Do not allow duplicate mounts

migrations/schema.sql

@@ -85,7 +85,6 @@ CREATE TABLE IF NOT EXISTS apps(
     dataDir VARCHAR(256) UNIQUE,
     taskId INTEGER, // current task
     errorJson TEXT,
-    bindsJson TEXT, // bind mounts
     servicesConfigJson TEXT, // app services configuration
 
     FOREIGN KEY(mailboxDomain) REFERENCES domains(domain),
@@ -248,6 +247,8 @@ CREATE TABLE IF NOT EXISTS volumes(
 CREATE TABLE IF NOT EXISTS appMounts(
     appId VARCHAR(128) NOT NULL,
     volumeId VARCHAR(128) NOT NULL,
+    readOnly BOOLEAN DEFAULT 1,
+    UNIQUE KEY appMounts_appId_volumeId (appId, volumeId),
     FOREIGN KEY(appId) REFERENCES apps(id),
     FOREIGN KEY(volumeId) REFERENCES volumes(id));