generated: '2026-09-19'
method: searched
source: >-
  Observed behaviour of https://mcp.hakuto-0209.com/mcp and https://mcp.hakuto-0209.com/a2a/v1 (live probes
  2026-09-19), the agent card, the provider quickstart at https://mcp.hakuto-0209.com/ and the data policy
  at https://mcp.hakuto-0209.com/terms. b612 exposes MCP and A2A only — there is no REST/OpenAPI surface,
  so the REST-shaped sections (pagination, expansion, versioning header) are recorded as not applicable
  rather than derived.
description: >-
  Cross-cutting runtime semantics of the b612 agent surfaces: how an agent authenticates, what the
  request/response shapes are on each protocol, how errors come back, what the rate-limit and body-size
  signals are, and — the point that matters for an agent — that the entire surface is read-only reference
  lookup, so idempotency, reversibility and dry-run are not applicable rather than absent.

surfaces:
  mcp:
    endpoint: https://mcp.hakuto-0209.com/mcp
    style: 'MCP Streamable HTTP, JSON-RPC 2.0 over POST; responses as text/event-stream (event: message / data: <json>)'
    protocol_version: '2025-06-18'
    required_headers: ['Content-Type: application/json', 'Accept: application/json, text/event-stream', 'x-b612-key: <license key> (keyless for principles/rules)']
    get_behaviour: '406 application/json — {"jsonrpc":"2.0","error":{"code":-32000,"message":"Not Acceptable: Client must accept text/event-stream"},"id":null}'
  a2a:
    endpoint: https://mcp.hakuto-0209.com/a2a/v1
    style: A2A 0.3 JSON-RPC 2.0 over POST
    required_headers: ['Content-Type: application/json', 'x-b612-key: <license key>']
    get_behaviour: 401 unauthenticated (JSON envelope)

authentication:
  scheme: API key in the x-b612-key header (b612 license key)
  keyless_tier: principles and rules (card); confirmed over MCP for b612_principles
  detail: authentication/hakuto-0209-com-authentication.yml

surface_mutability:
  read_only: true
  basis: >-
    All ten MCP tools return reference text and declare execution.taskSupport "forbidden"; the server's
    initialize instructions state it has no input for source code. The six A2A skills return checklists,
    presets, patterns and rules; scan-code accepts source text but the data policy states it is analysed in
    memory and discarded — nothing is created, changed or persisted on the provider side by any call.
    b612_notes READS a per-licence memo store that is written through the provider's LINE account, not
    through this surface.

idempotency:
  coverage: na
  supported: null
  mechanism: null
  applies_to: none — no mutating operation exists on either protocol
  note: >-
    Every call is a safe read; repeating it yields the same reference content. No Idempotency-Key header is
    documented and none is needed. Recorded as na so the read-only surface leaves the denominator rather
    than scoring zero.

reversibility:
  coverage: na
  write_surfaces: []
  note: >-
    No write surface exists, so there is nothing to cancel, refund, void or restore. The only side effects
    the provider documents are its own usage counters per licence hash (data policy §8), which are not
    caller-reversible and not exposed through the API.

dry_run_mode:
  coverage: na
  note: The keyless tier (principles, rules over MCP at 20 req/min per IP) lets an agent exercise the protocol without a licence, but that is a free read tier, not a dry-run of a mutation.

pagination:
  style: none
  note: >-
    No list endpoints. b612_patterns bounds its own output instead — heading index by default, `query` to
    return matching sections, `full` + `max_chars` (default 20000) for the whole text, with dropped section
    names stated when the cap truncates.

field_expansion: {supported: false}
metadata: {supported: false}

request_id_tracing:
  header: null
  note: No request-id header is documented or returned; Vercel's x-vercel-id edge header is present on every response but is an infrastructure trace, not an API contract.

versioning:
  scheme: semver on the server/card (0.1.0); A2A protocolVersion 0.3 with supportedInterfaces[] also declaring 1.0; MCP protocol negotiated at initialize (2025-06-18)
  header: null
  detail: lifecycle/hakuto-0209-com-lifecycle.yml

error_envelope:
  a2a_http_layer: '{"error":{"code":"<slug>","message":"<ja>","hint":"<ja>"}} — e.g. code "unauthenticated" with HTTP 401'
  mcp: 'JSON-RPC 2.0 error object {"code":-32601,"message":"Method not found"} inside a 200 text/event-stream'
  format: custom (not RFC 9457)
  detail: errors/hakuto-0209-com-problem-types.yml

rate_limit_signaling:
  documented_limits: '20 requests/min per IP on the keyless skills (agent card); all requests rate limited per IP (data policy)'
  response_headers: none observed (no RateLimit-*, X-RateLimit-* or Retry-After on the probed responses)
  exhaustion_status: not documented
  body_limit: 4 MB per request (data policy §5)
  detail: rate-limits/hakuto-0209-com-rate-limits.yml

localization:
  note: Tool titles, descriptions, instructions and error messages are Japanese with English mirrors in the agent card; an agent should expect Japanese text in every payload.