feat(#1956): flag cross-artifact fact drift in the plan drift guard (#3259)

* test(#1956): failing-first contract for cross-artifact fact-drift pass

* feat(#1956): flag cross-artifact fact drift in the plan drift guard

* fix(#1956): correct config-key assertion and bidirectional lifecycle-lag exemption

* docs(#1956): document the cross-artifact axis in the architecture reference

* feat(#1956): decide the phase-status drift axis deterministically

* fix(#1956): scope the progress-table lookup, abstain without a position section, rank deferred

* docs(#1956): backfill changeset pr number

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Co-authored-by: sim <sim@local>

docs/USER-GUIDE.md

@@ -560,6 +560,8 @@ claude --dangerously-skip-permissions
 
 **Default-on.** The plan drift guard (`plan_review.source_grounding: true`) runs during plan review and verifies that every symbol your plans cite — decorators, classes, functions, CLI flags — actually exists in your source tree at review time. This catches hallucinated names before any execution agent runs.
 
+**Two axes, one switch.** The same guard also runs a cross-artifact fact-drift pass: when ROADMAP.md, PLAN.md, STATE.md and CONTEXT.md state the *same* fact in contradictory ways — a phase marked complete in one and in progress in the other, a success criterion the plan restates with a different outcome, a term used against its CONTEXT.md definition — you get an advisory finding in REVIEWS.md naming both locations and which one is authoritative. It keys on contradicting *knowledge*, not on similar-looking text, so a plan that simply restates a criterion in its own words is not flagged. The findings never block convergence.
+
 **What it catches:**
 
 - Functions referenced in a PLAN.md step that don't exist in source