Leave room for the answer: ALEX2ESP_MAX_MESSAGE defaults to ALEX2ESP_MAX_DIRECTIVE + 1024

Both limits were 2047 bytes. An answer repeats the correlationToken of its directive, which is most of a large directive, and adds 140 to 170 bytes for every property. So a directive between about 1,750 and 2,047 bytes was accepted, the sketch acted on it, and the answer was refused: the lamp switched and Alexa reported a device that does not respond.

The limit for messages now follows the limit for directives unless it is set: 2047 + 1024 = 3071 bytes, room for six properties on top of the largest directive. Both defines moved to src/AlexaLimits.h, next to each other, with the relation in the comment. The limit also applies to the discovery object of a device, which may now be 3071 bytes.

For a sketch: a report between 2,048 and 3,071 bytes is sent, where it was refused with an error. A project that sets ALEX2ESP_MAX_MESSAGE keeps its value.

Measured with the bridge built for the host against a fake MQTT client (not in the repository), a TurnOn of 2,047 bytes answered with two properties:
  8ea7778      handler ran, send() false, "2374 bytes not sent, the limit is 2047"
  this commit  handler ran, send() true, 2,374 bytes published

Tests: test_largest_directive_can_be_answered puts a directive of ALEX2ESP_MAX_DIRECTIVE bytes through the receive buffer, builds the Response of a lamp to it and checks it against ALEX2ESP_MAX_MESSAGE, also with six properties. 33 host tests pass.

examples/basicLight.cpp for d1_mini, static RAM / flash in bytes: 34,116 / 336,757 -> 34,116 / 336,757, no warnings.

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

readme.md

@@ -141,7 +141,7 @@ Everything goes over MQTT (port 1883 of `alex2mqtt.stormysdream.club`); the libr
 - **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"]`. One directive is handled at a time; a directive that arrives twice (a broker that mirrors its topics delivers every message twice) is handled once.
 - **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`.
-- **Limits.** A directive and a report (or the discovery object of one device) may be 2047 bytes each; `-DALEX2ESP_MAX_DIRECTIVE=<bytes>` and `-DALEX2ESP_MAX_MESSAGE=<bytes>` in `build_flags` change that. `send()` returns `false` when the report was not sent: no session with the broker, the MQTT client or the heap cannot take it, or it is too large. Nothing is ever sent truncated, and nothing is dropped without a line on Serial.
+- **Limits.** A directive may be 2047 bytes (`ALEX2ESP_MAX_DIRECTIVE`), a report or the discovery object of one device 3071 (`ALEX2ESP_MAX_MESSAGE`). The second limit is the first plus 1024 unless it is set: an answer repeats the `correlationToken` of its directive, which is most of a large directive, and adds 140 to 170 bytes per property, so the largest directive can be answered with six properties. `-DALEX2ESP_MAX_DIRECTIVE=<bytes>` and `-DALEX2ESP_MAX_MESSAGE=<bytes>` in `build_flags` change the limits. `send()` returns `false` when the report was not sent: no session with the broker, the MQTT client or the heap cannot take it, or it is too large. Nothing is ever sent truncated, and nothing is dropped without a line on Serial.
 - **Serial output.** Every line of the library starts with `[Alex2ESP]`, a problem with `[Alex2ESP] error:`. `alexClient.setLogLevel(AlexaLogLevel::ERROR)` leaves only the problems, `AlexaLogLevel::NONE` nothing; the default, `AlexaLogLevel::INFO`, adds the session, discovery and one line per directive (`[Alex2ESP] ESP-01 <- Alexa.PowerController.TurnOn`). `AlexaLogLevel::DEBUG` (sizes and free heap per message) has to be compiled in with `-DALEX2ESP_LOG_MAX=3`; `-DALEX2ESP_LOG_MAX=0` compiles every line out. Credentials and correlation tokens are never printed. A sketch that defines a macro named `DEBUG`, `ERROR` or `INFO` cannot write the level of that name; it passes the number instead, for example `alexClient.setLogLevel(static_cast<AlexaLogLevel>(3))` for `DEBUG`.
 
