Reconnect with back-off on every disconnect reason and log it

The session is opened again whatever AsyncMqttClient gives as the reason, after 1 s doubling
to 60 s (AlexaReconnectBackoff, reset when a session opens), and only while Wi-Fi is up.
1.1.0 retried a lost TCP connection every 5 s and nothing else, silently: a refused password
or a broker that was restarting left the board offline until a reset.
Every disconnect prints its reason in words and the wait before the next attempt. The first
connect waits for Wi-Fi; a connect without an answer after 30 s counts as failed, because the
MQTT client reports nothing when no TCP connection was made. Keep-alive 30 s.
basicLight: RAM 34,452 -> 34,476 B, flash 337,461 -> 338,281 B; host tests 41 -> 45.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

readme.md

@@ -137,7 +137,7 @@ An `ActionMapping` takes an optional third argument, the directive payload as JS
 
 Everything goes over MQTT (port 1883 of `alex2mqtt.stormysdream.club`); the library makes no HTTP requests.
 
-- **Session.** `begin()` starts SNTP (`pool.ntp.org`, `time.nist.gov`) and returns; `loop()` opens the MQTT session once the clock is set, or after 5 s without an answer, and subscribes to `<root>/discover` and `<root>/+/alexaDirective`. `getState()` is `CONNECTED` when the broker has acknowledged both subscriptions; `[Alex2ESP] error: the broker refused the subscription to <topic>` means that the root topic is not the one of the account. A sketch that sets the clock itself (its own `configTime()` with a time zone, an RTC) calls `alexClient.setTimeSource(false)` before `begin()`. The board has to reach an NTP server: DNS for the two names and outbound UDP port 123. Without the time of day the session still opens, the reports carry a `timeOfSample` in 1970, and the library prints `[Alex2ESP] error: the clock is not set, ...` when it connects and then at most once a minute while reports are sent.
+- **Session.** `begin()` starts SNTP (`pool.ntp.org`, `time.nist.gov`) and returns; `loop()` opens the MQTT session once Wi-Fi is up and the clock is set, or after 5 s of Wi-Fi without an answer, and subscribes to `<root>/discover` and `<root>/+/alexaDirective`. `getState()` is `CONNECTED` when the broker has acknowledged both subscriptions; `[Alex2ESP] error: the broker refused the subscription to <topic>` means that the root topic is not the one of the account. A session that ends or cannot be opened prints `[Alex2ESP] error: disconnected: <reason>; next attempt in N s` and is opened again after 1 s, then 2 s, 4 s and so on up to once a minute, for as long as Wi-Fi is up; the wait starts at 1 s again once a session is open. `the broker refused the username or the password` is the reason to look for when a board never shows up in Alexa. A sketch that sets the clock itself (its own `configTime()` with a time zone, an RTC) calls `alexClient.setTimeSource(false)` before `begin()`. The board has to reach an NTP server: DNS for the two names and outbound UDP port 123. Without the time of day the session still opens, the reports carry a `timeOfSample` in 1970, and the library prints `[Alex2ESP] error: the clock is not set, ...` when it connects and then at most once a minute while reports are sent.
 - **Discovery.** On `<root>/discover` the library answers with one discovery object per device on `<root>/discover_r`. The backend accepts one endpoint object per message and collects everything that arrives within 1 s for Alexa's discovery answer (up to 5 s for its proactive AddOrUpdate push), so all devices are published back to back from the next `loop()`. Each object sits on the heap (about 1 KB) until the MQTT client has sent it; when the client cannot take another one (free heap under 4 KB), the library prints `[Alex2ESP] discovery deferred at <endpointId>` and sends the rest from `loop()` as the queue drains, for up to 5 s after the request. `[Alex2ESP] error: discovery gave up: N device(s) not announced` means those devices missed this answer - on the backend's proactive discovery that can remove them from Alexa until the next one.
 - **Directives.** The directive arrives as JSON on `<root>/<endpointId>/alexaDirective`. A directive larger than one TCP segment arrives in fragments, which are put together in one heap block that exists only until `loop()` has parsed it. `loop()` then fires `ReportState` or `Event` (and `DirectiveReceived`, if registered) with the directive: `directive["header"]`, `directive["endpoint"]`, `directive["payload"]`. Every call of `loop()` handles one directive, in the order of arrival. Up to eight directives wait for it: Alexa sends a group command ("turn off the kitchen") as one directive per endpoint, and they arrive faster than a busy sketch calls `loop()`. A directive that arrives twice (a broker that mirrors its topics delivers every message twice) is handled once; the repeat is recognised while it arrives and takes no place among the waiting ones.
 - **Reports.** `send()` publishes the report on `<root>/<endpointId>/alexaResponce` at once. The backend waits 7 s for it, so answer from the event handler. Every property carries the board's UTC time as `timeOfSample`.
@@ -251,14 +251,15 @@ Behaviour changes:
 - Discovery is answered from `loop()`, not inside the MQTT callback. A discovery object over 3071 bytes (`ALEX2ESP_MAX_MESSAGE`) is refused with an error; the other devices are still announced.
 - `getState()` stays `INITIALIZED` until the first connect, and becomes `CONNECTED` when the broker has acknowledged both subscriptions (1.1.0: the first of them). A subscription that the broker refuses prints an error that names the topic and what to check, the root topic passed to `begin()`; the state stays `SUBSCRIBING`. When the MQTT client does not take a subscription, the session is closed and the next one subscribes again.
 - Serial output goes through one log with levels. `alexClient.setLogLevel()` takes `AlexaLogLevel::NONE`, `ERROR`, `INFO` (the default) or `DEBUG`; `-DALEX2ESP_LOG_MAX=<0..3>` in `build_flags` sets the highest level that is compiled in (default 2, `INFO`). This replaces the `Alex2ESP_DEBUG` define inside `AlexaUtils.cpp`. 1.1.0 printed the memory figures for every MQTT message and the whole directive, correlation token included, for every directive; both are gone. A sketch or a build flag that defines `DEBUG`, `ERROR` or `INFO` as a macro (`#define DEBUG 1`, `-DDEBUG`) still compiles: the library sets those macros aside where it declares its levels and passes a level by its number everywhere else.
+- The session is opened again whatever ended it, and the reason is printed in words: `disconnected: the broker refused the username or the password, check the two passed to begin(); next attempt in 1 s`. 1.1.0 reconnected every 5 s after a lost TCP connection only and printed nothing; a board with a wrong password, or one that met the broker while it was restarting, stayed offline until it was reset. The wait is 1 s after a session ended and doubles with every attempt that fails, up to 60 s. Nothing is tried while Wi-Fi is down, and the first connect waits for Wi-Fi as well (`waiting for Wi-Fi: ...` is printed once). A connect that has no answer after 30 s counts as failed. The MQTT keep-alive is 30 s (1.1.0: the 15 s of the MQTT client).
 - `getDevice()` before `begin()` prints an error: the device would have no root topic. A second `begin()` is ignored with an error.
 - A report is sent through the client that created its device. An `AlexaDevice` or an `AlexaStatusMessage` that a sketch constructs itself has no client: `send()` returns `false` and prints `report for <endpointId> not sent: its device was not created by getDevice()`, where 1.1.0 queued the report. Use `getDevice()` and `buildStatusMessage()`. Both constructors take the client as an optional last argument, an `AlexaTransport*`.
 - New: `Alex2ESP::setLogLevel()`, `Alex2ESP::setTimeSource()`, `AlexaDevice::hasEndpointId()`, `AlexaLog`, `AlexaSendResult`, and `AlexaTransport`, the interface a device sends and stamps its reports through. `Alex2ESP` implements it with `publish(topic, document)`, which sends a `JsonDocument` on the session of the library under the same checks as a report and returns an `AlexaSendResult`, and `timestamp(buffer, size)`, which writes the current time as `timeOfSample` has it.
 - Removed: the queues and buffers of `AlexaUtils` (`enqueue`, `dequeue`, `dequeueVals`, `enqueueReceive`, `dequeueReceive`, `isQueueEmpty`, `isQueueFull`, `isReceiveQueueEmpty`, `isReceiveQueueFull`, `receivePayload`, `nextMessageId`) and its `log`/`logln`, which printed nothing unless the library was edited; `AlexaUtils::printMemoryInfo()` stays. `MAX_STATUS_REPORT_SIZE` (the limit is `ALEX2ESP_MAX_MESSAGE`). The library no longer includes `ESP8266HTTPClient`.
 
