Continuable cron jobs (attach_to_session / cron.mirror_delivery, default
OFF) now prefer a dedicated thread on thread-capable platforms, falling
back to origin-DM mirroring where threads don't exist.
- Thread-capable (Telegram topics, Discord/Slack threads): open a fresh
thread for the job via the shipped adapter.create_handoff_thread,
route the brief into it, and seed the thread-keyed session so the
user's in-thread reply continues with full context. This is the
'continuable cron opens its own thread' interface.
- DM-only (WhatsApp/Signal/SMS): create_handoff_thread returns None ->
fall back to mirroring into the origin DM session (existing behaviour).
Reuses existing infrastructure end-to-end — no new adapter surface, no
provider-chain signature change:
- adapter.create_handoff_thread (already implemented per-platform,
returns None on unsupported platforms = the fallback signal)
- the live SessionStore via adapter._session_store (already set on every
adapter), reached without threading a new param through the frozen
CronScheduler.start() contract
- gateway.mirror.mirror_to_session for the seed/append
- existing per-target delivery routing carries the new thread_id for free
Mirrors GatewayRunner._process_handoff's open-thread-or-fallback +
seed pattern, standalone for the cron delivery path. thread_seeded
guards against a double-mirror after seeding. Scoped to the origin
target only; fan-out/broadcast targets are never threaded or mirrored.
Config docs updated (cron.mirror_delivery) + cronjob tool
attach_to_session description reframed around continuable/thread-preferred.
Tests: +5 (thread id returned on thread platform; None on DM platform;
None without capability/loop; seed creates thread session + mirrors;
seed no-op on empty). 22/22 in TestCronDeliveryMirror; 532 cron tests
pass (4 failures pre-existing: croniter-not-installed + TZ).
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