🔨 chore(db): make push_tokens unique constraint device-only

Drop the userId prefix from the push_tokens unique index — one row per
device, reassigned to the new user on switch (upsert by deviceId).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/development/database-schema.dbml

@@ -1326,7 +1326,7 @@ table push_tokens {
   last_seen_at "timestamp with time zone" [not null, default: `now()`]
 
   indexes {
-    (user_id, device_id) [name: 'idx_push_tokens_user_device', unique]
+    device_id [name: 'idx_push_tokens_device', unique]
     user_id [name: 'idx_push_tokens_user']
     last_seen_at [name: 'idx_push_tokens_last_seen']
   }

packages/database/migrations/0104_topic_usage_push_tokens_tasks_doc_shares.sql

@@ -39,7 +39,7 @@ ALTER TABLE "push_tokens" DROP CONSTRAINT IF EXISTS "push_tokens_user_id_users_i
 ALTER TABLE "push_tokens" ADD CONSTRAINT "push_tokens_user_id_users_id_fk" FOREIGN KEY ("user_id") REFERENCES "public"."users"("id") ON DELETE cascade ON UPDATE no action;--> statement-breakpoint
 CREATE UNIQUE INDEX IF NOT EXISTS "document_shares_document_id_unique" ON "document_shares" USING btree ("document_id");--> statement-breakpoint
 CREATE INDEX IF NOT EXISTS "document_shares_user_id_idx" ON "document_shares" USING btree ("user_id");--> statement-breakpoint
-CREATE UNIQUE INDEX IF NOT EXISTS "idx_push_tokens_user_device" ON "push_tokens" USING btree ("user_id","device_id");--> statement-breakpoint
+CREATE UNIQUE INDEX IF NOT EXISTS "idx_push_tokens_device" ON "push_tokens" USING btree ("device_id");--> statement-breakpoint
 CREATE INDEX IF NOT EXISTS "idx_push_tokens_user" ON "push_tokens" USING btree ("user_id");--> statement-breakpoint
 CREATE INDEX IF NOT EXISTS "idx_push_tokens_last_seen" ON "push_tokens" USING btree ("last_seen_at");--> statement-breakpoint
 CREATE INDEX IF NOT EXISTS "topics_model_idx" ON "topics" USING btree ("model");--> statement-breakpoint

packages/database/migrations/meta/0104_snapshot.json

@@ -6,7 +6,7 @@
   },
   "dialect": "postgresql",
   "enums": {},
-  "id": "fe7c1962-3f6f-4c00-b2dd-7ce035fecb9f",
+  "id": "07e041f5-28d5-443a-b5c5-59aa6122ba48",
   "policies": {},
   "prevId": "e8bb3ce2-fead-4b3d-810e-307c98e891b7",
   "roles": {},
@@ -10001,15 +10001,9 @@
         }
       },
       "indexes": {
-        "idx_push_tokens_user_device": {
-          "name": "idx_push_tokens_user_device",
+        "idx_push_tokens_device": {
+          "name": "idx_push_tokens_device",
           "columns": [
-            {
-              "expression": "user_id",
-              "isExpression": false,
-              "asc": true,
-              "nulls": "last"
-            },
             {
               "expression": "device_id",
               "isExpression": false,

packages/database/migrations/meta/_journal.json

@@ -732,7 +732,7 @@
     {
       "idx": 104,
       "version": "7",
-      "when": 1779942758520,
+      "when": 1779943832837,
       "tag": "0104_topic_usage_push_tokens_tasks_doc_shares",
       "breakpoints": true
     }

packages/database/src/schemas/pushToken.ts

@@ -6,8 +6,8 @@ import { users } from './user';
 /**
  * Stores Expo push notification tokens registered by mobile clients.
  *
- * One row per (userId, deviceId) — a single user may have multiple devices
- * (e.g. iPhone + Android tablet), each receiving its own notifications.
+ * One row per device — on user switch the row is reassigned to the new user
+ * (re-registration upserts by deviceId).
  *
  * Tokens are validated at registration time but may become invalid over time
  * (app uninstall, OS reinstall). Cleanup happens via the Expo receipt cron
@@ -38,8 +38,8 @@ export const pushTokens = pgTable(
     lastSeenAt: timestamptz('last_seen_at').defaultNow().notNull(),
   },
   (table) => [
-    /** Same user + device = one row; re-registration upserts in place */
-    uniqueIndex('idx_push_tokens_user_device').on(table.userId, table.deviceId),
+    /** One row per device; re-registration upserts in place */
+    uniqueIndex('idx_push_tokens_device').on(table.deviceId),
     /** PushChannel.deliver fans out by userId */
     index('idx_push_tokens_user').on(table.userId),
     /** Future: cleanup long-inactive tokens by lastSeenAt */