
+impl rustls::client::danger::ServerCertVerifier for PinVerify {
+    fn verify_server_cert(
+        &self,
+        end_entity: &rustls::pki_types::CertificateDer<'_>,
+        _intermediates: &[rustls::pki_types::CertificateDer<'_>],
+        _server_name: &rustls::pki_types::ServerName<'_>,
+        _ocsp: &[u8],
+        _now: rustls::pki_types::UnixTime,
+    ) -> std::result::Result<rustls::client::danger::ServerCertVerified, rustls::Error>
+    {
+        let fp = cert_fingerprint(end_entity.as_ref());
+        *self.observed.lock().unwrap() = Some(fp);
+        if let Some(expected) = self.pin {
+            if fp != expected {
+                return Err(rustls::Error::InvalidCertificate(
+                    rustls::CertificateError::ApplicationVerificationFailure,
+                ));
+            }
+        }
+        Ok(rustls::client::danger::ServerCertVerified::assertion())
+    }
+
+    // The handshake signatures MUST be verified for real even though we pin the cert:
+    // CertificateVerify is what proves the peer *holds the pinned cert's private key* —
+    // skip it and an active MITM can replay the host's (public) certificate, match the
+    // pin, and complete the handshake with its own key.
+    fn verify_tls12_signature(
+        &self,
+        message: &[u8],
+        cert: &rustls::pki_types::CertificateDer<'_>,
+        dss: &rustls::DigitallySignedStruct,
+    ) -> std::result::Result<rustls::client::danger::HandshakeSignatureValid, rustls::Error>
+    {
+        rustls::crypto::verify_tls12_signature(
+            message,
+            cert,
+            dss,
+            &rustls::crypto::ring::default_provider().signature_verification_algorithms,
+        )
+    }
+
+    fn verify_tls13_signature(
+        &self,
+        message: &[u8],
+        cert: &rustls::pki_types::CertificateDer<'_>,
+        dss: &rustls::DigitallySignedStruct,
+    ) -> std::result::Result<rustls::client::danger::HandshakeSignatureValid, rustls::Error>
+    {
+        rustls::crypto::verify_tls13_signature(
+            message,
+            cert,
+            dss,
+            &rustls::crypto::ring::default_provider().signature_verification_algorithms,
+        )
+    }
+
+    fn supported_verify_schemes(&self) -> Vec<rustls::SignatureScheme> {
+        rustls::crypto::ring::default_provider()
+            .signature_verification_algorithms
+            .supported_schemes()
+    }
+}

crates/punktfunk-core/src/quic/io.rs

@@ -0,0 +1,20 @@
+/// Read one framed message (bounded at 64 KiB — control messages are tiny).
+pub async fn read_msg(recv: &mut quinn::RecvStream) -> std::io::Result<Vec<u8>> {
+    let mut len = [0u8; 2];
+    recv.read_exact(&mut len)
+        .await
+        .map_err(std::io::Error::other)?;
+    let n = u16::from_le_bytes(len) as usize;
+    let mut buf = vec![0u8; n];
+    recv.read_exact(&mut buf)
+        .await
+        .map_err(std::io::Error::other)?;
+    Ok(buf)
+}
+
+/// Write one framed message.
+pub async fn write_msg(send: &mut quinn::SendStream, payload: &[u8]) -> std::io::Result<()> {
+    send.write_all(&super::frame(payload))
+        .await
+        .map_err(std::io::Error::other)
+}

crates/punktfunk-core/src/quic/mod.rs

@@ -0,0 +1,64 @@
+//! `punktfunk/1` — the native control plane, gated behind the `quic` feature.
+//!
+//! GameStream is punktfunk's compatibility layer; this is the start of its own protocol. A QUIC
+//! connection (quinn, tokio — control plane only, never the per-frame path) carries a
+//! length-prefixed binary handshake on one bidirectional stream:
+//!
+//! ```text
+//!   client → host  Hello   { abi_version }
+//!   host → client  Welcome { abi_version, session: full data-plane Config + mode + UDP port }
+//!   client → host  Start   { client_udp_port }
+//! ```
+//!
+//! after which both sides bring up a [`crate::session::Session`] over a plain
+//! [`UdpTransport`](crate::transport::udp) (native threads, no async) and the host streams.
+//! The Welcome carries everything the core negotiates — FEC scheme (including GF(2¹⁶)
+//! Leopard, which GameStream can't express), shard sizing, crypto key/salt — so the data
+//! plane is exactly the hardened core `Session`.
+//!
+//! Transport security: the host presents a long-lived self-signed certificate
+//! ([`endpoint::server_with_identity`]) and the client pins its SHA-256 fingerprint
+//! ([`endpoint::client_pinned`]; no pin = trust-on-first-use, with the observed fingerprint
+//! reported back for persisting). The data plane adds AES-GCM on top.
+//! All integers little-endian; every message is `u16 length || payload`.
+//!
+//! Split by concern (networking-audit deferred plan §3 — a pure move): [`msgs`] the
+//! handshake + typed control messages, [`pake`] the pairing SPAKE2, [`datagram`] the
+//! 0xC9–0xCF plane codecs, [`io`] framed stream IO, [`clock`] skew estimation + mid-stream
+//! re-sync, [`endpoint`] the quinn constructors. Every item is re-exported here, so all
+//! existing `crate::quic::X` paths compile unchanged.
+
+/// Protocol magic + version, first bytes of the positional handshake (Hello/Welcome/Start).
+pub const MAGIC: &[u8; 4] = b"PKF1";
+
+/// Magic for typed post-handshake / pairing control messages. A distinct magic keeps the
+/// typed namespace disjoint from the positional handshake: a `Hello` (whose abi_version
+/// byte sits where a type byte would) can never be misparsed as a control message, and
+/// vice-versa, regardless of field values.
+pub const CTL_MAGIC: &[u8; 4] = b"PKFc";
+
+mod clock;
+mod datagram;
+mod msgs;
+
+/// quinn endpoint constructors. Host: self-signed identity (fresh, or persisted PEMs via
+/// [`endpoint::server_with_identity`]). Client: fingerprint pinning / TOFU via
+/// [`endpoint::client_pinned`] ([`endpoint::client_insecure`] is the no-pin special case).
+pub mod endpoint;
+
+/// Async framed-message IO over a quinn stream (`u16 LE length || payload`).
+pub mod io;
+
+/// SPAKE2 over Ed25519 for the pairing ceremony. The two roles use the asymmetric flow so
+/// the identities are ordered; each side binds **both** certificate fingerprints as the
+/// SPAKE2 identities, so the derived key only matches when client and host agree on the PIN
+/// *and* saw the same two certificates (a MITM, presenting different certs to each leg,
+/// cannot reach a shared key).
