Due reminders entered their Session as user-role messages whose fixed text told
the model to treat the reminder prompt as untrusted content rather than new user
instructions. Both delivery paths now open with one shared origin line,
"This is a scheduled message from the user", so the message states where it came
from instead of what standing to give its own payload.
One-shot and recurring batch framing share SCHEDULED_MESSAGE_FRAMING, so the two
paths cannot drift. The bracketed markers and the JSON-encoded dynamic fields are
unchanged, so a prompt still cannot forge framing lines.
The rationale and alternatives are recorded in the Agent Note
.agents/notes/implemented/architecture/2026-09-24-scheduled-message-framing.md.
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