 Boards that run 1.1.0 or older keep working: the backend still publishes the token on `<root>/<endpointId>/alexaDirective_e` and serves the HTTP routes they use.
@@ -243,12 +243,12 @@ For instance, to manually report the state of a PowerController, you can use the
 
 Behaviour changes:
 - Directives arrive over MQTT. The library subscribes to `<root>/+/alexaDirective`, where Alex2MQTT has always published the whole directive, instead of fetching it over HTTP with the token from `<root>/<endpointId>/alexaDirective_e`. The HTTP detour dates from 2024, when a directive larger than one TCP segment reached the MQTT callback in pieces; the pieces are now put together by their offset and the total length, in one heap block that lives until `loop()` has parsed the directive. `loop()` no longer stalls for two HTTP round trips per directive.
-- Reports leave over MQTT. `send()` publishes on `<root>/<endpointId>/alexaResponce` at once, where 1.1.0 queued the report for an HTTP POST from a later `loop()`. It returns `false` when there is no session with the broker, when the MQTT client or the heap cannot take the report, or when the report is over 2047 bytes (`ALEX2ESP_MAX_MESSAGE`); each case prints its reason. The 5-slot send queue is gone.
+- Reports leave over MQTT. `send()` publishes on `<root>/<endpointId>/alexaResponce` at once, where 1.1.0 queued the report for an HTTP POST from a later `loop()`. It returns `false` when there is no session with the broker, when the MQTT client or the heap cannot take the report, or when the report is over 3071 bytes (`ALEX2ESP_MAX_MESSAGE`, by default 1024 more than the largest directive, so that every directive that is accepted can be answered); each case prints its reason. The 5-slot send queue is gone.
 - `timeOfSample` is the board's own time in UTC, for example `2026-09-28T13:05:09Z`. 1.1.0 sent the placeholder `{REPLACE_WITH_DATETIME}`, which only the backend's HTTP route replaced. `begin()` starts SNTP (`pool.ntp.org`, `time.nist.gov`) and no longer connects itself: `loop()` opens the MQTT session once the clock is set, or after 5 s without an answer, so the session comes up a few seconds later than before. `alexClient.setTimeSource(false)` before `begin()` leaves the clock to the sketch. `AddContextProp()` fills `timeOfSample` in when the property has none or carries the old placeholder.
 - A directive is parsed and handed to the sketch from `loop()`, one at a time. One that arrives while the previous one still waits for `loop()` is dropped, as is one over 2047 bytes (`ALEX2ESP_MAX_DIRECTIVE`); both print an error.
 - A directive that arrives twice is handled once: the Alex2MQTT broker currently delivers every message twice through a mirror. The `messageId`s of the last four directives are remembered; the repeat prints `repeated directive ... ignored`.
 - The subscription delivers the directives of every endpoint of the account. Those for endpoints of another board are recognised by their topic and neither buffered nor parsed.
-- Discovery is answered from `loop()`, not inside the MQTT callback. A discovery object over 2047 bytes is refused with an error; the other devices are still announced.
+- 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 refused subscription prints an error.
 - 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.
 - `getDevice()` before `begin()` prints an error: the device would have no root topic. A second `begin()` is ignored with an error.
@@ -257,7 +257,7 @@ Behaviour changes:
 
 Memory: `examples/basicLight.cpp` for a D1 mini takes 34,116 bytes of static RAM (1.1.0: 52,768) and 336,757 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 32 host tests of the receive and publish logic (reassembly of fragments, the two size limits, repeated directives, topics, time stamps). No board is needed.
+Tests: `pio test -e native` in the repository runs 33 host tests of the receive and publish logic (reassembly of fragments, the two size limits, repeated directives, topics, time stamps). No board is needed.
 
 Boards that run 1.1.0 are not affected: the backend keeps the token topic and the HTTP routes.