ftl: add P0 bench verification probes (#85)

Add two bench empirical verification probes for the whole-volume stale
view investigation:

1. Write-commit readback probe in dhara_nand_prog(): after a successful
   program, immediately read back the same physical page and compare
   byte-by-byte. Log ECC errors and data mismatches with a counter.

2. Map state logging in ftl_flush_cache(): after each successful
   dhara_map_write, log the journal root/head/tail/epoch/count to
   correlate with bench stale-view events.

Both probes are marked as bench-only and should be removed before
production release.

Drivers/BSP/GD5F2GQ5UE/nand_ftl.c

@@ -143,6 +143,10 @@ static uint8_t                s_cache_dirty;
 /* 拷贝临时缓冲区 */
 static uint8_t                s_copy_buf[FTL_PAGE_SIZE];
 
+/* 【#85 P0 台架实证】写提交回读探针缓冲 + 计数 */
+static uint8_t                s_prog_verify_buf[FTL_PAGE_SIZE];
+static volatile uint32_t      s_prog_verify_mismatch;
+
 /* 初始化状态 */
 static uint8_t                s_initialized;
 
@@ -276,6 +280,15 @@ static bsp_err_t ftl_flush_cache(void) {
         return cls;
     }
 
+    /* 【#85 P0 台架实证】map 状态日志：每次写后打 root/head/tail/epoch/count，
+     * 对照台架打回时刻的 map 状态，确认 root 是否回退。仅台架实证用，量产前移除。 */
+    DBG_INFO("map_write: root=%lu head=%lu tail=%lu epoch=%u count=%lu",
+             (unsigned long)s_map.journal.root,
+             (unsigned long)s_map.journal.head,
+             (unsigned long)s_map.journal.tail,
+             (unsigned)s_map.journal.epoch,
+             (unsigned long)s_map.count);
+
     s_cache_dirty = 0;
     return BSP_OK;
 }
@@ -381,10 +394,29 @@ int dhara_nand_prog(const struct dhara_nand *n, dhara_page_t p, const uint8_t *d
         return -1;
     }
 
-    /* 编程正确性以 P_FAIL 状态位（gd5f_program_exec 内检查）+ 读时 ECC +
-     * journal 读时门（magic/CRC）为准；数据路径不做整页回读比对——
-     * 2026-09-20 曾加回读校验（GD5F_PROG_VERIFY），2026-09-21 经评估整体
-     * 移除（依据见 docs/内存管理/存储栈RAM优化调研.md 与 GD5F Trap Records TRAP-GD5F-05） */
+    /* 【#85 P0 台架实证】写提交回读探针：编程成功后立即回读同 PPN 做字节比对。
+     * 2026-09-20 曾加回读校验（GD5F_PROG_VERIFY），2026-09-21 经评估整体移除。
+     * 现以低频探针形式恢复：仅台架实证用，量产前移除。
+     * 目的：在 FTL 层直接抓到"编程成功但回读不一致"的窗口，
+     * 区分"NAND 编程未落地" vs "map 指旧 PPN"。 */
+    {
+        int32_t vret;
+        vret = gd5f_page_read(phy_pg);
+        if (vret == GD5F_OK) {
+            vret = gd5f_read_from_cache(0, s_prog_verify_buf, FTL_PAGE_SIZE);
+            if (vret == GD5F_OK) {
+                if (gd5f_check_ecc() == GD5F_ECC_ERROR) {
+                    DBG_ERROR("Prog verify: ECC error on readback page=%lu",
+                              (unsigned long)phy_pg);
+                    s_prog_verify_mismatch++;
+                } else if (memcmp(data, s_prog_verify_buf, FTL_PAGE_SIZE) != 0) {
+                    DBG_ERROR("Prog verify: MISMATCH page=%lu (data differs after prog)",
+                              (unsigned long)phy_pg);
+                    s_prog_verify_mismatch++;
+                }
+            }
+        }
+    }
     return 0;
 }