diff --git a/.changeset/26603-setting-audit-hash-description.md b/.changeset/26603-setting-audit-hash-description.md
new file mode 100644
index 00000000000..6ef24db026c
--- /dev/null
+++ b/.changeset/26603-setting-audit-hash-description.md
@@ -0,0 +1,16 @@
+---
+'@objectstack/platform-objects': patch
+---
+
+fix(platform-objects): the settings audit `old_hash` / `new_hash` columns describe both digest formats they carry
+
+Clause-②: no
+Metadata-protocol: none
+
+`sys_setting_audit` described `old_hash` and `new_hash` as "SHA-256 of the … value (canonicalised)", and `sys_platform_setting_audit` named no format. A secret row never carries an unkeyed SHA-256, so an operator or agent checking a row against the declared format read every secret row as malformed. Both objects now state what the settings audit writer records:
+
+- **A non-secret value:** `sha256:` followed by the hex SHA-256 of its canonical JSON.
+- **A secret value (`encrypted: true`):** the crypto provider's keyed digest, `hmac-sha256:…`. Never an unkeyed hash, which would let anyone holding the trail confirm a guessed secret.
+- **Null:** `old_hash` when the previous value was unset, `new_hash` on reset, and either one for a secret when no keyed digest is available.
+
+Rows written before the `sha256:` digest may carry `fnv32:`; compare only values with the same prefix. Only the description text changes: no column type, length or name, and nothing about what is written.
diff --git a/packages/platform-objects/src/apps/translations/en.objects.generated.ts b/packages/platform-objects/src/apps/translations/en.objects.generated.ts
index e0a569e11f3..3c10dcf93a5 100644
--- a/packages/platform-objects/src/apps/translations/en.objects.generated.ts
+++ b/packages/platform-objects/src/apps/translations/en.objects.generated.ts
@@ -3457,11 +3457,11 @@ export const enObjects: NonNullable<TranslationData['objects']> = {
       },
       old_hash: {
         label: "Old Hash",
-        help: "SHA-256 of the previous value (canonicalised). Null when previously unset."
+        help: "Digest of the previous value, never the plaintext: sha256: hex for a plain value, the keyed hmac-sha256: digest for a secret. Null when previously unset, or for a secret with no keyed digest."
       },
       new_hash: {
         label: "New Hash",
-        help: "SHA-256 of the new value (canonicalised). Null on reset."
+        help: "Digest of the new value, never the plaintext: sha256: hex for a plain value, the keyed hmac-sha256: digest for a secret. Null on reset, or for a secret with no keyed digest."
       },
       encrypted: {
         label: "Encrypted",
diff --git a/packages/platform-objects/src/apps/translations/es-ES.objects.generated.ts b/packages/platform-objects/src/apps/translations/es-ES.objects.generated.ts
index f0cac66c7f0..9a732d8e98a 100644
--- a/packages/platform-objects/src/apps/translations/es-ES.objects.generated.ts
+++ b/packages/platform-objects/src/apps/translations/es-ES.objects.generated.ts
@@ -3457,11 +3457,11 @@ export const esESObjects: NonNullable<TranslationData['objects']> = {
       },
       old_hash: {
         label: "Hash anterior",
-        help: "SHA-256 del valor anterior (canonicalizado). Null cuando antes no estaba establecido."
+        help: "Resumen del valor anterior, nunca el texto plano: sha256: en hexadecimal para un valor normal, el resumen con clave hmac-sha256: para un valor secreto. Null cuando antes no estaba establecido, o para un valor secreto sin resumen con clave."
       },
       new_hash: {
         label: "Hash nuevo",
-        help: "SHA-256 del valor nuevo (canonicalizado). Null al restablecer."
+        help: "Resumen del valor nuevo, nunca el texto plano: sha256: en hexadecimal para un valor normal, el resumen con clave hmac-sha256: para un valor secreto. Null al restablecer, o para un valor secreto sin resumen con clave."
       },
       encrypted: {
         label: "Cifrado",
diff --git a/packages/platform-objects/src/apps/translations/ja-JP.objects.generated.ts b/packages/platform-objects/src/apps/translations/ja-JP.objects.generated.ts
index 5532b684250..3d835cd861e 100644
--- a/packages/platform-objects/src/apps/translations/ja-JP.objects.generated.ts
+++ b/packages/platform-objects/src/apps/translations/ja-JP.objects.generated.ts
@@ -3457,11 +3457,11 @@ export const jaJPObjects: NonNullable<TranslationData['objects']> = {
       },
       old_hash: {
         label: "変更前ハッシュ",
-        help: "変更前の値の SHA-256（正規化済み）。未設定の場合は null。"
+        help: "変更前の値のダイジェスト（平文ではない）：通常の値は sha256: の16進ダイジェスト、機密値は鍵付きの hmac-sha256: ダイジェスト。未設定の場合、または鍵付きダイジェストを得られない機密値の場合は null。"
       },
       new_hash: {
         label: "変更後ハッシュ",
-        help: "新しい値の SHA-256（正規化済み）。リセット時は null。"
+        help: "新しい値のダイジェスト（平文ではない）：通常の値は sha256: の16進ダイジェスト、機密値は鍵付きの hmac-sha256: ダイジェスト。リセット時、または鍵付きダイジェストを得られない機密値の場合は null。"
       },
       encrypted: {
         label: "暗号化",
diff --git a/packages/platform-objects/src/apps/translations/zh-CN.objects.generated.ts b/packages/platform-objects/src/apps/translations/zh-CN.objects.generated.ts
index 0ea28f2ea22..879f0bd3e15 100644
--- a/packages/platform-objects/src/apps/translations/zh-CN.objects.generated.ts
+++ b/packages/platform-objects/src/apps/translations/zh-CN.objects.generated.ts
@@ -3457,11 +3457,11 @@ export const zhCNObjects: NonNullable<TranslationData['objects']> = {
       },
       old_hash: {
         label: "旧哈希",
-        help: "旧值（规范化后）的 SHA-256。此前未设置时为 Null。"
+        help: "旧值的摘要，绝不是明文：普通值为 sha256: 十六进制摘要，机密值为带密钥的 hmac-sha256: 摘要。此前未设置时为 Null，机密值没有可用的带密钥摘要时也为 Null。"
       },
       new_hash: {
         label: "新哈希",
-        help: "新值（规范化后）的 SHA-256。重置时为 Null。"
+        help: "新值的摘要，绝不是明文：普通值为 sha256: 十六进制摘要，机密值为带密钥的 hmac-sha256: 摘要。重置时为 Null，机密值没有可用的带密钥摘要时也为 Null。"
       },
       encrypted: {
         label: "已加密",
diff --git a/packages/platform-objects/src/system/sys-platform-setting-audit.object.ts b/packages/platform-objects/src/system/sys-platform-setting-audit.object.ts
index 20192f9dc6a..ff2c6252296 100644
--- a/packages/platform-objects/src/system/sys-platform-setting-audit.object.ts
+++ b/packages/platform-objects/src/system/sys-platform-setting-audit.object.ts
@@ -134,18 +134,26 @@ export const SysPlatformSettingAudit = ObjectSchema.create({
       description: 'Free-text justification provided by the actor (optional).',
     }),
 
