Backward-compat replay gate for the A2A JSON-RPC protocol surface.
Every PR that touches normalizeA2APayload OR bumps the a-2-a-sdk
version pin runs every shape in testdata/a2a_corpus/ through the
current code and asserts:
valid/ — every shape MUST parse without error and produce a
canonical v0.3 payload (params.message.parts list).
invalid/ — every shape MUST be rejected with the documented
status code and error substring.
What this prevents
The 2026-04-29 v0.2 → v0.3 silent-drop bug (PR #2349) shipped
because the SDK bump PR didn't replay v0.2-shaped inputs against
the new code; the shape-mismatch surfaced only in production when
the receiver's Pydantic validator silently rejected inbound
messages.
This gate would have caught it pre-merge. Hand-verified: reverting
the v0.2 string→parts shim in normalizeA2APayload fails 3 of the
v0.2 corpus entries with the exact rejection class the production
bug exhibited.
Corpus contents (11 entries)
valid/ (10):
v0_2_string_content — basic v0.2 (the broken case)
v0_2_string_content_no_message_id — v0.2 + auto-fill messageId
v0_2_list_content — v0.2 with content as Part list
v0_3_parts_text_only — canonical v0.3
v0_3_parts_multi_text — multi-Part list
v0_3_parts_with_file — multimodal (text + file)
v0_3_parts_with_context — contextId for multi-turn
v0_3_streaming_method — message/stream variant
v0_3_unicode_text — emoji + multi-script
v0_3_long_text — 10KB text Part
no_jsonrpc_envelope — bare params/method without
outer envelope (legacy senders)
invalid/ (3):
no_content_or_parts — message has neither field
content_is_integer — wrong type for v0.2 content
content_is_bool — wrong type, separate from int
so the failure msg identifies
which type-class regressed
Plus 4 inline malformed-JSON cases (truncated, not-JSON, empty,
whitespace) that can't be expressed as JSON corpus entries.
Coverage tests
The gate has 4 test functions:
1. TestA2ACorpus_ValidShapesParse — replay valid/ corpus,
assert no error + canonical v0.3 output (parts list non-empty,
messageId non-empty, content field deleted).
2. TestA2ACorpus_InvalidShapesRejected — replay invalid/ corpus,
assert rejection matches recorded status + error substring.
3. TestA2ACorpus_MalformedJSONRejected — inline cases for
non-parseable bodies.
4. TestA2ACorpus_HasMinimumCoverage — at least one v0.2 +
one v0.3 entry exists (loses neither side of the bridge).
5. TestA2ACorpus_EveryEntryHasMetadata — _comment/_added/_source
on every entry per the README policy; _expect_error and
_expect_status on invalid entries.
Documentation
testdata/a2a_corpus/README.md describes the corpus contract:
- When to add entries (new SDK shape, new production-observed
shape).
- When NOT to add (test scaffolding, hypothetical futures).
- Removal policy (breaking change, deprecation window required).
Verification
- All 24 corpus subtests pass on current main.
- Hand-test: revert the v0.2 compat shim → 3 v0.2 entries fail
the gate with the exact rejection class the production bug
exhibited. Confirmed.
- Whole-module go test ./... green.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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