+pub mod pake;
+
+pub use clock::*;
+pub use datagram::*;
+pub use msgs::*;
+
+#[cfg(test)]
+mod tests;

crates/punktfunk-core/src/quic/pake.rs

@@ -0,0 +1,80 @@
+use crate::error::{PunktfunkError, Result};
+use hmac::{Hmac, Mac};
+use spake2::{Ed25519Group, Identity, Password, Spake2};
+
+/// In-progress SPAKE2 state plus the identity transcript for key confirmation.
+pub struct PairingPake {
+    state: Spake2<Ed25519Group>,
+    transcript: Vec<u8>,
+}
+
+/// Start the exchange. `client_fp`/`host_fp` are the two certificate fingerprints (the
+/// client passes what it observed via TOFU; the host passes its own + the client's
+/// presented cert). Returns the state and this side's outbound SPAKE2 message.
+pub fn start(
+    is_client: bool,
+    pin: &str,
+    client_fp: &[u8; 32],
+    host_fp: &[u8; 32],
+) -> (PairingPake, Vec<u8>) {
+    let pw = Password::new(pin.as_bytes());
+    let id_client = Identity::new(client_fp);
+    let id_host = Identity::new(host_fp);
+    let (state, msg) = if is_client {
+        Spake2::<Ed25519Group>::start_a(&pw, &id_client, &id_host)
+    } else {
+        Spake2::<Ed25519Group>::start_b(&pw, &id_client, &id_host)
+    };
+    let mut transcript = Vec::with_capacity(64);
+    transcript.extend_from_slice(client_fp);
+    transcript.extend_from_slice(host_fp);
+    (PairingPake { state, transcript }, msg)
+}
+
+/// Key confirmation MAC for one direction (`label` distinguishes host vs client), keyed
+/// by the SPAKE2 shared key and bound to the fingerprint transcript.
+fn confirm(key: &[u8], label: &[u8], transcript: &[u8]) -> [u8; 32] {
+    let mut mac =
+        <Hmac<sha2::Sha256> as Mac>::new_from_slice(key).expect("hmac takes any key length");
+    mac.update(label);
+    mac.update(transcript);
+    mac.finalize().into_bytes().into()
+}
+
+/// `Hmac` verification is constant-time via `ct_eq` in the underlying crate; we compare
+/// our recomputed tag the same way.
+fn ct_eq(a: &[u8; 32], b: &[u8; 32]) -> bool {
+    a.iter()
+        .zip(b.iter())
+        .fold(0u8, |acc, (x, y)| acc | (x ^ y))
+        == 0
+}
+
+/// Confirmation tags both sides expect, given the agreed SPAKE2 key.
+pub struct Confirmations {
+    /// MAC the host sends (client verifies).
+    pub host: [u8; 32],
+    /// MAC the client sends (host verifies).
+    pub client: [u8; 32],
+}
+
+impl PairingPake {
+    /// Finish SPAKE2 with the peer's message → the pair of confirmation tags. `Err` if
+    /// the peer's message is malformed (a wrong PIN does NOT error here — it yields a
+    /// *different* key, so the confirmation MACs simply won't match).
+    pub fn finish(self, peer_msg: &[u8]) -> Result<Confirmations> {
+        let key = self
+            .state
+            .finish(peer_msg)
+            .map_err(|_| PunktfunkError::Crypto)?;
+        Ok(Confirmations {
+            host: confirm(&key, b"punktfunk-pair-host", &self.transcript),
+            client: confirm(&key, b"punktfunk-pair-client", &self.transcript),
+        })
+    }
+}
+
+/// Constant-time tag comparison for the confirmation step.
+pub fn verify(expected: &[u8; 32], got: &[u8; 32]) -> bool {
+    ct_eq(expected, got)
+}

crates/punktfunk-core/src/quic/tests.rs

@@ -0,0 +1,955 @@
+use super::*;
+use crate::config::{CompositorPref, FecConfig, FecScheme, GamepadPref, Mode};
+
+#[test]
+fn welcome_roundtrip() {
+    let w = Welcome {
+        abi_version: 1,
+        udp_port: 9999,
+        mode: Mode {
+            width: 2560,
+            height: 1440,
+            refresh_hz: 240,
+        },
+        fec: FecConfig {
+            scheme: FecScheme::Gf16,
+            fec_percent: 20,
+            max_data_per_block: 4096,
+        },
+        shard_payload: 1200,
+        encrypt: true,
+        key: [7u8; 16],
+        salt: [1, 2, 3, 4],
+        frames: 600,
+        compositor: CompositorPref::Gamescope,
+        gamepad: GamepadPref::DualSense,
+        bitrate_kbps: 50_000,
+        bit_depth: 10,
+        color: ColorInfo::HDR10_BT2020_PQ,
+        chroma_format: CHROMA_IDC_444,
+        audio_channels: 2,
+        codec: CODEC_H264, // exercise a non-default codec through the roundtrip
+        host_caps: HOST_CAP_GAMEPAD_STATE,
+    };
+    assert_eq!(Welcome::decode(&w.encode()).unwrap(), w);
+}
+
+#[test]
+fn codec_negotiation_and_back_compat() {
+    // resolve_codec precedence (HEVC > AV1 > H.264), no preference (0).
+    assert_eq!(
+        resolve_codec(CODEC_H264 | CODEC_HEVC, CODEC_HEVC | CODEC_AV1, 0),
+        Some(CODEC_HEVC)
+    );
+    assert_eq!(
+        resolve_codec(CODEC_H264 | CODEC_AV1, CODEC_AV1 | CODEC_H264, 0),
+        Some(CODEC_AV1)
+    );
+    assert_eq!(resolve_codec(CODEC_H264, CODEC_H264, 0), Some(CODEC_H264));
+    // A software host (H.264 only) + an HEVC-only client share nothing → refuse.
+    assert_eq!(resolve_codec(CODEC_HEVC, CODEC_H264, 0), None);
+    // An older client (0 = no codec byte) is treated as HEVC-only.
+    assert_eq!(
+        resolve_codec(0, CODEC_HEVC | CODEC_H264, 0),
+        Some(CODEC_HEVC)
+    );
+    assert_eq!(resolve_codec(0, CODEC_H264, 0), None);
+
+    // Soft preference: honored when the host can also emit it, overriding precedence...
+    assert_eq!(
+        resolve_codec(CODEC_H264 | CODEC_HEVC, CODEC_H264 | CODEC_HEVC, CODEC_H264),
+        Some(CODEC_H264)
+    );
+    assert_eq!(
+        resolve_codec(CODEC_HEVC | CODEC_AV1, CODEC_HEVC | CODEC_AV1, CODEC_AV1),
+        Some(CODEC_AV1)
+    );
+    // ...but falls back to precedence when the preferred codec isn't in the shared set.
+    assert_eq!(
+        resolve_codec(CODEC_HEVC | CODEC_H264, CODEC_HEVC | CODEC_H264, CODEC_AV1),
+        Some(CODEC_HEVC)
+    );
+    // A preference the host can't emit still can't rescue a no-shared-codec case.
