feat(tracking): add local OpenXR OSC and BlueZ heart-rate tools

README.md

@@ -204,6 +204,7 @@ Frame's software fits together, all checked against a real headset and labelled
 | [SSH](docs/ssh.md) · [Streaming](docs/streaming.md) · [Files](docs/file-transfer.md) · [Panels](docs/panels.md) · [Tailscale](docs/tailscale.md) | Topic notes |
 | [Frame Control for iPhone](docs/iphone.md) | The iPhone and iPad app, how it runs the server on the Frame, pairing |
 | [Recovery and OS images](docs/recovery-and-images.md) | Where to download the Frame's OS, what's inside, testing without the headset |
+| [Eye tracking and heart rate](docs/tracking.md) | Our OpenXR → OSC bridge, BlueZ heart-rate panel and optional local session log; SlimeVR feasibility notes |
 | [Testing](docs/testing.md) | Unit tests, end-to-end tests against a fake Frame in Docker, and the headset smoke test |
 | [Open questions](docs/open-questions.md) | What's still unchecked |
 

docs/how-the-frame-works.md

@@ -20,6 +20,15 @@ SteamVR  (vrserver, vrcompositor, vrdashboard)       ← renders the room + pane
 Lepton (Android 11, podman container "lepton-dev") ← its own panel, app 3056000
 ```
 
+## Tracking additions (verified 2026-09-28)
+
+On SteamOS 0.4.1, build `20260925.6191901`, SteamVR exposes combined gaze
+through `XR_EXT_eye_gaze_interaction` in a headless OpenXR 1.0 session. Our
+reader obtained valid tracked samples and sent OSC to a configured loopback
+receiver. BlueZ LE discovery works; GTK4/GI can render our heart-rate panel.
+No BLE strap or SlimeVR trackers were attached. See [tracking](tracking.md)
+for the evidence, privacy defaults and untested integration boundaries.
+
 ## Facts worth knowing
 
 | Fact | Where it matters |

docs/testing.md

@@ -148,3 +148,10 @@ For example, on 2026-09-27 the smoke test found that Steam's `create-shortcut`
 refuses ids with a hyphen (`missing/invalid arguments`), which the fake had
 accepted. The fake now refuses them the same way, and Frame Control makes ids
 Steam accepts.
+
+## Tracking protocols and fake BlueZ
+
+`tests/test_tracking.py` exercises our gaze conversion, OSC sender, HRS parser
+and BlueZ lifecycle with an in-memory fake object tree. It runs in the normal
+unit suite without Bluetooth, GTK or OpenXR. Real Frame results and the absent
+strap/tracker boundaries are recorded in [tracking](tracking.md).

docs/tracking.md

@@ -0,0 +1,188 @@
+# Eye tracking and heart rate
+
+Frame Control's own tools run on the Frame, using OpenXR and BlueZ. No
+VRCFaceTracking, LunaHR, Pulsoid or other tracking app is required. This is a
+command-line first version; it does not add a desktop app tab.
+
+## What was checked
+
+**Verified 2026-09-28**, on a real aarch64 Frame running SteamOS 0.4.1,
+BUILD_ID `20260925.6191901`:
+
+| Check | Result |
+|---|---|
+| OpenXR gaze | SteamVR advertises `XR_EXT_eye_gaze_interaction`, `XR_MND_headless` and `XR_KHR_convert_timespec_time`. `supportsEyeGazeInteraction=1`. A headless session reached FOCUSED and produced 269 valid, tracked orientations in the first ten-second probe. |
+| Our gaze → OSC bridge | A separate ten-second run produced 280 valid samples and 280 correctly padded 44-byte `/tracking/eye/CenterPitchYaw` messages at an explicitly configured loopback receiver. Only counters and packet-layout checks were retained. |
+| Bluetooth stack | BlueZ active, adapter powered, central/peripheral roles available. LE discovery started and stopped successfully. No pairing or adapter power settings changed. |
+| Our heart-rate panel | GTK4/GI runs on the stock image. A **synthetic 72 BPM** notification displayed in our X11 window, tagged `STEAM_GAME=2000000027`. Window capture checked; no real heart-rate measurement was taken. |
+| SlimeVR, separate feasibility check | Native aarch64 server v21.1.0 ran with an isolated Temurin 21 JRE, created its driver sockets and accepted a local TCP connection on port 21110. Driver v6.0.0 loaded with all shared libraries resolved; `HmdDriverFactory("IServerTrackedDeviceProvider_004")` returned a non-null provider and error 0. |
+
+![Our heart-rate panel on the Frame, showing synthetic 72 BPM](img/heart-rate-panel.png)
+
+The image is a capture of our own Frame window using a fake notification,
+not a real sensor reading.
+
+**Untested:** a real BLE strap's notifications, physical fit/contact behaviour,
+end-to-end heart-rate display/OSC/log with a strap, avatar response in VRChat,
+gaze accuracy/calibration, coexistence with every immersive app, in-headset
+panel placement, SlimeVR tracker/calibration data and the SlimeVR driver running
+inside SteamVR. No trackers or strap are attached. The driver was loaded in a
+separate process; it was **not registered or activated in SteamVR**. Steam and
+SteamVR were not stopped or restarted.
+
+**Verified blocker resolved:** importing `tkinter` fails because `libtk8.6.so`
+is absent. The panel uses the installed GTK4/GI bindings instead. The Frame's
+OpenXR headers advertise a newer API version than the runtime accepts; our
+reader requests OpenXR 1.0 explicitly.
+
+## Install our tools
+
+From this checkout on your computer, while the Frame is awake:
+
+```sh
+python3 scripts/tracking-on-frame.py install
+```
+
+This copies our Python code and compiles our small C OpenXR reader into
+`~/.local/share/frame-control/tracking/` on the Frame. It uses the Frame's
+existing compiler, OpenXR headers/loader, Python, dbus-python, GI and GTK4.
+Nothing is downloaded, and no sudo, driver registration, system setting,
+service or autostart is added. `FRAME_ALIAS` can select another SSH alias.
+The desktop app/server keeps its existing stdlib-only dependency set.
