Test custom regex resource boundaries

[dmoliveira]

Summary

• Add exact and one-over resource-boundary coverage for isolated custom regex redaction.
• Cover request-wide match spans, output allocation, batch operations/input, object key/value probes, capacity rejection, and every worker terminal path.

Validation

• npm test (984/984)
• Focused secret-redaction suite (53/53)
• npm run build
• npm run lint
• make validate
• pre-commit run --all-files
• git diff --check

Review

• Final implementation review: no blockers.