step 5 (partial): strip dropped packages from production code

Removed all references to dropped packages in non-test code.
Zero dropped imports, store refs, or model types remaining.

Major removals:
  - scheduler/ package (entire dir) — tasks moved to extension track
  - taskutil/ package (entire dir)
  - health/ package (entire dir) — provider/tool health
  - sandbox/provider_module.go — provider.complete module
  - handlers: workflow_entry, workflow_instances, workflow_forms,
    workflow_assignments, workflow_monitor, health_admin (6 files)
  - auth/session.go, middleware/session_auth.go
  - store/{postgres,sqlite}/sessions.go, tasks.go

Rewrites:
  - store/{postgres,sqlite}/health.go — kernel-only Prune
    (ws_tickets, rate_limit_counters, stale presence)
  - handlers/admin.go: 847→467 lines (stripped provider CRUD)
  - handlers/teams.go: 520→411 lines (stripped model listing)
  - sandbox/runner.go: removed ProviderResolver
  - sandbox/workflow_module.go: 216→83 lines (definition-only)
  - main.go: 1579→1325 lines (stripped dropped package init)
  - pages/pages.go: stripped channel/session lookups
  - events/types.go: stripped chat/channel/workspace event routes
  - models: stripped stale types, constants, notification types

Store interface cleanup:
  - Removed SessionStore, TaskStore from Stores struct
  - Stripped workflow assignment methods from WorkflowStore iface
  - Stripped assignment methods from PG+SQLite workflow stores
  - Updated testhelper.go table list to kernel-only

Migrations: removed 008_tasks.sql (both dialects)

-9665/+69 lines across 51 files.

server/store/postgres/workflows.go

@@ -220,7 +220,7 @@ func (s *WorkflowStore) CreateStage(ctx context.Context, st *models.WorkflowStag
 	transRules := jsonOrEmpty(st.TransitionRules)
 	stageMode := st.StageMode
 	if stageMode == "" {
-		stageMode = models.StageModeChatOnly
+		stageMode = models.StageModeCustom
 	}
 	return DB.QueryRowContext(ctx, `
 		INSERT INTO workflow_stages (workflow_id, ordinal, name, persona_id, assignment_team_id,
@@ -267,7 +267,7 @@ func (s *WorkflowStore) UpdateStage(ctx context.Context, st *models.WorkflowStag
 	transRules := jsonOrEmpty(st.TransitionRules)
 	stageMode := st.StageMode
 	if stageMode == "" {
-		stageMode = models.StageModeChatOnly
+		stageMode = models.StageModeCustom
 	}
 	_, err := DB.ExecContext(ctx, `
 		UPDATE workflow_stages
@@ -377,207 +377,6 @@ func nullIfEmpty(s string) interface{} {
 
 // ── Assignments (v0.29.0-cs3) ───────────────────────────────────────────
 
-func (s *WorkflowStore) CreateAssignment(ctx context.Context, a *store.WorkflowAssignment) error {
-	a.ID = store.NewID()
-	_, err := DB.ExecContext(ctx, `
-		INSERT INTO workflow_assignments (id, channel_id, stage, team_id)
-		VALUES ($1, $2, $3, $4)
-	`, a.ID, a.ChannelID, a.Stage, a.TeamID)
-	return err
-}
-
-func (s *WorkflowStore) ListAssignmentsForTeam(ctx context.Context, teamID, status string) ([]store.WorkflowAssignment, error) {
-	rows, err := DB.QueryContext(ctx, `
-		SELECT id, channel_id, stage, team_id, assigned_to, status,
-		       created_at, claimed_at, completed_at
-		FROM workflow_assignments
-		WHERE team_id = $1 AND status = $2
-		ORDER BY created_at DESC
-	`, teamID, status)
-	if err != nil {
-		return nil, err
-	}
-	defer rows.Close()
-	return scanAssignments(rows)
-}
-
-func (s *WorkflowStore) ListAssignmentsMine(ctx context.Context, userID string) ([]store.WorkflowAssignment, error) {
-	rows, err := DB.QueryContext(ctx, `
-		SELECT DISTINCT wa.id, wa.channel_id, wa.stage, wa.team_id, wa.assigned_to, wa.status,
-		       wa.created_at, wa.claimed_at, wa.completed_at
-		FROM workflow_assignments wa
-		LEFT JOIN team_members tm ON tm.team_id = wa.team_id AND tm.user_id = $1
-		WHERE (wa.assigned_to = $2 AND wa.status = 'claimed')
-		   OR (wa.status = 'unassigned' AND tm.user_id IS NOT NULL)
-		ORDER BY wa.created_at DESC
-	`, userID, userID)
-	if err != nil {
-		return nil, err
-	}
-	defer rows.Close()
-	return scanAssignments(rows)
-}
-
-func (s *WorkflowStore) ClaimAssignment(ctx context.Context, assignmentID, userID string) (int64, error) {
-	res, err := DB.ExecContext(ctx, `
-		UPDATE workflow_assignments
-		SET assigned_to = $1, status = 'claimed', claimed_at = $2
-		WHERE id = $3 AND status = 'unassigned'
-	`, userID, time.Now().UTC(), assignmentID)
-	if err != nil {
-		return 0, err
-	}
-	return res.RowsAffected()
-}
-
-func (s *WorkflowStore) CompleteAssignment(ctx context.Context, assignmentID string) (int64, error) {
-	res, err := DB.ExecContext(ctx, `
-		UPDATE workflow_assignments
-		SET status = 'completed', completed_at = $1
-		WHERE id = $2 AND status = 'claimed'
-	`, time.Now().UTC(), assignmentID)
-	if err != nil {
-		return 0, err
-	}
-	return res.RowsAffected()
-}
-
-func (s *WorkflowStore) GetAssignmentChannelID(ctx context.Context, assignmentID string) (string, error) {
-	var channelID string
-	err := DB.QueryRowContext(ctx,
-		`SELECT channel_id FROM workflow_assignments WHERE id = $1`, assignmentID).Scan(&channelID)
-	return channelID, err
-}
-
 // ── Lifecycle operations (v0.37.15) ──
 