+    assert_eq!(resolve_codec(CODEC_HEVC, CODEC_H264, CODEC_HEVC), None);
+
+    // A Hello advertising codecs roundtrips, and the wire form of a codec-only Hello decodes on
+    // a build that ignores the trailing byte (back-compat: extra bytes are skipped).
+    let h = Hello {
+        abi_version: 2,
+        mode: Mode {
+            width: 1280,
+            height: 720,
+            refresh_hz: 60,
+        },
+        compositor: CompositorPref::Auto,
+        gamepad: GamepadPref::Auto,
+        bitrate_kbps: 0,
+        name: None,
+        launch: None,
+        video_caps: 0,
+        audio_channels: 2, // stereo — forces the video_caps/audio_channels placeholders
+        video_codecs: CODEC_H264 | CODEC_HEVC,
+        preferred_codec: CODEC_H264,
+    };
+    let enc = h.encode();
+    let dec = Hello::decode(&enc).unwrap();
+    assert_eq!(dec.video_codecs, CODEC_H264 | CODEC_HEVC);
+    assert_eq!(dec.preferred_codec, CODEC_H264);
+    // Drop the preferred_codec byte → still decodes, video_codecs intact, preference gone.
+    let no_pref = &enc[..enc.len() - 1];
+    assert_eq!(
+        Hello::decode(no_pref).unwrap().video_codecs,
+        CODEC_H264 | CODEC_HEVC
+    );
+    assert_eq!(Hello::decode(no_pref).unwrap().preferred_codec, 0);
+    // A pre-codec Hello (no video_codecs/preferred bytes) decodes to 0 → HEVC-only.
+    let legacy = &enc[..enc.len() - 2];
+    assert_eq!(Hello::decode(legacy).unwrap().video_codecs, 0);
+    assert_eq!(Hello::decode(legacy).unwrap().preferred_codec, 0);
+
+    // A pre-codec Welcome (no codec byte) decodes to HEVC.
+    let mut w = Welcome::decode(
+        &Welcome {
+            abi_version: 2,
+            udp_port: 1,
+            mode: h.mode,
+            fec: FecConfig {
+                scheme: FecScheme::Gf16,
+                fec_percent: 0,
+                max_data_per_block: 1024,
+            },
+            shard_payload: 1024,
+            encrypt: false,
+            key: [0; 16],
+            salt: [0; 4],
+            frames: 0,
+            compositor: CompositorPref::Auto,
+            gamepad: GamepadPref::Auto,
+            bitrate_kbps: 0,
+            bit_depth: 8,
+            color: ColorInfo::SDR_BT709,
+            chroma_format: CHROMA_IDC_420,
+            audio_channels: 2,
+            codec: CODEC_H264,
+            host_caps: 0,
+        }
+        .encode(),
+    )
+    .unwrap();
+    assert_eq!(w.codec, CODEC_H264);
+    w.codec = CODEC_HEVC;
+    let wenc = w.encode();
+    assert_eq!(
+        Welcome::decode(&wenc[..wenc.len() - 1]).unwrap().codec,
+        CODEC_HEVC
+    );
+}
+
+#[test]
+fn hdr_meta_datagram_roundtrip_and_truncation() {
+    let m = HdrMeta {
+        // BT.2020 display primaries in 1/50000 units (the DXGI/ST.2086 reference values).
+        display_primaries: [[8500, 39850], [6550, 2300], [35400, 14600]],
+        white_point: [15635, 16450],                 // D65
+        max_display_mastering_luminance: 10_000_000, // 1000 nits in 0.0001 cd/m²
+        min_display_mastering_luminance: 1,          // 0.0001 nits
+        max_cll: 1000,
+        max_fall: 400,
+    };
+    let d = encode_hdr_meta_datagram(&m);
+    assert_eq!(d[0], HDR_META_MAGIC);
+    assert_eq!(decode_hdr_meta_datagram(&d), Some(m));
+    // Truncated buffers and a wrong tag are rejected (never partially read).
+    for n in 0..d.len() {
+        assert_eq!(decode_hdr_meta_datagram(&d[..n]), None);
+    }
+    let mut bad = d.clone();
+    bad[0] = HIDOUT_MAGIC;
+    assert_eq!(decode_hdr_meta_datagram(&bad), None);
+}
+
+#[test]
+fn host_timing_datagram_roundtrip_and_truncation() {
+    let t = HostTiming {
+        pts_ns: 1_751_500_000_123_456_789, // a realistic 2026 CLOCK_REALTIME capture stamp
+        host_us: 4_321,
+    };
+    let d = encode_host_timing_datagram(&t);
+    assert_eq!(d[0], HOST_TIMING_MAGIC);
+    assert_eq!(d.len(), 13);
+    assert_eq!(decode_host_timing_datagram(&d), Some(t));
+    // Truncated buffers and a wrong tag are rejected (never partially read).
+    for n in 0..d.len() {
+        assert_eq!(decode_host_timing_datagram(&d[..n]), None);
+    }
+    let mut bad = d.clone();
+    bad[0] = HDR_META_MAGIC;
+    assert_eq!(decode_host_timing_datagram(&bad), None);
+}
+
+#[test]
+fn hello_start_roundtrip() {
+    let h = Hello {
+        abi_version: 1,
+        mode: Mode {
+            width: 1280,
+            height: 720,
+            refresh_hz: 120,
+        },
+        compositor: CompositorPref::Kwin,
+        gamepad: GamepadPref::DualSense,
+        bitrate_kbps: 25_000,
+        name: Some("Test Device".into()),
+        launch: Some("steam:570".into()),
+        video_caps: VIDEO_CAP_10BIT,
+        audio_channels: 2,
+        video_codecs: CODEC_H264 | CODEC_HEVC, // exercise the codec bitfield roundtrip
+        preferred_codec: CODEC_HEVC,
+    };
+    assert_eq!(Hello::decode(&h.encode()).unwrap(), h);
+    let s = Start {
+        client_udp_port: 1234,
+    };
+    assert_eq!(Start::decode(&s.encode()).unwrap(), s);
+}
+
+#[test]
+fn compositor_pref_wire_and_names() {
+    for p in [
+        CompositorPref::Auto,
+        CompositorPref::Kwin,
+        CompositorPref::Wlroots,
+        CompositorPref::Mutter,
+        CompositorPref::Gamescope,
+    ] {
+        assert_eq!(CompositorPref::from_u8(p.to_u8()), p);
+        assert_eq!(CompositorPref::from_name(p.as_str()), Some(p));
+    }
+    // Aliases + unknowns.
+    assert_eq!(CompositorPref::from_name("KDE"), Some(CompositorPref::Kwin));
+    assert_eq!(
+        CompositorPref::from_name("sway"),
+        Some(CompositorPref::Wlroots)
+    );
+    assert_eq!(CompositorPref::from_name("nope"), None);
+    // Unknown wire byte degrades to Auto (forward-compatible).
