meta(ai): Add a skill for writing changelog entries

.agents/skills/changelog-entry/SKILL.md

@@ -0,0 +1,45 @@
+---
+name: changelog-entry
+description: Write the changelog entry for an Objectstore PR, or exclude a PR from the changelogs. Use when opening a PR, writing its title or description, or adding a `### Changelog Entry` section.
+---
+
+# Changelog Entries
+
+The Python client, the Rust client and the server are released separately as
+Craft workspaces (see `.craft.yml`), each with its own changelog:
+
+- `clients/python/CHANGELOG.md`
+- `clients/rust/CHANGELOG.md`
+- `objectstore-server/CHANGELOG.md`, which also covers `objectstore-service`
+  (`includePaths` in `.craft.yml`)
+
+Craft lists a merged PR in the changelog of every workspace whose files it
+changes, and adds the author and a link to the PR.
+
+## Deciding on the Entry
+
+1. **Exclude PRs that users won't notice**, for example changes to tests, CI,
+   internal refactors, or a fix for a bug that was never released. To exclude
+   one, write `#skip-changelog` anywhere in the PR description. Craft ignores
+   the marker inside code spans and code blocks. PRs that only change files
+   outside all workspaces are never listed and need no marker.
+2. **Use the PR title if it's a good entry.** Craft groups the PR by the
+   conventional commit type of its title (`feat`, `fix`, ...), and uses the
+   rest of the title as the entry text. If the title follows the rules below
+   and needs no details, there's nothing more to do.
+3. **Otherwise, add a `### Changelog Entry` section** at the end of the PR
+   description, after the description and any references such as
+   `Fixes FS-123`, following the rules below. It replaces the title in every
+   changelog the PR is listed in.
+
+## Writing the Entry
+
+- Write one top-level bullet, about a line long. Put relevant details in
+  sub-bullets, only when they're needed.
+- Describe the change in behavior that a user of the library notices, not the
+  implementation or the problem statement from the PR description. Say what
+  the library does now, not which problem no longer happens.
+- For a breaking change or deprecation, add a sub-bullet with the migration
+  step.
+- The entry appears in every changelog the PR touches, so it must make sense to
+  the readers of each. If it can't, suggest to split the PR.

AGENTS.md

@@ -73,7 +73,6 @@ cargo doc --workspace --all-features --no-deps --document-private-items
 
 ## Pull Requests
 
-The Python client, the Rust client and the server are released separately as Craft workspaces (see `.craft.yml`), each with its own changelog (`clients/python/CHANGELOG.md`, `clients/rust/CHANGELOG.md`, `objectstore-server/CHANGELOG.md`). Changelog entries are generated from PR titles:
+Changelogs are generated from PR titles and descriptions. When opening a PR or writing its title or description, use the `changelog-entry` skill to write its changelog entry or exclude it from the changelogs.
 
-- A PR is listed in the changelog of every workspace whose files it changes, grouped by the conventional commit type of its title (`feat`, `fix`, ...). The scope doesn't matter. The server's changelog also covers `objectstore-service` (`includePaths` in `.craft.yml`); files outside all workspaces aren't listed anywhere.
-- If the title doesn't describe the change well for users, add a `### Changelog Entry` section to the PR description with the text to use instead. It's used for every changelog the PR is listed in.
+Mark breaking changes with `!` after the type in the PR title, for example `ref(types)!: ...`.