When groupPolicy is 'allowlist', messages from senders not in
groupAllowFrom were completely dropped (allowed: false + continue).
This meant the agent couldn't see messages from other bots or
non-allowlisted group members in its context window.
The docs state that non-mentioned messages should be 'stored for
context only', but this only applied after access control passed.
Changes:
- Add storeForContext flag to InboundAccessControlResult
- When a group message fails groupAllowFrom, set storeForContext: true
instead of silently dropping
- Pass contextOnly flag through to WebInboundMessage
- In on-message handler, store contextOnly messages in group history
without triggering a reply
- Skip read receipts for context-only messages
Fixes: group members not in groupAllowFrom are now visible in the
agent's '[Chat messages since your last reply]' context block.
