feat(store): persist subagent tasks to PostgreSQL (#600)

- Migration 000034: subagent_tasks table with tenant scope, JSONB
  metadata + GIN index, partial index for archival candidates
- SubagentTaskStore interface with Create/Get/UpdateStatus/List/Archive
- PG implementation with parameterized queries and tenant isolation
- SQLite schema v3→4 migration + no-op stub for Lite edition
- Wire into store.Stores and factories

internal/store/sqlitestore/factory.go

@@ -50,7 +50,8 @@ func NewSQLiteStores(cfg store.StoreConfig) (*store.Stores, error) {
 		Activity:         NewSQLiteActivityStore(db),
 		APIKeys:          NewSQLiteAPIKeyStore(db),
 		ConfigPermissions: NewSQLiteConfigPermissionStore(db),
-		Memory: NewSQLiteMemoryStore(db),
+		Memory:         NewSQLiteMemoryStore(db),
+		SubagentTasks:  NewSQLiteSubagentTaskStore(),
 		// Phase 2 Batch B+C stores (nil = gracefully skipped by gateway):
 		// AgentLinks, KnowledgeGraph, SecureCLI
 	}, nil

internal/store/sqlitestore/schema.go

@@ -14,7 +14,7 @@ var schemaSQL string
 
 // SchemaVersion is the current SQLite schema version.
 // Bump this when adding new migration steps below.
-const SchemaVersion = 3
+const SchemaVersion = 4
 
 // migrations maps version → SQL to apply when upgrading FROM that version.
 // schema.sql always represents the LATEST full schema (for fresh DBs).
@@ -42,6 +42,36 @@ UPDATE cron_jobs SET
   deliver_to = COALESCE(json_extract(payload, '$.to'), ''),
   wake_heartbeat = COALESCE(json_extract(payload, '$.wake_heartbeat'), 0)
 WHERE payload IS NOT NULL;`,
+	// Version 3 → 4: add subagent_tasks table for subagent lifecycle persistence.
+	3: `CREATE TABLE IF NOT EXISTS subagent_tasks (
+    id                TEXT PRIMARY KEY,
+    tenant_id         TEXT NOT NULL REFERENCES tenants(id) ON DELETE CASCADE,
+    parent_agent_key  VARCHAR(255) NOT NULL,
+    session_key       VARCHAR(500),
+    subject           VARCHAR(255) NOT NULL,
+    description       TEXT NOT NULL,
+    status            VARCHAR(20) NOT NULL DEFAULT 'running',
+    result            TEXT,
+    depth             INTEGER NOT NULL DEFAULT 1,
+    model             VARCHAR(255),
+    provider          VARCHAR(255),
+    iterations        INTEGER NOT NULL DEFAULT 0,
+    input_tokens      INTEGER NOT NULL DEFAULT 0,
+    output_tokens     INTEGER NOT NULL DEFAULT 0,
+    origin_channel    VARCHAR(50),
+    origin_chat_id    VARCHAR(255),
+    origin_peer_kind  VARCHAR(20),
+    origin_user_id    VARCHAR(255),
+    spawned_by        TEXT,
+    completed_at      TEXT,
+    archived_at       TEXT,
+    metadata          TEXT NOT NULL DEFAULT '{}',
+    created_at        TEXT DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
+    updated_at        TEXT DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now'))
+);
+CREATE INDEX IF NOT EXISTS idx_subagent_tasks_parent_status ON subagent_tasks(tenant_id, parent_agent_key, status);
+CREATE INDEX IF NOT EXISTS idx_subagent_tasks_session ON subagent_tasks(session_key);
+CREATE INDEX IF NOT EXISTS idx_subagent_tasks_created ON subagent_tasks(tenant_id, created_at);`,
 }
 
 // EnsureSchema creates tables if they don't exist and applies incremental migrations.

internal/store/sqlitestore/schema.sql

@@ -1311,3 +1311,38 @@ CREATE TABLE IF NOT EXISTS system_configs (
 );
 
 CREATE INDEX IF NOT EXISTS idx_system_configs_tenant ON system_configs(tenant_id);
+
+-- ============================================================
+-- Table: subagent_tasks
+-- ============================================================
+
+CREATE TABLE IF NOT EXISTS subagent_tasks (
+    id                TEXT PRIMARY KEY,
+    tenant_id         TEXT NOT NULL REFERENCES tenants(id) ON DELETE CASCADE,
+    parent_agent_key  VARCHAR(255) NOT NULL,
+    session_key       VARCHAR(500),
+    subject           VARCHAR(255) NOT NULL,
+    description       TEXT NOT NULL,
+    status            VARCHAR(20) NOT NULL DEFAULT 'running',
+    result            TEXT,
+    depth             INTEGER NOT NULL DEFAULT 1,
+    model             VARCHAR(255),
+    provider          VARCHAR(255),
+    iterations        INTEGER NOT NULL DEFAULT 0,
+    input_tokens      INTEGER NOT NULL DEFAULT 0,
+    output_tokens     INTEGER NOT NULL DEFAULT 0,
+    origin_channel    VARCHAR(50),
+    origin_chat_id    VARCHAR(255),
+    origin_peer_kind  VARCHAR(20),
+    origin_user_id    VARCHAR(255),
+    spawned_by        TEXT,
+    completed_at      TEXT,
+    archived_at       TEXT,
+    metadata          TEXT NOT NULL DEFAULT '{}',
+    created_at        TEXT DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
+    updated_at        TEXT DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now'))
+);
+
+CREATE INDEX IF NOT EXISTS idx_subagent_tasks_parent_status ON subagent_tasks(tenant_id, parent_agent_key, status);
+CREATE INDEX IF NOT EXISTS idx_subagent_tasks_session ON subagent_tasks(session_key);
+CREATE INDEX IF NOT EXISTS idx_subagent_tasks_created ON subagent_tasks(tenant_id, created_at);

internal/store/sqlitestore/subagent_tasks.go

@@ -0,0 +1,38 @@
+//go:build sqlite || sqliteonly
+
+package sqlitestore
+
+import (
+	"context"
+	"time"
+
+	"github.com/google/uuid"
+
+	"github.com/nextlevelbuilder/goclaw/internal/store"
+)
+
+// SQLiteSubagentTaskStore is a no-op implementation for the desktop/lite edition.
+// Subagent task persistence is a standard-edition feature.
+type SQLiteSubagentTaskStore struct{}
+
+func NewSQLiteSubagentTaskStore() *SQLiteSubagentTaskStore { return &SQLiteSubagentTaskStore{} }
+
+func (s *SQLiteSubagentTaskStore) Create(context.Context, *store.SubagentTaskData) error { return nil }
+func (s *SQLiteSubagentTaskStore) Get(context.Context, uuid.UUID) (*store.SubagentTaskData, error) {
+	return nil, nil
+}
+func (s *SQLiteSubagentTaskStore) UpdateStatus(context.Context, uuid.UUID, string, *string, int, int64, int64) error {
+	return nil
+}
+func (s *SQLiteSubagentTaskStore) ListByParent(context.Context, string, string) ([]store.SubagentTaskData, error) {
+	return nil, nil
+}
+func (s *SQLiteSubagentTaskStore) ListBySession(context.Context, string) ([]store.SubagentTaskData, error) {
+	return nil, nil
+}
+func (s *SQLiteSubagentTaskStore) Archive(context.Context, time.Duration) (int64, error) {
+	return 0, nil
+}
+func (s *SQLiteSubagentTaskStore) UpdateMetadata(context.Context, uuid.UUID, map[string]any) error {
+	return nil
+}