+
+## Eye tracking → OSC
+
+Start with a ten-second capability/data-availability check:
+
+```sh
+python3 scripts/tracking-on-frame.py gaze --seconds 10
+```
+
+This prints support, session-state numbers and sample counters. It opens no
+OSC socket and prints no gaze coordinates. Exit 0 means at least one valid
+sample, 3 means no valid sample was observed, and 1 means an API/runtime error.
+If there are no valid samples, wake/wear the headset and check its tracking
+setup; a successful capability check alone does not prove usable gaze.
+
+To send to VRChat running **on the Frame**, explicitly enable OSC in VRChat
+and choose its local UDP endpoint:
+
+```sh
+python3 scripts/tracking-on-frame.py gaze --seconds 3600 --osc 127.0.0.1 9000
+```
+
+For a receiver on another computer, replace `127.0.0.1` with that computer's
+IP address and choose its listening port. Addresses are IP literals (IPv4 or
+IPv6); there is no discovery or default destination. Loopback here always
+means **the Frame**, not the computer running the SSH command. OSC uses
+unencrypted UDP: configure only a receiver you intend to receive this data.
+
+**Documented:** [VRChat's eye OSC interface](https://docs.vrchat.com/docs/osc-eye-tracking)
+accepts `/tracking/eye/CenterPitchYaw` with two floats in degrees, positive down
+and right. We locate OpenXR's combined gaze pose relative to VIEW (the head),
+rotate its -Z forward vector and convert that direction to these angles.
+Only active, orientation-valid **and tracked** samples are sent, at up to
+30 Hz. No eyelid/blink, individual-eye or face values are invented. We do not
+send neutral gaze on tracking loss; VRChat's documented timeout restores its
+automatic eye behaviour after input stops.
+
+**Privacy:** gaze is personal data. It stays in process memory and a private
+pipe between our reader and bridge. There is no gaze log option, telemetry,
+OSC receiver or raw gaze on stdout/stderr. Only an explicit `--osc IP PORT`
+opens an output socket. Runtime diagnostics and validity counters are not
+measurements. Stop with Ctrl-C or let `--seconds` expire (maximum 24 hours).
+A lost headless session ends the run; it does not silently reconnect.
+
+## BLE heart rate → our panel, OSC and optional log
+
+First discover/pair your strap in SteamOS's Bluetooth settings. Select that
+strap's Bluetooth address explicitly; our tool does not scan for or connect
+to arbitrary nearby devices.
+
+```sh
+python3 scripts/tracking-on-frame.py heart \
+  --device AA:BB:CC:DD:EE:FF --panel --seconds 3600
+```
+
+This uses BlueZ's standard Heart Rate Service (`180d`) and Heart Rate
+Measurement (`2a37`) notifications. It finds the characteristic only beneath
+the selected device's HRS service. The reader handles 8- and 16-bit BPM,
+contact flags and optional energy/RR fields; energy and RR intervals are
+validated for length but discarded. Zero BPM, reported loss of skin contact,
+malformed packets and readings older than five seconds are not shown as a
+current measurement. A disconnect stops the run; reconnect and start again.
+This is a social/fitness readout, not a medical monitor.
+
+The panel is our GTK4 window on gamescope's X display. Use SteamVR's panel
+controls to float/dock it (see [panels](panels.md)). **Stop**, closing the panel,
+Ctrl-C, SSH hangup or the duration limit ends our subscription. A connection
+that was already open when we started is preserved; a connection we opened
+is disconnected on exit. No Bluetooth power or pairing state is changed.
+
+Add either output explicitly:
+
+```sh
+python3 scripts/tracking-on-frame.py heart \
+  --device AA:BB:CC:DD:EE:FF --panel --seconds 3600 \
+  --osc 127.0.0.1 9000 --address /avatar/parameters/HeartRate \
+  --log /home/steamos/heart-session.csv
+```
+
+The OSC value is integer BPM. `HeartRate` is a chosen avatar parameter, **not a
+built-in VRChat heart-rate feature**; your avatar/receiver must define the
+matching parameter. `--address` can select another literal OSC path. The local
+panel works without OSC, a log or an avatar integration.
+
+The optional CSV contains only `unix_seconds,bpm`. It is created privately
+(mode 0600), refuses existing files/symlinks, and lives **on the Frame** at the
+path you specify. Nothing is logged by default, and heart-rate values are not
+printed to the terminal. Delete your session file when you no longer need it.
+
+## SlimeVR: feasibility only
+
+SlimeVR is an independent application stack. Neither of our features installs,
+launches or depends on it. Users who want it can follow
+[SlimeVR's setup documentation](https://docs.slimevr.dev/server/index.html).
+The consented upstream releases tested were
+[server v21.1.0](https://github.com/SlimeVR/SlimeVR-Server/releases/tag/v21.1.0)
+and [driver v6.0.0](https://github.com/SlimeVR/SlimeVR-OpenVR-Driver/releases/tag/v6.0.0),
+under SlimeVR's MIT/Apache-2.0 licensing.
+
+**Verified layout, read-only:** the Frame's registered runtime is `/opt/steamvr`;
+its native driver is `drivers/cv/bin/linuxarm64/driver_cv.so`, with a
+`drivers/cv/driver.vrdrivermanifest`. Frame controller manifests/resources are
+under `drivers/frame_controller/`. Configuration is under
+`~/.config/openvr/config/`, not the Steam client's config directory. The
+SlimeVR release also uses `slimevr/bin/linuxarm64/driver_slimevr.so` plus its
+manifest. Nothing in those installed SteamVR directories was changed.
+
+**Inferred:** the matching ABI/layout and standalone factory success make
+SteamVR integration plausible. They do not prove successful driver `Init`,
+server/driver IPC, tracking, or calibration. That needs a separate integration
+check with hardware and an agreed SteamVR restart. No Java executable was on
+PATH for this check, so an isolated JRE was used. SlimeVR's server opens LAN
+listeners; our temporary server was stopped and the temporary downloads,
+configuration and logs were removed. It is not left installed or running.
+
+## Tests and remaining checks
+
+```sh
+python3 -m unittest discover -s tests
+```
+
+`tests/test_tracking.py` covers HRS packet parsing, contact/staleness, OSC
+padding/types and a real loopback socket, quaternion signs, opt-in networking,
+private/exclusive logging and a fake BlueZ object tree. The fake checks service
+ownership, notification routing, delayed GATT discovery and connection cleanup.
