When an isolated cron session has no lastAccountId (e.g. first-run or
fresh session), the message tool receives an undefined accountId which
defaults to "default". In multi-account setups where accounts are named
(e.g. "willy", "betty"), this causes resolveTelegramToken() to fail
because accounts["default"] doesn't exist.
This change adds a fallback in resolveDeliveryTarget(): when the
session-derived accountId is undefined, look up the agent's bound
account from the bindings config using buildChannelAccountBindings().
This mirrors the same binding resolution used for inbound routing,
closing the gap between inbound and outbound account resolution.
Session-derived accountId still takes precedence when present.
Fixes#17889
Related: #12628, #16259
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
