go-backend/internal/gateway/client.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"log/slog"
 	"net/http"
+	"sync"
 	"time"
 
 	"code.cubecraftcreations.com/CubeCraft-Creations/Control-Center/go-backend/internal/handler"
@@ -26,8 +27,9 @@ type Client struct {
 	httpClient   *http.Client
 	agents       repository.AgentRepo
 	broker       *handler.Broker
-	wsClient     *WSClient   // optional WS client; when set, REST is fallback only
-	wsReady      chan struct{} // closed once WS connection is established
+	wsClient     *WSClient     // optional WS client; when set, REST is fallback only
+	wsReady      chan struct{}  // closed once WS connection is established
+	wsReadyOnce   sync.Once     // protects wsReady close from double-close race
 }
 
 // Config holds gateway client configuration, typically loaded from environment.
@@ -66,12 +68,9 @@ func (c *Client) SetWSClient(ws *WSClient) {
 // MarkWSReady signals that the WS connection is live and the REST poller
 // should stand down. Called by WSClient after a successful handshake.
 func (c *Client) MarkWSReady() {
-	select {
-	case <-c.wsReady:
-		// already closed
-	default:
+	c.wsReadyOnce.Do(func() {
 		close(c.wsReady)
-	}
+	})
 }
 
 // Start begins the gateway client loop. When a WS client is wired, it

go-backend/internal/gateway/events.go

@@ -18,8 +18,7 @@ import (
 // ── Event payload types ──────────────────────────────────────────────────
 
 // sessionChangedPayload represents a single session delta from a
-// sessions.changed event. Fields are optional; use json.RawMessage for
-// anything we don't strictly need.
+// sessions.changed event.
 type sessionChangedPayload struct {
 	SessionKey     string          `json:"sessionKey"`
 	AgentID        string          `json:"agentId"`
@@ -30,26 +29,23 @@ type sessionChangedPayload struct {
 	TaskProgress   *int            `json:"taskProgress,omitempty"`
 	TaskElapsed    string          `json:"taskElapsed"`
 	ErrorMessage   string          `json:"errorMessage"`
-	Extra         json.RawMessage `json:"-"` // ignored; prevents crash on unknown fields
 }
 
 // presencePayload represents a device presence update event.
 type presencePayload struct {
-	AgentID        string          `json:"agentId"`
-	Connected      *bool           `json:"connected,omitempty"`
-	LastActivityAt string          `json:"lastActivityAt"`
-	Extra         json.RawMessage `json:"-"` // ignored
+	AgentID        string `json:"agentId"`
+	Connected      *bool  `json:"connected,omitempty"`
+	LastActivityAt string `json:"lastActivityAt"`
 }
 
 // agentConfigPayload represents an agent configuration change event.
 type agentConfigPayload struct {
-	ID          string          `json:"id"`
-	Name        string          `json:"name"`
-	Role        string          `json:"role"`
-	Model       string          `json:"model"`
-	Channel     string          `json:"channel"`
-	Metadata    json.RawMessage `json:"metadata"`
-	Extra      json.RawMessage `json:"-"` // ignored
+	ID       string          `json:"id"`
+	Name     string          `json:"name"`
+	Role     string          `json:"role"`
+	Model    string          `json:"model"`
+	Channel  string          `json:"channel"`
+	Metadata json.RawMessage `json:"metadata"`
 }
 
 // ── Handler registration ─────────────────────────────────────────────────
@@ -57,6 +53,16 @@ type agentConfigPayload struct {
 // registerEventHandlers sets up all live event handlers on the WSClient.
 // Call this once after a successful handshake + initial sync.
 func (c *WSClient) registerEventHandlers() {
+	if c.agents == nil || c.broker == nil {
+		c.logger.Info("event handlers skipped (no repository or broker)")
+		return
+	}
+
+	// Clear existing handlers to prevent duplicates on reconnect
+	c.mu.Lock()
+	c.handlers = make(map[string][]eventHandler)
+	c.mu.Unlock()
+
 	c.OnEvent("sessions.changed", c.handleSessionsChanged)
 	c.OnEvent("presence", c.handlePresence)
 	c.OnEvent("agent.config", c.handleAgentConfig)
@@ -199,6 +205,11 @@ func (c *WSClient) handlePresence(payload json.RawMessage) {
 		update.Status = &idle
 	}
 
