refactor(background-tasks): split task definitions into metadata and handler

[adrians5j]

First of six. Ships the mechanism, migrates nothing, changes no behaviour.

The problem

GetTaskDefinitionUseCase finds one task by looping every registered definition and comparing definition.id. There are 24 of them, and a definition carries its dependencies:

export const MockDataManagerTaskDefinition = TaskDefinition.createImplementation({
    implementation: MockDataManagerTask,
    dependencies: [CmsContext, OpenSearchClient, CmsModelOpenSearchIndexProvider]
});

So looking up any task builds a CMS context, an OpenSearch client and an index provider, 24 times over, for the 23 you didn't ask for.

This is the same shape #5668 fixed for HTTP routes, and worse in one way. The injection is a constructor parameter:

dependencies: [[TaskDefinition, { multiple: true }]]

HttpRouter at least resolved inside route(), so the cost landed per request. Here the whole set is built when the use case itself is constructed, whether or not anything ever looks a task up.

The split

Mirrors HttpRouteDefinition / HttpRouteHandler:

	carries	built
ITaskMetadata	id, title, description, maxIterations, databaseLogs, isPrivate, selfCleanup	always, but it has no dependencies
ITaskHandler	run() and the lifecycle hooks	only for the task being run

A definition points at its handler class, and the use case resolves that one handler once it knows which task was asked for.

Why the hooks went with the handler

The code answers this one. MockDataManagerTask.onError and onAbort both use this.openSearchClient and this.indexProvider, the same dependencies injected for run(). The hooks need what the handler needs, so they live with it and metadata stays dependency-free.

Why a resolver instead of injecting the container

Something has to turn definition.handler into an instance, and that needs the container. Injecting a container into a use case is the service-locator pattern we keep out of DI classes, so it sits behind one narrow abstraction instead:

export interface ITaskHandlerResolver {
    resolve<I, O>(handler: Constructor<TaskDefinition.Handler<I, O>>): TaskDefinition.Handler<I, O>;
}

One infrastructure class holds the container. Everything else depends on resolve(handler) and stays stubbable, which is exactly what the tests do.

A handler must be a createImplementation result, not a bare class. resolveImplementation reads dependency metadata off the class:

RawZero:     THROWS -> No abstraction metadata found for RawZero
RawWithDep:  THROWS -> No abstraction metadata found for RawWithDep
Proper:      ok -> 42

Why hooks chain instead of coming from one side

toRunnable composes hooks from BOTH halves, handler first and definition second, because they mean different things. The handler's is the task author's. The definition's is whatever a decorator added, and SelfCleaningTaskDecorator contributes exactly that: an onDone that deletes the finished task.

Taking only the handler's would silently drop every definition-level decorator. Taking only the definition's would drop the task's own. The handler half is guarded, so a throwing user hook still lets the decorator's half run, matching what the old single-object implementation did with its own safeCall.

This also answers a question I had left open here: whether SelfCleaningTaskDecorator should become a handler decorator that looks metadata up by definitionId, or whether self-cleanup should move into the runner. Neither. Composing both halves where they already meet keeps selfCleanup extensible by decoration and leaves the decorator untouched.

Transitional shape

run is optional on ITaskDefinition so both shapes coexist while packages migrate. A definition with neither run nor handler fails with TaskDefinitionNotRunnableError rather than a TypeError somewhere downstream.

The optionality is temporary and goes away in the last PR of the series, once all 24 carry a handler. It is called out in the interface doc comment so nobody takes it as the intended design.

Also

Removed three console.* calls from RunnableTaskDecorator and SelfCleaningTaskDecorator, against the rule that backend code injects the DI Logger. Both files were being rewritten anyway.

Verification

• 96 background-tasks tests, 181 api-core, 139 webhooks, all passing
• all 11 packages that declare task definitions build, plus api-core and background-tasks
• adio, oxlint, oxfmt --check clean

Eight new tests. The two that carry the most weight: one registers two handler-based definitions and asserts that looking up greet builds GreetHandler and nothing else; another asserts a throwing handler hook still lets the decorator's half run.

What's next

PR	scope	definitions
this	mechanism	0
#5692	background-tasks	1 + fixtures
3	bulk-actions, cms-tasks, cms-es-tasks, search-index-tasks	8
4	fm-s3, fm-server, api-aco	9
5	ai-powerups, remote-components, webhooks, website-builder	7
6	remove compat, drop both multiple: true, fix the context.container service locator in TaskControl	0

The win accrues per PR rather than landing all at the end: a migrated definition becomes a zero-dependency metadata object, so each package that moves over drops its construction cost out of the lookup path immediately.

Review note

The second commit fixes two defects in the first one's code, both found while migrating real definitions on top of it: hooks were taken from the handler alone, and the test fixtures used bare classes as handlers. If you read an earlier version of this description, those are the parts that changed, and the counts above are corrected (24 definitions across 11 packages, not 29 across 12; the extra five were test fixtures).

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Added support for task definitions backed by reusable handler classes.
  • Task handlers can participate in execution, validation, and lifecycle hooks.
  • Existing task definitions using a direct run() method remain supported.
  • Added clearer handling for task definitions that cannot be executed.

