Configurable LUD-09 success actions (url) + LUD-11 disposable

[Chemaclass]

Context

The invoice callback response hard-codes two protocol fields:

• src/Invoice/Application/InvoiceGenerator.php — mapResponseAsArray() always emits successAction => { tag: 'message', message: <config successMessage> } and disposable => false.

LUD-09 (successAction) supports a url action (open a URL after payment) in addition to message; LUD-11 defines disposable.

Goal

Make successAction and disposable configurable so operators can send a URL success action (e.g. an order/receipt page) and control disposability, per LUD-09 / LUD-11.

Scope / Tasks

• Config for success action: keep the current message default, add an optional url action. Suggested API: LightningConfig::setSuccessUrl(string $description, string $url) (LUD-09 url action requires both a description and a url). Add matching InvoiceConfig getters + ConfigKey entries.
• Config for disposability: LightningConfig::setDisposable(bool) → InvoiceConfig::isDisposable(): bool, default false (unchanged).
• InvoiceGenerator::mapResponseAsArray() emits the configured successAction (message or url) and disposable from config.
• Update the facade/generator return-shape docblocks (the successAction shape becomes a union) and the README.

Implementation notes

• LUD-09 url action shape: { "tag": "url", "description": <string>, "url": <string> }; message action: { "tag": "message", "message": <string ≤144 chars> }. Enforce the 144-char cap on message.
• Default remains the message action using the existing success-message config, so current configs are unaffected.
• Follow the established config plumbing (LightningConfig fluent setter + jsonSerialize(), InvoiceConfig::get(ConfigKey::…)).

Acceptance criteria

• Default config → identical response to today (message action, disposable:false).
• Configuring a URL action → callback returns the url successAction.
• disposable reflects config.
• Unit tests for message action (default), url action, and disposable=true.
• composer test-all green.

References

• LUD-09: https://github.com/lnurl/luds/blob/luds/09.md
• LUD-11: https://github.com/lnurl/luds/blob/luds/11.md