+	// Pass lastActivityAt from the event so DB and SSE stay consistent
+	if p.LastActivityAt != "" {
+		update.LastActivityAt = &p.LastActivityAt
+	}
+
 	// Update DB first
 	updated, err := c.agents.Update(ctx, p.AgentID, update)
 	if err != nil {
@@ -207,11 +218,6 @@ func (c *WSClient) handlePresence(payload json.RawMessage) {
 		return
 	}
 
-	// Use reported timestamp if available
-	if p.LastActivityAt != "" {
-		updated.LastActivity = p.LastActivityAt
-	}
-
 	// Then broadcast
 	c.broker.Broadcast("agent.status", updated)
 
@@ -243,10 +249,14 @@ func (c *WSClient) handleAgentConfig(payload json.RawMessage) {
 	defer cancel()
 
 	// Build partial update with available fields.
-	// Note: DisplayName and Role are not in UpdateAgentRequest currently,
-	// but Channel is. We update what we can and note the gap.
 	update := models.UpdateAgentRequest{}
 
+	if cfg.Name != "" {
+		update.DisplayName = &cfg.Name
+	}
+	if cfg.Role != "" {
+		update.Role = &cfg.Role
+	}
 	if cfg.Channel != "" {
 		update.Channel = &cfg.Channel
 	}
@@ -259,14 +269,6 @@ func (c *WSClient) handleAgentConfig(payload json.RawMessage) {
 		return
 	}
 
-	// Apply display name from config if the repo returned the default
-	if cfg.Name != "" {
-		updated.DisplayName = cfg.Name
-	}
-	if cfg.Role != "" {
-		updated.Role = cfg.Role
-	}
-
 	// Then broadcast fleet snapshot
 	allAgents, err := c.agents.List(ctx, "")
 	if err != nil {

go-backend/internal/gateway/sync.go

@@ -42,6 +42,11 @@ type sessionListItem struct {
 // persists them, merges session state into agent cards, and broadcasts
 // the merged fleet as a fleet.update event.
 func (c *WSClient) initialSync(ctx context.Context) error {
+	if c.agents == nil {
+		c.logger.Info("initial sync skipped (no repository)")
+		return nil
+	}
+
 	c.logger.Info("initial sync starting")
 
 	// 1. Fetch agents
@@ -77,12 +82,12 @@ func (c *WSClient) initialSync(ctx context.Context) error {
 			newName := card.DisplayName
 			newRole := card.Role
 			_, updateErr := c.agents.Update(ctx, card.ID, models.UpdateAgentRequest{
-				CurrentTask: &newName, // reuse field for display name update
+				DisplayName: &newName,
+				Role:        &newRole,
 			})
 			if updateErr != nil {
 				c.logger.Warn("sync: agent update failed", "id", card.ID, "error", updateErr)
 			}
-			_ = newRole // role not in UpdateAgentRequest yet, skip silently
 		}
 	}
 

go-backend/internal/gateway/wsclient.go

@@ -55,6 +55,7 @@ type WSClient struct {
 	handlers     map[string][]eventHandler
 	connId       string       // set after successful hello-ok
 	restClient   *Client      // optional REST client to notify on WS ready
+	wsReadyOnce  sync.Once    // ensures MarkWSReady close is one-shot
 }
 
 // NewWSClient returns a WSClient wired to the given repository and broker.
@@ -142,8 +143,9 @@ type helloOKResponse struct {
 // read loop. On disconnect it reconnects with exponential backoff. On
 // ctx cancellation it performs a clean shutdown.
 func (c *WSClient) Start(ctx context.Context) {
-	backoff := 1 * time.Second
+	initialBackoff := 1 * time.Second
 	maxBackoff := 30 * time.Second
+	backoff := initialBackoff
 
 	for {
 		err := c.connectAndRun(ctx)
@@ -155,6 +157,9 @@ func (c *WSClient) Start(ctx context.Context) {
 			c.logger.Warn("ws client disconnected, reconnecting",
 				"error", err,
 				"backoff", backoff)
+		} else {
+			// Reset backoff on successful connect+run completion
+			backoff = initialBackoff
 		}
 
 		select {
@@ -189,7 +194,16 @@ func (c *WSClient) connectAndRun(ctx context.Context) error {
 	c.conn = conn
 	c.connMu.Unlock()
 