+    assert_eq!(CompositorPref::from_u8(200), CompositorPref::Auto);
+}
+
+#[test]
+fn gamepad_pref_wire_and_names() {
+    for p in [
+        GamepadPref::Auto,
+        GamepadPref::Xbox360,
+        GamepadPref::DualSense,
+        GamepadPref::XboxOne,
+        GamepadPref::DualShock4,
+    ] {
+        assert_eq!(GamepadPref::from_u8(p.to_u8()), p);
+        assert_eq!(GamepadPref::from_name(p.as_str()), Some(p));
+    }
+    // Distinct wire bytes (forward-compat with peers that only know 0..=2).
+    assert_eq!(GamepadPref::XboxOne.to_u8(), 3);
+    assert_eq!(GamepadPref::DualShock4.to_u8(), 4);
+    // Aliases + unknowns.
+    assert_eq!(GamepadPref::from_name("PS5"), Some(GamepadPref::DualSense));
+    assert_eq!(GamepadPref::from_name("x360"), Some(GamepadPref::Xbox360));
+    assert_eq!(GamepadPref::from_name("ps4"), Some(GamepadPref::DualShock4));
+    assert_eq!(GamepadPref::from_name("DS4"), Some(GamepadPref::DualShock4));
+    assert_eq!(
+        GamepadPref::from_name("xbox-one"),
+        Some(GamepadPref::XboxOne)
+    );
+    assert_eq!(GamepadPref::from_name("series"), Some(GamepadPref::XboxOne));
+    assert_eq!(GamepadPref::from_name("nope"), None);
+    // Unknown wire byte degrades to Auto (forward-compatible).
+    assert_eq!(GamepadPref::from_u8(200), GamepadPref::Auto);
+}
+
+#[test]
+fn hello_welcome_compositor_back_compat() {
+    // Trailing optional bytes (compositor at 20/53, gamepad at 21/54): a legacy peer's
+    // shorter message still decodes (missing fields = Auto), and a legacy peer reading a
+    // new message ignores the trailing bytes. Simulate both directions by truncation.
+    let h = Hello {
+        abi_version: 2,
+        mode: Mode {
+            width: 1920,
+            height: 1080,
+            refresh_hz: 60,
+        },
+        compositor: CompositorPref::Mutter,
+        gamepad: GamepadPref::DualSense,
+        bitrate_kbps: 80_000,
+        name: None,
+        launch: None,
+        video_caps: 0,
+        audio_channels: 2,
+        video_codecs: 0,
+        preferred_codec: 0,
+    };
+    let enc = h.encode();
+    assert_eq!(enc.len(), 26);
+    // Legacy (20-byte) Hello → both Auto, no bitrate, mode intact.
+    let legacy = Hello::decode(&enc[..20]).unwrap();
+    assert_eq!(legacy.compositor, CompositorPref::Auto);
+    assert_eq!(legacy.gamepad, GamepadPref::Auto);
+    assert_eq!(legacy.bitrate_kbps, 0);
+    assert_eq!(legacy.mode, h.mode);
+    // Compositor-era (21-byte) Hello → compositor intact, gamepad Auto.
+    let mid = Hello::decode(&enc[..21]).unwrap();
+    assert_eq!(mid.compositor, CompositorPref::Mutter);
+    assert_eq!(mid.gamepad, GamepadPref::Auto);
+    // Gamepad-era (22-byte) Hello → compositor + gamepad intact, bitrate 0 (host default).
+    let pre_bitrate = Hello::decode(&enc[..22]).unwrap();
+    assert_eq!(pre_bitrate.gamepad, GamepadPref::DualSense);
+    assert_eq!(pre_bitrate.bitrate_kbps, 0);
+    // Full message → bitrate intact.
+    assert_eq!(Hello::decode(&enc).unwrap().bitrate_kbps, 80_000);
+
+    let w = Welcome {
+        abi_version: 2,
+        udp_port: 7000,
+        mode: h.mode,
+        fec: FecConfig {
+            scheme: FecScheme::Gf16,
+            fec_percent: 20,
+            max_data_per_block: 4096,
+        },
+        shard_payload: 1200,
+        encrypt: true,
+        key: [3u8; 16],
+        salt: [9, 8, 7, 6],
+        frames: 0,
+        compositor: CompositorPref::Kwin,
+        gamepad: GamepadPref::Xbox360,
+        bitrate_kbps: 120_000,
+        bit_depth: 10,
+        color: ColorInfo::HDR10_BT2020_PQ,
+        chroma_format: CHROMA_IDC_444,
+        audio_channels: 6, // 5.1 — exercises the non-default trailing byte
+        codec: CODEC_HEVC,
+        host_caps: HOST_CAP_GAMEPAD_STATE,
+    };
+    let wenc = w.encode();
+    assert_eq!(wenc.len(), 68); // 60 base + 4 colour + chroma + audio-channels + codec + host-caps
+    let legacy_w = Welcome::decode(&wenc[..53]).unwrap();
+    assert_eq!(legacy_w.compositor, CompositorPref::Auto);
+    assert_eq!(legacy_w.gamepad, GamepadPref::Auto);
+    assert_eq!(legacy_w.bitrate_kbps, 0);
+    assert_eq!(legacy_w.frames, 0);
+    assert_eq!(legacy_w.key, w.key);
+    let mid_w = Welcome::decode(&wenc[..54]).unwrap();
+    assert_eq!(mid_w.compositor, CompositorPref::Kwin);
+    assert_eq!(mid_w.gamepad, GamepadPref::Auto);
+    // Gamepad-era (55-byte) Welcome → gamepad intact, bitrate 0 (unknown).
+    let pre_bitrate_w = Welcome::decode(&wenc[..55]).unwrap();
+    assert_eq!(pre_bitrate_w.gamepad, GamepadPref::Xbox360);
+    assert_eq!(pre_bitrate_w.bitrate_kbps, 0);
+    assert_eq!(pre_bitrate_w.bit_depth, 8); // older host (no trailing byte) → 8-bit assumed
+    assert_eq!(legacy_w.bit_depth, 8);
+    // A pre-colour (60-byte) Welcome → SDR BT.709 (the only colour those hosts produced).
+    let pre_color_w = Welcome::decode(&wenc[..60]).unwrap();
+    assert_eq!(pre_color_w.bit_depth, 10);
+    assert_eq!(pre_color_w.color, ColorInfo::SDR_BT709);
+    assert_eq!(pre_color_w.chroma_format, CHROMA_IDC_420); // pre-chroma host → 4:2:0
+    assert_eq!(legacy_w.color, ColorInfo::SDR_BT709);
+    assert_eq!(legacy_w.chroma_format, CHROMA_IDC_420);
+    // A pre-chroma (64-byte) Welcome carries colour but no chroma/audio bytes → 4:2:0 + stereo.
