Debug Console: the listener is checked and retried, and debug off <seconds> comes back by itself

The framework's server begin() fails without a word: the console's task now
asks whether it listens, says so, and tries again. `debug off <seconds>`
closes the console and reopens it after the pause, which is the only way to
test its closing and reopening from afar.

Checked on the device: 25 closings and reopenings, each back a second after
the pause. Free heap dips about 270 bytes for each connection the device
closes and is all back two minutes later (TCP keeps a closed connection that
long): not a leak.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

docs/milestones/R1.md

@@ -147,6 +147,8 @@ The issue asked for a token that could be set, so that Debug Builds could be pub
 - **Two settings,** `DebugConsole` and `DebugToken`, with the others: validated, and invalid stored values count as missing.
 - **The console's task and ring come and go with the setting.** `Console::openRing` allocates the ring; switching off closes the socket, frees it and ends the task. `tick` follows the settings once a second, so a switch off and on again takes a second or two.
 - **Measured against the two builds it replaces:** 1,881,799 bytes of flash and 54,700 of static RAM. The release build was 1,851,387 and 54,612 (so 30 KB more flash and 88 bytes more RAM); the Debug Build was 1,874,887 and 58,780 (4 KB of RAM back: the ring is no longer a static array).
+- **The listener is asked whether it listens.** The framework's `begin()` returns nothing and fails without a word; the task now checks, says so on the console, and tries again every two seconds.
+- **`debug off <seconds>`** closes the console and brings it back by itself: the only way to try its closing and reopening from afar, since switching it on is for the device and the cable only.
 - **`scripts/rdbg.py`** answers the challenge, and fetches a release's ELF from Gitea when a crash names a version that isn't in `.pio/elves/`.
 
 ### Checks
@@ -164,6 +166,9 @@ The issue asked for a token that could be set, so that Debug Builds could be pub
 | Three `crash abort` in a row | **Safe Mode**, with the console reachable: `info` works, `ls /` says `not available in Safe Mode`. `rdbg.py crash` decodes the backtrace to `runCommand` at the `abort()` line. `reboot` leaves Safe Mode |
 | An update over Wi-Fi with the console on | The setting and the token survive: the console is back by itself after the restart |
 | `debug off` over the console | The client is dropped and port 2323 refuses connections; the update port still answers |
+| `debug off 2`, 10 times in a row, then 15 | It came back each time, a second after the pause. Free heap dips by about 270 bytes for each connection the device closes and **is all back two minutes later** (107.2 KB before, 103.2 right after 15, 107.0 at two minutes): TCP holds a closed connection that long. Not a leak, though it looked like one for an hour |
 | Memory, console on with a client | 108 KB free (the Debug Build it replaces: 104 KB). In Safe Mode: 178 KB free |
 
+**One false alarm:** after the tests the console "wouldn't come back on". It was off: the setting had been left off by `debug off`, and the page's "Switch it on?" dialog opens on **Cancel**, so Enter twice leaves it off. Nothing was lost.
+
 **Not checked:** `scripts/flash.sh --debug` over USB (no device on USB here); "New token" and "Type a token" from the page (the code paths are the ones `debug token` uses, which need the cable); the Toast itself on screen (the console is closed while it shows; its Notification is in the log); free memory with the console off, which only the serial port could say (the static figures above are the evidence); fetching a release's ELF, which needs a crash on a released version.