fix(delivery): drop env-var knob, flag all chunking adapters

Follow-up to ScotterMonk's cron-truncation fix:

- Remove HERMES_DELIVERY_MAX_PLATFORM_OUTPUT env var. Behavioral config
  belongs in config.yaml, not a new HERMES_* env var (.env is secrets
  only). The actual bug is fixed entirely by the adapter-aware skip; the
  configurable cap was unneeded scope. MAX_PLATFORM_OUTPUT is a constant
  again, collapsing the max_output=0 disable branch and the
  audit-vs-truncation threshold divergence.
- Flag the remaining verified-chunking adapters (slack, matrix, feishu,
  mattermost, teams, whatsapp, whatsapp_cloud, weixin, bluebubbles,
  yuanbao) with splits_long_messages=True so the fix covers the whole
  bug class, not just Discord/Telegram. Each verified to chunk in its
  own send() via truncate_message().
- SMS deliberately left False: it chunks for normal replies but a
  multi-segment cron blast is cost-bearing; the 4000-cap + file save is
  the safer default there.
- Update tests: drop the two env-override tests, add a test asserting a
  save failure during truncation (non-chunking) propagates.

plugins/platforms/feishu/adapter.py

@@ -1410,6 +1410,7 @@ class FeishuAdapter(BasePlatformAdapter):
     """Feishu/Lark bot adapter."""
 
     supports_code_blocks = True  # Feishu renders fenced code blocks
+    splits_long_messages = True  # send() chunks via truncate_message(MAX_MESSAGE_LENGTH)
 
     MAX_MESSAGE_LENGTH = 8000
     # Max distinct chat IDs retained in _chat_locks before LRU eviction kicks in.

plugins/platforms/matrix/adapter.py

@@ -775,6 +775,7 @@ class MatrixAdapter(BasePlatformAdapter):
     """Gateway adapter for Matrix (any homeserver)."""
 
     supports_code_blocks = True  # Matrix renders fenced code blocks (HTML/markdown)
+    splits_long_messages = True  # send() chunks via truncate_message(MAX_MESSAGE_LENGTH)
 
     # Matrix clients commonly reserve typed "/" for client-local commands;
     # the adapter accepts "!command" as the alias that always reaches Hermes

plugins/platforms/mattermost/adapter.py

@@ -71,6 +71,8 @@ def check_mattermost_requirements() -> bool:
 class MattermostAdapter(BasePlatformAdapter):
     """Gateway adapter for Mattermost (self-hosted or cloud)."""
 
+    splits_long_messages = True  # send() chunks via truncate_message(MAX_POST_LENGTH)
+
     def __init__(self, config: PlatformConfig):
         super().__init__(config, Platform.MATTERMOST)
 

plugins/platforms/slack/adapter.py

@@ -321,6 +321,7 @@ class SlackAdapter(BasePlatformAdapter):
 
     MAX_MESSAGE_LENGTH = 39000  # Slack API allows 40,000 chars; leave margin
     supports_code_blocks = True  # Slack mrkdwn renders fenced code blocks
+    splits_long_messages = True  # send() chunks via truncate_message(MAX_MESSAGE_LENGTH)
     # Slack blocks typed native slash commands inside threads ("/approve is
     # not supported in threads. Sorry!").  The adapter rewrites a leading
     # "!" to "/" for known commands (see _handle_slack_message), so "!" is

plugins/platforms/teams/adapter.py

@@ -691,6 +691,7 @@ class TeamsAdapter(BasePlatformAdapter):
     """Microsoft Teams adapter using the microsoft-teams-apps SDK."""
 
     MAX_MESSAGE_LENGTH = 28000  # Teams text message limit (~28 KB)
+    splits_long_messages = True  # send() chunks via truncate_message()
 
     def __init__(self, config: PlatformConfig):
         super().__init__(config, Platform("teams"))

plugins/platforms/whatsapp/adapter.py

@@ -337,6 +337,7 @@ class WhatsAppAdapter(WhatsAppBehaviorMixin, BasePlatformAdapter):
 
     # Default bridge location resolved via shared helper
     _DEFAULT_BRIDGE_DIR = None  # resolved in __init__
+    splits_long_messages = True  # send() chunks via truncate_message()
 
     def __init__(self, config: PlatformConfig):
         super().__init__(config, Platform.WHATSAPP)