+    let pre_chroma_w = Welcome::decode(&wenc[..64]).unwrap();
+    assert_eq!(pre_chroma_w.color, ColorInfo::HDR10_BT2020_PQ);
+    assert_eq!(pre_chroma_w.chroma_format, CHROMA_IDC_420);
+    assert_eq!(pre_chroma_w.audio_channels, 2); // audio byte (offset 65) absent → stereo
+                                                // A pre-audio (65-byte) Welcome carries chroma but no audio byte → 4:4:4 + stereo.
+    let pre_audio_w = Welcome::decode(&wenc[..65]).unwrap();
+    assert_eq!(pre_audio_w.chroma_format, CHROMA_IDC_444);
+    assert_eq!(pre_audio_w.audio_channels, 2);
+    assert_eq!(Welcome::decode(&wenc).unwrap().bitrate_kbps, 120_000);
+    assert_eq!(Welcome::decode(&wenc).unwrap().bit_depth, 10); // full form carries it
+    assert_eq!(
+        Welcome::decode(&wenc).unwrap().color,
+        ColorInfo::HDR10_BT2020_PQ
+    );
+    assert_eq!(
+        Welcome::decode(&wenc).unwrap().chroma_format,
+        CHROMA_IDC_444
+    ); // full form carries 4:4:4
+    assert_eq!(Welcome::decode(&wenc).unwrap().audio_channels, 6); // ...and 5.1
+                                                                   // A pre-host-caps (67-byte) Welcome → 0 (legacy input only); the full form carries the bit.
+    assert_eq!(Welcome::decode(&wenc[..67]).unwrap().host_caps, 0);
+    assert_eq!(
+        Welcome::decode(&wenc).unwrap().host_caps,
+        HOST_CAP_GAMEPAD_STATE
+    );
+}
+
+#[test]
+fn hello_name_roundtrip_and_back_compat() {
+    let base = Hello {
+        abi_version: 2,
+        mode: Mode {
+            width: 1280,
+            height: 720,
+            refresh_hz: 60,
+        },
+        compositor: CompositorPref::Auto,
+        gamepad: GamepadPref::Auto,
+        bitrate_kbps: 0,
+        name: Some("Enrico's MacBook".into()),
+        launch: None,
+        video_caps: 0,
+        audio_channels: 2,
+        video_codecs: 0,
+        preferred_codec: 0,
+    };
+    let enc = base.encode();
+    assert_eq!(
+        Hello::decode(&enc).unwrap().name.as_deref(),
+        Some("Enrico's MacBook")
+    );
+    // A bitrate-era (26-byte) peer reading a named Hello ignores the trailing name; a named
+    // host reading a bitrate-era Hello decodes name = None.
+    assert_eq!(Hello::decode(&enc[..26]).unwrap().name, None);
+    // No name → wire form is byte-identical to the bitrate-era message (26 bytes).
+    let unnamed = Hello {
+        name: None,
+        ..base.clone()
+    };
+    assert_eq!(unnamed.encode().len(), 26);
+    // Over-long names truncate to a char boundary within HELLO_NAME_MAX on encode.
+    let long = Hello {
+        name: Some(format!("{}ü", "x".repeat(HELLO_NAME_MAX - 1))), // ü straddles the cap
+        ..base.clone()
+    };
+    let dec = Hello::decode(&long.encode()).unwrap();
+    let n = dec.name.expect("truncated name still present");
+    assert!(n.len() <= HELLO_NAME_MAX && n.starts_with('x'));
+    // A corrupt length byte (longer than the buffer) or bad UTF-8 degrades to None, never Err.
+    let mut bad_len = unnamed.encode();
+    bad_len.push(40); // claims 40 name bytes, none follow
+    assert_eq!(Hello::decode(&bad_len).unwrap().name, None);
+    let mut bad_utf8 = unnamed.encode();
+    bad_utf8.extend_from_slice(&[2, 0xFF, 0xFE]);
+    assert_eq!(Hello::decode(&bad_utf8).unwrap().name, None);
+}
+
+#[test]
+fn hello_launch_roundtrip_and_back_compat() {
+    let base = Hello {
+        abi_version: 2,
+        mode: Mode {
+            width: 1920,
+            height: 1080,
+            refresh_hz: 60,
+        },
+        compositor: CompositorPref::Auto,
+        gamepad: GamepadPref::Auto,
+        bitrate_kbps: 0,
+        name: None,
+        launch: None,
+        video_caps: 0,
+        audio_channels: 2,
+        video_codecs: 0,
+        preferred_codec: 0,
+    };
+    // launch alone (no name): a zero-length name placeholder keeps the offset deterministic.
+    let with_launch = Hello {
+        launch: Some("steam:570".into()),
+        ..base.clone()
+    };
+    assert_eq!(Hello::decode(&with_launch.encode()).unwrap(), with_launch);
+    // launch + name together.
+    let both = Hello {
+        name: Some("Enrico's Mac".into()),
+        launch: Some("custom:abc123".into()),
+        ..base.clone()
+    };
+    assert_eq!(Hello::decode(&both.encode()).unwrap(), both);
+    // name but no launch (a name-era client): launch decodes None.
+    let name_only = Hello {
+        name: Some("Enrico's Mac".into()),
+        ..base.clone()
+    };
+    assert_eq!(Hello::decode(&name_only.encode()).unwrap().launch, None);
+    // Neither field → still the 26-byte bitrate-era form (no launch placeholder emitted).
+    assert_eq!(base.encode().len(), 26);
+    assert_eq!(Hello::decode(&base.encode()).unwrap().launch, None);
+    // A bitrate-era (26-byte) peer reading a launch-bearing Hello ignores it.
+    assert_eq!(
+        Hello::decode(&with_launch.encode()[..26]).unwrap().launch,
+        None
+    );
+    // Over-long ids truncate on a char boundary within HELLO_LAUNCH_MAX.
+    let long = Hello {
+        launch: Some(format!("{}ü", "x".repeat(HELLO_LAUNCH_MAX - 1))),
+        ..base.clone()
+    };
+    let dec = Hello::decode(&long.encode())
+        .unwrap()
+        .launch
+        .expect("present");
+    assert!(dec.len() <= HELLO_LAUNCH_MAX && dec.starts_with('x'));
+}
+
+#[test]
+fn reconfigure_roundtrip() {
+    let rq = Reconfigure {
+        mode: Mode {
+            width: 1920,
+            height: 1080,
+            refresh_hz: 144,
+        },
+    };
+    assert_eq!(Reconfigure::decode(&rq.encode()).unwrap(), rq);
+    for accepted in [true, false] {
+        let rs = Reconfigured {
+            accepted,
+            mode: rq.mode,
+        };
+        assert_eq!(Reconfigured::decode(&rs.encode()).unwrap(), rs);
+    }
+    // The type byte separates the post-handshake messages from each other.