+    /**
+     * Same formats as `sys_setting_audit.old_hash`: `sha256:` + hex SHA-256
+     * of the canonical JSON for a non-secret value, the crypto provider's keyed
+     * `hmac-sha256:` digest for a secret (never an unkeyed hash). Null when
+     * previously unset, and null for a secret when no keyed digest is
+     * available. Older rows may carry `fnv32:`; compare only same-prefix values.
+     */
     old_hash: Field.text({
       label: 'Old Hash',
       readonly: true,
       maxLength: 128,
-      description: 'Digest of the previous value. Never the plaintext. Null when previously unset.',
+      description: 'Digest of the previous value, never the plaintext: sha256: hex for a plain value, the keyed hmac-sha256: digest for a secret. Null when previously unset, or for a secret with no keyed digest.',
     }),
 
+    /** Same formats as `old_hash`. Null on `reset`, and for a secret with no keyed digest. */
     new_hash: Field.text({
       label: 'New Hash',
       readonly: true,
       maxLength: 128,
-      description: 'Digest of the new value. Never the plaintext. Null on reset.',
+      description: 'Digest of the new value, never the plaintext: sha256: hex for a plain value, the keyed hmac-sha256: digest for a secret. Null on reset, or for a secret with no keyed digest.',
     }),
 
     encrypted: Field.boolean({
diff --git a/packages/platform-objects/src/system/sys-setting-audit.object.ts b/packages/platform-objects/src/system/sys-setting-audit.object.ts
index c638fb5d986..421184f012a 100644
--- a/packages/platform-objects/src/system/sys-setting-audit.object.ts
+++ b/packages/platform-objects/src/system/sys-setting-audit.object.ts
@@ -137,22 +137,33 @@ export const SysSettingAudit = ObjectSchema.create({
     /**
      * Content digest of the previous value. Never the plaintext —
      * lets operators detect duplicate writes without leaking secrets.
-     * Format: hex SHA-256 of the canonicalised JSON, or null when
-     * the previous value was unset.
+     * The format depends on the value:
+     *  - a non-secret value: `sha256:` + hex SHA-256 of its canonical JSON;
+     *  - a secret value (`encrypted: true`): the crypto provider's keyed
+     *    digest, `hmac-sha256:…`. Never an unkeyed hash: one of a short
+     *    secret lets anyone holding the trail confirm a guess.
+     * Null when the previous value was unset, and null for a secret when
+     * no keyed digest is available. Rows written before the SHA-256 digest
+     * (#26465) may carry `fnv32:`; compare only values with the same prefix.
      */
     old_hash: Field.text({
       label: 'Old Hash',
       readonly: true,
       maxLength: 128,
-      description: 'SHA-256 of the previous value (canonicalised). Null when previously unset.',
+      description: 'Digest of the previous value, never the plaintext: sha256: hex for a plain value, the keyed hmac-sha256: digest for a secret. Null when previously unset, or for a secret with no keyed digest.',
     }),
 
-    /** Content digest of the new value. Null on `reset`. */
+    /**
+     * Content digest of the new value, in the same formats as `old_hash`
+     * (`sha256:` for a non-secret value, the keyed `hmac-sha256:` digest
+     * for a secret). Null on `reset`, and null for a secret when no keyed
+     * digest is available.
+     */
     new_hash: Field.text({
       label: 'New Hash',
       readonly: true,
       maxLength: 128,
-      description: 'SHA-256 of the new value (canonicalised). Null on reset.',
+      description: 'Digest of the new value, never the plaintext: sha256: hex for a plain value, the keyed hmac-sha256: digest for a secret. Null on reset, or for a secret with no keyed digest.',
     }),
 
     /** True when the field is encrypted — flags secret rotation events. */