feat: add persist.h — WAL types, persist_config_t, slot_key_t (P0-B)

- Define wal_entry_hdr_t (40 bytes, _Static_assert enforced)
- Define wal_entry_type enum (WAL_JOB_SUBMIT=1 … WAL_CHECKPOINT=100)
- Define persist_config_t with persist_config_defaults() inline helper
- Define slot_key_t (index, key[XCE_MAXNAME_LEN], key_len)
- Forward-declare persist_t opaque struct and full persist_* API surface
- Bootstrap controller Unity test suite (controller_unit_test binary)
- Register test('controller test', …, suite: 'controller') in meson
- 4 new tests all PASS: wal_header_size, wal_entry_types,
  persist_config_defaults, slot_key_t_fields

src/include/persist.h

@@ -0,0 +1,106 @@
+#pragma once
+#include <pthread.h>
+#include <stdatomic.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#include "config.h"
+
+/* Forward declaration */
+typedef struct cluster_s cluster_t;
+
+/* ============================================================
+ * WAL entry header — 40 bytes, 8-byte aligned (Part 2.2)
+ * ============================================================ */
+typedef struct {
+    uint64_t term;        /* Election term (incremented on failover) */
+    uint64_t lsn;         /* Log sequence number within this term */
+    uint64_t timestamp;   /* Epoch microseconds */
+    uint32_t type;        /* wal_entry_type enum value */
+    uint32_t payload_len; /* Bytes of payload following this header */
+    uint32_t crc;         /* CRC32(header[0..WAL_HDR_CRC_SIZE-1] + payload) */
+    uint32_t prev_crc;    /* CRC of previous record; WAL_CRC_NONE for first in segment */
+} wal_entry_hdr_t;
+_Static_assert(sizeof(wal_entry_hdr_t) == 40,
+               "wal_entry_hdr_t must be 40 bytes for on-disk format stability");
+
+/* ============================================================
+ * WAL entry types (Part 2.3)
+ * ============================================================ */
+typedef enum {
+    WAL_JOB_SUBMIT  = 1,  /* SYNC replication */
+    WAL_JOB_START   = 2,
+    WAL_JOB_FINISH  = 3,
+    WAL_JOB_FAIL    = 4,
+    WAL_JOB_STOP    = 5,
+    WAL_JOB_RESUME  = 6,
+    WAL_JOB_UPDATE  = 7,
+    WAL_JOB_RUSAGE  = 8,
+    WAL_JOB_CKPT    = 9,
+    WAL_JOB_PREASON = 10,
+    WAL_QUEUE_CTRL  = 20,
+    WAL_WORKER_CTRL = 30,
+    WAL_CHECKPOINT  = 100, /* Local WAL marker only — never replicated */
+} wal_entry_type;
+
+/* ============================================================
+ * Persistence configuration (Part 2.6)
+ * ============================================================ */
+typedef struct {
+    uint32_t wal_sync_ms;             /* fsync interval in ms (default 10) */
+    uint32_t snap_interval_s;         /* checkpoint interval in seconds (default 60) */
+    uint32_t snap_wal_size_mb;        /* checkpoint when WAL exceeds this MB (default 64) */
+    uint32_t snap_keep_n;             /* snapshots to retain (default 2) */
+    uint32_t transient_job_timeout_s; /* seconds before TRANSIENT job auto-terminates (default 300) */
+    uint32_t finished_retain_s;       /* retain finished jobs N seconds (default 3600) */
+    uint32_t worker_retain_s;         /* retain unavailable workers N seconds (default 86400) */
+    uint32_t sync_timeout_ms;         /* sync replication ACK timeout ms (default 50) */
+} persist_config_t;
+
+static inline persist_config_t persist_config_defaults(void)
+{
+    persist_config_t c;
+    c.wal_sync_ms             = DEFAULT_WAL_SYNC_MS;
+    c.snap_interval_s         = DEFAULT_SNAP_INTERVAL_S;
+    c.snap_wal_size_mb        = DEFAULT_SNAP_WAL_SIZE_MB;
+    c.snap_keep_n             = DEFAULT_SNAP_KEEP_N;
+    c.transient_job_timeout_s = DEFAULT_TRANSIENT_JOB_TIMEOUT_S;
+    c.finished_retain_s       = DEFAULT_FINISHED_RETAIN_S;
+    c.worker_retain_s         = DEFAULT_WORKER_RETAIN_S;
+    c.sync_timeout_ms         = DEFAULT_SYNC_TIMEOUT_MS;
+    return c;
+}
+
+/* ============================================================
+ * Key→index mapping for checkpoint serialization (Part 3.8)
+ * ============================================================ */
+typedef struct {
+    int    index;                 /* shadow slot index in the frozen zarray */
+    char   key[XCE_MAXNAME_LEN]; /* owned deep copy — not a borrowed kvtab pointer */
+    size_t key_len;              /* length including null terminator */
+} slot_key_t;
+
+/* ============================================================
+ * persist_t — opaque; defined in persist.c (Task 7)
+ * ============================================================ */
+typedef struct persist_s persist_t;
+
+/* Lifecycle */
+int  persist_init(persist_t* p, persist_config_t* config, cluster_t* c);
+int  persist_start(persist_t* p);
+void persist_stop(persist_t* p);
+void persist_fini(persist_t* p);
+int  persist_recover(persist_t* p);
+
+/* WAL write paths */
+int persist_wal_async(persist_t* p, uint32_t type,
+                      const void* payload, uint32_t len);
+int persist_wal_sync_append(persist_t* p, uint32_t type,
+                            const void* payload, uint32_t len,
+                            int* sync_rc_out);
+
+/* Checkpoint */
+int persist_checkpoint(persist_t* p);
+
+/* Logging helper — never logs payload content (security invariant) */
+void persist_log_entry_metadata(const wal_entry_hdr_t* hdr);