+    assert!(Reconfigure::decode(
+        &Reconfigured {
+            accepted: true,
+            mode: rq.mode
+        }
+        .encode()
+    )
+    .is_err());
+}
+
+#[test]
+fn request_keyframe_roundtrip() {
+    let bytes = RequestKeyframe.encode();
+    assert!(RequestKeyframe::decode(&bytes).is_ok());
+    // Distinct from the other control messages — its type byte must not collide.
+    let mode = Mode {
+        width: 1280,
+        height: 720,
+        refresh_hz: 60,
+    };
+    assert!(RequestKeyframe::decode(&Reconfigure { mode }.encode()).is_err());
+    assert!(Reconfigure::decode(&bytes).is_err());
+    // Length is exact (no trailing bytes accepted).
+    assert!(RequestKeyframe::decode(&[bytes.as_slice(), &[0]].concat()).is_err());
+}
+
+#[test]
+fn loss_report_roundtrip() {
+    for loss_ppm in [0u32, 1, 12_345, 50_000, 1_000_000] {
+        let r = LossReport { loss_ppm };
+        assert_eq!(LossReport::decode(&r.encode()).unwrap(), r);
+    }
+    // Disjoint from the other control messages (type byte + length).
+    assert!(LossReport::decode(&RequestKeyframe.encode()).is_err());
+    assert!(RequestKeyframe::decode(&LossReport { loss_ppm: 0 }.encode()).is_err());
+    assert!(LossReport::decode(
+        &[LossReport { loss_ppm: 0 }.encode().as_slice(), &[0]].concat()
+    )
+    .is_err());
+}
+
+#[test]
+fn window_loss_ppm_estimates_and_caps() {
+    // No traffic → 0. A clean window (nothing recovered) → 0.
+    assert_eq!(window_loss_ppm(0, 0, 0), 0);
+    assert_eq!(window_loss_ppm(0, 1000, 0), 0);
+    // 50 recovered of 1000 total (950 received + 50 recovered) = 5%.
+    assert_eq!(window_loss_ppm(50, 950, 0), 50_000);
+    // An unrecoverable frame adds the +5% bump (push FEC past the current cap).
+    assert_eq!(window_loss_ppm(50, 950, 1), 100_000);
+    // A total-loss window with a drop but nothing received still reports the bump, capped at 1e6.
+    assert_eq!(window_loss_ppm(0, 0, 3), 50_000);
+    assert!(window_loss_ppm(u64::MAX, 1, 9) <= 1_000_000);
+}
+
+#[test]
+fn bitrate_messages_roundtrip() {
+    let req = SetBitrate {
+        bitrate_kbps: 14_000,
+    };
+    assert_eq!(SetBitrate::decode(&req.encode()).unwrap(), req);
+    let ack = BitrateChanged {
+        bitrate_kbps: 14_000,
+    };
+    assert_eq!(BitrateChanged::decode(&ack.encode()).unwrap(), ack);
+    // Same payload shape as LossReport — the type byte alone must keep them disjoint.
+    assert!(LossReport::decode(&req.encode()).is_err());
+    assert!(SetBitrate::decode(&ack.encode()).is_err());
+    assert!(BitrateChanged::decode(&req.encode()).is_err());
+    assert!(SetBitrate::decode(&LossReport { loss_ppm: 7 }.encode()).is_err());
+}
+
+#[test]
+fn probe_messages_roundtrip() {
+    let req = ProbeRequest {
+        target_kbps: 250_000,
+        duration_ms: 2000,
+    };
+    assert_eq!(ProbeRequest::decode(&req.encode()).unwrap(), req);
+    let res = ProbeResult {
+        bytes_sent: 62_500_000,
+        packets_sent: 480,
+        duration_ms: 2003,
+        wire_packets_sent: 41_000,
+        send_dropped: 1_200,
+    };
+    assert_eq!(ProbeResult::decode(&res.encode()).unwrap(), res);
+    assert_eq!(res.encode().len(), 29);
+    // A pre-wire-stats host's 21-byte ProbeResult still decodes, with the new fields zeroed.
+    let legacy = {
+        let full = res.encode();
+        full[..21].to_vec()
+    };
+    let decoded = ProbeResult::decode(&legacy).unwrap();
+    assert_eq!(decoded.wire_packets_sent, 0);
+    assert_eq!(decoded.send_dropped, 0);
+    assert_eq!(decoded.bytes_sent, res.bytes_sent);
+    // Type bytes keep the control messages disjoint from each other.
+    assert!(ProbeRequest::decode(&res.encode()).is_err());
+    assert!(Reconfigure::decode(&req.encode()).is_err());
+    assert!(ProbeResult::decode(&req.encode()).is_err());
+}
+
+#[test]
+fn clock_messages_roundtrip() {
+    let probe = ClockProbe {
+        t1_ns: 1_700_000_000_123,
+    };
+    assert_eq!(ClockProbe::decode(&probe.encode()).unwrap(), probe);
+    let echo = ClockEcho {
+        t1_ns: 1_700_000_000_123,
+        t2_ns: 1_700_000_050_456,
+        t3_ns: 1_700_000_050_789,
+    };
+    assert_eq!(ClockEcho::decode(&echo.encode()).unwrap(), echo);
+    // Disjoint from the other control messages (distinct type bytes).
+    assert!(ClockProbe::decode(&echo.encode()).is_err());
+    assert!(ProbeRequest::decode(&probe.encode()).is_err());
+    assert!(ClockEcho::decode(&probe.encode()).is_err());
+}
+
+#[test]
+fn clock_offset_picks_min_rtt_and_recovers_offset() {
+    // Host clock is +1_000_000 ns ahead of the client. Construct samples where a symmetric
+    // round-trip recovers exactly that offset, and a noisy (asymmetric, high-RTT) sample is
+    // present but must be ignored by the min-RTT selection.
+    const OFF: i64 = 1_000_000;
+    // Clean sample: client t1=0, one-way=200µs each way → t2 = t1 + 200_000 + OFF (host clock),
+    // t3 = t2 + 50_000 (host processing), t4 = t3 - OFF + 200_000 (back in client clock).
+    let t1 = 0u64;
+    let t2 = (t1 as i64 + 200_000 + OFF) as u64;
+    let t3 = t2 + 50_000;
+    let t4 = (t3 as i64 - OFF + 200_000) as u64;
+    // Noisy sample: same offset but a fat, asymmetric RTT (slow return path) — higher RTT.
+    let n1 = 1_000_000u64;
+    let n2 = (n1 as i64 + 200_000 + OFF) as u64;
+    let n3 = n2 + 50_000;
+    let n4 = (n3 as i64 - OFF + 5_000_000) as u64; // 5 ms return → big RTT
+    let (offset, rtt) =
+        clock_offset_ns(&[(n1, n2, n3, n4), (t1, t2, t3, t4)]).expect("non-empty");
+    // The min-RTT sample recovers the offset exactly; its RTT is 2x200us, and the noisy
+    // (asymmetric, 5 ms return) sample is ignored by the min-RTT selection.
