refactor: split flat core into capability packages, layer the conversations service, English defaults for every model-facing text

src/beaver_gateway/conversations/kinds.py

@@ -0,0 +1,18 @@
+"""Conversation kinds (§3.1) as one closed type for agents, frontends, service."""
+
+from __future__ import annotations
+
+from typing import Literal, get_args
+
+__all__ = ["KINDS", "Kind", "as_kind"]
+
+Kind = Literal["master", "branch", "deep", "job", "fork"]
+KINDS: tuple[Kind, ...] = get_args(Kind)
+
+
+def as_kind(value: str) -> Kind:
+    for kind in KINDS:
+        if value == kind:
+            return kind
+    msg = f"unknown conversation kind {value!r}"
+    raise ValueError(msg)