refactor(session): scope pi sessions to agents instead of tasks

Sessions were keyed by (task, agent). Every task switch started a fresh
transcript — the agent lost everything it had learned on the previous
task. That breaks the product premise: a CEO should remember its past
decisions, an engineer should carry context between bugs.

Move pi's AgentMessage transcript to be agent-scoped. One session per
agent (per company). Tasks enter the ongoing conversation as user turns;
rotation/compaction boundaries follow the agent's long-running session.

Additive schema only — no row rewrites on the live production DB.

- Migration v34: `ALTER TABLE agents ADD COLUMN session_id TEXT` +
  `idx_agents_session_id`. `ensureOptionalColumns` mirror for fresh DBs.
- `AgentRecord.sessionId?: string | null` in the read model; included
  in every full-agent SELECT (entity-crud, snapshot, agents-hierarchy
  chain-of-command / direct-reports / heartbeat-eligible).
- `db.ensureAgentSession({ agentId, companyId, adapterType })` —
  idempotent: returns existing `agents.session_id` if set, else inserts
  a new `task_sessions` row with an empty `task_id` sentinel (agent-
  scoped, task-id is now metadata) and stores the id on the agent.
- `db.setAgentSessionId(agentId, sessionId)` — used by rotation.
- `db.updateTasksActiveSessionForAgent(agentId, sessionId)` — mirrors
  the agent's current session onto every task the agent owns, so
  existing per-task readers (`tasks.active_session_id`) still work.
- `turn-context.resolveSession`: pulls the agent's session via
  `ensureAgentSession` instead of `getActiveTaskSession(task.id)`,
  then points the current task at it so UI continues to resolve.
- `session-management-service.rotateSession`: new session carries
  `taskId:""`, then `setAgentSessionId` + `updateTasksActiveSessionForAgent`
  so every task the agent owns follows the rotation boundary.
- `session-entries.listActive`: `ORDER BY created_at, sequence` — the
  created_at timestamp is authoritative; sequence stays as same-ms
  tiebreaker. Forward-safety for future merge scenarios.

Existing agents' first post-upgrade run creates a fresh agent-scoped
session. Their pre-migration per-task transcripts remain in the DB as
historical records but are not loaded for new runs. This is a one-time
transcript reset, accepted over a risky lossy merge on the live DB.

Documented in a code comment on `ensureAgentSession`.

src/main/database/agents-hierarchy.ts

@@ -66,7 +66,7 @@ export function buildAgentHierarchyMethods(
                   model, capabilities, role_level as roleLevel, budget_monthly_usd as budgetMonthlyUsd,
                   spent_monthly_usd as spentMonthlyUsd, metadata_json as metadataJson,
                   heartbeat_enabled as heartbeatEnabled, heartbeat_interval_sec as heartbeatIntervalSec,
-                  last_heartbeat_at as lastHeartbeatAt, created_at as createdAt, updated_at as updatedAt,
+                  last_heartbeat_at as lastHeartbeatAt, session_id as sessionId, created_at as createdAt, updated_at as updatedAt,
                   0 as depth
            FROM agents WHERE id = ?
            UNION ALL
@@ -75,7 +75,7 @@ export function buildAgentHierarchyMethods(
                   a.model, a.capabilities, a.role_level, a.budget_monthly_usd,
                   a.spent_monthly_usd, a.metadata_json,
                   a.heartbeat_enabled, a.heartbeat_interval_sec,
-                  a.last_heartbeat_at, a.created_at, a.updated_at,
+                  a.last_heartbeat_at, a.session_id, a.created_at, a.updated_at,
                   c.depth + 1
            FROM agents a JOIN chain c ON a.id = c.reportsTo
            WHERE c.depth < 20
@@ -92,7 +92,7 @@ export function buildAgentHierarchyMethods(
 
