diff --git a/packages/core/migration/20260604150931_harden_v2_sequence_indexes/migration.sql b/packages/core/migration/20260604150931_harden_v2_sequence_indexes/migration.sql
new file mode 100644
index 0000000000..fdbb41ac6f
--- /dev/null
+++ b/packages/core/migration/20260604150931_harden_v2_sequence_indexes/migration.sql
@@ -0,0 +1,7 @@
+DROP INDEX IF EXISTS `event_aggregate_seq_idx`;--> statement-breakpoint
+DROP INDEX IF EXISTS `event_aggregate_type_seq_idx`;--> statement-breakpoint
+DROP INDEX IF EXISTS `session_message_session_seq_idx`;--> statement-breakpoint
+DROP INDEX IF EXISTS `session_message_session_time_created_id_idx`;--> statement-breakpoint
+DROP INDEX IF EXISTS `session_message_time_created_idx`;--> statement-breakpoint
+CREATE UNIQUE INDEX `event_aggregate_seq_idx` ON `event` (`aggregate_id`,`seq`);--> statement-breakpoint
+CREATE UNIQUE INDEX `session_message_session_seq_idx` ON `session_message` (`session_id`,`seq`);
diff --git a/packages/core/migration/20260604150931_harden_v2_sequence_indexes/snapshot.json b/packages/core/migration/20260604150931_harden_v2_sequence_indexes/snapshot.json
new file mode 100644
index 0000000000..a066459c7e
--- /dev/null
+++ b/packages/core/migration/20260604150931_harden_v2_sequence_indexes/snapshot.json
@@ -0,0 +1,1900 @@
+{
+  "version": "7",
+  "dialect": "sqlite",
+  "id": "4a2f3a76-7952-44cc-abb4-122fb76e17a3",
+  "prevIds": [
+    "fc92fa34-8074-44c3-88f0-a5417f7fd92d"
+  ],
+  "ddl": [
+    {
+      "name": "workspace",
+      "entityType": "tables"
+    },
+    {
+      "name": "data_migration",
+      "entityType": "tables"
+    },
+    {
+      "name": "account_state",
+      "entityType": "tables"
+    },
+    {
+      "name": "account",
+      "entityType": "tables"
+    },
+    {
+      "name": "control_account",
+      "entityType": "tables"
+    },
+    {
+      "name": "event_sequence",
+      "entityType": "tables"
+    },
+    {
+      "name": "event",
+      "entityType": "tables"
+    },
+    {
+      "name": "permission",
+      "entityType": "tables"
+    },
+    {
+      "name": "project_directory",
+      "entityType": "tables"
+    },
+    {
+      "name": "project",
+      "entityType": "tables"
+    },
+    {
+      "name": "message",
+      "entityType": "tables"
+    },
+    {
+      "name": "part",
+      "entityType": "tables"
+    },
+    {
+      "name": "session_input",
+      "entityType": "tables"
+    },
+    {
+      "name": "session_message",
+      "entityType": "tables"
+    },
+    {
+      "name": "session",
+      "entityType": "tables"
+    },
+    {
+      "name": "todo",
+      "entityType": "tables"
+    },
+    {
+      "name": "session_share",
+      "entityType": "tables"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "id",
+      "entityType": "columns",
+      "table": "workspace"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "type",
+      "entityType": "columns",
+      "table": "workspace"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": "''",
+      "generated": null,
+      "name": "name",
+      "entityType": "columns",
+      "table": "workspace"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "branch",
+      "entityType": "columns",
+      "table": "workspace"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "directory",
+      "entityType": "columns",
+      "table": "workspace"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "extra",
+      "entityType": "columns",
+      "table": "workspace"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "project_id",
+      "entityType": "columns",
+      "table": "workspace"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_used",
+      "entityType": "columns",
+      "table": "workspace"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "name",
+      "entityType": "columns",
+      "table": "data_migration"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_completed",
+      "entityType": "columns",
+      "table": "data_migration"
+    },
+    {
+      "type": "integer",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "id",
+      "entityType": "columns",
+      "table": "account_state"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "active_account_id",
+      "entityType": "columns",
+      "table": "account_state"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "active_org_id",
+      "entityType": "columns",
+      "table": "account_state"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "id",
+      "entityType": "columns",
+      "table": "account"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "email",
+      "entityType": "columns",
+      "table": "account"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "url",
+      "entityType": "columns",
+      "table": "account"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "access_token",
+      "entityType": "columns",
+      "table": "account"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "refresh_token",
+      "entityType": "columns",
+      "table": "account"
+    },
+    {
+      "type": "integer",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "token_expiry",
+      "entityType": "columns",
+      "table": "account"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_created",
+      "entityType": "columns",
