Add clarifying comments and improve documentation based on code review

Co-authored-by: link2xt <18373967+link2xt@users.noreply.github.com>

src/calls.rs

@@ -196,8 +196,10 @@ impl Context {
             ..Default::default()
         };
         
-        // Set a placeholder parameter so the message is recognized as a call
-        // This will be used by mimefactory until the DB entry is available
+        // Set a placeholder parameter so the message is recognized as a call during sending.
+        // This ensures mimefactory can read the SDP during the brief window between
+        // send_msg() starting and the calls table entry being available.
+        // The param will be removed after send_msg() completes.
         call.param.set(Param::WebrtcRoom, &place_call_info);
         call.id = send_msg(self, chat_id, &mut call).await?;
 
@@ -521,7 +523,9 @@ impl Context {
             return Ok(None);
         }
 
-        // Load SDP from calls table
+        // Load SDP from calls table. Returns empty strings if no record exists,
+        // which can happen for old messages from before the migration or for
+        // calls where SDPs have been cleaned up by housekeeping.
         let (place_call_info, accept_call_info) = self
             .sql
             .query_row_optional(

src/sql.rs

@@ -921,12 +921,13 @@ pub async fn housekeeping(context: &Context) -> Result<()> {
         .log_err(context)
         .ok();
 
-    // Delete call SDPs for ended calls (older than 24 hours) or orphaned calls.
+    // Delete call SDPs for ended calls (older than 24 hours) or trashed calls.
     // We clean up calls that ended more than 24 hours ago to protect privacy
     // as SDPs contain IP addresses. Ended calls are identified by having
-    // the CALL_ENDED_TIMESTAMP parameter (Param::Arg4) set.
-    // The ON DELETE CASCADE foreign key will handle orphaned entries automatically,
-    // but we also check for trash and old ended calls.
+    // the CALL_ENDED_TIMESTAMP parameter (Param::Arg4='H') set.
+    // The pattern '%H=%' matches this parameter since params are stored as
+    // newline-separated key=value pairs (e.g., "E=123\nH=456\n").
+    // The ON DELETE CASCADE foreign key handles orphaned entries automatically.
     context
         .sql
         .execute(