     getDirectReports(agentId: string, companyId: string): AgentRecord[] {
       return readAll<AgentRecord>(
-        "select id, company_id as companyId, name, role, title, department, status, reports_to as reportsTo, connector_id as connectorId, workspace_id as workspaceId, model, capabilities, role_level as roleLevel, budget_monthly_usd as budgetMonthlyUsd, spent_monthly_usd as spentMonthlyUsd, metadata_json as metadataJson, heartbeat_enabled as heartbeatEnabled, heartbeat_interval_sec as heartbeatIntervalSec, last_heartbeat_at as lastHeartbeatAt, created_at as createdAt, updated_at as updatedAt from agents where company_id = ? and reports_to = ?",
+        "select id, company_id as companyId, name, role, title, department, status, reports_to as reportsTo, connector_id as connectorId, workspace_id as workspaceId, model, capabilities, role_level as roleLevel, budget_monthly_usd as budgetMonthlyUsd, spent_monthly_usd as spentMonthlyUsd, metadata_json as metadataJson, heartbeat_enabled as heartbeatEnabled, heartbeat_interval_sec as heartbeatIntervalSec, last_heartbeat_at as lastHeartbeatAt, session_id as sessionId, created_at as createdAt, updated_at as updatedAt from agents where company_id = ? and reports_to = ?",
         companyId,
         agentId,
       ).map((record) => ({
@@ -201,7 +201,7 @@ export function buildAgentHierarchyMethods(
 
     listHeartbeatEligibleAgents(companyId: string): AgentRecord[] {
       return readAll<AgentRecord>(
-        "select id, company_id as companyId, name, role, title, department, status, reports_to as reportsTo, connector_id as connectorId, workspace_id as workspaceId, model, capabilities, role_level as roleLevel, budget_monthly_usd as budgetMonthlyUsd, spent_monthly_usd as spentMonthlyUsd, metadata_json as metadataJson, heartbeat_enabled as heartbeatEnabled, heartbeat_interval_sec as heartbeatIntervalSec, last_heartbeat_at as lastHeartbeatAt, created_at as createdAt, updated_at as updatedAt from agents where company_id = ? and heartbeat_enabled = 1 and status not in ('terminated', 'paused', 'error', 'pending_approval')",
+        "select id, company_id as companyId, name, role, title, department, status, reports_to as reportsTo, connector_id as connectorId, workspace_id as workspaceId, model, capabilities, role_level as roleLevel, budget_monthly_usd as budgetMonthlyUsd, spent_monthly_usd as spentMonthlyUsd, metadata_json as metadataJson, heartbeat_enabled as heartbeatEnabled, heartbeat_interval_sec as heartbeatIntervalSec, last_heartbeat_at as lastHeartbeatAt, session_id as sessionId, created_at as createdAt, updated_at as updatedAt from agents where company_id = ? and heartbeat_enabled = 1 and status not in ('terminated', 'paused', 'error', 'pending_approval')",
         companyId,
       ).map((record) => ({
         ...record,

src/main/database/entity-crud.ts

@@ -64,7 +64,7 @@ export function buildEntityCrudMethods(
     getAgent(id: string): AgentRecord {
       const row = getDb()
         .prepare(
-          "select id, company_id as companyId, name, role, title, department, status, reports_to as reportsTo, connector_id as connectorId, workspace_id as workspaceId, model, capabilities, role_level as roleLevel, budget_monthly_usd as budgetMonthlyUsd, spent_monthly_usd as spentMonthlyUsd, metadata_json as metadataJson, heartbeat_enabled as heartbeatEnabled, heartbeat_interval_sec as heartbeatIntervalSec, last_heartbeat_at as lastHeartbeatAt, created_at as createdAt, updated_at as updatedAt from agents where id = ?",
+          "select id, company_id as companyId, name, role, title, department, status, reports_to as reportsTo, connector_id as connectorId, workspace_id as workspaceId, model, capabilities, role_level as roleLevel, budget_monthly_usd as budgetMonthlyUsd, spent_monthly_usd as spentMonthlyUsd, metadata_json as metadataJson, heartbeat_enabled as heartbeatEnabled, heartbeat_interval_sec as heartbeatIntervalSec, last_heartbeat_at as lastHeartbeatAt, session_id as sessionId, created_at as createdAt, updated_at as updatedAt from agents where id = ?",
         )
         .get(id) as AgentRecord | undefined;
       if (!row) throw new Error(`Agent not found: ${id}`);
@@ -75,7 +75,7 @@ export function buildEntityCrudMethods(
     findAgent(id: string): AgentRecord | null {
       const row = getDb()
         .prepare(
-          "select id, company_id as companyId, name, role, title, department, status, reports_to as reportsTo, connector_id as connectorId, workspace_id as workspaceId, model, capabilities, role_level as roleLevel, budget_monthly_usd as budgetMonthlyUsd, spent_monthly_usd as spentMonthlyUsd, metadata_json as metadataJson, heartbeat_enabled as heartbeatEnabled, heartbeat_interval_sec as heartbeatIntervalSec, last_heartbeat_at as lastHeartbeatAt, created_at as createdAt, updated_at as updatedAt from agents where id = ?",
+          "select id, company_id as companyId, name, role, title, department, status, reports_to as reportsTo, connector_id as connectorId, workspace_id as workspaceId, model, capabilities, role_level as roleLevel, budget_monthly_usd as budgetMonthlyUsd, spent_monthly_usd as spentMonthlyUsd, metadata_json as metadataJson, heartbeat_enabled as heartbeatEnabled, heartbeat_interval_sec as heartbeatIntervalSec, last_heartbeat_at as lastHeartbeatAt, session_id as sessionId, created_at as createdAt, updated_at as updatedAt from agents where id = ?",
         )
         .get(id) as AgentRecord | undefined;
       if (!row) return null;