+      "table": "account"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_updated",
+      "entityType": "columns",
+      "table": "account"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "email",
+      "entityType": "columns",
+      "table": "control_account"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "url",
+      "entityType": "columns",
+      "table": "control_account"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "access_token",
+      "entityType": "columns",
+      "table": "control_account"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "refresh_token",
+      "entityType": "columns",
+      "table": "control_account"
+    },
+    {
+      "type": "integer",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "token_expiry",
+      "entityType": "columns",
+      "table": "control_account"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "active",
+      "entityType": "columns",
+      "table": "control_account"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_created",
+      "entityType": "columns",
+      "table": "control_account"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_updated",
+      "entityType": "columns",
+      "table": "control_account"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "aggregate_id",
+      "entityType": "columns",
+      "table": "event_sequence"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "seq",
+      "entityType": "columns",
+      "table": "event_sequence"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "owner_id",
+      "entityType": "columns",
+      "table": "event_sequence"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "id",
+      "entityType": "columns",
+      "table": "event"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "aggregate_id",
+      "entityType": "columns",
+      "table": "event"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "seq",
+      "entityType": "columns",
+      "table": "event"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "type",
+      "entityType": "columns",
+      "table": "event"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "data",
+      "entityType": "columns",
+      "table": "event"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "id",
+      "entityType": "columns",
+      "table": "permission"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "project_id",
+      "entityType": "columns",
+      "table": "permission"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "action",
+      "entityType": "columns",
+      "table": "permission"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "resource",
+      "entityType": "columns",
+      "table": "permission"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_created",
+      "entityType": "columns",
+      "table": "permission"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_updated",
+      "entityType": "columns",
+      "table": "permission"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "project_id",
+      "entityType": "columns",
+      "table": "project_directory"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "directory",
+      "entityType": "columns",
+      "table": "project_directory"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "type",
+      "entityType": "columns",
+      "table": "project_directory"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_created",
+      "entityType": "columns",
+      "table": "project_directory"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "id",
+      "entityType": "columns",
+      "table": "project"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "worktree",
+      "entityType": "columns",
+      "table": "project"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "vcs",
+      "entityType": "columns",
+      "table": "project"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "name",
+      "entityType": "columns",
+      "table": "project"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "icon_url",
+      "entityType": "columns",
+      "table": "project"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "icon_url_override",
+      "entityType": "columns",
+      "table": "project"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "icon_color",
+      "entityType": "columns",
+      "table": "project"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_created",
+      "entityType": "columns",
+      "table": "project"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_updated",
+      "entityType": "columns",
+      "table": "project"
+    },
+    {
+      "type": "integer",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_initialized",
+      "entityType": "columns",
+      "table": "project"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "sandboxes",
+      "entityType": "columns",
+      "table": "project"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "commands",
+      "entityType": "columns",
+      "table": "project"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "id",
+      "entityType": "columns",
+      "table": "message"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "session_id",
+      "entityType": "columns",
+      "table": "message"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_created",
+      "entityType": "columns",