+It does not pretend to be a physical strap or a real OpenXR runtime.
+
+Before calling hardware support complete, attach a strap and check BPM against
+its own display/reference, loss of contact, disconnect/reconnect, Stop, OSC and
+CSV together. Check avatar eyes while looking up/down/left/right in a supported
+VRChat session. No third-party tracking app is needed for either test.
+
+Independent review attempt: `devin -p --model swe-2-max` with the frozen diff,
+contribution standards and read-only instructions returned no output for ten
+minutes. It was terminated with exit 143. No completed review or actual model
+identity was returned; hardware checks and independent review remain follow-up
+work before making the draft ready.

frame/tracking/gaze.c

@@ -0,0 +1,135 @@
+/* Frame Control's OpenXR gaze source. No values on stdout/stderr or disk.
+ * The Python bridge supplies a private pipe with --fd; standalone probes only
+ * report counters. Uses a headless session, never submits frames or takes focus. */
+#define XR_USE_TIMESPEC
+#include <time.h>
+#include <openxr/openxr.h>
+#include <openxr/openxr_platform.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+static volatile sig_atomic_t stopped;
+static void stop(int sig) { (void)sig; stopped = 1; }
+#define CHECK(call) do { result = (call); if (XR_FAILED(result)) { \
+    fprintf(stderr, "%s failed (%d)\n", #call, result); goto cleanup; } } while (0)
+
+int main(int argc, char **argv) {
+    int seconds = 10, fd = -1, running = 0, rc = 1;
+    unsigned active = 0, valid = 0, samples = 0;
+    for (int i = 1; i < argc; i++) {
+        if (!strcmp(argv[i], "--seconds") && i+1 < argc) seconds = atoi(argv[++i]);
+        else if (!strcmp(argv[i], "--fd") && i+1 < argc) fd = atoi(argv[++i]);
+        else { fprintf(stderr, "usage: gaze [--seconds 1..86400] [--fd private-pipe]\n"); return 2; }
+    }
+    if (seconds < 1 || seconds > 86400 || (fd != -1 && fd < 3)) return 2;
+    FILE *out = fd == -1 ? NULL : fdopen(fd, "w");
+    if (fd != -1 && !out) return 2;
+    signal(SIGINT, stop); signal(SIGTERM, stop); signal(SIGHUP, stop); signal(SIGPIPE, SIG_IGN);
+    XrResult result;
+    XrInstance instance = XR_NULL_HANDLE;
+    XrSession session = XR_NULL_HANDLE;
+    XrActionSet set = XR_NULL_HANDLE;
+    XrSpace gaze = XR_NULL_HANDLE, view = XR_NULL_HANDLE;
+    const char *extensions[] = {"XR_EXT_eye_gaze_interaction", "XR_MND_headless", "XR_KHR_convert_timespec_time"};
+    XrInstanceCreateInfo create = {.type = XR_TYPE_INSTANCE_CREATE_INFO};
+    strcpy(create.applicationInfo.applicationName, "Frame Control gaze");
+    create.applicationInfo.apiVersion = XR_MAKE_VERSION(1, 0, 0);
+    create.enabledExtensionCount = 3; create.enabledExtensionNames = extensions;
+    CHECK(xrCreateInstance(&create, &instance));
+    XrSystemGetInfo get = {.type = XR_TYPE_SYSTEM_GET_INFO, .formFactor = XR_FORM_FACTOR_HEAD_MOUNTED_DISPLAY};
+    XrSystemId system;
+    CHECK(xrGetSystem(instance, &get, &system));
+    XrSystemEyeGazeInteractionPropertiesEXT eye = {.type = XR_TYPE_SYSTEM_EYE_GAZE_INTERACTION_PROPERTIES_EXT};
+    XrSystemProperties props = {.type = XR_TYPE_SYSTEM_PROPERTIES, .next = &eye};
+    CHECK(xrGetSystemProperties(instance, system, &props));
+    printf("supportsEyeGazeInteraction=%u\n", eye.supportsEyeGazeInteraction);
+    if (!eye.supportsEyeGazeInteraction) goto cleanup;
+    XrSessionCreateInfo sc = {.type = XR_TYPE_SESSION_CREATE_INFO, .systemId = system};
+    CHECK(xrCreateSession(instance, &sc, &session));
+    XrActionSetCreateInfo asc = {.type = XR_TYPE_ACTION_SET_CREATE_INFO};
+    strcpy(asc.actionSetName, "gaze"); strcpy(asc.localizedActionSetName, "Gaze");
+    CHECK(xrCreateActionSet(instance, &asc, &set));
+    XrActionCreateInfo ac = {.type = XR_TYPE_ACTION_CREATE_INFO, .actionType = XR_ACTION_TYPE_POSE_INPUT};
+    strcpy(ac.actionName, "gaze_pose"); strcpy(ac.localizedActionName, "Gaze pose");
+    XrAction action;
+    CHECK(xrCreateAction(set, &ac, &action));
+    XrPath profile, input;
+    CHECK(xrStringToPath(instance, "/interaction_profiles/ext/eye_gaze_interaction", &profile));
+    CHECK(xrStringToPath(instance, "/user/eyes_ext/input/gaze_ext/pose", &input));
+    XrActionSuggestedBinding binding = {action, input};
+    XrInteractionProfileSuggestedBinding suggested = {.type = XR_TYPE_INTERACTION_PROFILE_SUGGESTED_BINDING,
+        .interactionProfile = profile, .countSuggestedBindings = 1, .suggestedBindings = &binding};
+    CHECK(xrSuggestInteractionProfileBindings(instance, &suggested));
+    XrSessionActionSetsAttachInfo attach = {.type = XR_TYPE_SESSION_ACTION_SETS_ATTACH_INFO, .countActionSets = 1, .actionSets = &set};
+    CHECK(xrAttachSessionActionSets(session, &attach));
+    XrActionSpaceCreateInfo space = {.type = XR_TYPE_ACTION_SPACE_CREATE_INFO, .action = action, .poseInActionSpace.orientation.w = 1};
+    CHECK(xrCreateActionSpace(session, &space, &gaze));
+    XrReferenceSpaceCreateInfo ref = {.type = XR_TYPE_REFERENCE_SPACE_CREATE_INFO, .referenceSpaceType = XR_REFERENCE_SPACE_TYPE_VIEW,
+        .poseInReferenceSpace.orientation.w = 1};
+    CHECK(xrCreateReferenceSpace(session, &ref, &view));
