feat(v0.6): tri-state PID liveness probe (ProcessAlive/Dead/Unknown)

internal/session/pidcheck.go

@@ -0,0 +1,22 @@
+package session
+
+// ProcessState is the tri-state result of a PID liveness check. The call
+// site decides how to treat ProcessUnknown; IsStale treats it
+// conservatively by falling back to wall-clock freshness.
+type ProcessState int
+
+const (
+	// ProcessAlive: the OS confirms a process with this PID exists.
+	ProcessAlive ProcessState = iota
+	// ProcessDead: the OS confirms no process with this PID exists.
+	ProcessDead
+	// ProcessUnknown: the liveness check was inconclusive (permission
+	// error, unexpected OS error). Callers must NOT treat this as dead.
+	ProcessUnknown
+)
+
+// checkProcess is the test seam for PID liveness. Production code uses the
+// platform-specific defaultCheckProcess. Tests override this package-level
+// variable; such tests must restore it via t.Cleanup and must NOT run with
+// t.Parallel().
+var checkProcess = defaultCheckProcess