perf(me): optimize mentions query with materialized CTEs scoped to candidates

The `query_mentioned_in` SQL previously joined notes directly against
the full issues/merge_requests tables, with per-row subqueries for
author/assignee/reviewer exclusion. On large databases this produced
pathological query plans where SQLite scanned the entire notes table
before filtering to relevant entities.

Refactor into a dedicated `build_mentioned_in_sql()` builder that:

1. Pre-filters candidate issues and MRs into MATERIALIZED CTEs
   (state open OR recently closed, not authored by user, not
   assigned/reviewing). This narrows the working set before any
   notes join.

2. Computes note timestamps (my_ts, others_ts, any_ts) as separate
   MATERIALIZED CTEs scoped to candidate entities only, rather than
   scanning all notes.

3. Joins mention-bearing notes against the pre-filtered candidates,
   avoiding the full-table scans.

Also adds a test verifying that authored issues are excluded from the
mentions results, and a unit test asserting all four CTEs are
materialized.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/cli/commands/me/me_tests.rs

@@ -880,6 +880,21 @@ fn mentioned_in_excludes_assigned_issue() {
     assert!(results.is_empty(), "should exclude assigned issues");
 }
 
+#[test]
+fn mentioned_in_excludes_authored_issue() {
+    let conn = setup_test_db();
+    insert_project(&conn, 1, "group/repo");
+    insert_issue(&conn, 10, 1, 42, "alice"); // alice IS author
+    let disc_id = 100;
+    insert_discussion(&conn, disc_id, 1, None, Some(10));
+    let t = now_ms() - 1000;
+    insert_note_at(&conn, 200, disc_id, 1, "bob", false, "hey @alice", t);
+
+    let recency_cutoff = now_ms() - 7 * 24 * 3600 * 1000;
+    let results = query_mentioned_in(&conn, "alice", &[], recency_cutoff).unwrap();
+    assert!(results.is_empty(), "should exclude authored issues");
+}
+
 #[test]
 fn mentioned_in_finds_mention_on_non_authored_mr() {
     let conn = setup_test_db();
@@ -1093,6 +1108,27 @@ fn mentioned_in_rejects_false_positive_email() {
 
 // ─── Helper Tests ──────────────────────────────────────────────────────────
 
+#[test]
+fn mentioned_in_sql_materializes_core_ctes() {
+    let sql = build_mentioned_in_sql("");
+    assert!(
+        sql.contains("candidate_issues AS MATERIALIZED"),
+        "candidate_issues should be materialized"
+    );
+    assert!(
+        sql.contains("candidate_mrs AS MATERIALIZED"),
+        "candidate_mrs should be materialized"
+    );
+    assert!(
+        sql.contains("note_ts_issue AS MATERIALIZED"),
+        "note_ts_issue should be materialized"
+    );
+    assert!(
+        sql.contains("note_ts_mr AS MATERIALIZED"),
+        "note_ts_mr should be materialized"
+    );
+}
+
 #[test]
 fn parse_attention_state_all_variants() {
     assert_eq!(

