Test scaffolding hand-rolls the pre-#174 leaky onError, so it cannot catch a code-leak regression

[Hazzng]

Follow-up to #174 / PR #179. Deliberately not fixed there to keep that PR reviewable.

Summary

Four test files build their own Hono app with an onError handler that is a verbatim copy of the line #174 just removed from production:

const code = (err as Error & { code?: string }).code ?? "INTERNAL_ERROR";

• src/api/tests/unit/exec-batch.test.ts:33
• src/api/tests/unit/exec-batch.perscript.test.ts:51
• src/api/tests/integration/multi-tenant.integration.test.ts:78
• src/api/tests/integration/writefiles-atomicity.integration.test.ts:63

Why it matters

No user-facing leak — this is test-only code. The problem is that these apps no longer have production's error shape. A future regression that reintroduces raw-code leakage would still pass every test built on this scaffolding, and any assertion written against these apps encodes the pre-fix contract as if it were current.

src/api/server.ts now routes through clientSafeErrorCode(err) (added in PR #179, src/api/errors.ts). The scaffolding should call the same helper so the test apps and production cannot drift.

Suggested fix

Replace the four hand-rolled handlers with clientSafeErrorCode(err), or better, export a shared test-app factory so there is one definition of the error contract to keep in sync.

Provenance

Found by the #174 implementation agent while auditing call sites for the leaked-code fix.