fix(session): invalidate snapshots before metadata write dispatch

Stop cached metadata replay before a provider write starts, including while its reply is pending or fails after applying the mutation. Keep snapshot import and export disabled until the target is reopened.

Validate failed replies, conflicting provider identity, and overlapping reads through the shared session boundary.

docs/cli.md

@@ -150,6 +150,10 @@ an exact result when the target bytes, operation, parameters, provider and
 settings match. Mutations and cursor-dependent calls are excluded from the
 cache. Snapshot files are local and use owner-only permissions.
 
+Dispatching a metadata write invalidates the active session's snapshot cache,
+even if its reply fails: the provider may already have applied the write.
+Close and reopen the target before importing or saving another snapshot.
+
 Snapshots retain eligible target-scoped question histories in full, including
 mutation Evidence recorded while another target was active. Observations and
 related questions must still belong to the saved target. If those dependencies