chore: clarify the compatibility and static-analysis rules for agent reviewers

.github/copilot-instructions.md

@@ -23,8 +23,15 @@ Prioritize actionable findings involving:
 ## Review behavior
 
 - Determine the PR base branch and apply the compatibility policy from
-  `AGENTS.md`. If the base branch cannot be determined, assume `develop`
-  and state that assumption.
+  `AGENTS.md`. When it is not visible, read it from the title prefix and
+  the labels as `AGENTS.md` describes, and otherwise assume `develop` and
+  state that assumption.
+- Before reporting a compatibility break, confirm the symbol exists in the
+  latest tagged release. A symbol introduced on the base branch since that
+  release is unreleased and may change freely, as `AGENTS.md` describes.
+- Do not report a PHPStan suppression or baseline entry covered by the
+  exceptions in `AGENTS.md`, or a missing reset of state that
+  `CIUnitTestCase::tearDown()` already restores.
 - Do not report formatting-only issues already enforced by PHP-CS-Fixer.
 - Every finding should identify a concrete failure scenario and the
   affected code.

.github/instructions/tests.instructions.md

@@ -14,6 +14,8 @@ applyTo: "tests/**/*.php"
   Avoid testing private implementation details.
 - Restore services, factories, environment variables, superglobals, handlers,
   locale, time-related state, and other global state modified by a test.
+  Check `CIUnitTestCase::tearDown()` first: a test need not repeat the
+  resets it already performs.
 - Tests must not depend on execution order or state left by another test.
 - Do not replace a meaningful assertion with a weaker assertion to make a test
   pass.

AGENTS.md

@@ -19,8 +19,13 @@ existing implementation before introducing a new abstraction or convention.
 ## Target branch and compatibility policy
 
 Compatibility is judged against the pull request's base branch, not the
-contributor's source or feature branch. When the base branch is unknown,
-apply the stricter `develop` policy.
+contributor's source or feature branch. When the base branch is not stated,
+take the cues from the title prefix and the labels. A `feat:` prefix and the
+`enhancement`, `new feature`, `breaking change`, or `4.x` labels point to the
+next minor branch. A `fix:`, `refactor:`, or `docs:` prefix and the `bug` or
+`refactor` labels can go either way, since the next minor branch also takes
+fixes to its own unreleased code, so look at what the change touches. When no
+cue settles it, apply the stricter `develop` policy.
 
 ### Base branch `develop`
 
@@ -50,6 +55,16 @@ complete the documented deprecation lifecycle.
 - Every accepted break needs tests for the new behavior, a minor-version
   changelog entry, and migration instructions in the upgrading guide.
 
+### Unreleased API
+
+A symbol first added on the base branch after its latest tagged release is
+unreleased. Nothing outside the repository can depend on it yet, so changing,
+renaming, or removing it is not a compatibility break: it needs no
+deprecation, no upgrading-guide entry, and no changelog line beyond the one
+describing the final shape. Check the version tags or the changelog of the
+unreleased version before reporting a break on such a symbol. The
+compatibility policy applies to what the latest tagged release ships.
+
 ### All base branches
 
 - Production code must run on PHP 8.2. Do not require a newer PHP version,
@@ -83,7 +98,15 @@ complete the documented deprecation lifecycle.
 - Add PHPDoc only when it contributes information that native types cannot
   express. Do not duplicate a parent or interface docblock.
 - Never suppress a static-analysis error or update a baseline to make a
-  check pass.
+  check pass. The accepted exceptions are:
+  - a false positive, when the usage is judged correct;
+  - a suppression needed to assert a runtime behavior in a test;
+  - a call to a function mocked in `system/Test/Mock/MockCommon.php`, such
+    as `is_cli(false)`, which PHPStan reports as `arguments.count`.
+
+  Regenerate the baseline with `composer phpstan:baseline`, never by editing
+  the `.neon` files, and add a test file that calls `is_cli()` with an
+  argument to the `RemoveExtraParametersRector` skip list in `rector.php`.
 
 ## FrankenPHP Worker Mode