docs: check org membership for public API exemption, point agents to sdk-specs

AGENTS.md

@@ -2,5 +2,10 @@
 
 - Read and follow [CONTRIBUTING.md](./CONTRIBUTING.md) before contributing to the SDK. It covers local development, running the example, CI-aligned checks, and the Rails package.
 - Read and follow [RELEASING.md](./RELEASING.md) when adding changesets or working on publishing.
-- Public API changes (a diff in `public_api_snapshot.txt`): if the author is a PostHog maintainer (git email ends in `@posthog.com`), the PR is the discussion, so don't open or suggest an issue. Otherwise, follow "Public API changes" in [CONTRIBUTING.md](./CONTRIBUTING.md): if there's no agreed issue, stop and tell the user. If a PR already exists, add a public-API note to its description and draft an issue body for the user to post. Never open an issue yourself. For SDK design guidance, read https://posthog.com/handbook/engineering/sdks/guidelines.md.
+- Public API changes: follow "Public API changes" in [CONTRIBUTING.md](./CONTRIBUTING.md). As an agent, also:
+    - When reviewing or fixing someone else's PR, don't ask for or open an issue, but note in the review when an external contributor's PR changes public API without one.
+    - The author is a PostHog maintainer when the PR's `author_association` is `MEMBER` or `OWNER` (`gh api repos/PostHog/posthog-ruby/pulls/<number> --jq .author_association`) or, before a PR exists, when `gh api orgs/PostHog/members/$(gh api user --jq .login)` succeeds. If the check fails or can't run, treat the author as an external contributor.
+    - A published [sdk-spec](https://github.com/PostHog/sdk-specs) that defines the API counts as the agreement, so no issue is needed.
+    - For an external contributor with no agreed issue and no spec, stop before implementing and draft the issue body for the user to post. Open it only if they ask.
+- Before implementing or reviewing SDK behavior, check [PostHog/sdk-specs](https://github.com/PostHog/sdk-specs) for a spec covering it (its README lists every capability). If one exists, use it as the cross-SDK contract for the behavior the PR changes, and call out any divergence in that behavior in the PR description. Don't fix or flag discrepancies between the spec and code the PR doesn't touch. If none exists, carry on.
 - Keep shared development guidance in `CONTRIBUTING.md` and release guidance in `RELEASING.md` rather than duplicating it here.

CONTRIBUTING.md

@@ -49,9 +49,10 @@ bundle exec rake public_api:generate
 
 Public API is hard to change once it ships, so agree on it before writing the implementation. Our [SDK guidelines](https://posthog.com/handbook/engineering/sdks/guidelines) explain how we design it.
 
-This section is for external contributors. PostHog Client Libraries maintainers agree on API shape in the PR itself, so they don't need a separate issue.
+This section is for external contributors. PostHog maintainers (members of the PostHog GitHub org) agree on API shape in the PR itself, so they don't need a separate issue.
 
 - **Before you start:** if you need something the SDK doesn't support and it would add or change a public option, method, or type, open an issue describing your use case. Wait for a maintainer to agree on the API shape there before you implement it. Context is more useful to us than code at this stage.
+- **Already specified?** If a published [sdk-spec](https://github.com/PostHog/sdk-specs) defines the API, that's the agreement, so you don't need an issue.
 - **Already have a PR open?** Don't stop or rewrite it. Call out the public API change at the top of the PR description, and link or open an issue so we can discuss the shape there.
 - Check first whether an existing option or hook, such as `before_send`, already covers the use case. We avoid offering two ways to do the same thing.
 - If a reviewer suggests a different API on your PR, confirm it with them before re-implementing. Treat it as a question, not an instruction.