CedarCopilot/cedar-mail

Branch: staging

fix(chat): stop V2 chat from reaching for Bash to edit existing Cedar docs

merged#2887CedarCopilot

CedarCopilot wants to merge 2 commits into staging from fix/chat-doc-edit-bash-detour

What Libra verified

Whole-document rewrites use upsert instead of full-document patching
Libra ran this behavior against the change and confirmed the check detects when it breaks.
Technical evidence
- the harness guidance selects upsert with complete replacement content for whole-document rewrites and reserves patch for small localized changes
Changed code: documentTool.schemas.ts.