Background writers that still carry a tombstoned profile as their Hermes
home (reasoning-caps warm thread, models cache, models.dev ETag, gateway
lifecycle ledger, MCP OAuth tokens, memory store) re-created
profiles/<name>/ with a bare mkdir right before an atomic write. Route the
parent-dir creation through mkdir_under_hermes_home so a deleted named
profile raises FileNotFoundError and stays gone, matching the tombstone
contract already enforced for logging and state.
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