`d` shortcut shows "DevTools not ready" even after VM Service is up

[jainam-bhavasar]

Scope

flutter run --machine reliably emits the VM Service URI via the app.debugPort JSON-RPC event, but it does not always print a human-readable DevTools URL line. Today open_devtools_all and the log-line capture path depend entirely on seeing app.devTools: <url> in the Flutter output. When that line never arrives, the d keybind reports:

[emulator] DevTools not ready yet — still building / VM Service not up
No DevTools URL captured yet — wait for the app to start and retry

…even though memory polling, network polling, and the VM Service itself are all healthy.

Reproduced on Android emulator (API 36) with flutter run --machine -t lib/main.dart --flavor staging. The log shows VM Service ready and successful getVM responses, but devtools_uri on the DeviceSession stays None indefinitely.

Root cause

1. DeviceSession::devtools_uri is only populated from a strip_prefix("app.devTools: ") match inside the event loop. In --machine mode Flutter often skips the human-readable DevTools log line entirely — the URL only exists as a structured daemon response or can be synthesised from the VM Service URI + a running DevTools server.

2. open_devtools_all has no fallback — if devtools_uri is None it emits the warning and gives up.

What to do

• Store the VM Service URI from AppStarted / app.debugPort on DeviceSession (new vm_service_uri slot).
• After AppStarted, probe for an already-running local DevTools server (ports 9100–9199) and synthesise the full http://<host>:<port>/?uri=<encoded-vm-uri> URL.
• If no server is found yet, send devtools.serve to the Flutter daemon — parse the {"result":{"host":"…","port":…}} response in parse_daemon_line and build the URL from that.
• Give open_devtools_all a last-resort probe so pressing d later still works even if the startup window was missed.
• Also capture the human-readable "Flutter DevTools … is available at: <url>" form for non-machine-mode edge cases.

Acceptance

• After VM Service ready, d opens DevTools in the browser without the "not ready" warning.
• Works from a clean process table (no pre-existing DevTools server).
• No new crate — url is already a workspace dependency.
• Existing cargo test --workspace --locked stays green.