feat(log): add bounded diagnostic transport

libs/kaptan-log/src/shutdown.rs

@@ -0,0 +1,34 @@
+//! Explicit shutdown taxonomy for a future platform-owned shutdown state machine.
+
+/// Why an orderly output-inhibited shutdown completed.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[repr(u8)]
+pub enum ShutdownReason {
+    /// An operator initiated the controlled stop.
+    Operator = 1,
+    /// Safety initiated the controlled stop.
+    Safety = 2,
+}
+
+/// One completed orderly firmware shutdown report.
+///
+/// This is a typed terminal-state observation from a future platform-owned
+/// shutdown coordinator. It is emitted only after that coordinator has
+/// inhibited outputs. It is deliberately not a shutdown request or a panic,
+/// hard-fault, or reset report.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct ShutdownReport {
+    reason: ShutdownReason,
+}
+
+impl ShutdownReport {
+    /// Creates one completed orderly shutdown report.
+    pub const fn new(reason: ShutdownReason) -> Self {
+        Self { reason }
+    }
+
+    /// Completed orderly shutdown reason.
+    pub const fn reason(self) -> ShutdownReason {
+        self.reason
+    }
+}