+    assert_eq!(offset, OFF);
+    assert_eq!(rtt, 400_000);
+    assert!(clock_offset_ns(&[]).is_none());
+}
+
+/// The mid-stream re-sync state machine: 8 rounds collected via matched echoes, stale
+/// echoes ignored, a restarted batch abandons the old one, and the batch result is the
+/// min-RTT estimate — the exact behavior the connect-time `clock_sync` loop has.
+#[test]
+fn clock_resync_collects_rounds_and_ignores_stale_echoes() {
+    // Host clock +1 ms ahead; symmetric 100 µs one-way paths except one congested round.
+    const OFF: i64 = 1_000_000;
+    let echo_for = |t1: u64, one_way: u64| ClockEcho {
+        t1_ns: t1,
+        t2_ns: (t1 as i64 + one_way as i64 + OFF) as u64,
+        t3_ns: (t1 as i64 + one_way as i64 + OFF) as u64 + 10_000,
+    };
+    let t4_for = |e: &ClockEcho, one_way: u64| (e.t3_ns as i64 - OFF + one_way as i64) as u64;
+
+    let mut rs = ClockResync::new();
+    // An unsolicited echo before any batch is ignored.
+    assert_eq!(rs.on_echo(&echo_for(42, 100_000), 500_000), ResyncStep::Idle);
+
+    let mut probe = rs.begin(1_000_000);
+    // A stale echo (wrong t1: the abandoned pre-begin probe) is ignored mid-batch.
+    assert_eq!(rs.on_echo(&echo_for(42, 100_000), 500_000), ResyncStep::Idle);
+    for round in 0..ClockResync::ROUNDS {
+        // Round 3 is congested (5 ms one-way) — it must lose the min-RTT selection.
+        let one_way = if round == 3 { 5_000_000 } else { 100_000 };
+        let echo = echo_for(probe.t1_ns, one_way);
+        let t4 = t4_for(&echo, one_way);
+        match rs.on_echo(&echo, t4) {
+            ResyncStep::Probe(p) => {
+                assert!(round < ClockResync::ROUNDS - 1, "batch overran its rounds");
+                probe = p;
+            }
+            ResyncStep::Done { offset_ns, rtt_ns } => {
+                assert_eq!(round, ClockResync::ROUNDS - 1, "batch ended early");
+                assert_eq!(offset_ns, OFF, "min-RTT round recovers the offset exactly");
+                assert_eq!(rtt_ns, 200_000); // 2×100 µs; host processing (t3−t2) excluded
+            }
+            ResyncStep::Idle => panic!("matched echo must advance the batch"),
+        }
+    }
+    // The batch is done: even a matching-t1 replay no longer advances anything.
+    assert_eq!(
+        rs.on_echo(&echo_for(probe.t1_ns, 100_000), probe.t1_ns + 300_000),
+        ResyncStep::Idle
+    );
+
+    // begin() mid-batch abandons the in-flight batch: its echo is stale afterwards.
+    let old = rs.begin(2_000_000);
+    let fresh = rs.begin(3_000_000);
+    assert_eq!(
+        rs.on_echo(&echo_for(old.t1_ns, 100_000), 2_300_000),
+        ResyncStep::Idle
+    );
+    assert!(matches!(
+        rs.on_echo(&echo_for(fresh.t1_ns, 100_000), 3_300_000),
+        ResyncStep::Probe(_)
+    ));
+}
+
+/// The acceptance guard: a batch measured through a congested window (fat RTT) must not
+/// replace the offset — its queueing delay biases the estimate exactly when frames
+/// already read late. Floor of 2 ms so a near-zero connect RTT (same-host/LAN) doesn't
+/// reject every later batch over normal jitter.
+#[test]
+fn clock_resync_acceptance_guard() {
+    // Generous connect RTT (10 ms): accept up to 1.5×.
+    assert!(accept_resync(14_000_000, 10_000_000));
+    assert!(!accept_resync(16_000_000, 10_000_000));
+    // Tiny connect RTT (200 µs, wired LAN): the 2 ms floor governs.
+    assert!(accept_resync(1_900_000, 200_000));
+    assert!(!accept_resync(2_100_000, 200_000));
+    // Boundary: exactly at the bound is accepted.
+    assert!(accept_resync(2_000_000, 0));
+    assert!(accept_resync(15_000_000, 10_000_000));
+}
+
+#[test]
+fn control_messages_disjoint_from_hello() {
+    // A Hello uses MAGIC (PKF1); control messages use CTL_MAGIC (PKFc). No Hello — at
+    // any abi_version — can be misparsed as a control message, and vice-versa.
+    for abi in [1u32, 2, 16, 0x10, 0x0113, 0x1410] {
+        let h = Hello {
+            abi_version: abi,
+            mode: Mode {
+                width: 1280,
+                height: 720,
+                refresh_hz: 60,
+            },
+            compositor: CompositorPref::Auto,
+            gamepad: GamepadPref::Auto,
+            bitrate_kbps: 0,
+            name: None,
+            launch: None,
+            video_caps: 0,
+            audio_channels: 2,
+            video_codecs: 0,
+            preferred_codec: 0,
+        }
+        .encode();
+        assert!(PairRequest::decode(&h).is_err(), "abi {abi} parsed as pair");
+        assert!(Reconfigure::decode(&h).is_err());
+    }
+    // And a PairRequest never parses as a Hello.
+    let pr = PairRequest {
+        name: "x".into(),
+        spake_a: vec![0u8; 33],
+    }
+    .encode();
+    assert!(Hello::decode(&pr).is_err());
+}
+
+#[test]
+fn pair_messages_roundtrip() {
+    let pr = PairRequest {
+        name: "Enrico's Mac".into(),
+        spake_a: vec![1, 2, 3, 4, 5],
+    };
+    assert_eq!(PairRequest::decode(&pr.encode()).unwrap(), pr);
+    let pc = PairChallenge {
+        spake_b: vec![9; 33],
+        confirm: [7u8; 32],
+    };
+    assert_eq!(PairChallenge::decode(&pc.encode()).unwrap(), pc);
+    let pp = PairProof { confirm: [3u8; 32] };
+    assert_eq!(PairProof::decode(&pp.encode()).unwrap(), pp);
+    for ok in [true, false] {
+        assert_eq!(
+            PairResult::decode(&PairResult { ok }.encode()).unwrap().ok,
+            ok
+        );
+    }
+    // Length-exact: a truncated/padded PairProof is rejected.
+    let mut bad = pp.encode();
+    bad.push(0);
+    assert!(PairProof::decode(&bad).is_err());
+}
+
+#[test]
+fn spake2_pairing_agrees_only_on_matching_pin_and_certs() {
+    let cfp = [0x11u8; 32];
+    let hfp = [0x22u8; 32];
+
+    // Right PIN, same fingerprint views on both sides → both confirmations agree.
