chore: add the empty changeset this PR needs

Check Changeset requires one on every PR; an empty-frontmatter changeset is the
sanctioned form for a change that releases nothing, and the gate's own error
message says so.

Second time this session — #4009 was a comment-only PR that failed the same way.
I fixed that one and did not draw the rule, which is that "this releases nothing"
is a reason to write an EMPTY changeset, not a reason to skip the file.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CYbS3kS8xzsHNXFTzp4e2z

Author: claude

.changeset/dispatcher-envelope-shared-predicate.md

@@ -0,0 +1,17 @@
+---
+---
+
+`domain-handler-registry.test.ts` now uses `envelopeViolations` instead of its own
+copy of the rule. Deliberately empty frontmatter: test-only, this releases nothing.
+
+That test hand-rolled "no key beside the envelope's own may hold the payload" for
+#4038. #4090 promoted the rule into the spec so it would stop having two
+definitions; leaving the local copy would have recreated the exact failure this
+line has been closing — one rule, two places, only one updated next time.
+
+The two were also not equivalent. The local set allowed any body whose top-level
+keys were `success` / `data` / `meta`, so it passed a success body with no `data`
+at all and one carrying an `error` beside `success: true`. The shared predicate
+rejects both, which makes this a strict tightening rather than a refactor:
+injecting `{ success: true }` into the producer now fails the suite, and used to
+pass it.