An implemented function's name has no auditable derivation

The name search records a derivation for every name it works out - and it only ever sees imports nothing can already name. Once a function is implemented, the registry resolves it, so it leaves the unnamed set and no search records anything about it again.

The consequence is quiet and worth stating: 57 of the 95 declared functions have no provenance record at all. The other 38 have one only by luck of ordering - a search confirmed them before anything implemented them, and write_symbol_db never removes a record once written. The 57 arrived the other way round: somebody worked out the name and declared it in the same step, so the search never targeted it and nothing recorded anything.

So orbistoun-cli audit covers the names we have not yet acted on, and covers the ones we have only where the order happened to favour it. The knowledge base has been papering over that with a hand-written found_by, which is why the field drifted into eleven contradictions before anything checked it (D213).

The cheapest fix is probably not a record at all. PROVENANCE.md is explicit that the audit "proves derivability, not history" - so for a declared name, hashing it and sweeping the space answers exactly the claim the audit already makes, with no reconstruction and no pretence of a contemporaneous record. One sweep covers all 95 at once, the same way --repair does, because a wider target set costs a sweep nothing. Roughly ninety seconds for the whole declared set, which is a names-time check rather than a per-commit one.

Two ways out, and the first is probably right:

• Record a derivation when a name is first confirmed, and keep it even after the function is implemented. Costs nothing at search time; the difficulty is that the names currently implemented were confirmed before anything was keeping the record, so a one-off --deep walk would be needed to reconstruct them - which is exactly the "a provenance record assembled afterwards is a reconstruction" problem, and should be recorded as such rather than dressed up.
• Have the knowledge base stop carrying found_by and read it from the symbol database, accepting that implemented functions show nothing. Simpler, and loses the only record those names have.