+    PFN_xrConvertTimespecTimeToTimeKHR convert;
+    CHECK(xrGetInstanceProcAddr(instance, "xrConvertTimespecTimeToTimeKHR", (PFN_xrVoidFunction *)&convert));
+    struct timespec start, now;
+    clock_gettime(CLOCK_MONOTONIC, &start);
+    while (!stopped) {
+        clock_gettime(CLOCK_MONOTONIC, &now);
+        if (now.tv_sec - start.tv_sec >= seconds) break;
+        XrEventDataBuffer event = {.type = XR_TYPE_EVENT_DATA_BUFFER};
+        while ((result = xrPollEvent(instance, &event)) == XR_SUCCESS) {
+            if (event.type == XR_TYPE_EVENT_DATA_SESSION_STATE_CHANGED) {
+                XrSessionState state = ((XrEventDataSessionStateChanged *)&event)->state;
+                printf("sessionState=%d\n", state); fflush(stdout);
+                if (state == XR_SESSION_STATE_READY && !running) {
+                    XrSessionBeginInfo begin = {.type = XR_TYPE_SESSION_BEGIN_INFO, .primaryViewConfigurationType = XR_VIEW_CONFIGURATION_TYPE_PRIMARY_STEREO};
+                    CHECK(xrBeginSession(session, &begin)); running = 1;
+                } else if (state == XR_SESSION_STATE_STOPPING) {
+                    CHECK(xrEndSession(session)); running = 0; stopped = 1;
+                } else if (state == XR_SESSION_STATE_EXITING || state == XR_SESSION_STATE_LOSS_PENDING) stopped = 1;
+            } else if (event.type == XR_TYPE_EVENT_DATA_INSTANCE_LOSS_PENDING) stopped = 1;
+            event.type = XR_TYPE_EVENT_DATA_BUFFER;
+        }
+        if (XR_FAILED(result)) goto cleanup;
+        if (running && !stopped) {
+            XrActiveActionSet activeSet = {set, XR_NULL_PATH};
+            XrActionsSyncInfo sync = {.type = XR_TYPE_ACTIONS_SYNC_INFO, .countActiveActionSets = 1, .activeActionSets = &activeSet};
+            CHECK(xrSyncActions(session, &sync));
+            if (result != XR_SUCCESS) {
+                struct timespec delay = {.tv_nsec = 33333333};
+                nanosleep(&delay, NULL);
+                continue; /* No stale gaze when the runtime denies focus. */
+            }
+            XrActionStateGetInfo ag = {.type = XR_TYPE_ACTION_STATE_GET_INFO, .action = action};
+            XrActionStatePose pose = {.type = XR_TYPE_ACTION_STATE_POSE};
+            CHECK(xrGetActionStatePose(session, &ag, &pose));
+            samples++;
+            if (pose.isActive) {
+                active++;
+                XrTime time; CHECK(convert(instance, &now, &time));
+                XrSpaceLocation location = {.type = XR_TYPE_SPACE_LOCATION};
+                CHECK(xrLocateSpace(gaze, view, time, &location));
+                XrSpaceLocationFlags needed = XR_SPACE_LOCATION_ORIENTATION_VALID_BIT | XR_SPACE_LOCATION_ORIENTATION_TRACKED_BIT;
+                if ((location.locationFlags & needed) == needed) {
+                    valid++;
+                    if (out) {
+                        XrQuaternionf q = location.pose.orientation;
+                        if (fprintf(out, "%g %g %g %g\n", q.x, q.y, q.z, q.w) < 0 || fflush(out)) goto cleanup;
+                    }
+                }
+            }
+        }
+        struct timespec delay = {.tv_nsec = 33333333}; nanosleep(&delay, NULL);
+    }
+    printf("samples=%u active=%u valid=%u\n", samples, active, valid);
+    rc = valid ? 0 : 3; /* Distinguish a working session from observed gaze. */
+cleanup:
+    if (view) xrDestroySpace(view);
+    if (gaze) xrDestroySpace(gaze);
+    if (session) xrDestroySession(session);
+    if (set) xrDestroyActionSet(set);
+    if (instance) xrDestroyInstance(instance);
+    if (out) fclose(out);
+    return rc;
+}

frame/tracking/tracking.py

@@ -0,0 +1,387 @@
+#!/usr/bin/env python3
+"""Frame-local tracking tools. No network destination or data log by default."""
+import argparse
+import math
+import os
+from pathlib import Path
+import signal
+import socket
+import struct
+import subprocess
+import time
+
+
+class TrackingError(RuntimeError):
+    """A safe, actionable status message containing no sensor data."""
+
+
+HRS = "0000180d-0000-1000-8000-00805f9b34fb"
+MEASUREMENT = "00002a37-0000-1000-8000-00805f9b34fb"
+DEVICE = "org.bluez.Device1"
+SERVICE = "org.bluez.GattService1"
+CHARACTERISTIC = "org.bluez.GattCharacteristic1"
+
+
+def heart_rate(data):
+    """Validate the Bluetooth HRS measurement, returning BPM/contact only.
+
+    Energy and RR intervals are checked for length but never retained.
+    None means contact is supported and the strap reports no skin contact.
+    """
+    data = bytes(data)
+    if len(data) < 2 or data[0] & 0xe0:
+        raise ValueError("invalid HRS measurement")
+    flags = data[0]
+    size = 2 if flags & 1 else 1
+    end = 1 + size + (2 if flags & 8 else 0)
+    if len(data) < end:
+        raise ValueError("truncated HRS measurement")
+    extra = len(data) - end
+    if (flags & 16 and (extra < 2 or extra % 2)) or (not flags & 16 and extra):
+        raise ValueError("invalid HRS optional fields")
+    if flags & 4 and not flags & 2:
+        return None
+    bpm = int.from_bytes(data[1:1 + size], "little")
+    return bpm if bpm else None
+
+
+def gaze_angles(quaternion):
+    """OpenXR head-relative -Z forward → VRChat degrees, down/right positive."""
