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, 23 insertions, 0 deletions

diff --git a/internal/askcli/runlock_stale_other.go b/internal/askcli/runlock_stale_other.go
new file mode 100644
index 0000000..21174c4
--- /dev/null
+++ b/internal/askcli/runlock_stale_other.go
@@ -0,0 +1,23 @@
+//go:build !linux
+
+package askcli
+
+import (
+	"os"
+	"syscall"
+)
+
+func lockHolderIsStale(pid int, expectedComm string) bool {
+	if pid <= 0 {
+		return false
+	}
+	_ = expectedComm
+	proc, err := os.FindProcess(pid)
+	if err != nil {
+		return true
+	}
+	if err := proc.Signal(syscall.Signal(0)); err != nil {
+		return true
+	}
+	return false
+}