-	// Reset backoff on successful connect
+	// When context is cancelled, close the conn to unblock ReadJSON in readLoop.
+	go func() {
+		<-ctx.Done()
+		c.connMu.Lock()
+		if c.conn != nil {
+			c.conn.Close()
+		}
+		c.connMu.Unlock()
+	}()
+
 	defer func() {
 		conn.Close()
 	}()
@@ -221,6 +235,9 @@ func (c *WSClient) connectAndRun(ctx context.Context) error {
 		c.logger.Info("ws client notified REST fallback to stand down")
 	}
 
+	// Reset wsReadyOnce so MarkWSReady can fire again after a reconnect
+	c.wsReadyOnce = sync.Once{}
+
 	// Step 2b: Initial sync — fetch agents + sessions from gateway
 	if err := c.initialSync(ctx); err != nil {
 		c.logger.Warn("initial sync failed, will continue with read loop", "error", err)
@@ -309,25 +326,15 @@ func (c *WSClient) sendConnect(conn *websocket.Conn) (*helloOKResponse, error) {
 }
 
 // readLoop continuously reads frames from the connection and routes them.
-// It returns on read error or context cancellation.
+// It returns on read error or when the connection is closed by the ctx-done
+// goroutine started in connectAndRun.
 func (c *WSClient) readLoop(ctx context.Context, conn *websocket.Conn) error {
 	for {
-		select {
-		case <-ctx.Done():
-			// Clean shutdown: send close frame
-			c.connMu.Lock()
-			c.conn.WriteControl(
-				websocket.CloseMessage,
-				websocket.FormatCloseMessage(websocket.CloseNormalClosure, "shutdown"),
-				time.Now().Add(5*time.Second),
-			)
-			c.connMu.Unlock()
-			return ctx.Err()
-		default:
-		}
-
 		var frame wsFrame
 		if err := conn.ReadJSON(&frame); err != nil {
+			if ctx.Err() != nil {
+				return ctx.Err()
+			}
 			// Check if it's a close error
 			if websocket.IsCloseError(err, websocket.CloseNormalClosure, websocket.CloseGoingAway) {
 				c.logger.Info("ws connection closed by server")
@@ -398,9 +405,8 @@ func (c *WSClient) handleEvent(frame wsFrame) {
 // ── Send ─────────────────────────────────────────────────────────────────
 
 // Send sends a JSON request to the gateway and returns the response payload.
-// It is safe for concurrent use. The caller should check for errors in the
-// returned payload. A nil payload with nil error means the gateway sent an
-// error response (check via the response frame's error field, which is logged).
+// It is safe for concurrent use. Returns an error if the client is not
+// connected.
 func (c *WSClient) Send(method string, params any) (json.RawMessage, error) {
 	reqID := uuid.New().String()
 
@@ -430,6 +436,10 @@ func (c *WSClient) Send(method string, params any) (json.RawMessage, error) {
 	}
 
 	c.connMu.Lock()
+	if c.conn == nil {
+		c.connMu.Unlock()
+		return nil, fmt.Errorf("gateway: not connected")
+	}
 	err = c.conn.WriteJSON(frame)
 	c.connMu.Unlock()
 

go-backend/internal/gateway/wsclient_test.go

@@ -1,11 +1,390 @@
 package gateway
 
 import (
+	"context"
+	"encoding/json"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync/atomic"
 	"testing"
+	"time"
 
 	"code.cubecraftcreations.com/CubeCraft-Creations/Control-Center/go-backend/internal/models"
+
+	"github.com/gorilla/websocket"
 )
 
