feat(channels): enhance Discord with mention-only mode, thread routing, and typing indicators (#2842)

* feat(channels): enhance Discord with mention-only mode, thread routing, and typing indicators

Add mention_only config to only respond when bot is mentioned, with
allowed_channels override. Add thread_mode for Hermes-style auto-thread
creation. Add periodic typing indicators while bot is processing.

* fix(discord): include allowed_channels in mention_only skip condition (line 274)

* docs: fix Discord config example to match boolean thread_mode implementation

* style: format with ruff

* fix(discord): apply Copilot review fixes and resolve lint errors

- Remove unused Optional import
- Fix thread_ts type hints to str | None
- Fix has_mention logic for None values
- Implement thread_mode fallback to channel replies on thread creation failure
- Fix thread_mode docstring alignment
- Fix allowed_channels comment formatting in config.example.yaml

* fix(discord): reset context for orphaned threads in mention_only mode

When a message arrives in a thread not tracked by _active_threads,
clear thread_id and typing_target so the message falls through to
the standard channel handling pipeline, which creates a fresh thread
instead of incorrectly routing to the stale thread.

* fix(discord): create new thread on @ when channel has existing tracked thread

When mention_only is enabled and a user @-s the bot in a channel
that already has a tracked thread, create a new thread instead of
incorrectly routing to the old one.

* fix(discord): allow no-@ thread replies while skipping no-@ channel messages

The skip block for no-@ messages was too aggressive — it blocked
continuation replies within tracked threads AND incorrectly routed
no-@ channel messages to the existing thread.

Now:
- Thread message, no @ → routed to existing tracked thread
- Channel message, no @ → skipped
- Channel message, with @ → creates new thread

* feat(discord): add checkmark reaction to acknowledge received messages

* Move discord.py to optional dependency and auto-detect from config.yaml

- Add discord extra to [project.optional-dependencies] in pyproject.toml
- Update detect_uv_extras.py to map channels.discord.enabled: true -> --extra discord
- Set UV_EXTRAS=discord in docker-compose-dev.yaml gateway env

* fix(discord): persist thread-channel mappings to store for recovery after restart

Discord's _active_threads dict was purely in-memory, so all channel-to-thread
mappings were lost on server restart. This fix bridges ChannelStore into
DiscordChannel:

- Save thread mappings to store.json after every thread creation
- Restore active threads from store on DiscordChannel startup
- Pass channel_store to all channels via service.py config injection

Store keys follow the pattern: discord:<channel_id>:<thread_id>

* fix(discord): address Copilot review — fix types, typing targets, cross-thread safety, and config comments

* fix(tests): add multitask_strategy param to mock for clarification follow-up test

* fix(tests): explicitly set model_name=None for title middleware test isolation

* fix(discord): use trigger_typing() instead of typing() for typing indicators

discord.py 2.x TextChannel.typing() and Thread.typing() are async context
managers, not one-shot coroutines. Use trigger_typing() for periodic
typing indicator pings.

* fix(discord): cancel typing tasks on channel shutdown

Prevents 'Task was destroyed but it is pending' warnings when the
Discord client stops while typing indicator loops are still running.

* fix(scripts): detect nested YAML config for discord extra

section_value() only matched top-level YAML sections. Added
nested_section_value() that handles two-level nesting (e.g.,
channels.discord.enabled), so auto-detection of the discord
extra works when config uses the standard nested format.

* fix(docker): remove hard-coded UV_EXTRAS=discord from dev compose

Relies on auto-detection via detect_uv_extras.py instead of forcing
discord.py install even when channels.discord.enabled is false.
Matches production docker-compose.yaml behavior (UV_EXTRAS:-).

* refactor(nginx): move proxy_buffering/proxy_cache to server level

DRY cleanup — these directives were repeated in 14 location blocks.
Set at server level once, reducing duplication and risk of drift.

* fix(discord): use dedicated JSON file for thread persistence

Replace ChannelStore usage for Discord thread-ID persistence with a
dedicated discord_threads.json file. ChannelStore is designed to map
IM conversations to DeerFlow thread IDs — using it to persist Discord
thread IDs was semantically wrong and confusing.

