* fix(#1906): require node-test clean-fixture causation control
The node-test fail-first proof accepted a deceptive content-independent
negative test — one that reds merely because GSD_PROHIB_SUBJECT is set,
ignoring the subject's content — whenever no cleanFixture was supplied,
because #1346's causation control was opt-in. The proof's observed signal
(RED) thus diverged from its target (RED caused by content) by default.
Make the causation control mandatory for the node-test kind: a descriptor
that omits cleanFixture is un-provable (fail-closed), never accepted under
the weaker violation-only proof. When a clean fixture is present, fail-first
is proven exactly as before (RED on violation AND non-vacuous GREEN on clean).
The lint-rule kind is unchanged (its subject IS the linted file; no
GSD_PROHIB_SUBJECT indirection).
Breaking (Hyrum): a previously-green node-test prohibition with no clean
fixture now hard-gates — blast radius is zero in-tree (no node-test
prohibition ships today; only the lint-rule local/no-source-grep dogfood).
Supersedes ADR-1606 Decision 4 / ADR-550 #1346 addendum's opt-in.
Closes#1906
Claude-Session: https://claude.ai/code/session_017vYn26e3nkDNxcpty1ciPJ
* docs(#1906): supersede the #1346 opt-in causation control (mandatory for node-test)
Record the node-test mandatory-causation-control supersede across the
governing surfaces:
- ADR-1606 (the enforcement decision-of-record): addendum + Decision 4
annotated + the "Mandatory causation control — REJECTED" alternative
flipped to accepted (premise no longer holds: zero in-tree node-test
consumers).
- ADR-550: the 2026-06-21 #1346 "Why opt-in, not required" paragraph
marked SUPERSEDED, pointing at ADR-1606.
- spec-phase.md: check_clean_fixture is now REQUIRED for node-test
(was "optional").
- CONTEXT.md: PROHIB.enforce.causation predicate updated.
Regenerated the shipped-artifact cascade from the spec-phase.md edit
(+149 B, well under the 40960 cap): 16 golden-install-parity fixtures
and the workflow size baseline.
Refs #1906
Claude-Session: https://claude.ai/code/session_017vYn26e3nkDNxcpty1ciPJ
