nx_docstage_gate.nx

nx_docstage_gate.nx -- THE REFEREE for nx_docstage (DM8, devmgmt rung). END-TO-END: forks the DEPLOYED nx_docstage elf, so it grades the artifact callers run. The accept rule, verbatim from devmgmt.plan: "the stage reports DOCUMENTED or UNDOCUMENTED per ship with ZERO false DOCUMENTED, measured against the symbols a session actually shipped." ZERO FALSE DOCUMENTED IS THE ONLY BAR THAT MATTERS HERE, so the fixture is built around the one way this check goes wrong: a SUBSTRING match. `nx_dora_page` contains `nx_dora`, and a scanner that does not test token boundaries reports the shipped symbol as written-down because a DIFFERENT symbol is mentioned somewhere. That failure is invisible -- it produces a green, plausible, wrong answer -- so the fixture carries all four boundary traps at once (`nx_dora_page`, `xnx_dora`, `_nx_dora`, `nx_dorax`) with NO real token, and demands UNDOCUMENTED. The positive control sits in the same gate: the same symbol, as a real token, must come back DOCUMENTED. A detector that answers "documented" for everything fails the first; one that answers "undocumented" for everything fails the second. Neither alone proves discrimination. The third state is tested too, because "I could not look" and "it is not written down" demand opposite actions and only one of them is ever safe to act on. Fixtures under /tmp/nx_docstage_gate/, rewritten O_TRUNC each run (idempotent). license_tier: ORIGINAL Read-only outside /tmp. No hw writes (Rule 26).