New generateCodexSecondOpinion resolver that adds an opt-in cross-model
cold read between premise challenge and alternatives generation.
Codex independently reviews the session's problem statement, answers,
and premises without seeing Claude's reasoning.
Includes: temp file prompt assembly (shell injection safe), two mode-
specific prompt variants (startup/builder), cross-model synthesis,
premise revision check, and 7 unit tests.
Garry Tan
91ea542323