crates/nuncio-mail/src/jmap.rs

@@ -451,18 +451,14 @@ impl JmapEngine {
         }
     }
 
-    /// Parse a raw JMAP `Email/get` JSON response payload into a list of
-    /// [`PlacedMessage`] and the new state string.
-    pub fn parse_email_get_response(
-        &self,
-        raw_json: &str,
-    ) -> Result<(Vec<PlacedMessage>, String), MailError> {
-        self.parse_email_get_response_in_folder(raw_json, "inbox")
-    }
-
     /// Parse a raw JMAP `Email/get` JSON response payload into the occupancies
     /// it establishes for `folder_id`, plus the account's Email state string.
     ///
+    /// The caller supplies the mailbox being parsed for because the placements
+    /// this produces are keyed by it: a placement labelled with a folder the
+    /// account does not sync can never be matched again, so a fixed label would
+    /// silently strand every message it produced.
+    ///
     /// A returned message whose `mailboxIds` is present and does NOT name
     /// `folder_id` is dropped rather than placed: `Email/changes` is
     /// account-wide (RFC 8621 section 4.2 offers no mailbox filter), so a
@@ -470,7 +466,7 @@ impl JmapEngine {
     /// here would invent an occupancy the server never reported. Membership
     /// that the server did not return at all is left alone -- unknown is not
     /// absent.
-    fn parse_email_get_response_in_folder(
+    pub fn parse_email_get_response(
         &self,
         raw_json: &str,
         folder_id: &str,
@@ -765,7 +761,7 @@ impl JmapEngine {
 
         let get_request = Self::build_email_get_request(jmap_account_id, Some(ids));
         let get_raw = self.post_jmap(api_url, &get_request).await?;
-        let (emails, state) = self.parse_email_get_response_in_folder(&get_raw, folder_id)?;
+        let (emails, state) = self.parse_email_get_response(&get_raw, folder_id)?;
 
         let present: Vec<PlacementKey> = emails.iter().map(|m| m.placement.key()).collect();
 
@@ -810,7 +806,7 @@ impl JmapEngine {
             let get_request =
                 Self::build_email_get_request(jmap_account_id, Some(changes.changed.clone()));
             let get_raw = self.post_jmap(api_url, &get_request).await?;
-            let (emails, _state) = self.parse_email_get_response_in_folder(&get_raw, folder_id)?;
+            let (emails, _state) = self.parse_email_get_response(&get_raw, folder_id)?;
             emails
         };
 
@@ -1118,7 +1114,7 @@ mod tests {
         }"#;
         let engine = JmapEngine::new("acct-1");
         let (emails, _state) = engine
-            .parse_email_get_response_in_folder(raw, "mb-inbox")
+            .parse_email_get_response(raw, "mb-inbox")
             .expect("parse get");
         let ids: Vec<&str> = emails
             .iter()
@@ -1142,7 +1138,9 @@ mod tests {
             ]
         }"#;
         let engine = JmapEngine::new("acct-1");
-        let (emails, _state) = engine.parse_email_get_response(raw).expect("parse get");
+        let (emails, _state) = engine
+            .parse_email_get_response(raw, "mb-inbox")
+            .expect("parse get");
 
         assert_eq!(
             emails[0].email.message_id.as_deref(),
@@ -1160,7 +1158,7 @@ mod tests {
     #[test]
     fn parse_invalid_jmap_json_fails() {
         let engine = JmapEngine::new("acct-1");
-        let res = engine.parse_email_get_response("{ invalid json }");
+        let res = engine.parse_email_get_response("{ invalid json }", "mb-inbox");
         assert!(res.is_err());
     }
 

crates/nuncio-mail/tests/imap_identity_test.rs

@@ -193,7 +193,7 @@ async fn an_imap_emailid_and_a_jmap_object_id_produce_the_same_key() {
            "receivedAt":1700001000,"isUnread":true}}]}},"c1"]]}}"#
     );
     let (jmap, _state) = JmapEngine::new(ACCOUNT)
-        .parse_email_get_response(&jmap_response)
+        .parse_email_get_response(&jmap_response, "mb-inbox")
         .expect("the JMAP response parses");
 
     assert_eq!(imap.upserts.len(), 1);

