An agent is replacing a parser behind a stable public function. Which assertion is the mo…

An agent is replacing a parser behind a stable public function. Which assertion is the most resilient guardrail?

1. Supported inputs return the specified values and malformed inputs produce the documented diagnostics
2. The parser creates exactly four private token objects
3. A private helper is called before another private helper
4. The new source has the same number of branches as the old source