+    if len(quaternion) != 4 or not all(math.isfinite(v) for v in quaternion):
+        raise ValueError("invalid gaze orientation")
+    norm = math.sqrt(sum(v * v for v in quaternion))
+    if not 0.9 < norm < 1.1:
+        raise ValueError("invalid gaze orientation")
+    x, y, z, w = (v / norm for v in quaternion)
+    # Rotate OpenXR's forward vector (0, 0, -1) into VIEW space.
+    dx, dy, dz = -2 * (x*z + w*y), 2 * (w*x - y*z), 2 * (x*x + y*y) - 1
+    return math.degrees(math.atan2(-dy, math.hypot(dx, dz))), math.degrees(math.atan2(dx, -dz))
+
+
+def osc_message(address, values):
+    if not address.startswith("/") or any(c.isspace() or c in '\0#*,?[]{}' for c in address):
+        raise ValueError("OSC address must be a literal path")
+    def string(value):
+        encoded = value.encode("utf-8") + b"\0"
+        return encoded + b"\0" * (-len(encoded) % 4)
+    tags, payload = ",", b""
+    for value in values:
+        if type(value) is int:
+            tags += "i"
+            payload += struct.pack(">i", value)
+        else:
+            if not math.isfinite(value):
+                raise ValueError("OSC value must be finite")
+            tags += "f"
+            payload += struct.pack(">f", value)
+    return string(address) + string(tags) + payload
+
+
+class Osc:
+    def __init__(self, endpoint=None):
+        self.sock = None
+        self.target = None
+        if endpoint:
+            import ipaddress
+            address = ipaddress.ip_address(endpoint[0])
+            port = int(endpoint[1])
+            if address.is_unspecified or address.is_multicast or not 1 <= port <= 65535:
+                raise ValueError("OSC needs a unicast IP address and port 1..65535")
+            self.sock = socket.socket(socket.AF_INET6 if address.version == 6 else socket.AF_INET, socket.SOCK_DGRAM)
+            self.target = (str(address), port)
+
+    def send(self, address, values):
+        if self.sock:
+            self.sock.sendto(osc_message(address, values), self.target)
+
+    def close(self):
+        if self.sock:
+            self.sock.close()
+
+
+class HeartSession:
+    def __init__(self, osc, address, log=None, clock=time.monotonic):
+        self.osc, self.address, self.clock = osc, address, clock
+        self.bpm, self.updated = None, None
+        self.log = None
+        if log:
+            # Exclusive creation refuses existing files and symlinks; mode is
+            # private even with a permissive process umask.
+            fd = os.open(log, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o600)
+            self.log = os.fdopen(fd, "w")
+            self.log.write("unix_seconds,bpm\n")
+
+    def notification(self, data):
+        self.bpm = heart_rate(data)
+        self.updated = self.clock()
+        if self.bpm is not None:
+            self.osc.send(self.address, [self.bpm])
+            if self.log:
+                self.log.write(f"{time.time():.3f},{self.bpm}\n")
+                self.log.flush()
+
+    def current(self):
+        if self.updated is None or self.clock() - self.updated > 5:
+            return None
+        return self.bpm
+
+    def close(self):
+        if self.log:
+            self.log.close()
+
+
+class BluezHeart:
+    """One explicitly selected, already discovered strap; no ambient scan."""
+    def __init__(self, bus, interface, address, on_value):
+        self.bus, self.interface, self.on_value = bus, interface, on_value
+        self.device = self.characteristic = None
+        self.connected_here = False
+        self.notifying = False
+        self.match = None
+        objects = self.objects()
+        matches = [path for path, interfaces in objects.items()
+                   if str(interfaces.get(DEVICE, {}).get("Address", "")).upper() == address.upper()]
+        if len(matches) != 1:
+            raise TrackingError("Strap not found uniquely in BlueZ; pair/discover it in SteamOS Bluetooth settings first")
+        self.device = matches[0]
+        self.match = bus.add_signal_receiver(self.changed, signal_name="PropertiesChanged",
+                                            dbus_interface="org.freedesktop.DBus.Properties",
+                                            bus_name="org.bluez", path_keyword="path")
+        try:
+            if not objects[self.device][DEVICE].get("Connected"):
+                self.call(self.device, DEVICE).Connect(timeout=20)
+                self.connected_here = True
+        except Exception:
+            self.close()
+            raise
+
+    def objects(self):
+        return self.call("/", "org.freedesktop.DBus.ObjectManager").GetManagedObjects()
+
+    def call(self, path, kind):
+        return self.interface(self.bus.get_object("org.bluez", path), kind)
+
+    def subscribe(self):
+        objects = self.objects()
+        if not objects.get(self.device, {}).get(DEVICE, {}).get("ServicesResolved"):
+            return False
+        services = {p for p, obj in objects.items() if str(obj.get(SERVICE, {}).get("UUID", "")).lower() == HRS
+                    and obj[SERVICE].get("Device") == self.device}
+        for path, obj in objects.items():
+            props = obj.get(CHARACTERISTIC, {})
+            if props.get("Service") in services and str(props.get("UUID", "")).lower() == MEASUREMENT:
+                if "notify" not in props.get("Flags", []):
+                    raise TrackingError("Heart-rate characteristic does not support notifications")
+                self.characteristic = path
+                self.call(path, CHARACTERISTIC).StartNotify()
+                self.notifying = True
+                return True
+        raise TrackingError("Selected device has no standard Heart Rate Service measurement")
+
+    def changed(self, kind, changes, invalidated, path=None):
+        if kind == CHARACTERISTIC and path == self.characteristic and "Value" in changes:
+            self.on_value(changes["Value"])
+        elif kind == DEVICE and path == self.device and "Connected" in changes and not changes["Connected"]:
+            self.on_value(None)
+
+    def close(self):
+        try:
+            if self.notifying:
+                self.call(self.characteristic, CHARACTERISTIC).StopNotify()
+        finally:
+            if self.match:
+                self.match.remove()
+            if self.connected_here:
+                self.call(self.device, DEVICE).Disconnect()
+
+
+def run_gaze(args, osc):
+    binary = Path(__file__).with_name("gaze")
+    command = [str(binary), "--seconds", str(args.seconds)]
+    if not args.osc:
+        return subprocess.call(command)
+    read_fd, write_fd = os.pipe()
+    process = None
+    try:
+        process = subprocess.Popen(command + ["--fd", str(write_fd)], pass_fds=(write_fd,))
+        os.close(write_fd)
+        write_fd = None
+        with os.fdopen(read_fd) as source:
+            read_fd = None
+            for line in source:
+                try:
+                    angles = gaze_angles([float(v) for v in line.split()])
+                except ValueError:
+                    continue
+                osc.send("/tracking/eye/CenterPitchYaw", angles)
+        return process.wait()
+    finally:
+        if read_fd is not None:
+            os.close(read_fd)
+        if write_fd is not None:
+            os.close(write_fd)
+        if process and process.poll() is None:
+            process.terminate()
+            try:
+                process.wait(timeout=5)
+            except subprocess.TimeoutExpired:
+                process.kill()
+                process.wait()
+
+
+class HeartPanel:
+    """Our GTK panel, using the Frame's existing GTK4/GI platform libraries."""
