⚡ Bolt: Optimize loop-invariant checks and dictionary lookups in emails API

.jules/bolt.md

@@ -43,3 +43,7 @@
 ## 2026-06-10 - Optimize redundant dictionary lookups in tight loops
  **Learning:** Using `dict.setdefault` and multiple `dict.get` or `key in dict` checks inside tight loops significantly impacts performance due to repeated dictionary lookups and unnecessary list allocations. Caching dictionary lookups (e.g., using a single `dict.get(key)`) and conditionally handling the logic based on the result is much more performant.
  **Action:** When aggregating or grouping items in a loop, avoid `setdefault`. Instead, check if the key exists using a single `.get()`, and perform initialization/updates conditionally. Additionally, hoist loop-invariant checks (e.g., `folder == "sent"`) outside the loop to avoid redundant evaluations.
+
+## 2026-06-10 - Optimize redundant dictionary lookups in tight loops
+**Learning:** Using `dict.setdefault` and multiple `dict.get` or `key in dict` checks inside tight loops significantly impacts performance due to repeated dictionary lookups and unnecessary list allocations. Caching dictionary lookups (e.g., using a single `dict.get(key)`) and conditionally handling the logic based on the result is much more performant.
+**Action:** When aggregating or grouping items in a loop, avoid `setdefault`. Instead, check if the key exists using a single `.get()`, and perform initialization/updates conditionally. Additionally, hoist loop-invariant checks (e.g., `folder == "sent"`) outside the loop to avoid redundant evaluations.

backend/api/emails.py

@@ -284,11 +284,15 @@ async def get_emails(
             if message_is_from_user(email, user_addresses):
                 has_sent_message[group_key] = True
 
-    visible_groups = [
-        email
-        for group_key, email in grouped.items()
-        if folder != "sent" or has_sent_message.get(group_key, False)
-    ]
+    if is_sent_folder:
+        visible_groups = [
+            email
+            for group_key, email in grouped.items()
+            if has_sent_message.get(group_key, False)
+        ]
+    else:
+        visible_groups = list(grouped.values())
+
     sorted_groups = sorted(visible_groups, key=lambda x: x.date, reverse=True)[:limit]
 
     items = []
@@ -391,12 +395,15 @@ def _build_email_lookup_dicts(
     by_fingerprint: dict[str, Email] = {}
     for email_row in existing_emails:
         for lookup_value in _email_message_lookup_values(email_row):
-            by_message_id.setdefault(lookup_value, email_row)
+            if lookup_value not in by_message_id:
+                by_message_id[lookup_value] = email_row
         row_fingerprint = email_strong_fingerprint(email_row)
         if row_fingerprint:
-            by_fingerprint.setdefault(row_fingerprint, email_row)
+            if row_fingerprint not in by_fingerprint:
+                by_fingerprint[row_fingerprint] = email_row
         if email_row.fingerprint:
-            by_fingerprint.setdefault(email_row.fingerprint, email_row)
+            if email_row.fingerprint not in by_fingerprint:
+                by_fingerprint[email_row.fingerprint] = email_row
     return by_message_id, by_fingerprint