id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
37400	Add metadata API to Tasks	Jake Howard		"A `TaskResult` should have `metadata` - a writable persistent `dict` (JSON-compatible) containing additional data about the task, but outside of its arguments.

Proposed API:

- `my_task.using(metadata={""trace_id"": 123}).enqueue(foo=1)` would enqueue the `my_task` task with metadata `{""trace_id"": 123}` and arguments `foo=1`.
- Metadata could be retrieved using task context `context.metadata`
- If the `context.metadata` is modified, it is saved when a task finishes (successfully or otherwise)
- Metadata can be saved within a task using `context.save_metadata()` (or `.asave_metadata`)
- `metadata` is always a `dict`, and must be strictly JSON-supported types (as task args and kwargs are currently)
- Metadata support is opt-in - backends must set the `supports_metadata` feature and implement `save_metadata` and/or `asave_metadata`
- By convention, metadata keys prefixed with `_` should not be used by end users. Keys prefixed with `_django` should be considered reserved by Django and its first-party backends. Backend or library developers are free to use their own narrow-scoped reservd prefixes, so long as they start with `_`. They may be stored, but are stripped out before being shown by the user, and are ignored during save.

See also https://github.com/django/new-features/issues/141"	New feature	new	Tasks	6.1	Normal			Jake Howard	Unreviewed	0	0	0	0	0	0