fix(server): validate cross-org resource ownership

Review of the org-scoping pass found that org_id on a query filter
protects the row you look up, but does nothing when a handler accepts a
foreign resource ID as data and a downstream unscoped query consumes it.

- AssignKey: verify key and server both belong to the org
- BuildAuthorizedKeys: resolve server first, scope assignments and keys
  to that server's org (was honouring foreign assignment rows)
- Workflows: validate TargetServerIDs on create/update and re-check at
  trigger time
- Monitor incidents/uptime handlers: gate on org-scoped GetMonitor
- GetChannels: take orgID; validate channel_ids on monitor create/update
- Secret and default-step unique indexes: scope to org_id so a second
  org no longer hits E11000
- DeleteServer/DeleteMonitor: scope cascading deletes

server/internal/services/channels.go

@@ -41,14 +41,14 @@ func GetChannel(orgID, channelID string) (*models.NotificationChannel, error) {
 	return &ch, nil
 }
 
-// GetChannels loads multiple channels by ID, skipping any not found.
-func GetChannels(channelIDs []string) ([]models.NotificationChannel, error) {
+// GetChannels loads multiple channels by ID within an org, skipping any not found.
+func GetChannels(orgID string, channelIDs []string) ([]models.NotificationChannel, error) {
 	if len(channelIDs) == 0 {
 		return nil, nil
 	}
 	ctx, cancel := monCtx()
 	defer cancel()
-	cur, err := db.Col("notification_channels").Find(ctx, bson.M{"channel_id": bson.M{"$in": channelIDs}})
+	cur, err := db.Col("notification_channels").Find(ctx, bson.M{"org_id": orgID, "channel_id": bson.M{"$in": channelIDs}})
 	if err != nil {
 		return nil, err
 	}
@@ -59,6 +59,21 @@ func GetChannels(channelIDs []string) ([]models.NotificationChannel, error) {
 	return out, nil
 }
 
+// validateChannelIDs rejects any channel that does not belong to the org.
+// Channel IDs arrive from the client as data on monitor writes.
+func validateChannelIDs(orgID string, channelIDs []string) error {
+	for _, id := range channelIDs {
+		ch, err := GetChannel(orgID, id)
+		if err != nil {
+			return err
+		}
+		if ch == nil {
+			return errors.New("channel " + id + " not found")
+		}
+	}
+	return nil
+}
+
 func CreateChannel(orgID string, ch *models.NotificationChannel) (*models.NotificationChannel, error) {
 	ctx, cancel := monCtx()
 	defer cancel()

server/internal/services/keys.go

@@ -175,6 +175,15 @@ func AssignKey(orgID, keyID, serverID string) (*models.Assignment, error) {
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()
 
+	// Both sides must belong to the caller's org — the IDs arrive from the
+	// client as data and are consumed by unscoped agent-path queries later.
+	if _, err := GetKey(orgID, keyID); err != nil {
+		return nil, fmt.Errorf("key not found")
+	}
+	if _, err := GetServer(orgID, serverID); err != nil {
+		return nil, fmt.Errorf("server not found")
+	}
+
 	// Check if already assigned and active
 	var existing models.Assignment
 	err := db.Col("assignments").FindOne(ctx, bson.M{

