mavweb: wait for core socket at startup instead of crash-looping

mavweb log.Fatal'd if mavend's socket wasn't up yet, so under compose it
crash-looped (relying on restart:unless-stopped) until core finished booting
its models. depends_on only orders container start, not socket readiness.
dialCoreWithRetry polls with capped backoff up to 60s; still fatal past the
deadline. Mid-life core restarts remain covered by ipc.Client's redial-on-drop.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

cmd/mavweb/main.go

@@ -80,7 +80,7 @@ func main() {
 
 	var core ipc.CoreAPI
 	if *coreSock != "" {
-		c, err := ipc.Dial(*coreSock)
+		c, err := dialCoreWithRetry(*coreSock, 60*time.Second)
 		if err != nil {
 			log.Fatalf("dial core %s: %v", *coreSock, err)
 		}
@@ -162,6 +162,36 @@ func main() {
 	}
 }
 
+// dialCoreWithRetry waits for core's IPC socket to appear before giving up.
+// Core loads models on boot and (esp. under compose) may come up after mavweb;
+// depends_on only orders container start, not socket readiness. Retrying with
+// capped backoff up to timeout stops mavweb crash-looping on a cold start. A
+// core still absent past the deadline is genuinely fatal. Mid-life core
+// restarts are handled separately by ipc.Client's redial-on-drop.
+func dialCoreWithRetry(path string, timeout time.Duration) (*ipc.Client, error) {
+	deadline := time.Now().Add(timeout)
+	delay := 200 * time.Millisecond
+	for attempt := 1; ; attempt++ {
+		c, err := ipc.Dial(path)
+		if err == nil {
+			if attempt > 1 {
+				log.Printf("core socket %s ready after %d attempts", path, attempt)
+			}
+			return c, nil
+		}
+		if time.Now().After(deadline) {
+			return nil, err
+		}
+		if attempt == 1 {
+			log.Printf("waiting for core socket %s ...", path)
+		}
+		time.Sleep(delay)
+		if delay < 2*time.Second {
+			delay *= 2
+		}
+	}
+}
+
 func handleWS(w http.ResponseWriter, r *http.Request, voiceAddr string) {
 	conn, err := websocket.Accept(w, r, &websocket.AcceptOptions{
 		OriginPatterns: []string{"*"},