Changes:
- _save_thread() now reads/writes a simple {channel_id: thread_id} JSON dict
- _load_active_threads() reads directly from the JSON file
- File path derived from ChannelStore directory (when available) or
  defaults to ~/.deer-flow/channels/discord_threads.json
- Removed unused ChannelStore import

* fix(discord): address WillemJiang's code review comments on PR #2842

1. Remove semantically incorrect message_in_thread variable. At this code
   point (after the Thread case is handled above), we're guaranteed to be in
   a channel, not a thread. Always apply mention_only check here.

2. Add _active_thread_ids reverse-lookup set for O(1) thread ID membership
   checks instead of O(n) scan of _active_threads.values(). Keep the set
   in sync with _active_threads in _load_active_threads() and _save_thread().

3. Add _thread_store_lock (threading.Lock) to protect _active_threads and
   the JSON file from concurrent access between the Discord loop thread
   (_run_client) and the main thread (_load_active_threads, _save_thread).

backend/uv.lock

@@ -1,5 +1,5 @@
 version = 1
-revision = 3
+revision = 2
 requires-python = ">=3.12"
 resolution-markers = [
     "python_full_version >= '3.14' and sys_platform == 'win32'",
@@ -763,6 +763,9 @@ dependencies = [
 ]
 
 [package.optional-dependencies]
+discord = [
+    { name = "discord-py" },
+]
 postgres = [
     { name = "deerflow-harness", extra = ["postgres"] },
 ]
@@ -781,6 +784,7 @@ requires-dist = [
     { name = "deerflow-harness", editable = "packages/harness" },
     { name = "deerflow-harness", extras = ["postgres"], marker = "extra == 'postgres'", editable = "packages/harness" },
     { name = "dingtalk-stream", specifier = ">=0.24.3" },
+    { name = "discord-py", marker = "extra == 'discord'", specifier = ">=2.7.0" },
     { name = "email-validator", specifier = ">=2.0.0" },
     { name = "fastapi", specifier = ">=0.115.0" },
     { name = "httpx", specifier = ">=0.28.0" },
@@ -795,7 +799,7 @@ requires-dist = [
     { name = "uvicorn", extras = ["standard"], specifier = ">=0.34.0" },
     { name = "wecom-aibot-python-sdk", specifier = ">=0.1.6" },
 ]
-provides-extras = ["postgres"]
+provides-extras = ["postgres", "discord"]
 
 [package.metadata.requires-dev]
 dev = [
@@ -923,6 +927,19 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/4c/44/102dede3f371277598df6aa9725b82e3add068c729333c7a5dbc12764579/dingtalk_stream-0.24.3-py3-none-any.whl", hash = "sha256:2160403656985962878bf60cdf5adf41619f21067348e06f07a7c7eebf5943ad", size = 27813, upload-time = "2025-10-24T09:36:57.497Z" },
 ]
 
+[[package]]
+name = "discord-py"
+version = "2.7.1"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "aiohttp" },
+    { name = "audioop-lts", marker = "python_full_version >= '3.13'" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/ef/57/9a2d9abdabdc9db8ef28ce0cf4129669e1c8717ba28d607b5ba357c4de3b/discord_py-2.7.1.tar.gz", hash = "sha256:24d5e6a45535152e4b98148a9dd6b550d25dc2c9fb41b6d670319411641249da", size = 1106326, upload-time = "2026-03-03T18:40:46.24Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/f7/a7/17208c3b3f92319e7fad259f1c6d5a5baf8fd0654c54846ced329f83c3eb/discord_py-2.7.1-py3-none-any.whl", hash = "sha256:849dca2c63b171146f3a7f3f8acc04248098e9e6203412ce3cf2745f284f7439", size = 1227550, upload-time = "2026-03-03T18:40:44.492Z" },
+]
+
 [[package]]
 name = "distro"
 version = "1.9.0"