+    let (ca, ma) = pake::start(true, "4321", &cfp, &hfp);
+    let (cb, mb) = pake::start(false, "4321", &cfp, &hfp);
+    let a = ca.finish(&mb).unwrap();
+    let b = cb.finish(&ma).unwrap();
+    assert!(pake::verify(&a.host, &b.host) && pake::verify(&a.client, &b.client));
+
+    // Wrong PIN → different keys → confirmations DON'T match (one online guess wasted).
+    let (ca, ma) = pake::start(true, "0000", &cfp, &hfp);
+    let (cb, mb) = pake::start(false, "4321", &cfp, &hfp);
+    let a = ca.finish(&mb).unwrap();
+    let b = cb.finish(&ma).unwrap();
+    assert!(!pake::verify(&a.client, &b.client));
+
+    // MITM: the two legs saw different host certs → no agreement even with the right PIN.
+    let attacker_hfp = [0x33u8; 32];
+    let (ca, ma) = pake::start(true, "4321", &cfp, &attacker_hfp);
+    let (cb, mb) = pake::start(false, "4321", &cfp, &hfp);
+    let a = ca.finish(&mb).unwrap();
+    let b = cb.finish(&ma).unwrap();
+    assert!(!pake::verify(&a.client, &b.client));
+}
+
+#[test]
+fn audio_datagram_roundtrip() {
+    let opus = [0x42u8; 97];
+    let d = encode_audio_datagram(7, 1_000_000_123, &opus);
+    assert_eq!(d[0], AUDIO_MAGIC);
+    let (seq, pts, payload) = decode_audio_datagram(&d).unwrap();
+    assert_eq!((seq, pts), (7, 1_000_000_123));
+    assert_eq!(payload, opus);
+    assert!(decode_audio_datagram(&d[..12]).is_none()); // truncated header
+    assert!(decode_audio_datagram(&[0u8; 13]).is_none()); // bad magic
+
+    // Empty payload is legal (DTX) — header-only datagram.
+    let header_only = encode_audio_datagram(0, 0, &[]);
+    let (_, _, empty) = decode_audio_datagram(&header_only).unwrap();
+    assert!(empty.is_empty());
+}
+
+#[test]
+fn rumble_datagram_roundtrip() {
+    let d = encode_rumble_datagram(1, 0x1234, 0xFFFF);
+    assert_eq!(d[0], RUMBLE_MAGIC);
+    assert_eq!(decode_rumble_datagram(&d), Some((1, 0x1234, 0xFFFF)));
+    assert!(decode_rumble_datagram(&d[..6]).is_none());
+}
+
+#[test]
+fn mic_datagram_roundtrip_and_disjoint_from_audio() {
+    let opus = [0x5Au8; 80];
+    let d = encode_mic_datagram(42, 9_999, &opus);
+    assert_eq!(d[0], MIC_MAGIC);
+    let (seq, pts, payload) = decode_mic_datagram(&d).unwrap();
+    assert_eq!((seq, pts), (42, 9_999));
+    assert_eq!(payload, opus);
+    assert!(decode_mic_datagram(&d[..12]).is_none()); // truncated
+                                                      // Tag separation: a mic datagram is not an audio datagram and vice-versa.
+    assert!(decode_audio_datagram(&d).is_none());
+    assert!(decode_mic_datagram(&encode_audio_datagram(1, 2, &opus)).is_none());
+    // Empty payload (DTX) is legal.
+    assert!(decode_mic_datagram(&encode_mic_datagram(0, 0, &[]))
+        .unwrap()
+        .2
+        .is_empty());
+}
+
+#[test]
+fn rich_input_roundtrip() {
+    for ev in [
+        RichInput::Touchpad {
+            pad: 1,
+            finger: 0,
+            active: true,
+            x: 40000,
+            y: 12345,
+        },
+        RichInput::Motion {
+            pad: 0,
+            gyro: [-100, 200, -300],
+            accel: [16384, -8192, 1],
+        },
+        RichInput::TouchpadEx {
+            pad: 2,
+            surface: 1,
+            finger: 1,
+            touch: true,
+            click: false,
+            x: -12345,
+            y: 30000,
+            pressure: 4000,
+        },
+    ] {
+        let d = ev.encode();
+        assert_eq!(d[0], RICH_INPUT_MAGIC);
+        assert_eq!(RichInput::decode(&d), Some(ev));
+    }
+    // Disjoint from the fixed input datagram (0xC8); unknown kind + truncation → None.
+    assert!(RichInput::decode(&[crate::input::INPUT_MAGIC; 18]).is_none());
+    assert!(RichInput::decode(&[RICH_INPUT_MAGIC, 0x7F]).is_none()); // unknown kind
+    assert!(RichInput::decode(&[RICH_INPUT_MAGIC, RICH_TOUCHPAD, 0]).is_none()); // short
+    assert!(RichInput::decode(&[RICH_INPUT_MAGIC, RICH_TOUCHPAD_EX, 0, 0, 0, 0]).is_none());
+    // short
+}
+
+#[test]
+fn hid_output_roundtrip() {
+    let cases = [
+        HidOutput::Led {
+            pad: 2,
+            r: 0xAA,
+            g: 0xBB,
+            b: 0xCC,
+        },
+        HidOutput::PlayerLeds {
+            pad: 0,
+            bits: 0b10101,
+        },
+        HidOutput::Trigger {
+            pad: 1,
+            which: 1,
+            effect: vec![0x26, 0x90, 0xA0, 0xFF, 0x00, 0x00],
+        },
+        HidOutput::TrackpadHaptic {
+            pad: 0,
+            side: 1,
+            amplitude: 0x1234,
+            period: 0x5678,
+            count: 9,
+        },
+    ];
+    for ev in &cases {
+        let d = ev.encode();
+        assert_eq!(d[0], HIDOUT_MAGIC);
+        assert_eq!(HidOutput::decode(&d).as_ref(), Some(ev));
+    }
+    assert!(HidOutput::decode(&[HIDOUT_MAGIC, 0x7F]).is_none()); // unknown kind
+                                                                 // A rich-input datagram is not a HID-output datagram.
+    assert!(HidOutput::decode(
+        &RichInput::Motion {
+            pad: 0,
+            gyro: [0; 3],
+            accel: [0; 3]
+        }
+        .encode()
+    )
+    .is_none());
+}
+
+#[test]
+fn fingerprint_is_sha256_of_der() {
+    // Stable across calls, distinct for distinct certs.
+    let a = endpoint::cert_fingerprint(b"cert-a");
+    assert_eq!(a, endpoint::cert_fingerprint(b"cert-a"));
+    assert_ne!(a, endpoint::cert_fingerprint(b"cert-b"));
+}