feat: Cross-Language SDK — Phases 2-4 + gRPC debt fix + dogfooding

[bkrabach]

Summary

Single squash of all Cross-Language SDK work (Phases 2-4), gRPC Phase 2 debt resolution, and integration dogfooding. 124 files changed, ~32,800 additions.

Phase 2: TypeScript/Napi-RS Bindings

• bindings/node/ — 4 kernel classes (AmplifierSession, Coordinator, HookRegistry, CancellationToken)
• JsToolBridge for TypeScript module authoring
• 6 enums + 5 typed struct interfaces + .d.ts auto-generation
• 64 Vitest tests across 9 test files
• CI: separate node-tests job with actions/setup-node@v4
• Dependency upgrades: pyo3 0.28.1→0.28.2 (HIGH severity fix), wasmtime 29→42 (8 Dependabot alerts cleared)

gRPC Phase 2 Debt Fix

• 5 proto optional field additions (backward-compatible wire change)
• Full bidirectional conversions: Role, Message (all 7 ContentBlock variants), ChatRequest, ChatResponse, HookResult
• All bridge fixes: GrpcContextBridge (full message fidelity + provider_name), GrpcProviderBridge::complete(), GrpcOrchestratorBridge (session_id routing)
• Session holds Arc<Coordinator> with coordinator_shared() for KernelService
• All 9 KernelService RPCs implemented (was 1 of 9): capabilities, module query, messages, hooks, provider complete, streaming
• Zero TODO(grpc-v2) markers remain in source

Phase 3: WASM Module Loading

• wit/amplifier-modules.wit — WIT interfaces for all 6 module types + kernel-service host imports
• crates/amplifier-guest/ — Rust guest SDK with traits, types, export_*! macros
• 6 WASM bridges: WasmToolBridge, WasmHookBridge, WasmContextBridge, WasmApprovalBridge, WasmProviderBridge, WasmOrchestratorBridge
• Shared WasmEngine with Arc<wasmtime::Engine>
• 6 compiled .wasm test fixtures (echo-tool, deny-hook, memory-context, auto-approve, echo-provider, passthrough-orchestrator)
• Transport dispatch: load_wasm_* for all 6 module types

Phase 4: Cross-Language Module Resolver

• module_resolver.rs (1,036 lines) — auto-detect transport from filesystem path
• Detection pipeline: amplifier.toml → .wasm scan + component metadata → Python package → error
• WASM component metadata parsing for module type detection (self-describing, zero config)
• PyO3 binding: resolve_module() + load_wasm_from_path()
• Napi-RS binding: resolveModule() + loadWasmFromPath()
• loader_dispatch.py WASM/gRPC branches wired to Rust

Dogfooding / Integration

• _session_init.py routes through loader_dispatch.load_module() (backward compat preserved)
• load_and_mount_wasm + PyWasmTool for real coordinator WASM mounting
• Mixed-transport E2E test: native Rust + WASM modules in same session — coordinator is transport-blind
• Examples: python-wasm-session.py, node-wasm-session.ts, calculator-tool WASM module

Design docs (in docs/plans/)

• Phase 2 design + implementation plan
• gRPC debt fix design + implementation plan
• Phase 3 WASM design + implementation plan
• Phase 4 module resolver design + implementation plan
• Dogfooding integration plan

Test Plan

• 396 Rust lib tests (non-WASM) — 0 failures
• 34 WASM + resolver lib tests — 0 failures
• 8 WASM E2E tests (all 6 module types including orchestrator→kernel→tool callback chain)
• 14 module resolver E2E tests
• 2 mixed-transport E2E tests (native + WASM in same session)
• cargo clippy (core + wasm) — 0 warnings
• cargo check --features wasm — builds clean
• CI workflow runs

Notes

• This is a squash of the dev/cross-language-sdk integration branch onto a clean branch from current main
• All WASM work is behind #[cfg(feature = "wasm")] — zero impact when feature is off
• Backward compatible: all existing Python module loading works identically