+      "table": "message"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_updated",
+      "entityType": "columns",
+      "table": "message"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "data",
+      "entityType": "columns",
+      "table": "message"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "id",
+      "entityType": "columns",
+      "table": "part"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "message_id",
+      "entityType": "columns",
+      "table": "part"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "session_id",
+      "entityType": "columns",
+      "table": "part"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_created",
+      "entityType": "columns",
+      "table": "part"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_updated",
+      "entityType": "columns",
+      "table": "part"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "data",
+      "entityType": "columns",
+      "table": "part"
+    },
+    {
+      "type": "integer",
+      "notNull": false,
+      "autoincrement": true,
+      "default": null,
+      "generated": null,
+      "name": "seq",
+      "entityType": "columns",
+      "table": "session_input"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "id",
+      "entityType": "columns",
+      "table": "session_input"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "session_id",
+      "entityType": "columns",
+      "table": "session_input"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "prompt",
+      "entityType": "columns",
+      "table": "session_input"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "delivery",
+      "entityType": "columns",
+      "table": "session_input"
+    },
+    {
+      "type": "integer",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "promoted_seq",
+      "entityType": "columns",
+      "table": "session_input"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_created",
+      "entityType": "columns",
+      "table": "session_input"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "id",
+      "entityType": "columns",
+      "table": "session_message"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "session_id",
+      "entityType": "columns",
+      "table": "session_message"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "type",
+      "entityType": "columns",
+      "table": "session_message"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "seq",
+      "entityType": "columns",
+      "table": "session_message"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_created",
+      "entityType": "columns",
+      "table": "session_message"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_updated",
+      "entityType": "columns",
+      "table": "session_message"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "data",
+      "entityType": "columns",
+      "table": "session_message"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "id",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "project_id",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "workspace_id",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "parent_id",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "slug",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "directory",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "path",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "title",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "version",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "share_url",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "integer",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "summary_additions",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "integer",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "summary_deletions",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "integer",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "summary_files",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "summary_diffs",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "metadata",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "real",
+      "notNull": true,
+      "autoincrement": false,
+      "default": "0",
+      "generated": null,
+      "name": "cost",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": "0",
+      "generated": null,
+      "name": "tokens_input",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": "0",
+      "generated": null,
+      "name": "tokens_output",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": "0",
+      "generated": null,
+      "name": "tokens_reasoning",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": "0",
+      "generated": null,
+      "name": "tokens_cache_read",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": "0",
+      "generated": null,
+      "name": "tokens_cache_write",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "revert",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "permission",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "agent",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "model",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_created",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_updated",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "integer",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_compacting",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "integer",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_archived",
