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, 19 insertions, 0 deletions

diff --git a/internal/askcli/runlock_stale_linux_test.go b/internal/askcli/runlock_stale_linux_test.go
new file mode 100644
index 0000000..7c581fb
--- /dev/null
+++ b/internal/askcli/runlock_stale_linux_test.go
@@ -0,0 +1,19 @@
+//go:build linux
+
+package askcli
+
+import (
+	"os/exec"
+	"testing"
+)
+
+func TestLockHolderIsStale_NonAskLiveProcess(t *testing.T) {
+	cmd := exec.Command("sleep", "60")
+	if err := cmd.Start(); err != nil {
+		t.Skip("sleep not available:", err)
+	}
+	defer func() { _ = cmd.Process.Kill() }()
+	if !lockHolderIsStale(cmd.Process.Pid, "ask") {
+		t.Fatal("expected sleep process to be stale when expecting ask")
+	}
+}