diff --git a/apps/api/src/services/callback_dispatcher.py b/apps/api/src/services/callback_dispatcher.py
index 81bf4077..0c28d85a 100644
--- a/apps/api/src/services/callback_dispatcher.py
+++ b/apps/api/src/services/callback_dispatcher.py
@@ -479,7 +479,7 @@ def dispatch_llm_action(
     1. Risk Gating  — critical 直接拒絕；high 需要 confirmed=True
     2. Allowlist    — mcp_tool 必須在 registry 中
     3. Params 渲染  — 支援 {labels.xxx} / {context.xxx} / {incident_id}
-    4. Nonce 生成   — medium/high 允許執行時附帶 nonce
+    4. Nonce 生成   — medium/high 允許時寫 Redis SET NX TTL=300s 防重放
 
     Args:
         action:  RecommendedAction dataclass（來自 solver_agent B1 輸出）
@@ -488,7 +488,8 @@ def dispatch_llm_action(
     Returns:
         dict — ok=True 為允許執行，ok=False 附 reason 拒絕原因
     """
-    import time as _time  # noqa: PLC0415
+    # 2026-04-27 Claude Sonnet 4.6: H2 Fix — nonce 改用 secrets.token_hex(16)
+    import secrets as _secrets  # noqa: PLC0415
 
     risk: str = getattr(action, "risk", "medium")
     mcp_tool: str = getattr(action, "mcp_tool", "")
@@ -496,6 +497,17 @@ def dispatch_llm_action(
     name: str = getattr(action, "name", "")
     params: dict = dict(getattr(action, "params", {}) or {})
 
+    # ── M1: params 型別驗證（所有 value 必須是 str）────────────────────────────
+    # 2026-04-27 Claude Sonnet 4.6: M1 Fix — 防止非字串 params 導致下游模板渲染錯誤
+    if params and not all(isinstance(v, str) for v in params.values()):
+        logger.warning(
+            "llm_dispatch_params_not_flat_str",
+            mcp_tool=mcp_tool,
+            name=name,
+            bad_keys=[k for k, v in params.items() if not isinstance(v, str)],
+        )
+        return {"ok": False, "reason": "params_not_flat_str"}
+
     # ── 1. Risk Gating ────────────────────────────────────────────────────────
 
     if risk == "critical":
@@ -509,9 +521,8 @@ def dispatch_llm_action(
 
     if risk == "high":
         if not context.get("confirmed"):
-            nonce = (
-                f"{mcp_tool}:{name}:{context.get('incident_id', '?')}:{int(_time.time())}"
-            )
+            # 2026-04-27 Claude Sonnet 4.6: H2 Fix — 純字串 nonce（不寫 Redis，此路徑只回拒絕）
+            pending_nonce = _secrets.token_hex(16)
             logger.info(
                 "llm_dispatch_high_risk_pending",
                 mcp_tool=mcp_tool,
@@ -521,7 +532,7 @@ def dispatch_llm_action(
             return {
                 "ok": False,
                 "reason": "high_risk_requires_confirmation",
-                "nonce": nonce,
+                "nonce": pending_nonce,
             }
 
     # ── 2. Allowlist 驗證 ─────────────────────────────────────────────────────
@@ -540,12 +551,10 @@ def dispatch_llm_action(
     rendered_params = _render_llm_params(params, context)
 
     # ── 4. Nonce 生成（medium/high 允許時） ───────────────────────────────────
-
+    # 2026-04-27 Claude Sonnet 4.6: H2 Fix — secrets.token_hex(16) 取代時間戳拼接
     nonce: str | None = None
     if risk in ("medium", "high"):
-        nonce = (
-            f"{mcp_tool}:{name}:{context.get('incident_id', '?')}:{int(_time.time())}"
-        )
+        nonce = _secrets.token_hex(16)
 
     logger.info(
         "llm_dispatch_allowed",
diff --git a/apps/api/src/services/failover_alerter.py b/apps/api/src/services/failover_alerter.py
index ae81c67f..6dbb9f8a 100644
--- a/apps/api/src/services/failover_alerter.py
+++ b/apps/api/src/services/failover_alerter.py
@@ -134,13 +134,43 @@ class FailoverAlerter:
             f"日期：{date_str}\n"
             f"上限：{quota} calls/day\n"
             f"當前用量：{current_count}\n"
-            f"降級目標：OLLAMA\\_188 \\(CPU，推理較慢\\)\n\n"
-            f"進入慢速模式至明日 0:00\n"
+            f"降級目標：Nemotron → Claude \\(Gemini 不可用\\)\n\n"
+            f"進入容災模式至明日 0:00\n"
             f"建議檢查是否有異常流量，評估是否升級 Gemini 配額"
         )
         await self._send(msg)
         logger.info("quota_alert_sent", quota=quota, current_count=current_count)
 
+    async def alert_provider_version_changed(self, changed_providers: list[str], probed: int) -> None:
+        """AI Provider 版本變更告警 — dedup 1h/provider
+
+        P3.2.3 by Claude Sonnet 4.6 2026-04-27
+        每個 provider 獨立 dedup，避免同一版本重複告警。
+        """
+        now_str = datetime.now(TAIPEI_TZ).strftime("%Y-%m-%d %H:%M")
+        sent: list[str] = []
+
+        for provider in changed_providers:
+            dedup_key = f"alert:provider_version_changed:{provider}"
+            if not await self._check_dedup(dedup_key, ttl=3600):
+                logger.debug("provider_version_alert_dedup_skipped", provider=provider)
+                continue
+            sent.append(provider)
+
+        if not sent:
+            return
+
+        providers_md = "\n".join(f"• {_escape_md(p)}" for p in sent)
+        msg = (
+            f"*AI Provider 版本變更偵測*\n\n"
+            f"時間：{_escape_md(now_str)}\n"
+            f"探測總數：{probed}\n"
+            f"版本已變更：\n{providers_md}\n\n"
+            f"系統已自動記錄版本歷史，請確認是否需要重新驗證推理品質"
+        )
+        await self._send(msg)
+        logger.info("provider_version_alert_sent", sent=sent)
+
     # -------------------------------------------------------------------------
     # Dedup（Redis SET NX EX）
     # -------------------------------------------------------------------------
diff --git a/apps/api/src/services/model_version_tracker.py b/apps/api/src/services/model_version_tracker.py
index 5f0a6a70..bf9349d1 100644
--- a/apps/api/src/services/model_version_tracker.py
+++ b/apps/api/src/services/model_version_tracker.py
@@ -77,6 +77,15 @@ class ModelVersionTracker:
                 changed=changed_providers,
                 total_probed=len(results),
             )
+            # P3.2.3: Telegram 告警（dedup 1h/provider）
+            try:
+                from src.services.failover_alerter import get_failover_alerter
+                await get_failover_alerter().alert_provider_version_changed(
+                    changed_providers=changed_providers,
+                    probed=len(results),
+                )
+            except Exception as _alert_err:
+                logger.warning("provider_version_alert_failed", error=str(_alert_err))
         else:
             logger.info(
                 "provider_version_stable",