diff --git a/apps/api/src/broker/write.ts b/apps/api/src/broker/write.ts
index 4ab54da..82fea6b 100644
--- a/apps/api/src/broker/write.ts
+++ b/apps/api/src/broker/write.ts
@@ -65,6 +65,17 @@ export async function updateCalendarEvent(
   icsString: string,
   etag: string | null,
 ): Promise<Response> {
+  // WR-03: a missing etag maps to NO If-Match header → an UNCONDITIONAL PUT, which
+  // defeats D-08 conflict detection for exactly the rows most likely to be stale (an
+  // event cached before an etag was captured, or one Fastmail omitted the etag for).
+  // We do not block the write (it would strand the user's edit), but we make the
+  // unconditional-write path observable so it can be diagnosed instead of silently
+  // overwriting a concurrent external edit with no 412.
+  if (etag == null || etag === '') {
+    console.warn(
+      `[write] updateCalendarObject dispatching with NO If-Match (unconditional PUT) — conflict detection disabled for url=${calendarObjectUrl}`,
+    )
+  }
   return client.updateCalendarObject({
     calendarObject: {
       url: calendarObjectUrl,
@@ -87,6 +98,13 @@ export async function deleteCalendarEvent(
   calendarObjectUrl: string,
   etag: string | null,
 ): Promise<Response> {
+  // WR-03: see updateCalendarEvent — a missing etag is an unconditional DELETE that
+  // bypasses D-08 conflict detection. Log so the path is observable rather than silent.
+  if (etag == null || etag === '') {
+    console.warn(
+      `[write] deleteCalendarObject dispatching with NO If-Match (unconditional DELETE) — conflict detection disabled for url=${calendarObjectUrl}`,
+    )
+  }
   return client.deleteCalendarObject({
     calendarObject: {
       url: calendarObjectUrl,