src/main/database/schema.ts

@@ -30,6 +30,8 @@ export function ensureOptionalColumns(db: DatabaseSync) {
   addColumnIfMissing("agents", "heartbeat_enabled", "alter table agents add column heartbeat_enabled integer not null default 0");
   addColumnIfMissing("agents", "heartbeat_interval_sec", "alter table agents add column heartbeat_interval_sec integer not null default 120");
   addColumnIfMissing("agents", "last_heartbeat_at", "alter table agents add column last_heartbeat_at text");
+  addColumnIfMissing("agents", "session_id", "alter table agents add column session_id text");
+  db.exec("create index if not exists idx_agents_session_id on agents(session_id)");
   addColumnIfMissing("companies", "auto_approve_hires", "alter table companies add column auto_approve_hires integer not null default 0");
   addColumnIfMissing("companies", "review_deliverables", "alter table companies add column review_deliverables integer not null default 0");
   addColumnIfMissing("companies", "execution_mode", "alter table companies add column execution_mode text not null default 'ai_ceo'");
@@ -501,6 +503,16 @@ export function runMigrations(
             );
             CREATE INDEX IF NOT EXISTS idx_credentials_status ON credentials(status)`,
     },
+    {
+      // Per-agent session scope. Agents carry a single active session across
+      // tasks — switching tasks becomes a "now work on X" user turn on the
+      // agent's ongoing transcript. Additive-only: existing task_sessions
+      // rows remain as historical records; new runs use the agent-scoped
+      // session created lazily on first post-upgrade run.
+      version: 34, name: "add_agents_session_id",
+      sql: `ALTER TABLE agents ADD COLUMN session_id TEXT;
+            CREATE INDEX IF NOT EXISTS idx_agents_session_id ON agents(session_id)`,
+    },
   ];
 
   for (const migration of migrations) {

src/main/database/session-entries.ts

@@ -82,7 +82,7 @@ export function buildSessionEntryMethods(
       is_superseded: number;
       created_at: string;
     }>(
-      "select id, task_session_id, sequence, kind, role, payload_json, is_superseded, created_at from session_entries where task_session_id = ? and is_superseded = 0 order by sequence asc",
+      "select id, task_session_id, sequence, kind, role, payload_json, is_superseded, created_at from session_entries where task_session_id = ? and is_superseded = 0 order by created_at asc, sequence asc",
       taskSessionId,
     );
     return rows.map((row) => ({

