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

---------

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

docs/ARCHITECTURE.md

@@ -792,6 +792,8 @@ remove or rewrite anything.
 
 The plan drift guard (`plan_review.source_grounding`) — which verifies symbol references in generated plans against live source before execution — is specified in [ADR 22](adr/22-plan-drift-guard.md).
 
+The same switch gates a second, cross-artifact axis: a fact-drift pass that compares the *same* fact as stated in `ROADMAP.md`, `PLAN.md`, `STATE.md` and `CONTEXT.md` and reports contradictions (a phase status, a success criterion, a requirement ID, a glossary term) with both locations and the authoritative side named. Where the source-grounding axis grounds a plan against code, this one grounds the planning artifacts against each other. It keys on contradicting knowledge rather than similar-looking text, and is advisory only — it never sets `hardBlock` and never contributes to the convergence counts.
+
 ### Platform Handling
 
 - **Windows:** `windowsHide` on child processes, EPERM/EACCES protection on protected directories, path separator normalization

docs/CONFIGURATION.md

@@ -702,7 +702,7 @@ The `plan_review.*` namespace controls the plan drift guard, which verifies that
 
 | Setting | Type | Default | Description |
 |---------|------|---------|-------------|
-| `plan_review.source_grounding` | boolean | `true` | Enable the plan drift guard. When `true` (the default), plan review resolves every symbol reference cited in a PLAN.md against the live source tree. Plans that cite a non-existent function, class, decorator, or CLI flag produce a `needs-acknowledgement` notice before the plan is approved. Disable with `false` to skip symbol verification entirely. Toggle during setup (`/gsd-new-project`) or at any time via `/gsd-settings`. |
+| `plan_review.source_grounding` | boolean | `true` | Enable the plan drift guard. When `true` (the default), plan review resolves every symbol reference cited in a PLAN.md against the live source tree. Plans that cite a non-existent function, class, decorator, or CLI flag produce a `needs-acknowledgement` notice before the plan is approved. The same key also gates the cross-artifact fact-drift pass, which reports when ROADMAP.md, PLAN.md, STATE.md and CONTEXT.md state the same fact in contradictory ways (advisory only — it never blocks convergence). Disable with `false` to skip both passes entirely. Toggle during setup (`/gsd-new-project`) or at any time via `/gsd-settings`. |
 | `plan_review.source_grounding_authority` | enum | `grep` | Selects the resolver adapter used to verify symbol existence. Allowed values: `grep` (default — ripgrep/grep search of source files, works in any project without additional tooling), `intel` (query the `.planning/intel/api-map.json` index built by `/gsd-map-codebase`; requires `intel.enabled: true`), `treesitter` (reserved for future tree-sitter adapter), `lsp` (reserved for future LSP adapter), `scip` (reserved for future SCIP/LSIF adapter). Use `intel` when you have run `/gsd-map-codebase` and want the faster, pre-indexed lookup. All other values beyond `grep` and `intel` are reserved and have no effect in the current release. |
 
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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