Snapshot the editor selection at send time (same live-ref pattern as
openPageRef in prepareSendMessagesRequest), carry it nested inside
openPage so it dies with the page on a fail-closed resolve, and surface
it to the model only through the existing core getCurrentPage tool.
The selection TEXT is returned exclusively in the tool result (untrusted
collaborative-page content, treated as data by SAFETY_FRAMEWORK); the
system prompt gets only a fixed one-line flag, never the text/before/
after. sanitizeSelection caps text (4000), before/after (200), blockIds
(<=64 chars, <=20). Selection is a hint, not ground truth — the tool
description tells the agent to localize the fragment before editing.
closes#388
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
agent_coder