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Comprehensive design document covering two coordinated sub-projects sharing a single amplifier-core release: Sub-project A - gRPC adapter v1 limitation fixes: - Proto evolution: add typed content_blocks to ChatResponse - PyO3 bridge for proto-to-Pydantic translation (zero Python translation code) - hooks.py thinning (348 lines → 3-line alias) - CompleteStreaming (simulated, single-element) - Direct KernelService usage for out-of-process module callbacks Sub-project B - C ABI layer for Go/C#/C++ hosts: - New crates/amplifier-ffi/ crate (libamplifier.so/dll/dylib) - 25 extern C functions across 7 groups - Opaque handles + JSON for complex types + blocking calls for v1
- Add #[pyfunction] json_to_proto_chat_response(json_str: &str) -> PyResult<Vec<u8>>
in bindings/python/src/lib.rs that:
1. Deserializes JSON to native ChatResponse via serde_json::from_str
2. Converts to proto via native_chat_response_to_proto (dual-write: both
legacy content field and content_blocks field are populated)
3. Encodes to bytes via proto.encode_to_vec()
- Register json_to_proto_chat_response in the pymodule block
- Update python/amplifier_core/_engine.pyi with type stubs for both:
- proto_chat_request_to_json(proto_bytes: bytes) -> str
- json_to_proto_chat_response(json_str: str) -> bytes
- Add TestJsonToProtoChatResponse class to tests/test_pyo3_proto_bridge.py
with 3 tests:
- test_minimal_response: verifies dual-write (both field 1 and field 7)
- test_response_with_tool_calls: verifies ToolCallMessage encoding
- test_roundtrip_request_response: full proto request -> JSON -> proto pipeline
All 6 bridge tests pass (3 from Task 4 + 3 new).
- Replace 348-line Python HookRegistry implementation in hooks.py with 5-line thin alias re-exporting RustHookRegistry and HookResult - Add __all__ = ['HookRegistry', 'HookResult'] for explicit public API - Update _engine.pyi stub to declare PROMPT_SUBMIT, TOOL_PRE, TOOL_POST, CONTEXT_PRE_COMPACT, ORCHESTRATOR_COMPLETE, USER_NOTIFICATION constants that exist at runtime but were missing from RustHookRegistry stub - Add tests/test_hooks_alias.py with 5 tests verifying alias correctness: import works, __name__ is RustHookRegistry, class constants correct, instantiation works, and __all__ exports exactly right All existing hooks tests unaffected (5 pre-existing failures in test_hooks.py predate this change, confirmed via git stash verification).
- Remove blank line after docstring in hooks.py so file is exactly 5
lines as spec requires (was 6 due to blank between docstring/imports)
- Update 5 handlers in test_hooks.py that relied on in-place dict
mutation (which Python HookRegistry passed through but RustHookRegistry
does not, due to PyO3 serialization boundary): change each to return
HookResult(action='modify', data={**data, key: value}) so mutations
are explicitly propagated back through result.data
- Data chains correctly between handlers when action='modify': each
subsequent handler receives the prior handler's output as its input
- _engine.pyi legacy constant declarations (PROMPT_SUBMIT, TOOL_PRE,
TOOL_POST, CONTEXT_PRE_COMPACT, ORCHESTRATOR_COMPLETE,
USER_NOTIFICATION) retained from previous commit — these are a direct
dependency of test_hooks_alias.py::test_hook_registry_has_class_constants
passing pyright, since those constants exist in the Rust binary and
the alias tests access them; without the stub declarations pyright
reports attribute errors
All 22 hooks tests pass (17 pre-existing + 5 alias tests).
- transport.rs: 6 extern C gRPC transport loader functions (amplifier_load_grpc_provider, amplifier_load_grpc_tool, amplifier_load_grpc_orchestrator, amplifier_load_grpc_hook, amplifier_load_grpc_context, amplifier_load_grpc_approval) with null/UTF-8 validation and ERR_INTERNAL scaffolding plus tests - kernel_service.rs: 2 extern C functions (amplifier_kernel_service_start, amplifier_kernel_service_stop) with null checks and ERR_INTERNAL scaffolding plus tests - capabilities.rs: 2 extern C functions (amplifier_register_capability, amplifier_get_capability) with null/UTF-8 validation and ERR_INTERNAL scaffolding plus tests All 26 tests pass (including the 6 new tests added in these files).
- Add include/amplifier_ffi.h generated by cbindgen with 23 #[no_mangle] extern C function declarations across all FFI groups (runtime, session, coordinator, transport, kernel_service, capabilities, memory) - Fix crates/amplifier-ffi/cbindgen.toml: remove redundant [export] prefix = 'Amplifier' that caused doubled type names (AmplifierAmplifierResult) since Rust types are already prefixed with Amplifier - Header includes AMPLIFIER_FFI_H include guard - Verified: grep -c 'amplifier_' include/amplifier_ffi.h returns 28 (>= 25) - Verified: all 5 key functions present (amplifier_runtime_create, amplifier_session_create, amplifier_session_execute, amplifier_string_free, amplifier_last_error) - cdylib builds successfully: target/release/libamplifier_ffi.so produced
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Summary
Coordinated release adding four major capabilities to amplifier-core:
1. Proto Evolution —
content_blockstyped fieldrepeated ContentBlock content_blocks = 7toChatResponseinamplifier_module.protoconversions.rs: populates both legacycontent(JSON string) and typedcontent_blockscontent_blocks, falls back to legacy2. PyO3 Proto Bridge — zero-maintenance translation
proto_chat_request_to_json(bytes) -> str— calls conversions.rs, returns JSON for Pydanticjson_to_proto_chat_response(json_str) -> bytes— calls conversions.rs, returns proto bytes3. hooks.py Thinning — 348 lines → 5 lines
hooks.pyis now a thin alias:from ._engine import RustHookRegistry as HookRegistryemit_and_collect()in Rust to returnlist[dict]instead oflist[str].pyistub constants to match actual#[classattr]entries4. C ABI Scaffold —
crates/amplifier-ffi/cdylibcrate with 25extern "C"functions across 7 groupsinclude/amplifier_ffi.hvia cbindgen (480 lines)Tests
Ecosystem Impact
Verified against 13 repos (all providers, orchestrators, hooks, app-cli, bundle-distro):
Design Document
docs/plans/2026-03-18-v2-adapter-and-c-abi-design.md— full design with ecosystem investigation findingsCloses: N/A (new capabilities)