feat: add proto2pydantic Pydantic model generation pipeline

.github/actions/spelling/allow.txt

@@ -107,6 +107,7 @@ proto
 protobuf
 Protobuf
 protoc
+protocgen
 pydantic
 pyi
 pypistats

.jscpd.json

@@ -6,7 +6,8 @@
     "**/src/a2a/grpc/**",
     "**/src/a2a/compat/**",
     "**/.nox/**",
-    "**/.venv/**"
+    "**/.venv/**",
+    "**/src/a2a/types/*_pydantic.py"
   ],
   "threshold": 3,
   "reporters": ["html", "markdown"]

buf.gen.yaml

@@ -29,3 +29,10 @@ plugins:
   # Generates *_pb2.pyi files.
   - remote: buf.build/protocolbuffers/pyi
     out: src/a2a/types
+  # Generate Pydantic models with ProtoJSON compatibility
+  - local: protoc-gen-proto2pydantic
+    out: src/a2a/types
+    opt:
+      - preset=a2a
+      - base_class=a2a._base.A2ABaseModel
+      - output_file=a2a_pydantic.py

scripts/gen_proto.sh

@@ -1,9 +1,17 @@
 #!/bin/bash
 set -e
 
+# Install proto2pydantic plugin for Pydantic model generation
+echo "Installing protoc-gen-proto2pydantic@v0.5.2..."
+go install github.com/protocgen/proto2pydantic@v0.5.2
+
 # Run buf generate to regenerate protobuf code and OpenAPI spec
 npx --yes @bufbuild/buf generate
 
+# Format generated Pydantic models (line-length wrapping for long Field() descriptions)
+echo "Formatting generated Pydantic models..."
+ruff format src/a2a/types/a2a_pydantic.py
+
 # The OpenAPI generator produces a file named like 'a2a.swagger.json' or similar.
 # We need it to be 'a2a.json' for the A2A SDK.
 # Find the generated json file in the output directory