chore: Limit open, non draft PRs to 3 for users without write access

.asf.yaml

@@ -82,6 +82,14 @@ github:
     # enable updating head branches of pull requests
     allow_update_branch: true
     allow_auto_merge: true
+    # Limit open pull requests per user without write access.
+    #
+    # The number of open PRs far exceeds our review capacity. We limit non
+    # committers to 3 open, non draft PRs, to help us curate and focus on a
+    # smaller number of higher quality PRs.
+    creation_cap:
+      enabled: true
+      max_open_pull_requests: 3
 
 # publishes the content of the `asf-site` branch to
 # https://arrow.apache.org/rust/

CONTRIBUTING.md

@@ -62,6 +62,17 @@ ideas with the community to get feedback on implementation.
 
 [good-first-issue]: https://github.com/apache/arrow-rs/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22
 
+## Creating Pull Requests
+
+With coding agents, the number of open PRs now far exceeds our review capacity.
+To encourage submitters to curate and prepare a small number of high quality PRs,
+and to help reviewers focus on them, users without write access are limited to
+**3 open, non-draft PRs** at a time.
+
+When possible, we recommend splitting your contributions into multiple smaller
+focused PRs rather than large PRs, because they are more likely to be reviewed
+quickly and are easier to understand and review.
+
 ## Developer's guide to Arrow Rust
 
 ### Setting Up Your Build Environment