tai/research/cap-protocol/conclusions/scope-and-phasing.md

Tai implements CAP both directions, phased, without gRPC

Metadata

Field	Value
Institute	Molodetz Institute — Research & Retrieval Division
Subject	cap-protocol
Document type	Conclusion Document
Decided	2026-10-18
Decided by	tai (agent), model: Muse Spark, on behalf of retoor
Research method	full read of CAP core + coding profile, quickstart, STATUS, all 5 example manifests; selective first-hand read of A2A spec + proto and 10 ACP pages; grep of reference A2A driver
Confidence	High
Status	Active

Question / problem statement

How does tai support "the literal whole protocol" as both agent (speaking CAP under a startup flag) and orchestrator (driving claude/codex/grok-class CLI agents, auto-answering their questions via research) while staying a single stdlib-only file?

Conclusion

Implement every binding except gRPC, in five phases: (1) events/errors/manifest registry plus --cap-manifest; (2) agent-side --cap-speak stream-json binding with coding artifacts; (3) orchestrator PTY driver on the reference heuristics; (4) stream-json driver plus §10 orchestration (URNs, mediated routing, worktrees, budget); (5) ACP-stdio and A2A drivers, reverse-RPC serving, and the research auto-answerer. gRPC is rejected: stdlib has no HTTP/2 or protobuf, and hand-rolling both for one optional binding fails the boring-technology rule. A bare grpc = true manifest still parses; binding selection falls through to PTY.

Supporting sources

• CAP Core v1: PTY-required/fast-path-optional layering makes full conformance reachable without gRPC; §7/§10/§14.2 are the build tables.
• CAP coding profile: reverse-RPC surface and scope table for the orchestrator side.
• STATUS: PTY heuristics (800ms settle, prompt gate, resubmit bound) and the codex-websocket dead-end warning.
• openclaude manifest: grpc = true carries no address, so the flag alone is undrivable anyway.
• ACP transports + prompt turn: stdio NDJSON JSON-RPC is a few dozen stdlib lines; turn boundary is the prompt response.
• A2A specification: message/stream/cancel/card subset is stdlib-feasible (http.client, SSE parse, http.server for expose).

Alternatives considered and rejected

• Full gRPC via hand-rolled HTTP/2 + protobuf: rejected, thousands of lines of bug surface for an optional binding whose own manifest example omits the server address.
• PTY-only orchestrator (skip all fast-paths): rejected, the reference fidelity tiers show structured paths are strictly more reliable, and stream-json is cheap once PTY exists.
• Separate package for CAP: rejected, the single-file stdlib-only constraint is load-bearing for tai distribution; CAP fits in Cap* classes plus a cap.md mapping doc.

Risks / open questions

• Regex flavor: spec says ERE-only but all examples use (?P<>); tai accepts Python-compatible patterns and rejects only backrefs/lookaround, flagged as a deliberate deviation.
• Reverse RPC over stream-json is unspecified; tai-as-agent offers no fs/terminal mediation on the speak path until the spec defines framing.
• ACP v2 migration and full terminal/fs param shapes still queued for Phase 5 reading.
• Research auto-answerer quality depends on verdict/judge reliability already flagged as unmeasured.

Action taken

Phases tracked as session todos; Phase 1 (events, errors, manifest registry, --cap-manifest, cap.md, tests) implemented same session. Later phases scheduled as follow-up turns.

Revisit when

• The spec leaves draft (breaking changes possible; watch revision field).
• A CAP conformance suite ships (adopt it as the integration gate).
• A2A draft endpoints disappear from the wild (drop the draft spelling).

Changelog

Date	Change
2026-10-18	Conclusion recorded.