+      "entityType": "columns",
+      "table": "session"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "session_id",
+      "entityType": "columns",
+      "table": "todo"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "content",
+      "entityType": "columns",
+      "table": "todo"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "status",
+      "entityType": "columns",
+      "table": "todo"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "priority",
+      "entityType": "columns",
+      "table": "todo"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "position",
+      "entityType": "columns",
+      "table": "todo"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_created",
+      "entityType": "columns",
+      "table": "todo"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_updated",
+      "entityType": "columns",
+      "table": "todo"
+    },
+    {
+      "type": "text",
+      "notNull": false,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "session_id",
+      "entityType": "columns",
+      "table": "session_share"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "id",
+      "entityType": "columns",
+      "table": "session_share"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "secret",
+      "entityType": "columns",
+      "table": "session_share"
+    },
+    {
+      "type": "text",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "url",
+      "entityType": "columns",
+      "table": "session_share"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_created",
+      "entityType": "columns",
+      "table": "session_share"
+    },
+    {
+      "type": "integer",
+      "notNull": true,
+      "autoincrement": false,
+      "default": null,
+      "generated": null,
+      "name": "time_updated",
+      "entityType": "columns",
+      "table": "session_share"
+    },
+    {
+      "columns": [
+        "project_id"
+      ],
+      "tableTo": "project",
+      "columnsTo": [
+        "id"
+      ],
+      "onUpdate": "NO ACTION",
+      "onDelete": "CASCADE",
+      "nameExplicit": false,
+      "name": "fk_workspace_project_id_project_id_fk",
+      "entityType": "fks",
+      "table": "workspace"
+    },
+    {
+      "columns": [
+        "active_account_id"
+      ],
+      "tableTo": "account",
+      "columnsTo": [
+        "id"
+      ],
+      "onUpdate": "NO ACTION",
+      "onDelete": "SET NULL",
+      "nameExplicit": false,
+      "name": "fk_account_state_active_account_id_account_id_fk",
+      "entityType": "fks",
+      "table": "account_state"
+    },
+    {
+      "columns": [
+        "aggregate_id"
+      ],
+      "tableTo": "event_sequence",
+      "columnsTo": [
+        "aggregate_id"
+      ],
+      "onUpdate": "NO ACTION",
+      "onDelete": "CASCADE",
+      "nameExplicit": false,
+      "name": "fk_event_aggregate_id_event_sequence_aggregate_id_fk",
+      "entityType": "fks",
+      "table": "event"
+    },
+    {
+      "columns": [
+        "project_id"
+      ],
+      "tableTo": "project",
+      "columnsTo": [
+        "id"
+      ],
+      "onUpdate": "NO ACTION",
+      "onDelete": "CASCADE",
+      "nameExplicit": false,
+      "name": "fk_permission_project_id_project_id_fk",
+      "entityType": "fks",
+      "table": "permission"
+    },
+    {
+      "columns": [
+        "project_id"
+      ],
+      "tableTo": "project",
+      "columnsTo": [
+        "id"
+      ],
+      "onUpdate": "NO ACTION",
+      "onDelete": "CASCADE",
+      "nameExplicit": false,
+      "name": "fk_project_directory_project_id_project_id_fk",
+      "entityType": "fks",
+      "table": "project_directory"
+    },
+    {
+      "columns": [
+        "session_id"
+      ],
+      "tableTo": "session",
+      "columnsTo": [
+        "id"
+      ],
+      "onUpdate": "NO ACTION",
+      "onDelete": "CASCADE",
+      "nameExplicit": false,
+      "name": "fk_message_session_id_session_id_fk",
+      "entityType": "fks",
+      "table": "message"
+    },
+    {
+      "columns": [
+        "message_id"
+      ],
+      "tableTo": "message",
+      "columnsTo": [
+        "id"
+      ],
+      "onUpdate": "NO ACTION",
+      "onDelete": "CASCADE",
+      "nameExplicit": false,
+      "name": "fk_part_message_id_message_id_fk",
+      "entityType": "fks",
+      "table": "part"
+    },
+    {
+      "columns": [
+        "session_id"
+      ],
+      "tableTo": "session",
+      "columnsTo": [
+        "id"
+      ],
+      "onUpdate": "NO ACTION",
+      "onDelete": "CASCADE",
+      "nameExplicit": false,
+      "name": "fk_session_input_session_id_session_id_fk",
+      "entityType": "fks",
+      "table": "session_input"
+    },
+    {
+      "columns": [
+        "session_id"
+      ],
+      "tableTo": "session",
+      "columnsTo": [
+        "id"
+      ],
+      "onUpdate": "NO ACTION",
+      "onDelete": "CASCADE",
+      "nameExplicit": false,
+      "name": "fk_session_message_session_id_session_id_fk",
+      "entityType": "fks",
+      "table": "session_message"
+    },
+    {
+      "columns": [
+        "project_id"
