diff --git a/src/db/index.js b/src/db/index.js
index d0ee081..b76da9d 100644
--- a/src/db/index.js
+++ b/src/db/index.js
@@ -13,7 +13,7 @@ export function createDatabase(config) {
 
     const db = new Database(config.dbPath);
     initializeSchema(db);
-    runMigrations(db, config);
     initializeAttachments(db);
+    runMigrations(db, config);
     return db;
 }
diff --git a/src/db/schema.js b/src/db/schema.js
index 37cb887..e432f37 100644
--- a/src/db/schema.js
+++ b/src/db/schema.js
@@ -265,6 +265,59 @@ export function runMigrations(db, {dropLegacyChats = false} = {}) {
     ensureColumn("users", userColumns, "role", "ALTER TABLE users ADD COLUMN role TEXT NOT NULL DEFAULT 'user' CHECK (role IN ('user', 'admin'))");
     ensureColumn("users", userColumns, "session_version", "ALTER TABLE users ADD COLUMN session_version INTEGER DEFAULT 0");
     db.prepare("UPDATE users SET session_version = 0 WHERE session_version IS NULL").run();
+
+    // Older databases allowed usernames that differed only by case. Repair those
+    // rows before adding the case-insensitive uniqueness guarantee. Keep the first
+    // account unchanged and give later accounts a stable, recoverable username;
+    // moving their owned rows prevents orphaned workspace data.
+    const conflictingUsers = db.prepare(`
+        SELECT LOWER(username) AS username_lower
+        FROM users
+        GROUP BY LOWER(username)
+        HAVING COUNT(*) > 1
+    `).all();
+    if (conflictingUsers.length > 0) {
+        const ownershipColumns = [
+            ["chat_sessions", "username"],
+            ["chat_memories", "username"],
+            ["persona_chat_state", "username"],
+            ["personas", "username"],
+            ["personas", "source_creator_username"],
+            ["user_settings", "username"],
+            ["persona_market", "creator_username"],
+            ["persona_versions", "username"],
+            ["prompt_templates", "username"],
+            ["persona_market_favorites", "username"],
+            ["persona_market_ratings", "username"],
+            ["persona_market_reports", "reporter_username"],
+            ["attachments", "username"],
+            ["upload_leases", "username"],
+            ["workspace_operation_leases", "username"]
+        ];
+        const existingTables = new Set(db.prepare("SELECT name FROM sqlite_master WHERE type = 'table'").all().map(({name}) => name));
+        const updateStatements = ownershipColumns
+            .filter(([table]) => existingTables.has(table))
+            .map(([table, column]) => [
+                table,
+                column,
+                db.prepare(`UPDATE "${table}" SET "${column}" = ? WHERE "${column}" = ?`)
+            ]);
+        const repairConflicts = db.transaction(() => {
+            db.pragma("defer_foreign_keys = ON");
+            for (const {username_lower: usernameLower} of conflictingUsers) {
+                const rows = db.prepare("SELECT rowid, username FROM users WHERE LOWER(username) = ? ORDER BY rowid").all(usernameLower);
+                for (const row of rows.slice(1)) {
+                    const suffix = `-legacy-${row.rowid}`;
+                    const nextUsername = `${row.username.slice(0, Math.max(1, 64 - suffix.length))}${suffix}`;
+                    for (const [, , statement] of updateStatements) {
+                        statement.run(nextUsername, row.username);
+                    }
+                    db.prepare("UPDATE users SET username = ? WHERE username = ?").run(nextUsername, row.username);
+                }
+            }
+        });
+        repairConflicts();
+    }
     db.exec("CREATE UNIQUE INDEX IF NOT EXISTS users_username_lower ON users (LOWER(username))");
 
     const personaColumns = db.prepare("PRAGMA table_info(personas)").all();