src/cli/commands/me/queries.rs

@@ -789,6 +789,87 @@ struct RawMentionRow {
     mention_body: String,
 }
 
+fn build_mentioned_in_sql(project_clause: &str) -> String {
+    format!(
+        "WITH candidate_issues AS MATERIALIZED (
+            SELECT i.id, i.iid, i.title, p.path_with_namespace, i.state,
+                   i.updated_at, i.web_url
+            FROM issues i
+            JOIN projects p ON i.project_id = p.id
+            WHERE (i.state = 'opened' OR (i.state = 'closed' AND i.updated_at > ?2))
+              AND (i.author_username IS NULL OR i.author_username != ?1)
+              AND NOT EXISTS (
+                SELECT 1 FROM issue_assignees ia
+                WHERE ia.issue_id = i.id AND ia.username = ?1
+              )
+              {project_clause}
+        ),
+        candidate_mrs AS MATERIALIZED (
+            SELECT m.id, m.iid, m.title, p.path_with_namespace, m.state,
+                   m.updated_at, m.web_url
+            FROM merge_requests m
+            JOIN projects p ON m.project_id = p.id
+            WHERE (m.state = 'opened'
+                   OR (m.state IN ('merged', 'closed') AND m.updated_at > ?2))
+              AND m.author_username != ?1
+              AND NOT EXISTS (
+                SELECT 1 FROM mr_reviewers rv
+                WHERE rv.merge_request_id = m.id AND rv.username = ?1
+              )
+              {project_clause}
+        ),
+        note_ts_issue AS MATERIALIZED (
+            SELECT d.issue_id,
+                MAX(CASE WHEN n.author_username = ?1 THEN n.created_at END) AS my_ts,
+                MAX(CASE WHEN n.author_username != ?1 THEN n.created_at END) AS others_ts,
+                MAX(n.created_at) AS any_ts
+            FROM notes n
+            JOIN discussions d ON n.discussion_id = d.id
+            JOIN candidate_issues ci ON ci.id = d.issue_id
+            WHERE n.is_system = 0
+            GROUP BY d.issue_id
+        ),
+        note_ts_mr AS MATERIALIZED (
+            SELECT d.merge_request_id,
+                MAX(CASE WHEN n.author_username = ?1 THEN n.created_at END) AS my_ts,
+                MAX(CASE WHEN n.author_username != ?1 THEN n.created_at END) AS others_ts,
+                MAX(n.created_at) AS any_ts
+            FROM notes n
+            JOIN discussions d ON n.discussion_id = d.id
+            JOIN candidate_mrs cm ON cm.id = d.merge_request_id
+            WHERE n.is_system = 0
+            GROUP BY d.merge_request_id
+        )
+        -- Issue mentions (scoped to candidate entities only)
+        SELECT 'issue', ci.iid, ci.title, ci.path_with_namespace, ci.state,
+               ci.updated_at, ci.web_url,
+               nt.my_ts, nt.others_ts, nt.any_ts,
+               n.body
+        FROM notes n
+        JOIN discussions d ON n.discussion_id = d.id
+        JOIN candidate_issues ci ON ci.id = d.issue_id
+        LEFT JOIN note_ts_issue nt ON nt.issue_id = ci.id
+        WHERE n.is_system = 0
+          AND n.author_username != ?1
+          AND LOWER(n.body) LIKE '%@' || LOWER(?1) || '%'
+        UNION ALL
+        -- MR mentions (scoped to candidate entities only)
+        SELECT 'mr', cm.iid, cm.title, cm.path_with_namespace, cm.state,
+               cm.updated_at, cm.web_url,
+               nt.my_ts, nt.others_ts, nt.any_ts,
+               n.body
+        FROM notes n
+        JOIN discussions d ON n.discussion_id = d.id
+        JOIN candidate_mrs cm ON cm.id = d.merge_request_id
+        LEFT JOIN note_ts_mr nt ON nt.merge_request_id = cm.id
+        WHERE n.is_system = 0
+          AND n.author_username != ?1
+          AND LOWER(n.body) LIKE '%@' || LOWER(?1) || '%'
+        ORDER BY 6 DESC
+        LIMIT 500",
+    )
+}
+
 /// Query issues and MRs where the user is @mentioned but not assigned/authored/reviewing.
 ///
 /// Includes open items unconditionally, plus recently-closed/merged items
@@ -802,77 +883,8 @@ pub fn query_mentioned_in(
     recency_cutoff_ms: i64,
 ) -> Result<Vec<MeMention>> {
     let project_clause = build_project_clause_at("p.id", project_ids, 3);
-
+    // Materialized CTEs avoid pathological query plans for project-scoped mentions.
-    // CTE: note timestamps per issue (for attention state computation)
+    let sql = build_mentioned_in_sql(&project_clause);
-    // CTE: note timestamps per MR
-    // Then UNION ALL of issue mentions + MR mentions
-    let sql = format!(
-        "WITH note_ts_issue AS (
-            SELECT d.issue_id,
-                MAX(CASE WHEN n.author_username = ?1 THEN n.created_at END) AS my_ts,
-                MAX(CASE WHEN n.author_username != ?1 THEN n.created_at END) AS others_ts,
-                MAX(n.created_at) AS any_ts
-            FROM notes n
-            JOIN discussions d ON n.discussion_id = d.id
-            WHERE n.is_system = 0 AND d.issue_id IS NOT NULL
-            GROUP BY d.issue_id
-        ),
-        note_ts_mr AS (
-            SELECT d.merge_request_id,
-                MAX(CASE WHEN n.author_username = ?1 THEN n.created_at END) AS my_ts,
-                MAX(CASE WHEN n.author_username != ?1 THEN n.created_at END) AS others_ts,
-                MAX(n.created_at) AS any_ts
-            FROM notes n
-            JOIN discussions d ON n.discussion_id = d.id
-            WHERE n.is_system = 0 AND d.merge_request_id IS NOT NULL
-            GROUP BY d.merge_request_id
-        )
-        -- Issue mentions
-        SELECT 'issue', i.iid, i.title, p.path_with_namespace, i.state,
-               i.updated_at, i.web_url,
-               nt.my_ts, nt.others_ts, nt.any_ts,
-               n.body
-        FROM notes n
-        JOIN discussions d ON n.discussion_id = d.id
-        JOIN issues i ON d.issue_id = i.id
-        JOIN projects p ON i.project_id = p.id
-        LEFT JOIN note_ts_issue nt ON nt.issue_id = i.id
-        WHERE n.is_system = 0
-          AND n.author_username != ?1
-          AND d.issue_id IS NOT NULL
-          AND LOWER(n.body) LIKE '%@' || LOWER(?1) || '%'
-          AND NOT EXISTS (
-            SELECT 1 FROM issue_assignees ia
-            WHERE ia.issue_id = d.issue_id AND ia.username = ?1
-          )
-          AND (i.state = 'opened' OR (i.state = 'closed' AND i.updated_at > ?2))
-          {project_clause}
-        UNION ALL
-        -- MR mentions
-        SELECT 'mr', m.iid, m.title, p.path_with_namespace, m.state,
-               m.updated_at, m.web_url,
-               nt.my_ts, nt.others_ts, nt.any_ts,
-               n.body
-        FROM notes n
-        JOIN discussions d ON n.discussion_id = d.id
-        JOIN merge_requests m ON d.merge_request_id = m.id
-        JOIN projects p ON m.project_id = p.id
-        LEFT JOIN note_ts_mr nt ON nt.merge_request_id = m.id
-        WHERE n.is_system = 0
-          AND n.author_username != ?1
-          AND d.merge_request_id IS NOT NULL
-          AND LOWER(n.body) LIKE '%@' || LOWER(?1) || '%'
-          AND m.author_username != ?1
-          AND NOT EXISTS (
-            SELECT 1 FROM mr_reviewers rv
-            WHERE rv.merge_request_id = d.merge_request_id AND rv.username = ?1
-          )
-          AND (m.state = 'opened'
-               OR (m.state IN ('merged', 'closed') AND m.updated_at > ?2))
-          {project_clause}
-        ORDER BY 6 DESC
-        LIMIT 500",
-    );
 
     let mut params: Vec<Box<dyn rusqlite::types::ToSql>> = Vec::new();
     params.push(Box::new(username.to_string()));