Implement bfebbx: Betaflight blackbox extractor

Cross-platform (macOS + Linux) C++17 CLI that extracts a Betaflight FC's
blackbox log in one command: auto-detect the serial port, read craft_name
over the Betaflight CLI, send `msc` to reboot into USB mass storage, wait
for the volume to mount, copy btfl_all.bbl to
<craft_name>_<YYYYMMDD>_<HHMMSS>.bbl, and eject.

Native throughout (termios serial, getmntinfo/proc-mounts mount detection,
DiskArbitration/umount eject); the only subprocess is the Linux udisksctl
eject fallback. Includes CMake/ctest build, unit tests for the pure logic
(naming, craft_name parsing, mount diff, serial via pty, CLI parsing),
README with a manual hardware integration procedure, and design/plan docs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/eject.cpp

@@ -0,0 +1,107 @@
+#include "eject.h"
+
+#include <stdexcept>
+#include <string>
+
+#if defined(__APPLE__)
+
+#include <CoreFoundation/CoreFoundation.h>
+#include <DiskArbitration/DiskArbitration.h>
+
+namespace bfebbx {
+
+namespace {
+struct EjectCtx {
+    bool done = false;
+    bool ok = false;
+};
+
+void unmountCallback(DADiskRef, DADissenterRef dissenter, void* c) {
+    auto* ctx = static_cast<EjectCtx*>(c);
+    ctx->ok = (dissenter == nullptr);
+    ctx->done = true;
+    CFRunLoopStop(CFRunLoopGetCurrent());
+}
+}  // namespace
+
+void ejectVolume(const MountEntry& vol) {
+    DASessionRef session = DASessionCreate(kCFAllocatorDefault);
+    if (!session) throw std::runtime_error("DASessionCreate failed");
+    DASessionScheduleWithRunLoop(session, CFRunLoopGetCurrent(), kCFRunLoopDefaultMode);
+
+    CFURLRef url = CFURLCreateFromFileSystemRepresentation(
+        kCFAllocatorDefault,
+        reinterpret_cast<const UInt8*>(vol.mountpoint.c_str()),
+        static_cast<CFIndex>(vol.mountpoint.size()), true);
+    DADiskRef disk = url ? DADiskCreateFromVolumePath(kCFAllocatorDefault, session, url)
+                         : nullptr;
+
+    EjectCtx ctx;
+    if (disk) {
+        DADiskUnmount(disk, kDADiskUnmountOptionWhole, unmountCallback, &ctx);
+        // Bound the wait: DiskArbitration's callback normally always fires, but a
+        // daemon crash or invalidated disk could otherwise hang the process forever.
+        const CFTimeInterval kUnmountTimeout = 15.0;  // seconds, total
+        while (!ctx.done) {
+            CFRunLoopRunResult r =
+                CFRunLoopRunInMode(kCFRunLoopDefaultMode, kUnmountTimeout, true);
+            if (r == kCFRunLoopRunTimedOut || r == kCFRunLoopRunFinished) break;
+            // kCFRunLoopRunStopped (callback called CFRunLoopStop) or
+            // kCFRunLoopRunHandledSource: re-check ctx.done and continue.
+        }
+        CFRelease(disk);
+    }
+    if (url) CFRelease(url);
+    DASessionUnscheduleFromRunLoop(session, CFRunLoopGetCurrent(), kCFRunLoopDefaultMode);
+    CFRelease(session);
+
+    if (!disk) throw std::runtime_error("could not resolve disk for " + vol.mountpoint);
+    if (!ctx.done) throw std::runtime_error("unmount timed out for " + vol.mountpoint);
+    if (!ctx.ok) throw std::runtime_error("unmount denied for " + vol.mountpoint);
+}
+
+}  // namespace bfebbx
+
+#elif defined(__linux__)
+
+#include <sys/mount.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <cerrno>
+#include <cstring>
+
+namespace bfebbx {
+
+namespace {
+// Run a command with no shell; returns the exit status (or -1 on spawn failure).
+int runNoShell(const char* const argv[]) {
+    pid_t pid = fork();
+    if (pid < 0) return -1;
+    if (pid == 0) {
+        execvp(argv[0], const_cast<char* const*>(argv));
+        _exit(127);
+    }
+    int status = 0;
+    while (waitpid(pid, &status, 0) < 0) {
+        if (errno == EINTR) continue;
+        return -1;
+    }
+    return WIFEXITED(status) ? WEXITSTATUS(status) : -1;
+}
+}  // namespace
+
+void ejectVolume(const MountEntry& vol) {
+    if (umount(vol.mountpoint.c_str()) == 0) return;
+    if (errno == EPERM || errno == EACCES) {
+        const char* argv[] = {"udisksctl", "unmount", "-b", vol.device.c_str(), nullptr};
+        if (runNoShell(argv) == 0) return;
+        throw std::runtime_error("umount denied and udisksctl fallback failed for " +
+                                 vol.mountpoint);
+    }
+    throw std::runtime_error("umount " + vol.mountpoint + ": " + std::strerror(errno));
+}
+
+}  // namespace bfebbx
+
+#endif