diff --git a/apps/api/src/services/adr100_remediation_service.py b/apps/api/src/services/adr100_remediation_service.py
index 39c0a213..82cf8833 100644
--- a/apps/api/src/services/adr100_remediation_service.py
+++ b/apps/api/src/services/adr100_remediation_service.py
@@ -11,6 +11,7 @@ T25: remediation queue items are now actionable without mutating incident state:
 from __future__ import annotations
 
 import asyncio
+import hashlib
 from datetime import datetime, timedelta, timezone
 from typing import Any, Literal, Protocol
 
@@ -770,7 +771,7 @@ def _approval_fingerprint(item: dict[str, Any]) -> str:
     playbook_id = str(item.get("playbook_id") or "")
     incident_id = str(item.get("incident_id") or "")
     basis = work_item_id or f"{incident_id}:{playbook_id}:{item.get('remediation_action') or ''}"
-    return f"adr100_playbook_authoring:{basis}"[:240]
+    return hashlib.sha256(f"adr100_playbook_authoring:{basis}".encode("utf-8")).hexdigest()
 
 
 def _approval_result_payload(
diff --git a/apps/api/tests/test_adr100_remediation_service.py b/apps/api/tests/test_adr100_remediation_service.py
index 9bbdae1f..7741cdb2 100644
--- a/apps/api/tests/test_adr100_remediation_service.py
+++ b/apps/api/tests/test_adr100_remediation_service.py
@@ -320,7 +320,7 @@ async def test_create_approval_request_is_record_only_and_does_not_authorize_rep
     assert result["mode"] == "approval"
     assert result["writes_approval_record"] is True
     assert result["deduplicated"] is False
-    assert result["fingerprint"].startswith("adr100_playbook_authoring:")
+    assert len(result["fingerprint"]) == 64
     assert result["writes_incident_state"] is False
     assert result["writes_auto_repair_result"] is False
     assert result["approval_id"] == "00000000-0000-0000-0000-00000000a100"
@@ -332,8 +332,9 @@ async def test_create_approval_request_is_record_only_and_does_not_authorize_rep
     assert approval_service.requests[0].metadata["approval_kind"] == "adr100_playbook_authoring"
     assert approval_service.requests[0].metadata["execution_authorized"] is False
     assert approval_service.requests[0].metadata["repair_executed"] is False
-    assert approval_service.fingerprints[0].startswith("lookup:adr100_playbook_authoring:")
-    assert approval_service.fingerprints[1].startswith("adr100_playbook_authoring:")
+    assert approval_service.fingerprints[0].startswith("lookup:")
+    assert len(approval_service.fingerprints[0].removeprefix("lookup:")) == 64
+    assert len(approval_service.fingerprints[1]) == 64
     assert alert_repo.calls[0]["event_type"] == "APPROVAL_ESCALATED"
     assert alert_repo.calls[0]["approval_id"] == "00000000-0000-0000-0000-00000000a100"
     assert alert_repo.calls[0]["context"]["writes_approval_record"] is True
diff --git a/docs/LOGBOOK.md b/docs/LOGBOOK.md
index 198f3fc9..5a30c279 100644
--- a/docs/LOGBOOK.md
+++ b/docs/LOGBOOK.md
@@ -69,7 +69,7 @@
 - `apps/api/src/services/adr100_remediation_service.py`：
   - 新增 `create_approval_request()`，可從 remediation work item 建立 `adr100_playbook_authoring` approval。
   - approval scope 明確為 `playbook_authoring_record_only`：`execution_authorized=false`、`repair_attempted=false`、`repair_executed=false`。
-  - 以 `adr100_playbook_authoring:{work_item}` fingerprint 收斂重複送審，避免同一個告警項目一直產生重複 approval。
+  - 以 `adr100_playbook_authoring:{work_item}` 的 SHA-256 fingerprint 收斂重複送審，符合 production `approval_records.fingerprint VARCHAR(64)` 限制。
   - 寫入 `approval_records`、`alert_operation_log(APPROVAL_ESCALATED)` 與 timeline；不寫 incident state、不寫 auto-repair result、不建立外部 ticket。
 - `apps/api/src/services/approval_execution.py`：
   - 新增 `playbook_authoring_record_only` 執行分支。