[improve][misc] Add AGENTS.md and split build/contributor/coding/architecture/security docs

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,18 +1,26 @@
 <!--
 ### Contribution Checklist
-
-  - PR title format should be *[type][component] summary*. For details, see *[Guideline - Pulsar PR Naming Convention](https://pulsar.apache.org/contribute/develop-semantic-title/)*. 
+
+  - PR title format should be *[type][component] summary*. The valid `[type]` and `[component]`/scope
+    prefixes are enforced by CI (see `.github/workflows/ci-semantic-pull-request.yml`); for details,
+    see *[Guideline - Pulsar PR Naming Convention](https://pulsar.apache.org/contribute/develop-semantic-title/)*.
 
   - Fill out the template below to describe the changes contributed by the pull request. That will give reviewers the context they need to do the review.
-
+
+  - The **Motivation** and **Modifications** sections are required: explain *why* (the problem/context)
+    and *what/how* (the change). A title alone, or a description that only restates the title, is not enough.
+
   - Each pull request should address only one issue, not mix up code from multiple issues.
-  
+
   - Each commit in the pull request has a meaningful commit message
 
+  - For the local build/test/PR workflow see `CONTRIBUTING.md`, and for coding conventions see
+    `CODING.md`. If you use an AI coding assistant, see `AGENTS.md`.
+
   - Once all items of the checklist are addressed, remove the above text and this checklist, leaving only the filled out template below.
 -->
 
-<!-- Either this PR fixes an issue, -->
+<!-- Either this PR fixes/closes an issue — use "Fixes #xyz" or, equivalently, "Closes #xyz", -->
 
 Fixes #xyz
 

.github/copilot-instructions.md

@@ -0,0 +1 @@
+../AGENTS.md

.github/instructions/gradle-build.instructions.md

@@ -0,0 +1,10 @@
+---
+description: Conventions for changing Apache Pulsar's Gradle build (build scripts, version catalog, convention plugins).
+applyTo: "**/*.gradle.kts,**/gradle.properties,gradle/libs.versions.toml,build-logic/**"
+---
+
+# Gradle build changes
+
+These files configure Apache Pulsar's **Gradle** build. Follow the guidance in
+[`ARCHITECTURE.md` → Changing the build](../../ARCHITECTURE.md#changing-the-build) (and the
+surrounding *Build infrastructure* section) when editing or reviewing a build file.

.github/instructions/java-coding.instructions.md

@@ -0,0 +1,10 @@
+---
+description: Coding conventions for Apache Pulsar Java source and test code.
+applyTo: "**/*.java"
+---
+
+# Java code changes
+
+Apache Pulsar is performance-critical, asynchronous, and concurrency-sensitive. The full reference is
+[`CODING.md`](../../CODING.md) (with [`CONTRIBUTING.md`](../../CONTRIBUTING.md) for running tests) —
+follow it when editing or reviewing Java code.