Add SSH host identity rotation controls

src/ssh_security.h

@@ -3,6 +3,7 @@
 
 #pragma once
 
+#include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ -38,7 +39,22 @@ esp_err_t ssh_security_copy_private_key(uint8_t *output, size_t capacity,
                                         size_t *output_length);
 esp_err_t ssh_security_get_metadata(ssh_security_metadata_t *metadata);
 
-/* Caller must stop SSH first. Rotation requires valid live material; reset replaces any stored state. */
+typedef struct {
+    ssh_security_metadata_t metadata;
+    bool busy;
+} ssh_security_identity_snapshot_t;
+
+/* Zero-wait atomic public projection; no private material. */
+esp_err_t ssh_security_get_identity_snapshot(ssh_security_identity_snapshot_t *snapshot);
+/* Owner transaction: nonreused token, reserve before side effects and retain through
+ * restart. Only the reserving task may replace once and release. Zero generation
+ * selects canonical semantics; reset additionally permits unavailable material. */
+esp_err_t ssh_security_reserve_identity(uint32_t generation, bool reset, uint32_t *token);
+esp_err_t ssh_security_replace_reserved(uint32_t token);
+void ssh_security_release_identity(uint32_t token);
+
+/* Rotation requires valid live material; reset replaces any stored state.
+ * Direct callers share the reservation but do not restart the transport. */
 esp_err_t ssh_security_rotate(void);
 esp_err_t ssh_security_reset(void);