[P0] arch-guard: ban mutable EventMeshFrame and unbounded attribute maps

[qqeasonchen]

Tracking sub-issue of #5354. Part of the production-HA acceptance plan (Phase 0, P0).

What this rule does

• Ban setter-style methods on EventMeshFrame (no public setAttribute, setPayload, setHeader).
• Ban exposure of mutable LinkedHashMap from getAttributes() / getHeaders().
• Ban EventMeshFrame with more than 64 attributes (the limit to be defined in [P0] harden EventMeshFrame: FrameLimits, immutability, fuzz/boundary tests #5361).
• Ban EventMeshFrame.encode(...) being called from any class other than the codec + the wire package.

Why P0

EventMeshFrame is the single internal data structure (issue #5299 made it the only wire format). If a frame can be mutated after publish, two concurrent dispatchers can race on the same instance. The current EventMeshFrame exposes Map<String, byte[]> getters that return the internal map directly, which the dispatcher can mutate. #5352 calls this out as a hardening target.

Acceptance criteria

• ruleEventMeshFrameImmutable and ruleEventMeshFrameMaxAttributes exist in ArchitectureRules.java.
• Matching *_check tests in ArchitectureRulesTest.java exercise:
  • EventMeshFrame has no public setters,
  • the maps returned by getters are unmodifiable,
  • the codec guards the 64-attribute cap (introduced in [P0] harden EventMeshFrame: FrameLimits, immutability, fuzz/boundary tests #5361) and the rule asserts on the constant.
• ./gradlew :eventmesh-architecture-guard:test is green.

Verification

./gradlew :eventmesh-architecture-guard:test --tests "*ArchitectureRulesTest*"

Depends on / blocks

• Depends on: nothing.
• Blocks: [P0] harden EventMeshFrame: FrameLimits, immutability, fuzz/boundary tests #5361 (the implementation work that adds bounds and the immutable API).

References

• eventmesh-common/src/main/java/org/apache/eventmesh/common/wire/EventMeshFrame.java
• eventmesh-common/src/main/java/org/apache/eventmesh/common/wire/EventMeshFrameCodec.java
• eventmesh-architecture-guard/.../ArchitectureRules.java

Part of the production-HA topology in #5354. See also #5352 and #5353.