+    def __init__(self):
+        os.environ["GDK_BACKEND"] = "x11"
+        import gi
+        gi.require_version("Gtk", "4.0")
+        gi.require_version("GdkX11", "4.0")
+        from gi.repository import Gtk, Gdk, GdkX11, GLib
+        Gtk.init()
+        self.running = True
+        self.window = Gtk.Window(title="Frame Control · Heart rate")
+        self.window.set_default_size(480, 320)
+        self.window.connect("close-request", self.stop)
+        Gtk.Settings.get_default().set_property("gtk-application-prefer-dark-theme", True)
+        box = Gtk.Box(orientation=Gtk.Orientation.VERTICAL, spacing=16)
+        box.set_valign(Gtk.Align.CENTER)
+        box.set_halign(Gtk.Align.CENTER)
+        box.set_size_request(440, -1)
+        for side in ("top", "bottom", "start", "end"):
+            getattr(box, "set_margin_" + side)(24)
+        self.window.set_child(box)
+        title = Gtk.Label(label="Heart rate")
+        title.add_css_class("title-2")
+        box.append(title)
+        self.reading = Gtk.Label(label="—")
+        self.reading.add_css_class("reading")
+        box.append(self.reading)
+        self.status = Gtk.Label(label="Waiting for strap")
+        box.append(self.status)
+        button = Gtk.Button(label="Stop")
+        button.connect("clicked", self.stop)
+        box.append(button)
+        css = Gtk.CssProvider()
+        css.load_from_data(b".reading { font-size: 144px; font-weight: 700; }")
+        Gtk.StyleContext.add_provider_for_display(Gdk.Display.get_default(), css, Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION)
+        self.window.present()
+        context = GLib.MainContext.default()
+        while context.pending():
+            context.iteration(False)
+        try:
+            xid = GdkX11.X11Surface.get_xid(self.window.get_surface())
+            subprocess.run(["xprop", "-id", str(xid), "-f", "STEAM_GAME", "32c", "-set", "STEAM_GAME", "2000000027"],
+                           check=True, stdout=subprocess.DEVNULL)
+        except Exception:
+            self.window.destroy()
+            raise
+
+    def stop(self, *args):
+        self.running = False
+        return True
+
+    def update(self, bpm):
+        self.reading.set_label(str(bpm) if bpm is not None else "—")
+        self.status.set_label("beats per minute" if bpm is not None else "Waiting for strap")
+
+    def close(self):
+        self.window.destroy()
+
+
+def run_heart(args, osc):
+    import dbus
+    from dbus.mainloop.glib import DBusGMainLoop
+    from gi.repository import GLib
+    DBusGMainLoop(set_as_default=True)
+    session = HeartSession(osc, args.address, args.log)
+    reader, root = None, None
+    failure = []
+    def value(data):
+        if data is None:
+            session.bpm = None
+            failure.append("Strap disconnected; reconnect and start again")
+            return
+        try:
+            session.notification(data)
+        except ValueError:
+            session.bpm = None
+        except OSError:
+            failure.append("OSC or session log write failed")
+    try:
+        reader = BluezHeart(dbus.SystemBus(), dbus.Interface, args.device, value)
+        context = GLib.MainContext.default()
+        deadline = time.monotonic() + 20
+        while not reader.subscribe():
+            if time.monotonic() > deadline:
+                raise TrackingError("Timed out waiting for the strap's GATT services")
+            while context.pending():
+                context.iteration(False)
+            time.sleep(0.1)
+        end = time.monotonic() + args.seconds
+        print("Heart-rate notifications started; readings stay local unless OSC or a log was selected.")
+        if args.panel:
+            root = HeartPanel()
+        running = lambda: root.running if root else True
+        while running() and time.monotonic() < end and not failure:
+            while context.pending():
+                context.iteration(False)
+            if root:
+                root.update(session.current())
+            time.sleep(0.05)
+        if failure:
+            raise TrackingError(failure[0])
+        return 0
+    finally:
+        if root:
+            root.close()
+        try:
+            if reader:
+                reader.close()
+        finally:
+            session.close()
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    commands = parser.add_subparsers(dest="command", required=True)
+    gaze = commands.add_parser("gaze", help="headless OpenXR; prints counters only without --osc")
+    heart = commands.add_parser("heart", help="standard BLE HRS from an explicitly selected strap")
+    for command in (gaze, heart):
+        command.add_argument("--osc", nargs=2, metavar=("IP", "PORT"), help="explicit UDP destination; no default")
+        command.add_argument("--seconds", type=int, default=10, help="bounded run, 1..86400 seconds (default: 10)")
+    heart.add_argument("--device", required=True, help="strap Bluetooth address already discovered by BlueZ")
+    heart.add_argument("--panel", action="store_true", help="show our panel on gamescope DISPLAY=:0")
+    heart.add_argument("--address", default="/avatar/parameters/HeartRate", help="integer BPM OSC parameter")
+    heart.add_argument("--log", help="new private CSV file; disabled by default")
+    args = parser.parse_args()
+    if not 1 <= args.seconds <= 86400:
+        parser.error("--seconds must be 1..86400")
+    def interrupted(signum, frame):
+        raise KeyboardInterrupt
+    signal.signal(signal.SIGTERM, interrupted)
+    if hasattr(signal, "SIGHUP"):
+        signal.signal(signal.SIGHUP, interrupted)
+    osc = None
+    try:
+        if args.command == "heart":
+            osc_message(args.address, [0])
+            if args.panel:
+                os.environ["DISPLAY"] = ":0"
+        osc = Osc(args.osc)
+        return run_gaze(args, osc) if args.command == "gaze" else run_heart(args, osc)
+    except TrackingError as error:
+        print(str(error))
+        return 1
+    except KeyboardInterrupt:
+        return 130
+    except Exception as error:
+        # Never dump notifications, gaze, BLE addresses or exception payloads.
