Make ordinary workspaces group shareable

docs/operations.md

@@ -284,6 +284,26 @@ Cache layout (durable S3 audio cache):
 
 - `{cache.root}/s3/{bucket}/...`
 
+### Workspace Permissions
+
+Ordinary Narratio workspace content is intentionally shareable with the
+workspace group. On POSIX systems, Narratio-created workspace, spool, and cache
+directories converge on setgid `02775`; ordinary files, including manifests,
+transcripts, generated configuration, logs, reports, and Notarius artifacts,
+converge on `0664`. Narratio explicitly applies these modes so a restrictive
+caller umask does not remove group write or setgid. It does not change file or
+directory ownership: the configured workspace's existing group is inherited.
+
+Windows does not implement POSIX mode bits or setgid semantics. Configure the
+workspace, spool, and cache locations with an ACL that grants the collaborating
+group read/write access, and configure credential locations with an ACL limited
+to the intended credential owner. Do not use POSIX mode displays as evidence of
+Windows access control.
+
+API keys are credentials, not ordinary workspace data. Store them outside the
+shared workspace or in a separately restricted credential location; ordinary
+workspace group access must never be treated as authorization to read keys.
+
 ## Cleanup
 
 Session-scoped cleanup: