CUB-203: fix Grimm review blocking issues (PR #41)

🔴 readLoop race: replace WriteControl close with ctx-done goroutine that closes conn
🔴 duplicate event handlers: clear handlers map before re-registering on reconnect
🔴 sync.go CurrentTask abuse: add DisplayName field to UpdateAgentRequest, use it
🔴 sync.go newRole dead code: add Role field to UpdateAgentRequest, use it
🔴 events.go handlePresence DB/SSE inconsistency: pass LastActivityAt in update, don't mutate after DB
🔴 events.go handleAgentConfig DB/SSE inconsistency: use DisplayName/Role fields in update
🟠 Send() nil-conn panic: check conn != nil before WriteJSON
🟠 readLoop prompt ctx cancellation: fixed by item #1
🟠 backoff never resets: reset to initialBackoff after successful connectAndRun
🟠 MarkWSReady double-close race: use sync.Once in Client
Extra json:"-" dead fields: removed from sessionChangedPayload, presencePayload, agentConfigPayload
UpdateAgentRequest: added DisplayName, Role, LastActivityAt fields

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 {