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[ajit-zer07]

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PR Description

Title: Sync runtime with upstream RFC spec — full proto realignment, new RPCs, and decision mode rewrite

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Summary

Brings the MACP runtime into exact compliance with the upstream RFC specification. This is a comprehensive update spanning proto schema restructuring, error code
alignment, new RPC implementations, and a complete decision mode rewrite.

• Replaced single macp.proto with canonical 3-file split structure (envelope.proto, core.proto, decision.proto)
• Implemented 5 new RPCs: Initialize, ListModes, GetManifest, ListRoots, StreamSession
• Rewrote decision mode from toy (payload == "resolve") to full RFC lifecycle (Proposal → Evaluation → Objection → Vote → Commitment)
• Aligned all error codes with the spec's error registry
• Updated all client binaries to exercise new RPCs and message types
• 122 tests passing (92 lib + 30 server), clean clippy, clean fmt

Details

Phase 1: Proto Schema Realignment

• Deleted proto/macp.proto (single-file layout)
• Added proto/macp/v1/envelope.proto — Envelope, Ack, MACPError (with bytes details), SessionState
• Added proto/macp/v1/core.proto — MACPRuntimeService with 10 RPCs, all wrapper request/response types, SessionStartPayload (8 fields), SessionMetadata,
  capability messages (ClientInfo, RuntimeInfo, Capabilities), AgentManifest, ModeDescriptor
• Added proto/macp/modes/decision/v1/decision.proto — ProposalPayload, EvaluationPayload, ObjectionPayload, VotePayload
• Updated build.rs to compile all three protos
• Updated src/lib.rs with pb and decision_pb modules

Phase 2: Server + Runtime Adaptation

• Renamed service impl from MacpService → MacpRuntimeService
• send_message(Envelope) → Ack → send(SendRequest) → SendResponse
• get_session(SessionQuery) → SessionMetadata → get_session(GetSessionRequest) → GetSessionResponse
• cancel_session returns CancelSessionResponse wrapping Ack
• SessionMetadata: removed resolution, mode_state, participants; added mode_version, configuration_version, policy_version
• MACPError.details: changed from map<string,string> to bytes
• SessionStartPayload: now 8 fields (intent, participants, mode_version, configuration_version, policy_version, ttl_ms, context, roots)
• Session struct extended with intent, mode_version, configuration_version, policy_version

Phase 3: Error Code Alignment

Aligned MacpError variants with the spec's registries/error-codes.md:

┌────────────────────────┬──────────────────────────────┐
│ Variant │ Wire Code │
├────────────────────────┼──────────────────────────────┤
│ InvalidMacpVersion │ UNSUPPORTED_PROTOCOL_VERSION │
├────────────────────────┼──────────────────────────────┤
│ InvalidEnvelope │ INVALID_ENVELOPE │
├────────────────────────┼──────────────────────────────┤
│ DuplicateSession │ INVALID_ENVELOPE │
├────────────────────────┼──────────────────────────────┤
│ UnknownSession │ SESSION_NOT_FOUND │
├────────────────────────┼──────────────────────────────┤
│ SessionNotOpen │ SESSION_NOT_OPEN │
├────────────────────────┼──────────────────────────────┤
│ TtlExpired │ SESSION_NOT_OPEN │
├────────────────────────┼──────────────────────────────┤
│ InvalidTtl │ INVALID_ENVELOPE │
├────────────────────────┼──────────────────────────────┤
│ UnknownMode │ MODE_NOT_SUPPORTED │
├────────────────────────┼──────────────────────────────┤
│ InvalidModeState │ INVALID_ENVELOPE │
├────────────────────────┼──────────────────────────────┤
│ InvalidPayload │ INVALID_ENVELOPE │
├────────────────────────┼──────────────────────────────┤
│ Forbidden │ FORBIDDEN │
├────────────────────────┼──────────────────────────────┤
│ Unauthenticated (new) │ UNAUTHENTICATED │
├────────────────────────┼──────────────────────────────┤
│ DuplicateMessage (new) │ DUPLICATE_MESSAGE │
├────────────────────────┼──────────────────────────────┤
│ PayloadTooLarge (new) │ PAYLOAD_TOO_LARGE │
├────────────────────────┼──────────────────────────────┤
│ RateLimited (new) │ RATE_LIMITED │
└────────────────────────┴──────────────────────────────┘

Phase 4: Initialize RPC

• Protocol version negotiation: intersects client's supported versions with ["1.0"]
• Returns RuntimeInfo, Capabilities (sessions, cancellation, mode_registry, etc.), and supported modes
• Rejects unsupported versions with UNSUPPORTED_PROTOCOL_VERSION

Phase 5: Discovery RPCs

• ListModes — returns mode descriptors for decision and multi_round with metadata (determinism class, participant model, message types)
• GetManifest — returns runtime's AgentManifest with supported modes and content types
• ListRoots — returns empty root list
• WatchModeRegistry / WatchRoots — return UNIMPLEMENTED (streaming watchers deferred)

Phase 6: Decision Mode Rewrite

Full RFC-compliant lifecycle replacing the toy implementation:

• State machine: Proposal → Evaluation/Objection → Vote → Commitment
• Typed payloads: ProposalPayload, EvaluationPayload, ObjectionPayload, VotePayload, CommitmentPayload
• Validation: proposal_id references checked, phase ordering enforced, vote deduplication (last vote wins per sender)
• Terminal: Commitment message resolves the session
• Backward compat: Legacy payload == b"resolve" on Message type still works

Phase 7: StreamSession

• Bidirectional streaming using async-stream crate
• Processes each inbound StreamSessionRequest envelope through runtime.process()
• Returns accepted envelopes and error responses on the stream

Phase 8: Client Binaries

• client.rs — Full decision lifecycle demo: Initialize → ListModes → SessionStart → Proposal → Evaluation → Vote → Commitment → GetSession
• fuzz_client.rs — Comprehensive error path testing: Initialize (good + bad version), all error codes, new RPCs (ListModes, GetManifest, ListRoots), multi-round
  convergence, CancelSession, participant validation
• multi_round_client.rs — Updated for new wrapper types and SessionStartPayload fields

Stats

• 24 files changed, +3,772 / -390 lines
• 122 tests passing (92 lib + 30 server)
• 0 clippy warnings

Test plan

• cargo build — compiles cleanly with split proto structure
• cargo test — all 122 tests pass
• cargo clippy — no warnings
• cargo run — server starts as MACPRuntimeService on 127.0.0.1:50051
• cargo run --bin client — full decision mode lifecycle demo
• cargo run --bin multi_round_client — multi-round convergence demo
• cargo run --bin fuzz_client — all error paths with spec-compliant codes
• Verify error codes match registries/error-codes.md exactly
• Verify proto messages match canonical spec protos verbatim