types: add Unhealthy and SessionEpoch fields to Node

Runtime-only fields (gorm:"-") that the upcoming refactor folds
into NodeStore's snapshot:

  - Unhealthy: replaces routes.PrimaryRoutes.unhealthy set; written
    by HA prober.
  - SessionEpoch: replaces the external connectGen sync.Map; bumped
    inside Connect's NodeStore update closure so stale Disconnect
    rejection becomes atomic with the mutation.

No behaviour change yet — fields are unread.

Updates #3203

hscontrol/types/node.go

@@ -154,6 +154,16 @@ type Node struct {
 	DeletedAt *time.Time
 
 	IsOnline *bool `gorm:"-"`
+
+	// Unhealthy excludes the node from primary route election while
+	// online. Written by the HA prober. Runtime-only.
+	Unhealthy bool `gorm:"-"`
+
+	// SessionEpoch identifies a poll session. Connect bumps it; a
+	// Disconnect carrying a stale value is dropped, so a deferred
+	// disconnect from a previous session cannot overwrite a newer
+	// Connect. Runtime-only.
+	SessionEpoch uint64 `gorm:"-"`
 }
 
 type Nodes []*Node

hscontrol/types/types_clone.go

@@ -106,6 +106,8 @@ var _NodeCloneNeedsRegeneration = Node(struct {
 	UpdatedAt      time.Time
 	DeletedAt      *time.Time
 	IsOnline       *bool
+	Unhealthy      bool
+	SessionEpoch   uint64
 }{})
 
 // Clone makes a deep copy of PreAuthKey.

hscontrol/types/types_view.go

@@ -258,7 +258,16 @@ func (v NodeView) DeletedAt() views.ValuePointer[time.Time] {
 
 func (v NodeView) IsOnline() views.ValuePointer[bool] { return views.ValuePointerOf(v.ж.IsOnline) }
 
-func (v NodeView) String() string { return v.ж.String() }
+// Unhealthy excludes the node from primary route election while
+// online. Written by the HA prober. Runtime-only.
+func (v NodeView) Unhealthy() bool { return v.ж.Unhealthy }
+
+// SessionEpoch identifies a poll session. Connect bumps it; a
+// Disconnect carrying a stale value is dropped, so a deferred
+// disconnect from a previous session cannot overwrite a newer
+// Connect. Runtime-only.
+func (v NodeView) SessionEpoch() uint64 { return v.ж.SessionEpoch }
+func (v NodeView) String() string       { return v.ж.String() }
 
 // A compilation failure here means this code must be regenerated, with the command at the top of this file.
 var _NodeViewNeedsRegeneration = Node(struct {
@@ -285,6 +294,8 @@ var _NodeViewNeedsRegeneration = Node(struct {
 	UpdatedAt      time.Time
 	DeletedAt      *time.Time
 	IsOnline       *bool
+	Unhealthy      bool
+	SessionEpoch   uint64
 }{})
 
 // View returns a read-only view of PreAuthKey.