+      ],
+      "tableTo": "project",
+      "columnsTo": [
+        "id"
+      ],
+      "onUpdate": "NO ACTION",
+      "onDelete": "CASCADE",
+      "nameExplicit": false,
+      "name": "fk_session_project_id_project_id_fk",
+      "entityType": "fks",
+      "table": "session"
+    },
+    {
+      "columns": [
+        "session_id"
+      ],
+      "tableTo": "session",
+      "columnsTo": [
+        "id"
+      ],
+      "onUpdate": "NO ACTION",
+      "onDelete": "CASCADE",
+      "nameExplicit": false,
+      "name": "fk_todo_session_id_session_id_fk",
+      "entityType": "fks",
+      "table": "todo"
+    },
+    {
+      "columns": [
+        "session_id"
+      ],
+      "tableTo": "session",
+      "columnsTo": [
+        "id"
+      ],
+      "onUpdate": "NO ACTION",
+      "onDelete": "CASCADE",
+      "nameExplicit": false,
+      "name": "fk_session_share_session_id_session_id_fk",
+      "entityType": "fks",
+      "table": "session_share"
+    },
+    {
+      "columns": [
+        "email",
+        "url"
+      ],
+      "nameExplicit": false,
+      "name": "control_account_pk",
+      "entityType": "pks",
+      "table": "control_account"
+    },
+    {
+      "columns": [
+        "project_id",
+        "directory"
+      ],
+      "nameExplicit": false,
+      "name": "project_directory_pk",
+      "entityType": "pks",
+      "table": "project_directory"
+    },
+    {
+      "columns": [
+        "session_id",
+        "position"
+      ],
+      "nameExplicit": false,
+      "name": "todo_pk",
+      "entityType": "pks",
+      "table": "todo"
+    },
+    {
+      "columns": [
+        "id"
+      ],
+      "nameExplicit": false,
+      "name": "workspace_pk",
+      "table": "workspace",
+      "entityType": "pks"
+    },
+    {
+      "columns": [
+        "name"
+      ],
+      "nameExplicit": false,
+      "name": "data_migration_pk",
+      "table": "data_migration",
+      "entityType": "pks"
+    },
+    {
+      "columns": [
+        "id"
+      ],
+      "nameExplicit": false,
+      "name": "account_state_pk",
+      "table": "account_state",
+      "entityType": "pks"
+    },
+    {
+      "columns": [
+        "id"
+      ],
+      "nameExplicit": false,
+      "name": "account_pk",
+      "table": "account",
+      "entityType": "pks"
+    },
+    {
+      "columns": [
+        "aggregate_id"
+      ],
+      "nameExplicit": false,
+      "name": "event_sequence_pk",
+      "table": "event_sequence",
+      "entityType": "pks"
+    },
+    {
+      "columns": [
+        "id"
+      ],
+      "nameExplicit": false,
+      "name": "event_pk",
+      "table": "event",
+      "entityType": "pks"
+    },
+    {
+      "columns": [
+        "id"
+      ],
+      "nameExplicit": false,
+      "name": "permission_pk",
+      "table": "permission",
+      "entityType": "pks"
+    },
+    {
+      "columns": [
+        "id"
+      ],
+      "nameExplicit": false,
+      "name": "project_pk",
+      "table": "project",
+      "entityType": "pks"
+    },
+    {
+      "columns": [
+        "id"
+      ],
+      "nameExplicit": false,
+      "name": "message_pk",
+      "table": "message",
+      "entityType": "pks"
+    },
+    {
+      "columns": [
+        "id"
+      ],
+      "nameExplicit": false,
+      "name": "part_pk",
+      "table": "part",
+      "entityType": "pks"
+    },
+    {
+      "columns": [
+        "seq"
+      ],
+      "nameExplicit": false,
+      "name": "session_input_pk",
+      "table": "session_input",
+      "entityType": "pks"
+    },
+    {
+      "columns": [
+        "id"
+      ],
+      "nameExplicit": false,
+      "name": "session_message_pk",
+      "table": "session_message",
+      "entityType": "pks"
+    },
+    {
+      "columns": [
+        "id"
+      ],
+      "nameExplicit": false,
+      "name": "session_pk",
+      "table": "session",
+      "entityType": "pks"
+    },
+    {
+      "columns": [
+        "session_id"
+      ],
+      "nameExplicit": false,
+      "name": "session_share_pk",
+      "table": "session_share",
+      "entityType": "pks"
+    },
+    {
+      "columns": [
+        {
+          "value": "aggregate_id",
+          "isExpression": false
+        },
+        {
+          "value": "seq",
+          "isExpression": false
+        }
+      ],
+      "isUnique": true,
+      "where": null,
+      "origin": "manual",
+      "name": "event_aggregate_seq_idx",
+      "entityType": "indexes",
+      "table": "event"
+    },
+    {
+      "columns": [
+        {
+          "value": "project_id",
+          "isExpression": false
+        },
+        {
+          "value": "action",
+          "isExpression": false
+        },
+        {
+          "value": "resource",
+          "isExpression": false
+        }
+      ],
+      "isUnique": true,
+      "where": null,
+      "origin": "manual",
+      "name": "permission_project_action_resource_idx",
+      "entityType": "indexes",
+      "table": "permission"
+    },
+    {
+      "columns": [
+        {
+          "value": "session_id",
+          "isExpression": false
+        },
+        {
+          "value": "time_created",
+          "isExpression": false
+        },
+        {
+          "value": "id",
+          "isExpression": false
+        }