server/internal/services/monitors.go

@@ -101,6 +101,9 @@ func getMonitorByID(monitorID string) (*models.Monitor, error) {
 func CreateMonitor(orgID string, m *models.Monitor) (*models.Monitor, error) {
 	ctx, cancel := monCtx()
 	defer cancel()
+	if err := validateChannelIDs(orgID, m.ChannelIDs); err != nil {
+		return nil, err
+	}
 	m.OrgID = orgID
 	m.MonitorID = uuid.NewString()
 	m.CreatedAt = time.Now()
@@ -123,6 +126,11 @@ func CreateMonitor(orgID string, m *models.Monitor) (*models.Monitor, error) {
 func UpdateMonitor(orgID, monitorID string, upd bson.M) error {
 	ctx, cancel := monCtx()
 	defer cancel()
+	if ids, ok := upd["channel_ids"].([]string); ok {
+		if err := validateChannelIDs(orgID, ids); err != nil {
+			return err
+		}
+	}
 	_, err := db.Col("monitors").UpdateOne(ctx, bson.M{"monitor_id": monitorID, "org_id": orgID}, bson.M{"$set": upd})
 	return err
 }
@@ -130,9 +138,15 @@ func UpdateMonitor(orgID, monitorID string, upd bson.M) error {
 func DeleteMonitor(orgID, monitorID string) error {
 	ctx, cancel := monCtx()
 	defer cancel()
-	if _, err := db.Col("monitors").DeleteOne(ctx, bson.M{"monitor_id": monitorID, "org_id": orgID}); err != nil {
+	res, err := db.Col("monitors").DeleteOne(ctx, bson.M{"monitor_id": monitorID, "org_id": orgID})
+	if err != nil {
 		return err
 	}
+	// Only cascade when the org-scoped delete actually removed a monitor —
+	// incidents/rollups carry no org_id of their own.
+	if res.DeletedCount == 0 {
+		return nil
+	}
 	db.Col("incidents").DeleteMany(ctx, bson.M{"monitor_id": monitorID})
 	db.Col("monitor_rollups").DeleteMany(ctx, bson.M{"monitor_id": monitorID})
 	return nil
@@ -263,7 +277,7 @@ func notifyTransition(m *models.Monitor, newStatus, message string) {
 	if len(m.ChannelIDs) == 0 {
 		return
 	}
-	channels, err := GetChannels(m.ChannelIDs)
+	channels, err := GetChannels(m.OrgID, m.ChannelIDs)
 	if err != nil {
 		log.Printf("notify: load channels for %s: %v", m.MonitorID, err)
 		return

server/internal/services/secrets.go

@@ -2,6 +2,7 @@ package services
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"sort"
 	"time"
@@ -13,18 +14,34 @@ import (
 	"go.mongodb.org/mongo-driver/v2/mongo/options"
 )
 
-// EnsureSecretIndexes creates the unique compound index on (group, key).
+// EnsureSecretIndexes creates the unique compound index on (org_id, group, key).
+// The pre-multi-tenant index was on (group, key) alone, which made a second org
+// collide on the same group/key — drop it if a live DB still carries it.
 func EnsureSecretIndexes() error {
 	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 	defer cancel()
 
+	if err := db.Col("secrets").Indexes().DropOne(ctx, "group_1_key_1"); err != nil && !isIndexNotFound(err) {
+		return err
+	}
+
 	_, err := db.Col("secrets").Indexes().CreateOne(ctx, mongo.IndexModel{
-		Keys:    bson.D{{Key: "group", Value: 1}, {Key: "key", Value: 1}},
+		Keys:    bson.D{{Key: "org_id", Value: 1}, {Key: "group", Value: 1}, {Key: "key", Value: 1}},
 		Options: options.Index().SetUnique(true),
 	})
 	return err
 }
 
+// isIndexNotFound reports whether err is Mongo's IndexNotFound (27), returned
+// when dropping an index that was never created.
+func isIndexNotFound(err error) bool {
+	var ce mongo.CommandError
+	if errors.As(err, &ce) {
+		return ce.Code == 27 || ce.Name == "IndexNotFound"
+	}
+	return false
+}
+
 // ListSecretGroups returns a summary of every group with its key count and
 // most recent update time.
 func ListSecretGroups(orgID string) ([]models.GroupSummary, error) {

server/internal/services/servers.go

@@ -257,7 +257,7 @@ func DeleteServer(orgID, serverID string) error {
 		return err
 	}
 	// Also remove assignments
-	_, err = db.Col("assignments").DeleteMany(ctx, bson.M{"server_id": serverID})
+	_, err = db.Col("assignments").DeleteMany(ctx, bson.M{"server_id": serverID, "org_id": orgID})
 	return err
 }
 

server/internal/services/sync.go

@@ -13,7 +13,15 @@ func BuildAuthorizedKeys(serverID string) ([]string, error) {
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()
 
