refactor(channels): Deduplicate send_response across messaging channels

[xinghaohuang91]

Summary

SMS, RCS, WhatsApp, and Chat each had a nearly-identical send_response() implementation (type/session/participant validation, building ActionChannelSettings, constructing the SendMessageActionRequest, calling create_action, and logging). This consolidates the shared logic into MessagingChannel.send_response() in src/tac/channels/messaging.py, leaving one overridable hook — _build_channel_settings() — for the one real behavioral difference: Chat requires channel_id (raises RuntimeError if missing), while SMS/RCS/WhatsApp treat it as optional.

Net effect: ~370 lines of duplicated logic removed from sms.py/rcs.py/whatsapp.py/chat.py, with no changes to public API signatures.

Behavior changes (minor, non-functional):

• Error/log messages now consistently use the wire channel name (SMS, RCS, WHATSAPP, CHAT) instead of a mix of that and a display form (WhatsApp, Chat) — two test assertions were updated to match.
• The "sent response" log line now includes both to_address and channel_id for every channel (previously Chat only logged channel_id, others only logged to_address).

Also clarified the send_response() docstring: the shared base interface's type annotation allows str | AsyncGenerator[...] (to accommodate the Voice channel, which supports streaming), but messaging channels only ever accept str and raise TypeError for anything else, since they send a single complete message via the Conversation Orchestrator Send API and have no streaming path.

How to test

• make check (lint + type-check + test) — all passing locally.
• No behavior change to the public send_response() call signature or contract; existing channel tests (test_sms_channel.py, test_rcs_channel.py, test_whatsapp_channel.py, test_chat_channel.py) cover this path.

SDK Parity

• Change is Python-specific (no TypeScript update needed) — this only reorganizes internal Python implementation, no public API or wire behavior change.

[Copilot]

Pull request overview

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Refactors messaging channels to remove duplicated send_response() logic by centralizing it in MessagingChannel, while keeping per-channel customization via _build_channel_settings() (notably: Chat requires channel_id).

Changes:

• Introduces shared MessagingChannel.send_response() and default _build_channel_settings() implementation.
• Removes per-channel send_response() duplicates from SMS/RCS/WhatsApp/Chat; Chat overrides _build_channel_settings() to require channel_id.
• Updates tests to expect standardized error messages using wire channel names.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/tac/channels/messaging.py	Adds shared send_response() and default ActionChannelSettings construction hook
src/tac/channels/chat.py	Replaces custom send_response() with _build_channel_settings() requiring channel_id
src/tac/channels/sms.py	Removes duplicated send_response() implementation in favor of base behavior
src/tac/channels/rcs.py	Removes duplicated send_response() implementation in favor of base behavior
src/tac/channels/whatsapp.py	Removes duplicated send_response() implementation in favor of base behavior
tests/test_chat_channel.py	Updates assertion to match standardized error message
tests/test_whatsapp_channel.py	Updates assertion to match standardized error message

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[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated no new comments.