diff --git a/gateway/platforms/webhook.py b/gateway/platforms/webhook.py
index 7c77a96b5b8..9d236f2198b 100644
--- a/gateway/platforms/webhook.py
+++ b/gateway/platforms/webhook.py
@@ -938,13 +938,34 @@ class WebhookAdapter(BasePlatformAdapter):
                 success=False, error="Missing repo or pr_number"
             )
 
+        # --- Input validation (prevent CLI argument injection) ---
+        # pr_number must be a positive integer.
+        try:
+            pr_int = int(pr_number)
+            if pr_int <= 0:
+                raise ValueError("non-positive")
+        except (ValueError, TypeError):
+            logger.error(
+                "[webhook] invalid pr_number: %r", pr_number
+            )
+            return SendResult(
+                success=False, error="Invalid pr_number"
+            )
+
+        # repo must match owner/name (alphanumeric, hyphens, underscores, dots).
+        if not re.fullmatch(r"[A-Za-z0-9._-]+/[A-Za-z0-9._-]+", repo):
+            logger.error("[webhook] invalid repo format: %r", repo)
+            return SendResult(
+                success=False, error="Invalid repo format"
+            )
+
         try:
             result = subprocess.run(
                 [
                     "gh",
                     "pr",
                     "comment",
-                    str(pr_number),
+                    str(pr_int),
                     "--repo",
                     repo,
                     "--body",
diff --git a/gateway/run.py b/gateway/run.py
index d449bdcf9f4..c32fbff0c87 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -10910,8 +10910,8 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
                         )
             except Exception:
                 logger.debug("Failed to persist inbound user message after agent exception", exc_info=True)
-            error_type = type(e).__name__
-            error_detail = str(e)[:300] if str(e) else "no details available"
+            # Log full details server-side only; never expose raw exception
+            # types or messages to end users (info-leakage risk).
             status_hint = ""
             status_code = getattr(e, "status_code", None)
             _hist_len = len(history) if 'history' in locals() else 0
@@ -10955,9 +10955,7 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
                 elif status_code == 400:
                     status_hint = " The request was rejected by the API."
             return (
-                f"Sorry, I encountered an error ({error_type}).\n"
-                f"{error_detail}\n"
-                f"{status_hint}"
+                f"Sorry, I encountered an unexpected error.{status_hint}\n"
                 "Try again or use /reset to start a fresh session."
             )
         finally: