feat(channel): add bot-at-bot support

[mazhe-nerd]

What & why

Support multiple bots collaborating in one chat — agents @-ing each other to
hand off work. The channel layer sits between the low-level OpenAPI SDK and the
app, so it's where the extra signals and guards a bot-to-bot handoff needs
belong. Everything here is opt-in and additive; default behavior is
unchanged.

Ports the bot-at-bot support from the Node channel SDK
(larksuite/channel-sdk-node#10) to the Python SDK.

Changes (SDK-facing)

Context — know who sent a message

• InboundMessage.sender_type ('user' | 'bot' | 'system' | 'anonymous' | 'app')
  and the convenience sender_is_bot, passed through from the raw event
  (previously dropped). Identity.is_bot semantics are unchanged.
• channel.get_bot_identity() → the bot's own BotIdentity (raises
  FeishuChannelError(code="not_connected") before connect()), e.g. to inline
  into a system prompt.
• Opt-in resolve_sender_names fills InboundMessage.sender_name from the chat
  roster.

Roster & outbound

• channel.get_chat_members(chat_id) — a chat's users (paginated, cached).
• channel.get_chat_bots(chat_id) — a chat's bots (users and bots are served
  by separate endpoints; this covers the bots).
• channel.reply(msg, ...) — replies to the triggering message and keeps the
  reply in-thread when that message was in a topic thread.
• @name → open_id resolution: name-only entries in OutboundText /
  OutboundPost mentions, and — with opt-in SendOpts.resolve_mentions_in_text
  — @name tokens in a text/markdown body, resolved against the chat roster. A
  name that is unknown or shared by more than one member is left as plain text
  and never mis-mentioned.
• resolve_chat_members hook to source the roster from your own directory
  instead of the API.
• <at> output is hardened: attacker-influenced display names are escaped and
  open_ids validated at every sink (the @all sentinel is preserved).

Policy & safety

• PolicyConfig docs clarify allow_from (sender ids ou_…) vs
  group_allowlist (chat ids oc_…); a misplaced app id (cli_…) now logs a
  warning instead of silently matching nothing.
• Opt-in policy.bot_loop_guard breaks bot ↔ bot @-mention ping-pong loops
  (sliding window over "another bot @-ed me" messages; on trip either drops or
  emits a reject with reason="bot_loop"; a human message resets it). New
  ChatMember / BotLoopGuardConfig are exported.
• An @-only mention (no body) is delivered as a valid wake — mentioned_bot
  is True with empty content_text, and the bot's own mention is stripped from
  the rendered content so mentioned_bot and not content_text.strip() detects a
  bare poke.

Compatibility

New fields are optional, new methods/options are additive, and every new
behavior is opt-in (off by default). Without opting in, receive/send/connect/
normalization behavior is identical to the previous release, except that a
message which @-mentions the bot no longer renders the bot's own @name in
content_text (it is stripped). New ChannelConfig fields are appended at the
end, preserving positional construction. Version 1.1.0 → 1.2.0.

Testing

• Unit tests for each new surface: sender-type normalization, the roster cache
  (name-collision → ambiguous, TTL, capacity), @name resolution (including
  linear-time / ReDoS-safe scanning), the <at> escaping/validation, the loop
  guard, reply, get_chat_members/get_chat_bots (pagination, caching,
  chat_id URL-encoding), the allowlist warning, and the empty-@ wake.
• An end-to-end double-bot scenario against a real chat exercises sender_type/
  sender_is_bot, get_bot_identity, get_chat_members/get_chat_bots, reply,
  the @-name handoff, the empty-@ wake, and the loop-guard trip.

[mazhe-nerd]

Addressed a round of review feedback (a2545a7). Highlights, all backward-compatible:

Behavior / correctness

• content_text default is now unchanged again — it keeps the rendered mention (including the bot's own). A new InboundMessage.body_text carries the bot-mention-stripped view for command parsing / bare-@ wake detection (mentioned_bot and not body_text.strip()).
• reply() keeps every chunk of a long reply in the thread (previously only the first chunk stayed in-thread; the rest fell to the main timeline).
• The plain-text chunker never splits an <at>…</at> tag across message boundaries.

Roster / cache

• Member cache is keyed by (chat_id, id_type) and the name→open_id index is built only from open_id members, so a user_id query can't leak the wrong id type.
• A full (force=True) refresh rebuilds the index from the fresh snapshot — departed members drop out and resolved name collisions become resolvable again. Pagination tracks completeness and warns on truncation.
• Mention collection and sender_name resolution now run only after the safety pipeline admits a message, so a rejected message can't seed the roster or trigger the members API.

Requests / safety

• The members request validates HTTP status and JSON shape (a non-2xx or non-object body is a typed error, not an empty-success cache entry); tenant-token verification runs off the event loop with a total timeout.
• policy.bot_loop_guard is reconfigured atomically on update_policy() (runtime enable/disable and threshold changes now take effect); config values are validated and out-of-order timestamps handled.
• resolve_mentions_in_text is honored when passed via a dict opts (not just SendOpts).

Docs: corrected the im:message.group_at_msg.include_bot:readonly permission name; documented body_text and the resolve_chat_members empty-list semantics.

A few lower-risk items (extra roster hardening, singleflight, thread-safety, name-scan boundary refinements) are tracked as follow-ups. Full test suite green across Python 3.8–3.12, plus an end-to-end double-bot run against a real chat.