+        print(f"Tracking stopped ({type(error).__name__}). Check the device, runtime and selected output.")
+        return 1
+    finally:
+        if osc:
+            osc.close()
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

scripts/tracking-on-frame.py

@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+"""Install or run our local-only tracking tools on the Frame.
+
+  python3 scripts/tracking-on-frame.py install
+  python3 scripts/tracking-on-frame.py gaze --seconds 10
+  python3 scripts/tracking-on-frame.py gaze --seconds 3600 --osc 127.0.0.1 9000
+  python3 scripts/tracking-on-frame.py heart --device AA:BB:CC:DD:EE:FF --panel
+
+FRAME_ALIAS overrides the SSH alias (default: frame). Runs in the foreground;
+Ctrl-C stops the reader. No service, autostart, sudo or SteamVR settings changes.
+"""
+import os
+from pathlib import Path
+import shlex
+import subprocess
+import sys
+import tarfile
+
+REMOTE = '"$HOME/.local/share/frame-control/tracking"'
+INSTALL = '''set -eu
+base="$HOME/.local/share/frame-control/tracking"
+mkdir -p "$base"
+stage=$(mktemp -d "$base/.install.XXXXXX")
+trap 'rm -rf "$stage"' EXIT
+ tar -xf - -C "$stage"
+cc -O2 -Wall -Wextra -Werror "$stage/gaze.c" \\
+  -L/opt/steamvr/bin/linuxarm64 -Wl,-rpath,/opt/steamvr/bin/linuxarm64 \\
+  -lopenxr_loader -o "$stage/gaze"
+chmod 700 "$stage/gaze" "$stage/tracking.py"
+mv "$stage/gaze" "$stage/tracking.py" "$base/"
+echo 'Installed Frame Control tracking tools (no service started).'
+'''
+
+
+def main():
+    if len(sys.argv) < 2 or sys.argv[1] not in ("install", "gaze", "heart"):
+        print(__doc__)
+        return 2
+    host = os.environ.get("FRAME_ALIAS", "frame")
+    if not host or host.startswith("-"):
+        raise ValueError("invalid SSH alias")
+    ssh = ["ssh", "-o", "BatchMode=yes", "-o", "ConnectTimeout=10", host]
+    if sys.argv[1] == "install":
+        import tempfile
+        source = Path(__file__).resolve().parents[1] / "frame" / "tracking"
+        with tempfile.TemporaryFile() as archive:
+            with tarfile.open(fileobj=archive, mode="w") as tar:
+                for name in ("gaze.c", "tracking.py"):
+                    tar.add(source / name, arcname=name)
+            archive.seek(0)
+            return subprocess.call(ssh + ["bash -c " + shlex.quote(INSTALL)], stdin=archive)
+    # Allocate a tty so SSH forwards Ctrl-C and hangup to the foreground process.
+    command = 'exec python3 ' + REMOTE + '/tracking.py ' + shlex.join(sys.argv[1:])
+    return subprocess.call(ssh[:-1] + ["-tt", host, command])
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

tests/test_tracking.py

@@ -0,0 +1,188 @@
+"""Tracking protocols and fake-Frame BlueZ lifecycle; no headset or strap needed."""
+import importlib.util
+import math
+import os
+from pathlib import Path
+import socket
+import stat
+import struct
+import tempfile
+import unittest
+from unittest.mock import Mock, patch
+
+SPEC = importlib.util.spec_from_file_location("tracking", Path(__file__).resolve().parents[1] / "frame/tracking/tracking.py")
+t = importlib.util.module_from_spec(SPEC)
+SPEC.loader.exec_module(t)
+
+
+class Protocols(unittest.TestCase):
+    def test_hrs_formats(self):
+        self.assertEqual(t.heart_rate(b"\x00\x48"), 72)
+        self.assertEqual(t.heart_rate(b"\x01\x2c\x01"), 300)
+        self.assertEqual(t.heart_rate(b"\x1e\x48\x01\x00\x00\x04\x00\x04"), 72)
+        self.assertEqual(t.heart_rate(b"\x02\x48"), 72)  # contact not supported
+        self.assertIsNone(t.heart_rate(b"\x04\x48"))  # no contact
+        self.assertIsNone(t.heart_rate(b"\x00\x00"))
+
+    def test_hrs_malformed(self):
+        for packet in (b"", b"\x00", b"\x01\x48", b"\x08\x48\x00", b"\x10\x48",
+                       b"\x10\x48\x00", b"\x00\x48\x01", b"\xe0\x48"):
+            with self.subTest(packet=packet), self.assertRaises(ValueError):
+                t.heart_rate(packet)
+
+    def test_gaze_coordinates(self):
+        self.assertEqual(t.gaze_angles([0, 0, 0, 1]), (0, 0))
+        angle = math.radians(15)
+        pitch, yaw = t.gaze_angles([math.sin(angle), 0, 0, math.cos(angle)])
+        self.assertAlmostEqual(pitch, -30)  # OpenXR +X rotation looks up
+        self.assertAlmostEqual(yaw, 0)
+        pitch, yaw = t.gaze_angles([0, -math.sin(angle), 0, math.cos(angle)])
+        self.assertAlmostEqual(pitch, 0)
+        self.assertAlmostEqual(yaw, 30)  # right
+
+    def test_invalid_gaze(self):
+        for pose in ([0, 0, 0, 0], [math.nan, 0, 0, 1], [0, 0, 0], [0, 0, 0, math.inf]):
+            with self.assertRaises(ValueError):
+                t.gaze_angles(pose)
+
+    def test_osc_wire(self):
+        self.assertEqual(t.osc_message('/x', [72]), b'/x\0\0,i\0\0' + struct.pack('>i', 72))
+        self.assertEqual(t.osc_message('/x', [1.0, -2.0]), b'/x\0\0,ff\0' + struct.pack('>ff', 1, -2))
+        for address in ('x', '/x\0y', '/x y', '/x*'):
+            with self.assertRaises(ValueError):
+                t.osc_message(address, [1])
+
+    def test_default_never_opens_socket(self):
+        with patch.object(t.socket, 'socket') as create:
+            osc = t.Osc()
+            osc.send('/x', [72])
+            osc.close()
+            create.assert_not_called()
+
+    def test_only_configured_endpoint(self):
+        with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as receiver:
+            receiver.bind(('127.0.0.1', 0))