crates/nuncio-mail/tests/wiremock_jmap_test.rs

@@ -81,7 +81,7 @@ async fn wiremock_jmap_session_discovery_and_email_get_sync() {
 
     let engine = JmapEngine::new("acct-100");
     let (emails, new_state) = engine
-        .parse_email_get_response(&resp.text().await.unwrap())
+        .parse_email_get_response(&resp.text().await.unwrap(), "mb-inbox")
         .expect("parse email get");
 
     assert_eq!(emails.len(), 1);

crates/nuncio-store/src/db.rs

@@ -1777,6 +1777,71 @@ impl DatabaseEngine {
             .collect())
     }
 
+    /// Every mailbox each of `message_keys` currently occupies, grouped by key.
+    ///
+    /// The batched form of [`Self::placements_of`], for callers holding a whole
+    /// page of messages: one query per chunk instead of one per message. Keys
+    /// absent from the result occupy no mailbox; callers that need an entry for
+    /// every requested key should treat a missing entry as an empty set.
+    ///
+    /// Each key's placements are ordered by folder id ascending, exactly as
+    /// [`Self::placements_of`] orders them -- callers take the first placement
+    /// as the message's canonical mailbox, so the order is part of the
+    /// contract, not an incidental property of the query plan.
+    ///
+    /// Chunked at [`MAX_KEYS_PER_IN_LIST`] for the same reason as
+    /// [`Self::existing_placements`]: the bind-parameter ceiling belongs to the
+    /// statement, so it can only be enforced where the statement is built.
+    /// Duplicate keys are collapsed first, so no key's placements can be
+    /// gathered from two chunks and appended twice.
+    pub async fn placements_of_batch(
+        &self,
+        message_keys: &[String],
+    ) -> Result<std::collections::HashMap<String, Vec<nuncio_core::model::Placement>>, DatabaseError>
+    {
+        let mut seen = std::collections::HashSet::new();
+        let unique: Vec<&String> = message_keys
+            .iter()
+            .filter(|key| seen.insert(key.as_str()))
+            .collect();
+
+        let mut grouped: std::collections::HashMap<String, Vec<nuncio_core::model::Placement>> =
+            std::collections::HashMap::new();
+
+        for chunk in unique.chunks(MAX_KEYS_PER_IN_LIST) {
+            let mut builder: sqlx::QueryBuilder<'_, sqlx::Sqlite> = sqlx::QueryBuilder::new(
+                "SELECT message_key, account_id, folder_id, uidvalidity, uid, read_flag
+                 FROM placements WHERE message_key IN (",
+            );
+            let mut separated = builder.separated(", ");
+            for key in chunk {
+                separated.push_bind(*key);
+            }
+            builder.push(") ORDER BY message_key ASC, folder_id ASC");
+
+            let rows: Vec<(String, String, String, String, String, i64)> = builder
+                .build_query_as()
+                .fetch_all(&self.pool)
+                .await
+                .map_err(DatabaseError::Query)?;
+
+            for (message_key, account_id, folder_id, uid_validity, remote_id, read_flag) in rows {
+                grouped
+                    .entry(message_key)
+                    .or_default()
+                    .push(nuncio_core::model::Placement {
+                        account_id,
+                        folder_id,
+                        uid_validity,
+                        remote_id,
+                        read: read_flag != 0,
+                    });
+            }
+        }
+
+        Ok(grouped)
+    }
+
     /// Messages occupying one folder of one account, newest first, paired with
     /// the placement they were found through.
     ///
@@ -5494,6 +5559,83 @@ mod tests {
         assert_eq!(known.len(), 1, "and the query must not echo its own input");
     }
 
