Add a per-room/global `sender_context_mode` setting that optionally
prefixes conversation messages with sender metadata before sending them
to the model provider.
This helps models distinguish between participants in multi-user rooms.
Three modes are supported:
- `disabled` (default, no change)
- `matrix_user_id` (prefixes with `[sender=@user:server]`)
- `matrix_user_id_and_timestamp` (adds `send_at`; Example: `[sender=@user:server sent_at=<ISO 8601>]`)
Sender context is applied to user and assistant text messages only,
skipping system prompts and non-text content.
Mixed-sender merged turns (something we intentionally do for Anthropic)
have their `sender_id` cleared to avoid misattribution.
This patch introduces a new `baibot_conversation_start_time_utc`
variable which indicates the time the conversation got started.
Using `baibot_now_utc` is still possible, but given that the current
time is a moving target, its use is in conflict with prompt caching.
Because the new `baibot_conversation_start_time_utc` prompt variable
is a more reasonable default, we're now using it in all sample configs.
This feature went through a few iterations. At some point,
a `(local timezone/time: unknown)` suffix was part of the
`baibot_now_utc` variable (hoping it improves the model's awareness that
it doesn't know the current local time), but the suffix was ultimately removed
as unnecessary.
Fixes https://github.com/etkecc/baibot/issues/10
This also includes them in the default prompts (for newly-created agents),
so that people can get a better experience out of the box.
