diff --git a/app/database.py b/app/database.py
index f85ad6e..23a2e3d 100644
--- a/app/database.py
+++ b/app/database.py
@@ -42,6 +42,10 @@ CREATE TABLE IF NOT EXISTS messages (
     signature TEXT,
     outgoing INTEGER DEFAULT 0,
     acked INTEGER DEFAULT 0,
+    -- Deduplication: identical text + timestamp in the same conversation is treated as a
+    -- mesh echo/repeat. Second-precision timestamps mean two intentional identical messages
+    -- within the same second would collide, but this is not feasible in practice — LoRa
+    -- transmission takes several seconds per message, and the UI clears the input on send.
     UNIQUE(type, conversation_key, text, sender_timestamp)
 );
 
diff --git a/app/routers/messages.py b/app/routers/messages.py
index 30a6753..22ffbd5 100644
--- a/app/routers/messages.py
+++ b/app/routers/messages.py
@@ -236,6 +236,9 @@ async def send_channel_message(request: SendChannelMessageRequest) -> Message:
                 detail="Failed to store outgoing message - unexpected duplicate",
             )
 
+        # Experimental: byte-perfect resend after a delay to improve delivery reliability.
+        # This intentionally holds the radio operation lock for the full delay — it is an
+        # opt-in experimental feature where blocking other radio operations is acceptable.
         if app_settings.experimental_channel_double_send:
             logger.debug(
                 "Experimental channel double-send enabled; waiting %ds before byte-perfect duplicate",