[6769][IMP] endpoint_json2: let a method declare its own response fields

[yostashiro]

QT6769

Lets an endpoint whose method is not read/search_read declare its response fields.

Problem

_check_json2_response_fields validated every response field against the target model's fields, for every endpoint. That is correct when the method is read or search_read, whose result rows are made of model fields. It is wrong for any other method: the keys are the method's own, and the model has no way to know them.

A method returning a derived value therefore could not name it at all — declaring it raised ValidationError, so the only way forward was to leave json2_response_fields empty. That turns off filtering and aliasing entirely and leaves the payload implicit in the Python, invisible to anyone reading the endpoint record.

Change

• Plain names are validated only for the methods in FIELD_READING_METHODS (read, search_read). That is a policy list, not a taxonomy of the ORM and is not meant to grow: read_group also returns model field values and is deliberately excluded, since its rows carry keys of its own (__count, __domain) too. A module wanting its own method checked should constrain it where the payload is defined, which can pin the exact keys rather than merely "is a field of the model".
• Dotted specs stay validated whatever the method is: _json2_resolve_dotted_fields resolves the base against Model._fields before fetching the related rows, so a base that is not a relational field can never resolve.
• The constraint now also depends on json2_method, so switching an endpoint back to search_read re-runs the check instead of leaving behind keys the model does not have.

Nothing changes at execution time: filtering, aliasing and dotted resolution were already applied to the result of any method, not only search_read.

Notes

• README.rst is not regenerated — the oca-gen-addon-readme hook is commented out in this repository's .pre-commit-config.yaml (line 57), so readme/CONFIGURE.md is updated but the generated file is left alone rather than hand-edited.
• The same change is wanted upstream in [19.0][ADD] endpoint_json2 OCA/web-api#135, which is still open.
• I could not execute the tests locally: addons_path is empty in this workspace's odoo.conf and a fresh database registered 667 modules with no endpoint* among them, so the namespace path did not include the repositories. Relying on CI here.

[yostashiro]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep it up!

Reviewed commit: b92970189d

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