Option B, per the operator. Closes the last inconsistency from the ACL work.
The agent path had drifted into an indefensible position: delete_snippet honoured
editor shares (I made it share-aware so widening the read wouldn't let a VIEWER
trash things) while update_snippet still resolved through the owner-only
notes.get_note. So through an agent you could destroy a colleague's snippet but
not improve it — and the refusal claimed "not found" for a record you could
plainly open.
Now update_snippet, merge_snippets and update_process all resolve the read scope
and then require can_write_note, matching the REST routes and the sharing UI's
own promise that viewer / editor / admin are distinct grants. A viewer grant is
refused with the actual reason ("shared with you read-only — ask its owner for
edit access, or record your own version"), because not-found would send an agent
hunting for a missing id instead of recording its own copy.
Authorised writes are performed as the OWNER, since the underlying note update is
owner-scoped and a shared editor's own id would match nothing.
Merge additionally requires each source to share the TARGET'S owner and to be
writable by the caller — merging trashes the source, so read access isn't enough,
and cross-owner merge stays out of scope (#231). Sources failing either test are
skipped rather than half-merged.
A record the caller cannot read at all still returns not-found rather than
forbidden, so the error can't be used to confirm that an id exists.
Also fixed _fake_snippet's missing user_id proactively — the same
auto-MagicMock-reads-as-foreign trap that broke CI twice (see note 2109).
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RLwAaV4DQEmVyn496HnEvt
