Allow known breaks in the version compatibility test

The version-compat job fails every pull request once master breaks
compatibility with the latest release on purpose. List those breaks in
scripts/version-compat-breaks.json keyed by the published version they
break against, each with a pr number and reason. Listed messages warn
instead of failing, connect skips the cluster test, entries for other
versions are ignored, and a listed message that did not change fails.

Add the two src changes from #1129 against 2.0.3 so master passes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/contributing.md

@@ -18,6 +18,7 @@ Read our [past decisions](/docs/decisions.md) for compatibility policies and des
     - [Checking your code for errors](#checking-your-code-for-errors)
     - [Cleaning generated and runtime files](#cleaning-generated-and-runtime-files)
     - [Submitting a Pull Request](#submitting-a-pull-request)
+    - [Breaking Compatibility with the Last Release](#breaking-compatibility-with-the-last-release)
     - [Editing your Feature Branch](#editing-your-feature-branch)
     - [Resolving Merge Conflicts](#resolving-merge-conflicts)
     - [Updating Your GitHub Fork](#updating-your-github-fork)
@@ -250,6 +251,30 @@ If there are more changes you want to have merged or mistakes you need to fix yo
 Pull request descriptions should contain a `### Changelog` section with additions for the changelog contained inside a code block, see the [CHANGELOG.md](/CHANGELOG.md) file for the formatting of changelog entries and possible sections to use.
 If there are no changelog entries to add, remove the code block and start the changelog section with the text `None.`, followed by an optional reason for why it is not is needed.
 
+### Breaking Compatibility with the Last Release
+
+The version-compat job in CI runs the local controller with the latest published host, and the published controller with the local host.
+It fails if a link message changed its src, dst, data or response schema since that release.
+If the break is intended, add an entry for the published version to [scripts/version-compat-breaks.json](../scripts/version-compat-breaks.json) in the same pull request:
+
+```json
+{
+	"2.0.3": {
+		"messages": {
+			"request FactorioVersionsRequest": { "pr": 1129, "reason": "Why it breaks and what stops working." }
+		},
+		"connect": { "pr": 1234, "reason": "Why a host cannot connect at all." }
+	}
+}
+```
+
+Listed messages are reported as warnings with the reason instead of failing the job.
+Only add `connect` when the published and local versions cannot connect at all, it skips starting the cluster.
+Listing a message that did not change fails the job.
+Entries only apply while their version is the latest release, after the next release they are ignored and can be removed.
+Describe the break in the Breaking Changes section of the changelog.
+
+
 ### Editing your Feature Branch
 
 Until your feature branch is merged you can edit it as you see fit by using the rebase tool.