-Memory: `examples/basicLight.cpp` for a D1 mini takes 34,452 bytes of static RAM (1.1.0: 52,768) and 337,461 bytes of flash (1.1.0: 350,885), as PlatformIO reports them (espressif8266 4.2.1, Arduino core 3.1.2). The static RAM was the five 2 KB queue slots, three more 2 KB buffers and the two HTTP clients. SNTP and the time stamp are 1.8 KB of the flash figure.
+Memory: `examples/basicLight.cpp` for a D1 mini takes 34,476 bytes of static RAM (1.1.0: 52,768) and 338,281 bytes of flash (1.1.0: 350,885), as PlatformIO reports them (espressif8266 4.2.1, Arduino core 3.1.2). The static RAM was the five 2 KB queue slots, three more 2 KB buffers and the two HTTP clients. SNTP and the time stamp are 1.8 KB of the flash figure.
 
-Tests: `pio test -e native` in the repository runs 41 host tests of the receive and publish logic (reassembly of fragments, the directives that wait for `loop()`, repeated directives, the size limits, a heap without room, topics, time stamps). No board is needed.
+Tests: `pio test -e native` in the repository runs 45 host tests of the receive and publish logic (reassembly of fragments, the directives that wait for `loop()`, repeated directives, the size limits, a heap without room, the wait between reconnects, topics, time stamps). No board is needed.
 
 Packaging: `library.json`, `library.properties` and the `softwareVersion` and `firmwareVersion` that a device reports in discovery say 1.2.0; the library has the number in one place, `ALEX2ESP_VERSION` in `src/AlexaVersion.h`. The `platformio.ini` of the repository is for the host tests; a sketch does not need it.