+            receiver.settimeout(1)
+            osc = t.Osc(receiver.getsockname())
+            try:
+                osc.send('/tracking/eye/CenterPitchYaw', [0.0, 30.0])
+                self.assertEqual(receiver.recv(1024), t.osc_message('/tracking/eye/CenterPitchYaw', [0.0, 30.0]))
+            finally:
+                osc.close()
+
+    def test_endpoint_validation(self):
+        for endpoint in [('example.org', 9000), ('0.0.0.0', 9000), ('224.0.0.1', 9000), ('127.0.0.1', 0), ('::1', 65536)]:
+            with self.assertRaises(ValueError):
+                t.Osc(endpoint)
+
+    def test_heart_staleness_contact_and_log(self):
+        now = [0]
+        osc = Mock()
+        with tempfile.TemporaryDirectory() as directory:
+            path = Path(directory) / 'session.csv'
+            session = t.HeartSession(osc, '/hr', path, lambda: now[0])
+            self.assertIsNone(session.current())
+            session.notification(b'\x00\x48')
+            self.assertEqual(session.current(), 72)
+            osc.send.assert_called_once_with('/hr', [72])
+            now[0] = 6
+            self.assertIsNone(session.current())
+            session.notification(b'\x04\x48')
+            self.assertIsNone(session.current())
+            self.assertEqual(osc.send.call_count, 1)
+            session.close()
+            self.assertEqual(path.read_text().splitlines()[0], 'unix_seconds,bpm')
+            self.assertEqual(len(path.read_text().splitlines()), 2)
+            if os.name != 'nt':
+                self.assertEqual(stat.S_IMODE(path.stat().st_mode), 0o600)
+            with self.assertRaises(FileExistsError):
+                t.HeartSession(osc, '/hr', path)
+
+    def test_no_log_by_default(self):
+        with patch.object(t.os, 'open') as create:
+            session = t.HeartSession(Mock(), '/hr')
+            session.notification(b'\x00\x48')
+            session.close()
+            create.assert_not_called()
+
+
+class FakeBluez(unittest.TestCase):
+    def setUp(self):
+        self.device = '/org/bluez/hci0/dev_TEST'
+        self.service = self.device + '/service1'
+        self.char = self.service + '/char1'
+        self.objects = {
+            self.device: {t.DEVICE: {'Address': 'AA:BB:CC:DD:EE:FF', 'Connected': False, 'ServicesResolved': True}},
+            self.service: {t.SERVICE: {'UUID': t.HRS, 'Device': self.device}},
+            self.char: {t.CHARACTERISTIC: {'UUID': t.MEASUREMENT, 'Service': self.service, 'Flags': ['notify']}},
+        }
+        self.api = Mock()
+        self.api.GetManagedObjects.side_effect = lambda: self.objects
+        self.bus = Mock()
+        self.interface = Mock(return_value=self.api)
+        self.values = Mock()
+
+    def reader(self):
+        return t.BluezHeart(self.bus, self.interface, 'AA:BB:CC:DD:EE:FF', self.values)
+
+    def test_subscribe_receive_and_cleanup(self):
+        reader = self.reader()
+        self.api.Connect.assert_called_once()
+        self.assertTrue(reader.subscribe())
+        self.api.StartNotify.assert_called_once()
+        reader.changed(t.CHARACTERISTIC, {'Value': [0, 72]}, [], self.char)
+        self.values.assert_called_once_with([0, 72])
+        reader.changed(t.CHARACTERISTIC, {'Value': [0, 73]}, [], '/other/strap')
+        self.assertEqual(self.values.call_count, 1)
+        reader.close()
+        self.api.StopNotify.assert_called_once()
+        self.api.Disconnect.assert_called_once()
+        self.bus.add_signal_receiver.return_value.remove.assert_called_once()
+
+    def test_preserve_existing_connection(self):
+        self.objects[self.device][t.DEVICE]['Connected'] = True
+        reader = self.reader()
+        reader.subscribe()
+        reader.close()
+        self.api.Connect.assert_not_called()
+        self.api.Disconnect.assert_not_called()
+
+    def test_only_selected_device_service(self):
+        self.objects[self.service][t.SERVICE]['Device'] = '/other/device'
+        reader = self.reader()
+        try:
+            with self.assertRaises(RuntimeError):
+                reader.subscribe()
+        finally:
+            reader.close()
+        self.api.StartNotify.assert_not_called()
+
+    def test_wait_for_services(self):
+        self.objects[self.device][t.DEVICE]['ServicesResolved'] = False
+        reader = self.reader()
+        self.assertFalse(reader.subscribe())
+        reader.close()
+        self.api.StartNotify.assert_not_called()
+        self.api.StopNotify.assert_not_called()
+
+    def test_disconnect_notification(self):
+        reader = self.reader()
+        reader.changed(t.DEVICE, {'Connected': 0}, [], self.device)  # dbus.Boolean behaves as int
+        self.values.assert_called_once_with(None)
+        reader.close()
+
+    def test_failed_notify_cleans_connection(self):
+        reader = self.reader()
+        self.api.StartNotify.side_effect = RuntimeError('failure')
+        with self.assertRaises(RuntimeError):
+            reader.subscribe()
+        reader.close()
+        self.api.StopNotify.assert_not_called()
+        self.api.Disconnect.assert_called_once()
+
+    def test_unknown_device_does_not_connect_or_scan(self):
+        self.objects.clear()
+        with self.assertRaises(RuntimeError):
+            self.reader()
+        self.api.Connect.assert_not_called()
+        self.api.StartDiscovery.assert_not_called()