docs: document PR ancestry and description quality gates

Author: Wibias

AGENTS.md

@@ -61,6 +61,11 @@ integration line to another, or rebasing a stale branch onto the current head,
 is ordinary maintenance rather than noise — open it as a normal pull request
 and name the source commits in the description.
 
+The required **`enforce-target`** CI check rejects pull requests whose head
+ancestry sits on the **`main`** tip while far behind **`dev`** or **`dev2-go`**,
+and rejects empty, thin, or malformed descriptions; authors with repository
+push permission skip the ancestry heuristic only.
+
 [`MAINTAINERS.md`](./MAINTAINERS.md) is authoritative for review and merge
 policy (approvals, CI requirements, security review, promotion). This file
 summarizes; it never overrides it.

MAINTAINERS.md

@@ -23,6 +23,10 @@ through GitHub repository settings.
   distinguish scoped Go port work from anything else aimed at `dev2-go`, so
   that boundary is enforced in review: redirect an out-of-scope pull request to
   `dev` rather than treating the automation's silence as approval.
+- The required **`enforce-target`** CI check rejects pull requests whose head
+  ancestry sits on the **`main`** tip while far behind **`dev`** or **`dev2-go`**,
+  and rejects empty, thin, or malformed descriptions; authors with repository
+  push permission skip the ancestry heuristic only.
 - A pull request requires approval from at least one maintainer and successful required CI checks
   before merge.
 - Authors do not approve their own pull requests.

docs-site/src/content/docs/contributing.md

@@ -103,6 +103,13 @@ integration line to another, or rebasing a stale branch onto the current head,
 is normal contribution rather than noise — note the source commits in the
 description.
 
+## Pull requests
+
+- Target **`dev`** (or **`dev2-go`** only for scoped Go native-port work). Do not open ordinary feature or fix pull requests against **`main`**.
+- Branch from the current **`dev`** tip, not from **`main`**. The required **`enforce-target`** check rejects heads whose merge base sits on the **`main`** tip while the branch is far behind the pull request base (the failure mode seen in #644).
+- Write a real description: a **Summary** of what changed and why, plus a **Test plan** (or equivalent substance). Empty bodies, placeholder-only text, and descriptions that use escaped `\n` instead of real line breaks fail the check.
+- Workflow changes in this repository use **`pull_request_target`**. Updated enforcement logic applies only after the workflow is promoted to the repository default branch — the same operational caveat documented in #631.
+
 ## Project maintainers
 
 The current maintainers, their responsibilities, and the review and merge policy are documented in