+      ],
+      "isUnique": false,
+      "where": null,
+      "origin": "manual",
+      "name": "message_session_time_created_id_idx",
+      "entityType": "indexes",
+      "table": "message"
+    },
+    {
+      "columns": [
+        {
+          "value": "message_id",
+          "isExpression": false
+        },
+        {
+          "value": "id",
+          "isExpression": false
+        }
+      ],
+      "isUnique": false,
+      "where": null,
+      "origin": "manual",
+      "name": "part_message_id_id_idx",
+      "entityType": "indexes",
+      "table": "part"
+    },
+    {
+      "columns": [
+        {
+          "value": "session_id",
+          "isExpression": false
+        }
+      ],
+      "isUnique": false,
+      "where": null,
+      "origin": "manual",
+      "name": "part_session_idx",
+      "entityType": "indexes",
+      "table": "part"
+    },
+    {
+      "columns": [
+        {
+          "value": "session_id",
+          "isExpression": false
+        },
+        {
+          "value": "promoted_seq",
+          "isExpression": false
+        },
+        {
+          "value": "delivery",
+          "isExpression": false
+        },
+        {
+          "value": "seq",
+          "isExpression": false
+        }
+      ],
+      "isUnique": false,
+      "where": null,
+      "origin": "manual",
+      "name": "session_input_session_pending_delivery_seq_idx",
+      "entityType": "indexes",
+      "table": "session_input"
+    },
+    {
+      "columns": [
+        {
+          "value": "session_id",
+          "isExpression": false
+        },
+        {
+          "value": "seq",
+          "isExpression": false
+        }
+      ],
+      "isUnique": true,
+      "where": null,
+      "origin": "manual",
+      "name": "session_message_session_seq_idx",
+      "entityType": "indexes",
+      "table": "session_message"
+    },
+    {
+      "columns": [
+        {
+          "value": "session_id",
+          "isExpression": false
+        },
+        {
+          "value": "type",
+          "isExpression": false
+        },
+        {
+          "value": "seq",
+          "isExpression": false
+        }
+      ],
+      "isUnique": false,
+      "where": null,
+      "origin": "manual",
+      "name": "session_message_session_type_seq_idx",
+      "entityType": "indexes",
+      "table": "session_message"
+    },
+    {
+      "columns": [
+        {
+          "value": "project_id",
+          "isExpression": false
+        }
+      ],
+      "isUnique": false,
+      "where": null,
+      "origin": "manual",
+      "name": "session_project_idx",
+      "entityType": "indexes",
+      "table": "session"
+    },
+    {
+      "columns": [
+        {
+          "value": "workspace_id",
+          "isExpression": false
+        }
+      ],
+      "isUnique": false,
+      "where": null,
+      "origin": "manual",
+      "name": "session_workspace_idx",
+      "entityType": "indexes",
+      "table": "session"
+    },
+    {
+      "columns": [
+        {
+          "value": "parent_id",
+          "isExpression": false
+        }
+      ],
+      "isUnique": false,
+      "where": null,
+      "origin": "manual",
+      "name": "session_parent_idx",
+      "entityType": "indexes",
+      "table": "session"
+    },
+    {
+      "columns": [
+        {
+          "value": "session_id",
+          "isExpression": false
+        }
+      ],
+      "isUnique": false,
+      "where": null,
+      "origin": "manual",
+      "name": "todo_session_idx",
+      "entityType": "indexes",
+      "table": "todo"
+    },
+    {
+      "columns": [
+        "id"
+      ],
+      "nameExplicit": false,
+      "name": "session_input_id_unique",
+      "entityType": "uniques",
+      "table": "session_input"
+    }
+  ],
+  "renames": []
+}
\ No newline at end of file
diff --git a/packages/core/src/database/migration.gen.ts b/packages/core/src/database/migration.gen.ts
index 9f2ba82eb3..ce115e8a4c 100644
--- a/packages/core/src/database/migration.gen.ts
+++ b/packages/core/src/database/migration.gen.ts
@@ -31,5 +31,6 @@ export const migrations = (
     import("./migration/20260603040000_session_message_projection_order"),
     import("./migration/20260603141458_session_input_inbox"),
     import("./migration/20260603160727_jittery_ezekiel_stane"),
+    import("./migration/20260604150931_harden_v2_sequence_indexes"),
   ])
 ).map((module) => module.default) satisfies DatabaseMigration.Migration[]
diff --git a/packages/core/src/database/migration/20260604150931_harden_v2_sequence_indexes.ts b/packages/core/src/database/migration/20260604150931_harden_v2_sequence_indexes.ts
new file mode 100644
index 0000000000..f6f7b83178
--- /dev/null
+++ b/packages/core/src/database/migration/20260604150931_harden_v2_sequence_indexes.ts
@@ -0,0 +1,19 @@
+import { Effect } from "effect"
+import type { DatabaseMigration } from "../migration"
+
+export default {
+  id: "20260604150931_harden_v2_sequence_indexes",
+  up(tx) {
+    return Effect.gen(function* () {
+      yield* tx.run(`DROP INDEX IF EXISTS \`event_aggregate_seq_idx\`;`)
+      yield* tx.run(`DROP INDEX IF EXISTS \`event_aggregate_type_seq_idx\`;`)
+      yield* tx.run(`DROP INDEX IF EXISTS \`session_message_session_seq_idx\`;`)
