Add custom background tasks in worker

AGENTS.md

@@ -145,11 +145,29 @@ Development workflow
     the editor/LSP after editing YAML.
  -  **Building Packages**: All packages are built automatically as part of
     setup.  Run `mise run build` to rebuild everything, or
-    `mise run prepare-each <pkg>` to rebuild just one (without the `@fedify/`
-    prefix).
- -  **Checking Code**: Run `mise run check` before committing.
- -  **Running Tests**: Use `mise run test:deno` for Deno tests or
-    `mise run test` for all environments.
+    `mise run prepare-each <pkgs>` to rebuild specific packages (without the
+    `@fedify/` prefix).
+ -  **Checking Code**: Run `mise run check` before committing, or run
+    `mise run check-each <pkgs>` to check specific packages. If any issues from
+    `check:fmt`, `check:lint` or `check:md`, are found, refers
+    **Formatting and Linting** section.
+ -  **Formatting and Linting**: Run `mise run fmt` to format all code and docs.
+ -  **Running Tests**:
+    While testing is certainly important, blindly running every test suite every
+    time is inefficient. Since Deno executes TS source code directly, it doesn't
+    waste resources on builds. Therefore, during development, run
+    `mise run test:deno {TEST_PATH} --filter <TEST_TITLE>` for most tests that
+    are independent of the runtime. If the test is dependent on a specific
+    runtime other than Deno, replace `test:deno` with `test:node` or `test:bun`.
+    Once development is complete, run `mise run test-each <pkgs>` to test the
+    modified packages (without the `@fedify/` prefix).
+    Finally, when ready for deployment, run `mise run test` to execute the
+    whole codebase-wide tests.
+     -  `mise run test`: Executes all the tests in every runtime.
+     -  `mise run test:<runtime:deno,node,bun>`:
+        Executes all the tests by the runtime.
+     -  `mise run test-each <pkgs>`: Executes tests in packages that include
+        `pkgs` in every runtime (without the `@fedify/` prefix).
 
 For detailed contribution guidelines, see *CONTRIBUTING.md*.
 
@@ -169,6 +187,13 @@ When working with federation code:
 Common tasks
 ------------
 
+### **BE WELL-ACQUAINTED WITH `mise tasks`**
+
+*mise.toml* has useful tasks. **Acquaint all of them** and use them in the right
+place at the right time. If it has too much information, use `mise tasks`. This
+command shows the summary of the tasks and descriptions. If `mise tasks` does
+not make it clear, use `mise tasks <task>` to check the details for the task.
+
 ### Adding ActivityPub vocabulary types
 
 1.  Create a new YAML file in *packages/vocab/vocab/* following existing

CHANGES.md

@@ -17,10 +17,59 @@ To be released.
     as a remote JSON-LD document, which is required for [FEP-ef61]
     portable objects.  [[#827], [#915]]
 
+ -  Added a custom background task API that generalizes Fedify's
+    enqueue-and-process-later pattern to arbitrary application-defined jobs:
+
+     -  `Federation` and `FederationBuilder` gained a `defineTask()` method
+        through the new `TaskRegistry` interface, which `Federatable` now
+        extends.
+     -  `Context` gained `enqueueTask()` and `enqueueTaskMany()` methods,
+        with `delay` and `orderingKey` options
+        (new `TaskEnqueueOptions` interface).
+     -  Every task requires a [Standard Schema]
+        (`schema` option) from which the payload type is inferred; payloads
+        are validated at enqueue time (fail fast) and again at dequeue time
+        (protection against schema drift across deployments).
+     -  Payloads are serialized by Fedify with devalue, so `Date`, `Map`,
+        `Set`, `URL`, `bigint`, circular references, and Activity Vocabulary
+        objects round-trip faithfully across every message queue backend.
+     -  Failed handlers are retried with exponential backoff by default;
+        tasks support per-task `retryPolicy` and `onError` options, the new
+        `FederationOptions.taskRetryPolicy` sets the federation-wide default,
+        and queues with `nativeRetrial` delegate retries to the backend.
+     -  Tasks can be isolated from activity delivery through the new
+        `FederationQueueOptions.task` slot or a per-task `queue` option;
+        without them, tasks fall back to the outbox queue unless the new
+        `FederationOptions.taskQueueResolution` option is set to `"strict"`.
+        `Federation.startQueue()` now accepts `queue: "task"` to run
+        a task-only worker.
+     -  Tasks can request at-most-once enqueue with a `deduplicationKey`
+        (new `TaskEnqueueOptions.deduplicationKey`).  A queue declaring the new
+        `MessageQueue.nativeDeduplication` capability owns the check and
+        receives the key through the new
+        `MessageQueueEnqueueOptions.deduplicationKey`; otherwise Fedify
+        performs a best-effort key–value guard through the optional
+        `KvStore.cas` primitive, under a new `taskDeduplication` key prefix.
+        The marker TTL and the no-`cas` fallback are tunable with the new
+        `FederationOptions.taskDeduplicationTtl` and
+        `FederationOptions.taskDeduplicationFallback` options.
+
+    [[#206], [#797], [#798], [#799], [#803], [#806], [#812], [#923] by
+    ChanHaeng Lee]
+
 [FEP-8b32]: https://w3id.org/fep/8b32
 [FEP-ef61]: https://w3id.org/fep/ef61
+[Standard Schema]: https://standardschema.dev/
+[#206]: https://github.com/fedify-dev/fedify/issues/206
+[#797]: https://github.com/fedify-dev/fedify/issues/797
+[#798]: https://github.com/fedify-dev/fedify/issues/798
+[#799]: https://github.com/fedify-dev/fedify/issues/799
+[#803]: https://github.com/fedify-dev/fedify/pull/803
+[#806]: https://github.com/fedify-dev/fedify/pull/806
+[#812]: https://github.com/fedify-dev/fedify/pull/812
 [#827]: https://github.com/fedify-dev/fedify/issues/827
 [#915]: https://github.com/fedify-dev/fedify/pull/915
+[#923]: https://github.com/fedify-dev/fedify/pull/923
 
 ### @fedify/vocab
 

docs/.vitepress/config.mts

@@ -151,6 +151,7 @@ const MANUAL = {
     { text: "Pragmatics", link: "/manual/pragmatics.md" },
     { text: "Key–value store", link: "/manual/kv.md" },
     { text: "Message queue", link: "/manual/mq.md" },
+    { text: "Background tasks", link: "/manual/tasks.md" },
     { text: "Circuit breaker", link: "/manual/circuit-breaker.md" },
     { text: "Integration", link: "/manual/integration.md" },
     { text: "Migration", link: "/manual/migrate.md" },