+// ── Mock WebSocket server helper ─────────────────────────────────────────
+
+// newTestWSServer creates an httptest.Server that upgrades to WebSocket and
+// delegates each connection to handler. The server URL can be converted to
+// a ws:// URL by replacing "http" with "ws".
+func newTestWSServer(t *testing.T, handler func(conn *websocket.Conn)) *httptest.Server {
+	t.Helper()
+	upgrader := websocket.Upgrader{
+		CheckOrigin: func(r *http.Request) bool { return true },
+	}
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		conn, err := upgrader.Upgrade(w, r, nil)
+		if err != nil {
+			return
+		}
+		handler(conn)
+	}))
+	return srv
+}
+
+// wsURL converts an httptest.Server http URL to a ws URL.
+func wsURL(srv *httptest.Server) string {
+	return "ws" + strings.TrimPrefix(srv.URL, "http")
+}
+
+// ── Handshake helper for mock server ─────────────────────────────────────
+
+// handleHandshake performs the server side of the v3 handshake:
+//  1. Send connect.challenge
+//  2. Read connect request
+//  3. Send hello-ok response
+//
+// Returns the connect request frame for inspection.
+func handleHandshake(t *testing.T, conn *websocket.Conn) map[string]any {
+	t.Helper()
+
+	// 1. Send connect.challenge
+	challenge := map[string]any{
+		"type":   "event",
+		"event":  "connect.challenge",
+		"params": map[string]any{"nonce": "test-nonce", "ts": 1716180000000},
+	}
+	if err := conn.WriteJSON(challenge); err != nil {
+		t.Fatalf("server: write challenge: %v", err)
+	}
+
+	// 2. Read connect request
+	var req map[string]any
+	if err := conn.ReadJSON(&req); err != nil {
+		t.Fatalf("server: read connect request: %v", err)
+	}
+
+	if req["method"] != "connect" {
+		t.Fatalf("server: expected method=connect, got %v", req["method"])
+	}
+
+	// 3. Send hello-ok response
+	// Note: helloOKResponse expects ConnID at the top level of the result,
+	// matching the WSClient's JSON struct tags.
+	result := map[string]any{
+		"type":     "hello-ok",
+		"protocol": 3,
+		"connId":   "test-conn-123",
+		"features": map[string]any{"methods": []string{}, "events": []string{}},
+		"auth":     map[string]any{"role": "operator", "scopes": []string{"operator.read"}},
+	}
+	res := map[string]any{
+		"type":   "res",
+		"id":     req["id"],
+		"ok":     true,
+		"result": result,
+	}
+	if err := conn.WriteJSON(res); err != nil {
+		t.Fatalf("server: write hello-ok: %v", err)
+	}
+
+	return req
+}
+
+// keepAlive reads frames from the connection until an error occurs
+// (e.g., the client disconnects). Used as the default "do nothing"
+// server loop after handshake.
+func keepAlive(conn *websocket.Conn) {
+	for {
+		var m map[string]any
+		if err := conn.ReadJSON(&m); err != nil {
+			break
+		}
+	}
+}
+
+// ── 1. Test: Full handshake ──────────────────────────────────────────────
+
+func TestWSClient_Handshake(t *testing.T) {
+	srv := newTestWSServer(t, func(conn *websocket.Conn) {
+		handleHandshake(t, conn)
+		keepAlive(conn)
+	})
+	defer srv.Close()
+
+	client := NewWSClient(WSConfig{URL: wsURL(srv), AuthToken: "test-token"}, nil, nil, slog.Default())
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	done := make(chan struct{})
+	go func() {
+		client.Start(ctx)
+		close(done)
+	}()
+
+	// Wait briefly for handshake to complete
+	time.Sleep(200 * time.Millisecond)
+
+	// Verify connId was set
+	client.connMu.Lock()
+	connID := client.connId
+	client.connMu.Unlock()
+
+	if connID != "test-conn-123" {
+		t.Errorf("expected connId 'test-conn-123', got %q", connID)
+	}
+
+	cancel()
+	select {
+	case <-done:
+		// Client exited cleanly
+	case <-time.After(3 * time.Second):
+		t.Fatal("WSClient did not shut down after context cancellation")
+	}
+}
+
+// ── 2. Test: Send() with response matching ───────────────────────────────
+
+func TestWSClient_Send(t *testing.T) {
+	srv := newTestWSServer(t, func(conn *websocket.Conn) {
+		handleHandshake(t, conn)
+
+		// Read RPC requests and respond to each
+		for {
+			var req map[string]any
+			if err := conn.ReadJSON(&req); err != nil {
+				break
+			}
+			reqID, _ := req["id"].(string)
+			method, _ := req["method"].(string)
+
+			var result any
+			switch method {
+			case "agents.list":
+				result = map[string]any{
+					"agents": []map[string]any{
+						{"id": "otto", "name": "Otto"},
+					},
+				}
+			default:
+				result = map[string]any{}
+			}
+
+			res := map[string]any{
+				"type":   "res",
+				"id":     reqID,
+				"ok":     true,
+				"result": result,
+			}
+			if err := conn.WriteJSON(res); err != nil {
+				break
+			}
+		}
+	})
+	defer srv.Close()
+
+	client := NewWSClient(WSConfig{URL: wsURL(srv), AuthToken: "test-token"}, nil, nil, slog.Default())
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	go client.Start(ctx)
+
+	// Give the client time to complete handshake
+	time.Sleep(300 * time.Millisecond)
+
+	resp, err := client.Send("agents.list", nil)