+    #[tokio::test]
+    async fn placements_of_batch_matches_per_message_placements_of_including_order() {
+        let (engine, _dir) = DatabaseEngine::connect_ephemeral().await.unwrap();
+
+        // Folders are saved in an order that is neither insertion-sorted nor
+        // reverse-sorted, so a batch query that forgot to order by folder id
+        // would come back visibly wrong rather than accidentally right.
+        for (key, folder, uid) in [
+            ("key-a", "Zeta", "1"),
+            ("key-a", "Alpha", "2"),
+            ("key-a", "Mid", "3"),
+            ("key-b", "Sent", "4"),
+            ("key-b", "Archive", "5"),
+            // Placed but never asked for: proves the `IN (...)` filter is real.
+            ("key-unrequested", "INBOX", "6"),
+        ] {
+            let (email, placement) = sample_message_and_placement(key, folder, uid);
+            engine
+                .save_email_at(
+                    &email,
+                    nuncio_core::model::IdentitySource::EmailId,
+                    &placement,
+                )
+                .await
+                .unwrap();
+        }
+
+        // "key-a" appears twice: a caller may hand over a page with repeats,
+        // and a key gathered from two chunks must not be appended twice.
+        let requested = [
+            "key-a".to_string(),
+            "key-b".to_string(),
+            "key-a".to_string(),
+            "key-never-saved".to_string(),
+        ];
+        let grouped = engine.placements_of_batch(&requested).await.unwrap();
+
+        for key in ["key-a", "key-b"] {
+            let one_at_a_time = engine.placements_of(key).await.unwrap();
+            assert!(
+                one_at_a_time.len() > 1 || key == "key-b",
+                "the fixture must exercise more than one placement per message"
+            );
+            assert_eq!(
+                grouped.get(key),
+                Some(&one_at_a_time),
+                "the batched read of '{key}' must equal the per-message read, element for element"
+            );
+
+            let folders: Vec<&str> = one_at_a_time
+                .iter()
+                .map(|placement| placement.folder_id.as_str())
+                .collect();
+            let mut sorted = folders.clone();
+            sorted.sort_unstable();
+            assert_eq!(
+                folders, sorted,
+                "the first placement of '{key}' is taken as its canonical mailbox, so folder id order is load-bearing"
+            );
+        }
+
+        assert_eq!(
+            grouped.get("key-a").map(Vec::len),
+            Some(3),
+            "a repeated key must not have its placements gathered twice"
+        );
+        assert!(
+            !grouped.contains_key("key-never-saved"),
+            "a key that occupies no mailbox must be absent, not invented"
+        );
+        assert!(
+            !grouped.contains_key("key-unrequested"),
+            "the batch must answer only for the keys it was asked about"
+        );
+        assert_eq!(grouped.len(), 2, "and for nothing else");
+    }
+
     /// A first sync of a real mailbox hands `existing_placements` the entire
     /// folder in one call. Each key spends four bind parameters, and SQLite
     /// caps a statement at 32766 of them, so an unchunked `IN (...)` list dies

crates/nunciod/src/grpc.rs

@@ -1025,25 +1025,25 @@ fn map_placement_ref_from_proto(placement: PlacementRefProto) -> nuncio_core::mo
 
 /// Fills each message's complete placement set from the store.
 ///
-/// This costs one query per message rather than one per page. That is the
-/// honest price of the field: occupancy is per-message state and a page can mix
-/// messages that sit in one mailbox with messages that sit in ten. A failure to
-/// read one message's placements leaves that message's set empty rather than
-/// failing the whole listing, and is logged -- a partial page is more useful
-/// than none, and the field is additive so a client that ignores it is
-/// unaffected.
+/// One batched query for the whole page rather than one per message: occupancy
+/// is per-message state, but reading it per message makes a page of fifty cost
+/// fifty-one round trips, which shows up directly as page latency. A failure to
+/// read the batch leaves every set empty rather than failing the whole listing,
+/// and is logged -- a page without placements is more useful than none, and the
+/// field is additive so a client that ignores it is unaffected.
 async fn fill_placements(db: &DatabaseEngine, messages: &mut [MessageProto]) {
+    let keys: Vec<String> = messages.iter().map(|message| message.id.clone()).collect();
+    let mut grouped = match db.placements_of_batch(&keys).await {
+        Ok(grouped) => grouped,
+        Err(e) => {
+            tracing::warn!("Mail: failed to read the placement sets for this page: {e}");
+            return;
+        }
+    };
+
     for message in messages.iter_mut() {
-        match db.placements_of(&message.id).await {
-            Ok(placements) => {
-                message.placements = placements.into_iter().map(map_placement_to_proto).collect();
-            }
-            Err(e) => {
-                tracing::warn!(
-                    message_id = %message.id,
-                    "Mail: failed to read the placement set: {e}"
-                );
-            }
+        if let Some(placements) = grouped.remove(&message.id) {
+            message.placements = placements.into_iter().map(map_placement_to_proto).collect();
         }
     }
 }