+	// Agent path — no session, so the org comes from the server record itself
+	// and both follow-up queries are scoped to it.
+	srv, err := getServerByID(serverID)
+	if err != nil {
+		return nil, err
+	}
+
 	cursor, err := db.Col("assignments").Find(ctx, bson.M{
+		"org_id":     srv.OrgID,
 		"server_id":  serverID,
 		"revoked_at": nil,
 	})
@@ -30,7 +38,7 @@ func BuildAuthorizedKeys(serverID string) ([]string, error) {
 	var lines []string
 	for _, a := range assignments {
 		var key models.Key
-		err := db.Col("keys").FindOne(ctx, bson.M{"key_id": a.KeyID}).Decode(&key)
+		err := db.Col("keys").FindOne(ctx, bson.M{"key_id": a.KeyID, "org_id": srv.OrgID}).Decode(&key)
 		if err != nil {
 			continue
 		}

server/internal/services/workflow_runner.go

@@ -30,6 +30,11 @@ func TriggerWorkflow(orgID, workflowID, actor string) (string, error) {
 	if len(wf.Steps) == 0 {
 		return "", fmt.Errorf("workflow has no steps")
 	}
+	// Re-check ownership at trigger time — targets may predate validation or a
+	// server may have been removed since the workflow was saved.
+	if err := validateTargetServers(orgID, wf.TargetServerIDs); err != nil {
+		return "", err
+	}
 
 	// Reject a concurrent run of the same workflow.
 	ctx, cancel := wfCtx()

server/internal/services/workflows.go

@@ -25,8 +25,13 @@ func EnsureWorkflowIndexes() error {
 	}); err != nil {
 		return err
 	}
+	// The pre-multi-tenant index was on slug alone, so seeding defaults for a
+	// second org collided — drop it if a live DB still carries it.
+	if err := db.Col("workflow_steps").Indexes().DropOne(ctx, "slug_1"); err != nil && !isIndexNotFound(err) {
+		return err
+	}
 	if _, err := db.Col("workflow_steps").Indexes().CreateOne(ctx, mongo.IndexModel{
-		Keys: bson.D{{Key: "slug", Value: 1}},
+		Keys: bson.D{{Key: "org_id", Value: 1}, {Key: "slug", Value: 1}},
 		Options: options.Index().SetUnique(true).
 			SetPartialFilterExpression(bson.M{"source": "default"}),
 	}); err != nil {
@@ -219,6 +224,9 @@ func CreateWorkflow(orgID string, w models.Workflow) (*models.Workflow, error) {
 	if err := ValidateWorkflow(w); err != nil {
 		return nil, err
 	}
+	if err := validateTargetServers(orgID, w.TargetServerIDs); err != nil {
+		return nil, err
+	}
 	normalizeInlineSteps(&w)
 	if _, err := db.Col("workflows").InsertOne(ctx, w); err != nil {
 		return nil, err
@@ -232,6 +240,9 @@ func UpdateWorkflow(orgID, id string, w models.Workflow) error {
 	if err := ValidateWorkflow(w); err != nil {
 		return err
 	}
+	if err := validateTargetServers(orgID, w.TargetServerIDs); err != nil {
+		return err
+	}
 	normalizeInlineSteps(&w)
 	_, err := db.Col("workflows").UpdateOne(ctx, bson.M{"workflow_id": id, "org_id": orgID}, bson.M{"$set": bson.M{
 		"name":              w.Name,
@@ -242,6 +253,18 @@ func UpdateWorkflow(orgID, id string, w models.Workflow) error {
 	return err
 }
 
+// validateTargetServers rejects any target server that does not belong to the
+// org. The IDs are client-supplied and are later consumed by the runner's
+// unscoped lookups, so ownership has to be proven at the write boundary.
+func validateTargetServers(orgID string, serverIDs []string) error {
+	for _, sid := range serverIDs {
+		if _, err := GetServer(orgID, sid); err != nil {
+			return fmt.Errorf("target server %s not found", sid)
+		}
+	}
+	return nil
+}
+
 // normalizeInlineSteps derives outputs for inline steps and strips fields that
 // only belong to library steps.
 func normalizeInlineSteps(w *models.Workflow) {