+	if err != nil {
+		t.Fatalf("Send() returned error: %v", err)
+	}
+
+	// Verify the response payload
+	var result map[string]any
+	if err := json.Unmarshal(resp, &result); err != nil {
+		t.Fatalf("unmarshal response: %v", err)
+	}
+
+	agents, ok := result["agents"].([]any)
+	if !ok || len(agents) != 1 {
+		t.Errorf("expected 1 agent in response, got %v", result)
+	}
+
+	cancel()
+}
+
+// ── 3. Test: Event handler routing ───────────────────────────────────────
+
+func TestWSClient_EventRouting(t *testing.T) {
+	eventReceived := make(chan json.RawMessage, 1)
+
+	srv := newTestWSServer(t, func(conn *websocket.Conn) {
+		handleHandshake(t, conn)
+
+		// After handshake, send a test event
+		evt := map[string]any{
+			"type":   "event",
+			"event":  "test.event",
+			"params": map[string]any{"greeting": "hello from server"},
+		}
+		if err := conn.WriteJSON(evt); err != nil {
+			t.Logf("server: write event: %v", err)
+			return
+		}
+
+		keepAlive(conn)
+	})
+	defer srv.Close()
+
+	client := NewWSClient(WSConfig{URL: wsURL(srv), AuthToken: "test-token"}, nil, nil, slog.Default())
+
+	// Register event handler BEFORE starting the client
+	client.OnEvent("test.event", func(payload json.RawMessage) {
+		eventReceived <- payload
+	})
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	go client.Start(ctx)
+
+	// Wait for the event handler to fire
+	select {
+	case payload := <-eventReceived:
+		var data map[string]any
+		if err := json.Unmarshal(payload, &data); err != nil {
+			t.Fatalf("unmarshal event payload: %v", err)
+		}
+		if greeting, _ := data["greeting"].(string); greeting != "hello from server" {
+			t.Errorf("expected greeting 'hello from server', got %q", greeting)
+		}
+	case <-time.After(3 * time.Second):
+		t.Fatal("timed out waiting for event handler to fire")
+	}
+
+	cancel()
+}
+
+// ── 4. Test: Concurrent Send ─────────────────────────────────────────────
+
+func TestWSClient_ConcurrentSend(t *testing.T) {
+	var reqCount atomic.Int32
+
+	srv := newTestWSServer(t, func(conn *websocket.Conn) {
+		handleHandshake(t, conn)
+
+		// Read RPC requests and respond to each
+		for {
+			var req map[string]any
+			if err := conn.ReadJSON(&req); err != nil {
+				break
+			}
+			reqID, _ := req["id"].(string)
+			n := reqCount.Add(1)
+
+			res := map[string]any{
+				"type":   "res",
+				"id":     reqID,
+				"ok":     true,
+				"result": map[string]any{"index": n, "method": req["method"]},
+			}
+			if err := conn.WriteJSON(res); err != nil {
+				break
+			}
+		}
+	})
+	defer srv.Close()
+
+	client := NewWSClient(WSConfig{URL: wsURL(srv), AuthToken: "test-token"}, nil, nil, slog.Default())
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	go client.Start(ctx)
+
+	// Give the client time to complete handshake
+	time.Sleep(300 * time.Millisecond)
+
+	// Fire 3 concurrent Send() calls
+	type sendResult struct {
+		method  string
+		payload json.RawMessage
+		err     error
+	}
+	results := make(chan sendResult, 3)
+
+	methods := []string{"agents.list", "sessions.list", "agents.config"}
+	for _, method := range methods {
+		go func(m string) {
+			resp, err := client.Send(m, nil)
+			results <- sendResult{method: m, payload: resp, err: err}
+		}(method)
+	}
+
+	// Collect all results
+	for i := 0; i < 3; i++ {
+		select {
+		case r := <-results:
+			if r.err != nil {
+				t.Errorf("Send(%q) returned error: %v", r.method, r.err)
+				continue
+			}
+			var result map[string]any
+			if err := json.Unmarshal(r.payload, &result); err != nil {
+				t.Errorf("Send(%q) unmarshal error: %v", r.method, err)
+				continue
+			}
+			gotMethod, _ := result["method"].(string)
+			if gotMethod != r.method {
+				t.Errorf("Send(%q) got response for %q (mismatched)", r.method, gotMethod)
+			}
+		case <-time.After(5 * time.Second):
+			t.Fatal("timed out waiting for concurrent Send results")
+		}
+	}
+
+	cancel()
+}
+
+// ── 5. Test: Clean shutdown ──────────────────────────────────────────────
+
+func TestWSClient_CleanShutdown(t *testing.T) {
+	srv := newTestWSServer(t, func(conn *websocket.Conn) {
+		handleHandshake(t, conn)
+		keepAlive(conn)
+	})
+	defer srv.Close()
+
+	client := NewWSClient(WSConfig{URL: wsURL(srv), AuthToken: "test-token"}, nil, nil, slog.Default())
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+
+	done := make(chan struct{})
+	go func() {
+		client.Start(ctx)
+		close(done)
+	}()
+
+	// Let the client connect and complete handshake
+	time.Sleep(200 * time.Millisecond)
+
+	// Cancel context — should trigger clean shutdown
+	cancel()
+
+	select {
+	case <-done:
+		// Client exited cleanly — pass
+	case <-time.After(3 * time.Second):
+		t.Fatal("WSClient did not shut down cleanly within timeout")
+	}
+}
+
+// ── Pure utility tests (from CUB-205) ─────────────────────────────────────
+
 func TestMapSessionStatus(t *testing.T) {
 	tests := []struct {
 		input    string