src/main/database/snapshot.ts

@@ -63,7 +63,7 @@ export function buildSnapshotMethods(
         ...companyArgs,
       ).map((record) => ({ ...record, isPrimary: toBoolean(record.isPrimary) })) as WorkspaceRecord[],
       agents: readAll<SqliteRow>(
-        `select id, company_id as companyId, name, role, title, department, status, reports_to as reportsTo, connector_id as connectorId, workspace_id as workspaceId, model, capabilities, role_level as roleLevel, budget_monthly_usd as budgetMonthlyUsd, spent_monthly_usd as spentMonthlyUsd, metadata_json as metadataJson, heartbeat_enabled as heartbeatEnabled, heartbeat_interval_sec as heartbeatIntervalSec, last_heartbeat_at as lastHeartbeatAt, created_at as createdAt, updated_at as updatedAt from agents${companyWhere} order by created_at asc`,
+        `select id, company_id as companyId, name, role, title, department, status, reports_to as reportsTo, connector_id as connectorId, workspace_id as workspaceId, model, capabilities, role_level as roleLevel, budget_monthly_usd as budgetMonthlyUsd, spent_monthly_usd as spentMonthlyUsd, metadata_json as metadataJson, heartbeat_enabled as heartbeatEnabled, heartbeat_interval_sec as heartbeatIntervalSec, last_heartbeat_at as lastHeartbeatAt, session_id as sessionId, created_at as createdAt, updated_at as updatedAt from agents${companyWhere} order by created_at asc`,
         ...companyArgs,
       ).map((record: SqliteRow) => ({ ...record, heartbeatEnabled: toBoolean(record.heartbeatEnabled) })) as AgentRecord[],
       goals: readAll<GoalRecord>(

src/main/database/tasks-crud.ts

@@ -440,6 +440,71 @@ export function buildTaskCrudMethods(
         .run(ts, reason, handoffMarkdown, ts, sessionId);
     },
 
+    /**
+     * Returns the agent's active session id, creating one lazily on first
+     * call. Session is scoped to the agent (not to any particular task);
+     * switching tasks emits a user turn on the ongoing transcript rather
+     * than spawning a new session.
+     *
+     * Existing agents with pre-migration per-task sessions start fresh
+     * after this upgrade: their first run creates a new agent-scoped
+     * session. The old task_sessions + session_entries rows remain in the
+     * DB as historical records but are not loaded for new runs. This is a
+     * one-time transcript reset, accepted over a risky merge on a live
+     * production DB.
+     */
+    ensureAgentSession(input: {
+      agentId: string;
+      companyId: string;
+      adapterType: string;
+    }): string {
+      const agentRow = getDb()
+        .prepare("SELECT session_id FROM agents WHERE id = ?")
+        .get(input.agentId) as { session_id: string | null } | undefined;
+      if (agentRow?.session_id) return agentRow.session_id;
+
+      const sessionId = randomUUID();
+      const ts = nowIso();
+      transaction(() => {
+        // task_id is left as empty string — the session is agent-scoped;
+        // the column persists for backwards-compatible schema but no
+        // longer keys the session to a particular task.
+        getDb()
+          .prepare(
+            `INSERT INTO task_sessions (id, company_id, task_id, agent_id, adapter_type,
+              session_params_json, session_display_id, run_count, total_input_tokens,
+              total_output_tokens, created_at, updated_at)
+             VALUES (?, ?, '', ?, ?, NULL, NULL, 0, 0, 0, ?, ?)`,
+          )
+          .run(sessionId, input.companyId, input.agentId, input.adapterType, ts, ts);
+        getDb()
+          .prepare("UPDATE agents SET session_id = ?, updated_at = ? WHERE id = ?")
+          .run(sessionId, ts, input.agentId);
+      });
+      return sessionId;
+    },
+
+    setAgentSessionId(agentId: string, sessionId: string): void {
+      const ts = nowIso();
+      getDb()
+        .prepare("UPDATE agents SET session_id = ?, updated_at = ? WHERE id = ?")
+        .run(sessionId, ts, agentId);
+    },
+
+    /**
+     * Point every task currently assigned to an agent at the agent's new
+     * active session. Called after session rotation so UI paths reading
+     * per-task active_session_id still see the agent's current session.
+     */
+    updateTasksActiveSessionForAgent(agentId: string, sessionId: string): void {
+      const ts = nowIso();
+      getDb()
+        .prepare(
+          "UPDATE tasks SET active_session_id = ?, updated_at = ? WHERE assignee_agent_id = ?",
+        )
+        .run(sessionId, ts, agentId);
+    },
+
     createNewSession(input: {
       taskId: string;
       companyId: string;