ask: serialize concurrent CLI with repo lock and stale PID recovery

Add advisory lock under .git/hexai-ask.lock around Taskwarrior execution,
with metadata (PID and process basename) and Linux /proc comm checks to
remove orphan lock files when the recorded holder is gone or not ask.

Extract internal/filelock for shared flock helpers; stats uses it too.

Made-with: Cursor

1 files changed, 33 insertions, 0 deletions

diff --git a/internal/askcli/runlock_stale_linux.go b/internal/askcli/runlock_stale_linux.go
new file mode 100644
index 0000000..183dfb2
--- /dev/null
+++ b/internal/askcli/runlock_stale_linux.go
@@ -0,0 +1,33 @@
+//go:build linux
+
+package askcli
+
+import (
+	"os"
+	"strconv"
+	"strings"
+
+	"golang.org/x/sys/unix"
+)
+
+func lockHolderIsStale(pid int, expectedComm string) bool {
+	if pid <= 0 {
+		return false
+	}
+	if err := unix.Kill(pid, 0); err != nil {
+		return true
+	}
+	data, err := os.ReadFile("/proc/" + strconv.Itoa(pid) + "/comm")
+	if err != nil {
+		return false
+	}
+	holder := strings.TrimSpace(string(data))
+	if holder == "" {
+		return false
+	}
+	want := expectedComm
+	if len(want) > 15 {
+		want = want[:15]
+	}
+	return holder != want
+}