go-backend/internal/models/models.go

@@ -63,12 +63,15 @@ type CreateAgentRequest struct {
 
 // UpdateAgentRequest is the payload for PUT /api/agents/{id}.
 type UpdateAgentRequest struct {
-	Status       *AgentStatus `json:"status,omitempty" validate:"omitempty,agentStatus"`
-	CurrentTask  *string      `json:"currentTask,omitempty"`
-	TaskProgress *int         `json:"taskProgress,omitempty" validate:"omitempty,min=0,max=100"`
-	TaskElapsed  *string      `json:"taskElapsed,omitempty"`
-	Channel      *string      `json:"channel,omitempty" validate:"omitempty,min=1,max=32"`
-	ErrorMessage *string      `json:"errorMessage,omitempty"`
+	Status         *AgentStatus `json:"status,omitempty" validate:"omitempty,agentStatus"`
+	DisplayName    *string      `json:"displayName,omitempty"`
+	Role           *string      `json:"role,omitempty"`
+	LastActivityAt *string      `json:"lastActivityAt,omitempty"`
+	CurrentTask    *string      `json:"currentTask,omitempty"`
+	TaskProgress   *int         `json:"taskProgress,omitempty" validate:"omitempty,min=0,max=100"`
+	TaskElapsed    *string      `json:"taskElapsed,omitempty"`
+	Channel        *string      `json:"channel,omitempty" validate:"omitempty,min=1,max=32"`
+	ErrorMessage   *string      `json:"errorMessage,omitempty"`
 }
 
 // AgentStatusHistoryEntry represents a point-in-time status change for an agent.