hermes-agent/gateway/relay/descriptor.py
Ben 3db49381d6 feat(relay): derive descriptor from PlatformEntry
CapabilityDescriptor.from_platform_entry() projects an existing PlatformEntry
(label, max_message_length, emoji, platform_hint, pii_safe, name) into a
descriptor, proving the descriptor is a projection of existing config rather
than a parallel concept. Runtime-only capabilities (len_unit, draft/edit/
thread/markdown) are caller-supplied. max_message_length==0 ('no limit') maps
to the stream_consumer 4096 default.

Phase 0 complete. Task 0.3 of the gateway-relay plan.
2026-06-17 16:37:45 -07:00

118 lines
5 KiB
Python

"""CapabilityDescriptor — the relay handshake payload. EXPERIMENTAL.
The connector hands a ``CapabilityDescriptor`` to the gateway's ``RelayAdapter``
at handshake time; it tells the adapter which platform it is fronting and which
capabilities to advertise to the ``GatewayStreamConsumer`` (char limit,
draft-streaming, edit/threading support, markdown dialect, length unit). It is
the linchpin of the generalization: one gateway adapter serves Discord,
Telegram, Matrix, Signal, ... without per-platform branching.
EXPERIMENTAL: this schema MAY CHANGE without a deprecation cycle until at least
two real Class-1 platforms have validated it. Evolution during the experimental
phase is additive-only, gated by ``contract_version`` (see
docs/relay-connector-contract.md).
Field origins (most are a wire-serializable projection of ``PlatformEntry`` plus
the per-instance capability methods on ``BasePlatformAdapter``):
- ``max_message_length`` -> ``PlatformEntry.max_message_length`` / adapter
``MAX_MESSAGE_LENGTH`` attribute (read by stream_consumer).
- ``len_unit`` -> selects which ``message_len_fn`` the adapter installs
("chars" = builtin len; "utf16" = Telegram-style UTF-16 code-unit counting).
- ``supports_draft_streaming`` -> adapter ``supports_draft_streaming()`` probe.
- ``supports_edit`` -> whether edit-based streaming is possible (Discord/
Telegram yes; Signal/SMS no -> consumer degrades to one-message-per-segment).
- ``supports_threads`` -> ``create_handoff_thread`` capability flag.
- ``markdown_dialect`` -> presentation hint (e.g. "markdown_v2", "discord").
- ``emoji`` / ``platform_hint`` / ``pii_safe`` -> ``PlatformEntry`` fields of the
same name.
"""
from __future__ import annotations
import json
from dataclasses import asdict, dataclass
# Bump additively (never reinterpret an existing field) during the experimental
# phase; a breaking change requires updating both repos in lockstep.
CONTRACT_VERSION = 1
@dataclass(frozen=True)
class CapabilityDescriptor:
"""Immutable capability descriptor negotiated at relay handshake.
Frozen so a descriptor cannot be mutated after handshake — the adapter
advertises a fixed capability profile for the life of the connection.
"""
contract_version: int
platform: str
label: str
max_message_length: int
supports_draft_streaming: bool
supports_edit: bool
supports_threads: bool
markdown_dialect: str
len_unit: str # "chars" | "utf16"
emoji: str = "\U0001f50c" # 🔌 default (matches PlatformEntry default)
platform_hint: str = ""
pii_safe: bool = False
def to_json(self) -> str:
"""Serialize to a compact, stable JSON string for the handshake frame."""
return json.dumps(asdict(self), sort_keys=True, ensure_ascii=False)
@classmethod
def from_json(cls, data: str) -> "CapabilityDescriptor":
"""Deserialize from a handshake JSON string.
Unknown keys are ignored (forward-compat: a newer connector may send
fields this gateway does not know yet); missing optional keys fall back
to dataclass defaults.
"""
raw = json.loads(data)
known = {f for f in cls.__dataclass_fields__} # type: ignore[attr-defined]
filtered = {k: v for k, v in raw.items() if k in known}
return cls(**filtered)
@classmethod
def from_platform_entry(
cls,
entry,
*,
len_unit: str = "chars",
supports_draft_streaming: bool = False,
supports_edit: bool = True,
supports_threads: bool = False,
markdown_dialect: str = "plain",
) -> "CapabilityDescriptor":
"""Project a ``gateway.platform_registry.PlatformEntry`` into a descriptor.
Demonstrates the descriptor is a *subset/projection* of what
``PlatformEntry`` already encodes, not a parallel concept: ``label``,
``max_message_length``, ``emoji``, ``platform_hint``, ``pii_safe`` and
the platform name come straight off the entry. The runtime capability
bits that ``PlatformEntry`` does NOT encode (length unit, draft/edit/
thread/markdown behavior) are supplied by the caller — in production
the connector fills these from the live adapter's capability methods.
``max_message_length`` of 0 on a ``PlatformEntry`` means "no limit";
we map that to the stream_consumer default of 4096 so the descriptor
always carries a concrete chunking bound.
"""
max_len = getattr(entry, "max_message_length", 0) or 4096
return cls(
contract_version=CONTRACT_VERSION,
platform=entry.name,
label=entry.label,
max_message_length=max_len,
supports_draft_streaming=supports_draft_streaming,
supports_edit=supports_edit,
supports_threads=supports_threads,
markdown_dialect=markdown_dialect,
len_unit=len_unit,
emoji=getattr(entry, "emoji", "\U0001f50c"),
platform_hint=getattr(entry, "platform_hint", ""),
pii_safe=getattr(entry, "pii_safe", False),
)