-func (s *WorkflowStore) CancelAssignmentsForChannel(ctx context.Context, channelID string) (int64, error) {
-	res, err := DB.ExecContext(ctx, `
-		UPDATE workflow_assignments
-		SET status = 'cancelled'
-		WHERE channel_id = $1 AND status IN ('unassigned', 'claimed')
-	`, channelID)
-	if err != nil {
-		return 0, err
-	}
-	return res.RowsAffected()
-}
-
-func (s *WorkflowStore) UnclaimAssignment(ctx context.Context, assignmentID string) (int64, error) {
-	res, err := DB.ExecContext(ctx, `
-		UPDATE workflow_assignments
-		SET status = 'unassigned', assigned_to = NULL, claimed_at = NULL
-		WHERE id = $1 AND status = 'claimed'
-	`, assignmentID)
-	if err != nil {
-		return 0, err
-	}
-	return res.RowsAffected()
-}
-
-func (s *WorkflowStore) ReassignAssignment(ctx context.Context, assignmentID, newUserID string) (int64, error) {
-	res, err := DB.ExecContext(ctx, `
-		UPDATE workflow_assignments
-		SET assigned_to = $1, claimed_at = $2
-		WHERE id = $3 AND status = 'claimed'
-	`, newUserID, time.Now().UTC(), assignmentID)
-	if err != nil {
-		return 0, err
-	}
-	return res.RowsAffected()
-}
-
-func (s *WorkflowStore) CancelAssignment(ctx context.Context, assignmentID string) (int64, error) {
-	res, err := DB.ExecContext(ctx, `
-		UPDATE workflow_assignments
-		SET status = 'cancelled'
-		WHERE id = $1 AND status IN ('unassigned', 'claimed')
-	`, assignmentID)
-	if err != nil {
-		return 0, err
-	}
-	return res.RowsAffected()
-}
-
-func (s *WorkflowStore) TryRoundRobin(ctx context.Context, teamID, assignmentID string) (string, error) {
-	// Find least-recently-assigned team member
-	rows, err := DB.QueryContext(ctx, `
-		SELECT m.user_id, COALESCE(MAX(wa.claimed_at), '1970-01-01T00:00:00Z') as last_claim
-		FROM team_members m
-		LEFT JOIN workflow_assignments wa ON wa.assigned_to = m.user_id AND wa.team_id = $1
-		WHERE m.team_id = $2
-		GROUP BY m.user_id
-		ORDER BY last_claim ASC
-		LIMIT 1
-	`, teamID, teamID)
-	if err != nil {
-		return "", err
-	}
-	defer rows.Close()
-
-	if !rows.Next() {
-		return "", nil // no team members
-	}
-	var userID, lastClaim string
-	if err := rows.Scan(&userID, &lastClaim); err != nil {
-		return "", err
-	}
-
-	// Claim for that user
-	_, err = DB.ExecContext(ctx, `
-		UPDATE workflow_assignments
-		SET assigned_to = $1, status = 'claimed', claimed_at = $2
-		WHERE id = $3 AND status = 'unassigned'
-	`, userID, time.Now().UTC(), assignmentID)
-	if err != nil {
-		return "", err
-	}
-	return userID, nil
-}
-
-func scanAssignments(rows *sql.Rows) ([]store.WorkflowAssignment, error) {
-	var result []store.WorkflowAssignment
-	for rows.Next() {
-		var a store.WorkflowAssignment
-		if err := rows.Scan(&a.ID, &a.ChannelID, &a.Stage, &a.TeamID,
-			&a.AssignedTo, &a.Status, &a.CreatedAt, &a.ClaimedAt, &a.CompletedAt); err != nil {
-			return nil, err
-		}
-		result = append(result, a)
-	}
-	if result == nil {
-		result = []store.WorkflowAssignment{}
-	}
-	return result, rows.Err()
-}
-
 // ── Review Comments (v0.35.0) ───────────────────────────
-
-func (s *WorkflowStore) GetAssignmentByID(ctx context.Context, id string) (*store.WorkflowAssignment, error) {
-	var a store.WorkflowAssignment
-	var rc []byte
-	err := DB.QueryRowContext(ctx, `
-		SELECT id, channel_id, stage, team_id, assigned_to, status,
-		       review_comments, created_at, claimed_at, completed_at
-		FROM workflow_assignments WHERE id = $1
-	`, id).Scan(&a.ID, &a.ChannelID, &a.Stage, &a.TeamID, &a.AssignedTo, &a.Status,
-		&rc, &a.CreatedAt, &a.ClaimedAt, &a.CompletedAt)
-	if err != nil {
-		return nil, err
-	}
-	a.ReviewComments = rc
-	return &a, nil
-}
-
-func (s *WorkflowStore) AddReviewComment(ctx context.Context, assignmentID string, comment store.ReviewComment) error {
-	commentJSON, err := json.Marshal(comment)
-	if err != nil {
-		return err
-	}
-	_, err = DB.ExecContext(ctx, `
-		UPDATE workflow_assignments
-		SET review_comments = review_comments || $1::jsonb
-		WHERE id = $2
-	`, "["+string(commentJSON)+"]", assignmentID)
-	return err
-}