Refine AGENTS.md changelog guidance: silence Codex noise and reserve .changed for breaking changes (#24275)

* Tell Codex review bot not to flag missing changelog entries

The Codex code-review bot derives its rules from AGENTS.md and was
raising a finding asking for a changelog entry on essentially every
non-draft PR. Changelog files are named
`<INTEGRATION>/changelog.d/<PR_NUMBER>.<TYPE>`, so they can only be
created after the PR number is assigned -- their absence at review time
is expected, not a defect, and the requirement is already enforced by
the check_changelog job in pr-quick-check.yml.

Add a Review Guidelines section instructing the reviewer to skip this
finding, without relaxing the changelog requirement for authored code.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* Reserve `.changed` changelog type for breaking changes only

Tighten the changelog guidance in AGENTS.md so agents stop tagging
non-breaking work as `.changed`. Rewords the `changed` definition to
backward-incompatible changes only, and adds a "Choosing .changed"
guardrail that instructs pausing to confirm the change is genuinely
breaking before using it.

Raised by Eric Weaver in #agent-integrations Slack.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Kyle-Neale

AGENTS.md

@@ -200,13 +200,17 @@ For `datadog_checks_dev` and `ddev` we also need to track changelog entries even
 The valid types are defined in `ddev/src/ddev/release/constants.py` (`ENTRY_TYPES`):
 
 - `added` - New features. Bumps the **minor** version (e.g., 1.0.0 → 1.1.0).
-- `changed` - Breaking changes or significant modifications. Bumps the **major** version (e.g., 1.0.0 → 2.0.0).
+- `changed` - Backward-incompatible changes only (e.g. removing or renaming a metric or service check, removing/renaming/retyping a config option, or changing default behavior in a way that alters emitted data). Bumps the **major** version (e.g., 1.0.0 → 2.0.0). Do **not** use for non-breaking improvements — those are `added` or `fixed`.
 - `deprecated` - Marks functionality as deprecated. Bumps the **minor** version.
 - `removed` - Removes functionality. Bumps the **major** version.
 - `fixed` - Bug fixes or internal modifications with no impact on outside users. These do not deserve a `changed` or `added` (major or minor) version bump. Bumps the **patch** version (e.g., 1.0.0 → 1.0.1).
 - `security` - Security-related fixes. Bumps the **minor** version.
 
-#### Examples
+### Choosing `.changed`
+
+Before writing a `.changed` entry, stop and confirm the change is genuinely breaking for an existing user — something that would break their current configuration, dashboards, monitors, or ingested data. If you cannot name specifically what breaks, it is **not** a `.changed` entry: use `added` for new capability or `fixed` for a bug fix. When in doubt, prefer the non-breaking type or ask the reviewer rather than defaulting to `.changed`.
+
+### Examples
 
 ```shell
 # New feature for kafka_consumer in PR #23700
@@ -216,6 +220,12 @@ echo "Bump OpenSSL in confluent-kafka to 3.4.1 on Windows." > kafka_consumer/cha
 echo "Fix a bug where ``tempdb`` is wrongly excluded from database files metrics." > sqlserver/changelog.d/23701.fixed
 ```
 
+## Review Guidelines
+
+These guidelines apply to automated code review (the Codex review bot). They do not relax any requirement above for code you author.
+
+- Do not raise findings for a missing changelog entry. Changelog files are named `<INTEGRATION>/changelog.d/<PR_NUMBER>.<TYPE>`, so they can only be created after the PR number is assigned; their absence when a PR is first opened is expected rather than a defect. The requirement is already enforced by the `check_changelog` job in `.github/workflows/pr-quick-check.yml`.
+
 ## Pull Requests
 
 - Open PRs in draft mode unless explicitly asked otherwise; mark them ready for review once the work is complete and CI passes.