+      yield* tx.run(`DROP INDEX IF EXISTS \`session_message_session_time_created_id_idx\`;`)
+      yield* tx.run(`DROP INDEX IF EXISTS \`session_message_time_created_idx\`;`)
+      yield* tx.run(`CREATE UNIQUE INDEX \`event_aggregate_seq_idx\` ON \`event\` (\`aggregate_id\`,\`seq\`);`)
+      yield* tx.run(
+        `CREATE UNIQUE INDEX \`session_message_session_seq_idx\` ON \`session_message\` (\`session_id\`,\`seq\`);`,
+      )
+    })
+  },
+} satisfies DatabaseMigration.Migration
diff --git a/packages/core/src/event/sql.ts b/packages/core/src/event/sql.ts
index 74f0ab4834..ef95e0b794 100644
--- a/packages/core/src/event/sql.ts
+++ b/packages/core/src/event/sql.ts
@@ -1,4 +1,4 @@
-import { sqliteTable, text, integer, index } from "drizzle-orm/sqlite-core"
+import { sqliteTable, text, integer, uniqueIndex } from "drizzle-orm/sqlite-core"
 import type { EventV2 } from "../event"
 
 export const EventSequenceTable = sqliteTable("event_sequence", {
@@ -18,8 +18,5 @@ export const EventTable = sqliteTable(
     type: text().notNull(),
     data: text({ mode: "json" }).$type<Record<string, unknown>>().notNull(),
   },
-  (table) => [
-    index("event_aggregate_seq_idx").on(table.aggregate_id, table.seq),
-    index("event_aggregate_type_seq_idx").on(table.aggregate_id, table.type, table.seq),
-  ],
+  (table) => [uniqueIndex("event_aggregate_seq_idx").on(table.aggregate_id, table.seq)],
 )
diff --git a/packages/core/src/session/sql.ts b/packages/core/src/session/sql.ts
index 8ecbbea240..c0865c637f 100644
--- a/packages/core/src/session/sql.ts
+++ b/packages/core/src/session/sql.ts
@@ -1,4 +1,4 @@
-import { sqliteTable, text, integer, index, primaryKey, real } from "drizzle-orm/sqlite-core"
+import { sqliteTable, text, integer, index, primaryKey, real, uniqueIndex } from "drizzle-orm/sqlite-core"
 import * as DatabasePath from "../database/path"
 import { ProjectTable } from "../project/sql"
 import type { SessionMessage } from "./message"
@@ -122,15 +122,14 @@ export const SessionMessageTable = sqliteTable(
       .notNull()
       .references(() => SessionTable.id, { onDelete: "cascade" }),
     type: text().$type<SessionMessage.Type>().notNull(),
+    /** Immutable sequence of the durable event that first projected this timeline row. */
     seq: integer().notNull(),
     ...Timestamps,
     data: text({ mode: "json" }).notNull().$type<SessionMessageData>(),
   },
   (table) => [
-    index("session_message_session_seq_idx").on(table.session_id, table.seq),
+    uniqueIndex("session_message_session_seq_idx").on(table.session_id, table.seq),
     index("session_message_session_type_seq_idx").on(table.session_id, table.type, table.seq),
-    index("session_message_session_time_created_id_idx").on(table.session_id, table.time_created, table.id),
-    index("session_message_time_created_idx").on(table.time_created),
   ],
 )
 
diff --git a/packages/core/test/database-migration.test.ts b/packages/core/test/database-migration.test.ts
index 4c0ccb9832..0e96f5c1b4 100644
--- a/packages/core/test/database-migration.test.ts
+++ b/packages/core/test/database-migration.test.ts
@@ -10,6 +10,7 @@ import { DatabaseMigration } from "@opencode-ai/core/database/migration"
 import sessionUsageMigration from "@opencode-ai/core/database/migration/20260510033149_session_usage"
 import normalizeStoragePathsMigration from "@opencode-ai/core/database/migration/20260601010001_normalize_storage_paths"
 import sessionMessageProjectionOrderMigration from "@opencode-ai/core/database/migration/20260603040000_session_message_projection_order"
+import hardenV2SequenceIndexesMigration from "@opencode-ai/core/database/migration/20260604150931_harden_v2_sequence_indexes"
 import { ProjectV2 } from "@opencode-ai/core/project"
 import { ProjectTable } from "@opencode-ai/core/project/sql"
 import { AbsolutePath } from "@opencode-ai/core/schema"
@@ -62,23 +63,115 @@ describe("DatabaseMigration", () => {
         expect(
           yield* db.get(sql`SELECT name FROM sqlite_master WHERE type = 'table' AND name = 'session_input'`),
         ).toEqual({ name: "session_input" })
-        expect(yield* db.get(sql`SELECT count(*) as count FROM migration`)).toEqual({ count: 29 })
+        expect(yield* db.get(sql`SELECT count(*) as count FROM migration`)).toEqual({ count: 30 })
         expect(
           yield* db.all(
-            sql`SELECT name FROM sqlite_master WHERE type = 'index' AND name IN ('event_aggregate_seq_idx', 'event_aggregate_type_seq_idx', 'session_input_session_pending_seq_idx', 'session_input_session_pending_delivery_seq_idx', 'session_message_session_idx', 'session_message_session_type_idx', 'session_message_session_seq_idx', 'session_message_session_type_seq_idx', 'session_message_session_time_created_id_idx') ORDER BY name`,
+            sql`SELECT name FROM sqlite_master WHERE type = 'index' AND name IN ('event_aggregate_seq_idx', 'event_aggregate_type_seq_idx', 'session_input_session_pending_seq_idx', 'session_input_session_pending_delivery_seq_idx', 'session_message_session_idx', 'session_message_session_type_idx', 'session_message_session_seq_idx', 'session_message_session_type_seq_idx', 'session_message_session_time_created_id_idx', 'session_message_time_created_idx') ORDER BY name`,
           ),
         ).toEqual([