• Bug Fixes

  • Lifecycle-hook failures are logged consistently without interrupting subsequent cleanup hooks.
  • Tasks without a run() method are handled safely when a handler is available.

• Tests

  • Expanded coverage for handler execution, legacy tasks, hook ordering, errors, and logging.

[github-actions]

🚓 Slop Cop

✅ Nothing worth flagging. The diff looks consistent with the PR's stated intent and the code-style rules.

The diff matches the stated intent (mechanism-only split of TaskDefinition into metadata/handler), is well-scoped to background-tasks/api-core, adds substantial tests, and the added code follows the project's style rules; no integrity red flags found.

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• packages/background-tasks/__tests__/features/GetTaskDefinitionUseCase.test.ts
• packages/background-tasks/src/api/features/GetTaskDefinition/GetTaskDefinitionUseCase.ts

🚧 Files skipped from review as they are similar to previous changes (2)

• packages/background-tasks/tests/features/GetTaskDefinitionUseCase.test.ts
• packages/background-tasks/src/api/features/GetTaskDefinition/GetTaskDefinitionUseCase.ts

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📝 Walkthrough

Walkthrough

Task definitions now support dependency-resolved handlers and legacy run methods. Background tasks register a handler resolver, adapt handlers into runnable definitions, chain lifecycle hooks, and report non-runnable definitions. Decorators and tests support the updated behavior.

Changes

Task handler flow

Layer / File(s)	Summary
Task metadata and handler contracts packages/api-core/src/features/task/TaskDefinition/abstractions.ts	Task contracts separate dependency-free metadata from handler behavior. Transitional definitions support either a handler constructor or legacy run behavior.
Request-scoped handler resolution packages/background-tasks/src/api/features/TaskHandlerResolver/*, packages/background-tasks/src/api/BackgroundTasksFeature.ts	The resolver constructs decorated handlers through the request container. Background task setup registers the resolver before task-definition features.
Task definition adaptation and errors packages/background-tasks/src/api/features/GetTaskDefinition/*, packages/background-tasks/src/api/domain/errors.ts	The get-definition use case resolves handlers, binds execution and validation, chains hooks, preserves legacy run, and returns a not-runnable error when needed.
Decorator handler delegation and logging packages/background-tasks/src/api/decorators/*	Decorators delegate optional handlers and optional run methods. Lifecycle-hook failures use structured logger calls.
Handler flow and decorator tests packages/background-tasks/__tests__/features/GetTaskDefinitionUseCase.test.ts, packages/background-tasks/__tests__/decorators/SelfCleaningTaskDecorator.test.ts	Tests cover handler resolution, metadata, legacy execution, missing runnability, hook chaining, error logging, and updated decorator construction.

Priority: ⬇️ Low

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Refactor · Unblocks: 1 PR

Sequence Diagram(s)

sequenceDiagram
  participant Caller
  participant GetTaskDefinitionUseCaseImpl
  participant TaskHandlerResolver
  participant RequestContainer
  Caller->>GetTaskDefinitionUseCaseImpl: request task definition
  GetTaskDefinitionUseCaseImpl->>TaskHandlerResolver: resolve handler constructor
  TaskHandlerResolver->>RequestContainer: resolveImplementation handler
  RequestContainer-->>TaskHandlerResolver: decorated handler instance
  TaskHandlerResolver-->>GetTaskDefinitionUseCaseImpl: return handler
  GetTaskDefinitionUseCaseImpl-->>Caller: return adapted runnable definition

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Merge Risk: ⚪ Minimal · up to 083a2

No concrete merge-blocking risk remains identified in the task-handler refactor.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: splitting task definitions into metadata and handlers.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Inline comments:
In
`@packages/background-tasks/src/api/features/GetTaskDefinition/GetTaskDefinitionUseCase.ts`:
- Around line 92-114: Update the handler wrapper around the bound
onBeforeTrigger hook to capture its rejection, still await the definition-level
decorated hook for decorator and cleanup behavior, then rethrow the original
handler error so task triggering aborts consistently with legacy definitions.
Add a regression test covering hook execution order and propagated rejection.

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📥 Commits

Reviewing files that changed from the base of the PR and between 5d72734 and 869a64c.

📒 Files selected for processing (13)

• packages/api-core/src/features/task/TaskDefinition/abstractions.ts
• packages/background-tasks/__tests__/decorators/SelfCleaningTaskDecorator.test.ts
• packages/background-tasks/__tests__/features/GetTaskDefinitionUseCase.test.ts
• packages/background-tasks/src/api/BackgroundTasksFeature.ts
• packages/background-tasks/src/api/decorators/RunnableTaskDecorator.ts
• packages/background-tasks/src/api/decorators/SelfCleaningTaskDecorator.ts
• packages/background-tasks/src/api/domain/errors.ts
• packages/background-tasks/src/api/features/GetTaskDefinition/GetTaskDefinitionUseCase.ts
• packages/background-tasks/src/api/features/GetTaskDefinition/abstractions.ts
• packages/background-tasks/src/api/features/TaskHandlerResolver/TaskHandlerResolver.ts
• packages/background-tasks/src/api/features/TaskHandlerResolver/abstractions.ts
• packages/background-tasks/src/api/features/TaskHandlerResolver/feature.ts
• packages/background-tasks/src/api/features/TaskHandlerResolver/index.ts

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