diff --git a/scripts/hooks/run-with-flags-shell.sh b/scripts/hooks/run-with-flags-shell.sh
index 4b064c32..227b8fc7 100755
--- a/scripts/hooks/run-with-flags-shell.sh
+++ b/scripts/hooks/run-with-flags-shell.sh
@@ -29,4 +29,8 @@ if [[ ! -f "$SCRIPT_PATH" ]]; then
   exit 0
 fi
 
-printf '%s' "$INPUT" | "$SCRIPT_PATH"
+# Extract phase prefix from hook ID (e.g., "pre:observe" -> "pre", "post:observe" -> "post")
+# This is needed by scripts like observe.sh that behave differently for PreToolUse vs PostToolUse
+HOOK_PHASE="${HOOK_ID%%:*}"
+
+printf '%s' "$INPUT" | "$SCRIPT_PATH" "$HOOK_PHASE"