           { name: "event_aggregate_seq_idx" },
-          { name: "event_aggregate_type_seq_idx" },
           { name: "session_input_session_pending_delivery_seq_idx" },
           { name: "session_message_session_seq_idx" },
-          { name: "session_message_session_time_created_id_idx" },
           { name: "session_message_session_type_seq_idx" },
         ])
       }),
     )
   })
 
+  test("enforces unique durable and timeline sequence positions", async () => {
+    await run(
+      Effect.gen(function* () {
+        const db = yield* makeDb
+        yield* db.run(
+          sql`CREATE TABLE event (id text PRIMARY KEY, aggregate_id text NOT NULL, seq integer NOT NULL, type text NOT NULL)`,
+        )
+        yield* db.run(sql`CREATE INDEX event_aggregate_seq_idx ON event (aggregate_id, seq)`)
+        yield* db.run(sql`CREATE INDEX event_aggregate_type_seq_idx ON event (aggregate_id, type, seq)`)
+        yield* db.run(
+          sql`CREATE TABLE session_message (id text PRIMARY KEY, session_id text NOT NULL, seq integer NOT NULL)`,
+        )
+        yield* db.run(sql`CREATE INDEX session_message_session_seq_idx ON session_message (session_id, seq)`)
+
+        yield* DatabaseMigration.applyOnly(db, [hardenV2SequenceIndexesMigration])
+
+        yield* db.run(sql`INSERT INTO event (id, aggregate_id, seq, type) VALUES ('event_1', 'session_1', 1, 'one')`)
+        yield* db.run(sql`INSERT INTO session_message (id, session_id, seq) VALUES ('message_1', 'session_1', 1)`)
+        expect(() =>
+          Effect.runSync(
+            db.run(sql`INSERT INTO event (id, aggregate_id, seq, type) VALUES ('event_2', 'session_1', 1, 'two')`),
+          ),
+        ).toThrow()
+        expect(() =>
+          Effect.runSync(
+            db.run(sql`INSERT INTO session_message (id, session_id, seq) VALUES ('message_2', 'session_1', 1)`),
+          ),
+        ).toThrow()
+      }),
+    )
+  })
+
+  test.each(["event", "session_message"] as const)(
+    "rejects duplicate existing %s sequence positions without dropping old indexes",
+    async (duplicate) => {
+      await run(
+        Effect.gen(function* () {
+          const db = yield* makeDb
+          yield* db.run(
+            sql`CREATE TABLE event (id text PRIMARY KEY, aggregate_id text NOT NULL, seq integer NOT NULL, type text NOT NULL)`,
+          )
+          yield* db.run(sql`CREATE INDEX event_aggregate_seq_idx ON event (aggregate_id, seq)`)
+          yield* db.run(sql`CREATE INDEX event_aggregate_type_seq_idx ON event (aggregate_id, type, seq)`)
+          yield* db.run(
+            sql`CREATE TABLE session_message (id text PRIMARY KEY, session_id text NOT NULL, type text NOT NULL, seq integer NOT NULL, time_created integer NOT NULL)`,
+          )
+          yield* db.run(sql`CREATE INDEX session_message_session_seq_idx ON session_message (session_id, seq)`)
+          yield* db.run(
+            sql`CREATE INDEX session_message_session_type_seq_idx ON session_message (session_id, type, seq)`,
+          )
+          yield* db.run(
+            sql`CREATE INDEX session_message_session_time_created_id_idx ON session_message (session_id, time_created, id)`,
+          )
+          yield* db.run(sql`CREATE INDEX session_message_time_created_idx ON session_message (time_created)`)
+
+          yield* db.run(sql`INSERT INTO event (id, aggregate_id, seq, type) VALUES ('event_1', 'session_1', 1, 'one')`)
+          yield* db.run(
+            sql`INSERT INTO session_message (id, session_id, type, seq, time_created) VALUES ('message_1', 'session_1', 'user', 1, 1)`,
+          )
+          if (duplicate === "event") {
+            yield* db.run(
+              sql`INSERT INTO event (id, aggregate_id, seq, type) VALUES ('event_2', 'session_1', 1, 'two')`,
+            )
+          }
+          if (duplicate === "session_message") {
+            yield* db.run(
+              sql`INSERT INTO session_message (id, session_id, type, seq, time_created) VALUES ('message_2', 'session_1', 'assistant', 1, 2)`,
+            )
+          }
+
+          expect(
+            (yield* DatabaseMigration.applyOnly(db, [hardenV2SequenceIndexesMigration]).pipe(Effect.exit))._tag,
+          ).toBe("Failure")
+          expect(
+            yield* db.all(sql`
+              SELECT name, [unique] AS is_unique FROM pragma_index_list('event') WHERE origin = 'c'
+              UNION ALL
+              SELECT name, [unique] AS is_unique FROM pragma_index_list('session_message') WHERE origin = 'c'
+              ORDER BY name
+            `),
+          ).toEqual([
+            { name: "event_aggregate_seq_idx", is_unique: 0 },
+            { name: "event_aggregate_type_seq_idx", is_unique: 0 },
+            { name: "session_message_session_seq_idx", is_unique: 0 },
+            { name: "session_message_session_time_created_id_idx", is_unique: 0 },
+            { name: "session_message_session_type_seq_idx", is_unique: 0 },
+            { name: "session_message_time_created_idx", is_unique: 0 },
+          ])
+          expect(yield* db.all(sql`SELECT id FROM migration`)).toEqual([])
+        }),
+      )
+    },
+  )
+
   test("resets incompatible projected Session messages before adding sequence order", async () => {
     await run(
       Effect.gen(function* () {