ADR-0010: a go-server tunnel registers the catalog of tools it implements, keyed by its tool_catalog_hash. Called ONLY when a hello_ok returned catalog_needed:true (cache-miss or eviction), so it's rare despite tunnel churn.

No auth needed: the hash is validated against the content (sha256), so a caller can only register a (hash, tools) pair that is internally consistent — it cannot make a hash map to a different list of tools without a sha256 collision. A bogus hash that no hello ever sends is inert: filtering only kicks in for a tunnel whose declared hash matches, and unknown hashes fail open to the full catalog.