android: the phone walk waits for the WebView instead of giving up on it

A launch leaves a window where the app is up, focused and has a pid while
the devtools socket the walk attaches to does not exist yet — on a loaded
machine it has been as long as ten seconds. attachPhone tried once and
reported "is SoulStream on screen?" about an app that plainly was. It now
tries for fifteen seconds, re-reading the pid each time in case the app
restarted underneath it.

tests/mobile/cdp.mjs

@@ -94,12 +94,30 @@ export async function attachPhone(port) {
             throw new Error("the phone is in use (" + who + " is on screen); not touching it");
         }
     }
-    const pid = adb("shell", "pidof", "com.soulstream.app").toString().trim();
+    /* The devtools socket is registered by the WebView, not by the process, so
+       there is a window after a launch where the app is up, focused and has a
+       pid, and the socket does not exist yet. On a loaded machine that window
+       has been as long as ten seconds — a walk that attached once and gave up
+       read it as "is SoulStream on screen?" when it plainly was. Try for a
+       while, re-reading the pid each time in case the app restarted under us. */
+    let pid = "";
+    let last = null;
+    for (let attempt = 0; attempt < 6; attempt++) {
+        pid = adb("shell", "pidof", "com.soulstream.app").toString().trim();
+        if (pid) {
+            adb("forward", "--remove-all");
+            adb("forward", `tcp:${port}`, `localabstract:webview_devtools_remote_${pid}`);
+            try {
+                const cdp = await CDP.attach(port, { phone: true });
+                return { cdp, pid };
+            } catch (e) {
+                last = e;
+            }
+        }
+        await sleep(2500);
+    }
     if (!pid) throw new Error("SoulStream is not running on the phone (adb shell pidof found nothing)");
-    adb("forward", "--remove-all");
-    adb("forward", `tcp:${port}`, `localabstract:webview_devtools_remote_${pid}`);
-    const cdp = await CDP.attach(port, { phone: true });
-    return { cdp, pid };
+    throw last ?? new Error("could not attach to the phone's WebView on port " + port);
 }
 
 /** The phone's own frame, status bar included. */