Reviewer (PR #2106, elevated): if capability-registry.cjs fails to load,
_hostBehaviors('claude') returned {} — silently routing a claude LOCAL install to
the repo-shared settings.json instead of the gitignored settings.local.json (#338),
skipping mergeClaudePermissions + the .gsd-source marker. The migration is what
introduced that registry dependency (pre-PR the path had none).
Add FALLBACK_HOST_BEHAVIORS (keyed by runtime id — a data lookup, not a
runtime==='claude' branch) mirroring the reference host's #338-privacy-critical keys
(settingsFileByScope, permissionsSchema, sourceMarkerFile), consulted only when the
registry (or the descriptor) is unavailable. Behavior degrades CLOSED, never open;
the live descriptor stays the source of truth. Normal (registry-present) output is
unchanged (golden parity preserved). Pinned by tests via a registry-injected
_resolveHostBehaviors helper.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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