types: add when a node's run of control sessions began

hscontrol/state/node_store_test.go

@@ -1912,7 +1912,7 @@ var nodeFieldImpact = map[string]string{
 	"RegisterMethod": "payload", "AuthKeyID": "payload", "AuthKey": "payload",
 	"Expiry": "election", "LastSeen": "payload", "CreatedAt": "payload",
 	"UpdatedAt": "payload", "DeletedAt": "payload",
-	"ActiveSessions": "payload", "SessionEpoch": "payload",
+	"ActiveSessions": "payload", "SessionEpoch": "payload", "SessionStart": "election",
 }
 
 // TestUpdateChangesCoversEveryNodeField guards against a new types.Node

hscontrol/types/node.go

@@ -210,6 +210,12 @@ type Node struct {
 	// returned by Connect as a "Connect ran" sentinel for its cleanup,
 	// and Disconnect logs it. Runtime-only.
 	SessionEpoch uint64 `gorm:"-"`
+
+	// SessionStart is when the node's current run of control sessions
+	// began: [State.Connect] sets it as the first of them opens, and an
+	// overlapping reconnect keeps it. Primary election prefers the
+	// oldest. Runtime-only.
+	SessionStart time.Time `gorm:"-"`
 }
 
 type Nodes []*Node

hscontrol/types/types_clone.go

@@ -108,6 +108,7 @@ var _NodeCloneNeedsRegeneration = Node(struct {
 	Unhealthy      bool
 	ActiveSessions int
 	SessionEpoch   uint64
+	SessionStart   time.Time
 }{})
 
 // Clone makes a deep copy of PreAuthKey.

hscontrol/types/types_view.go

@@ -281,7 +281,13 @@ func (v NodeView) ActiveSessions() int { return v.ж.ActiveSessions }
 // returned by Connect as a "Connect ran" sentinel for its cleanup,
 // and Disconnect logs it. Runtime-only.
 func (v NodeView) SessionEpoch() uint64 { return v.ж.SessionEpoch }
-func (v NodeView) String() string       { return v.ж.String() }
+
+// SessionStart is when the node's current run of control sessions
+// began: [State.Connect] sets it as the first of them opens, and an
+// overlapping reconnect keeps it. Primary election prefers the
+// oldest. Runtime-only.
+func (v NodeView) SessionStart() time.Time { return v.ж.SessionStart }
+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 {
@@ -311,6 +317,7 @@ var _NodeViewNeedsRegeneration = Node(struct {
 	Unhealthy      bool
 	ActiveSessions int
 	SessionEpoch   uint64
+	SessionStart   time.Time
 }{})
 
 // View returns a read-only view of PreAuthKey.