Add agent task sessions table, session types, and programmatic DB backup

Add agent_task_sessions table for per-task session state keyed by
(agent, adapter, taskKey). Add AgentTaskSession type, resetAgentSessionSchema
validator, and sessionDisplayId/sessionParamsJson to AgentRuntimeState.

Rework migration hash-resolution fallback ordering to prefer hash-based
matching over timestamp-based journal matching. Move backup-db.sh logic
into packages/db/src/backup.ts for programmatic use and simplify the shell
script to call the TypeScript implementation.

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

packages/db/src/schema/agent_task_sessions.ts

@@ -0,0 +1,39 @@
+import { pgTable, uuid, text, timestamp, jsonb, index, uniqueIndex } from "drizzle-orm/pg-core";
+import { companies } from "./companies.js";
+import { agents } from "./agents.js";
+import { heartbeatRuns } from "./heartbeat_runs.js";
+
+export const agentTaskSessions = pgTable(
+  "agent_task_sessions",
+  {
+    id: uuid("id").primaryKey().defaultRandom(),
+    companyId: uuid("company_id").notNull().references(() => companies.id),
+    agentId: uuid("agent_id").notNull().references(() => agents.id),
+    adapterType: text("adapter_type").notNull(),
+    taskKey: text("task_key").notNull(),
+    sessionParamsJson: jsonb("session_params_json").$type<Record<string, unknown>>(),
+    sessionDisplayId: text("session_display_id"),
+    lastRunId: uuid("last_run_id").references(() => heartbeatRuns.id),
+    lastError: text("last_error"),
+    createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),
+    updatedAt: timestamp("updated_at", { withTimezone: true }).notNull().defaultNow(),
+  },
+  (table) => ({
+    companyAgentTaskUniqueIdx: uniqueIndex("agent_task_sessions_company_agent_adapter_task_uniq").on(
+      table.companyId,
+      table.agentId,
+      table.adapterType,
+      table.taskKey,
+    ),
+    companyAgentUpdatedIdx: index("agent_task_sessions_company_agent_updated_idx").on(
+      table.companyId,
+      table.agentId,
+      table.updatedAt,
+    ),
+    companyTaskUpdatedIdx: index("agent_task_sessions_company_task_updated_idx").on(
+      table.companyId,
+      table.taskKey,
+      table.updatedAt,
+    ),
+  }),
+);

packages/db/src/schema/index.ts

@@ -3,6 +3,7 @@ export { agents } from "./agents.js";
 export { agentConfigRevisions } from "./agent_config_revisions.js";
 export { agentApiKeys } from "./agent_api_keys.js";
 export { agentRuntimeState } from "./agent_runtime_state.js";
+export { agentTaskSessions } from "./agent_task_sessions.js";
 export { agentWakeupRequests } from "./agent_wakeup_requests.js";
 export { projects } from "./projects.js";
 export { goals } from "./goals.js";