feat(#903): generate Loop Host Contract from workflow markers (ADR-857 phase 3a-impl-2) (#906)

Replace the inline LOOP_HOST_CONTRACT constant in the Capability Registry
generator with a generated-from-workflows contract (ADR-894 §3). The contract
is now derived from inert `<!-- gsd:loop-host ... -->` marker blocks in the five
step workflows, emitted as the committed gsd-core/bin/lib/loop-host-contract.cjs,
and required by gen-capability-registry.cjs — one source of truth, no drift.

Drift guards in gen-loop-host-contract.cjs: per-step point ownership (each step
must declare exactly its canonical loop points), multiple-block + duplicate-key
hard errors, and a word-boundary agent-role cross-check. Contract content is
byte-identical to the former constant; registry-only, nothing wired into the
live loop.

Closes #903

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

scripts/gen-capability-registry.cjs

@@ -29,61 +29,10 @@ const SCHEMA_VERSION = '1';
 
 // ─── Loop Host Contract ───────────────────────────────────────────────────────
 //
-// Inline constant — hardcoded from ADR-894 §3 (12 points + per-step agentRoles +
-// coreArtifacts). This represents the host contract that will be generated from
-// workflow markers once the workflow-marker infrastructure is in place.
-//
-// TODO 3a-impl-2: replace this constant with the generated-from-workflows host
-// contract (ADR-894 §3). The workflow markers (<loop-point>, <agent-role>,
-// <loop-artifact>) must be authored in each of the five step workflows; the
-// gen-loop-host-contract.cjs generator will parse them and produce this object.
-const LOOP_HOST_CONTRACT = [
-  {
-    step: 'discuss',
-    points: ['discuss:pre', 'discuss:post'],
-    agentRoles: ['orchestrator'],
-    coreArtifacts: {
-      produces: ['CONTEXT.md'],
-      consumes: [],
-    },
-  },
-  {
-    step: 'plan',
-    points: ['plan:pre', 'plan:post'],
-    agentRoles: ['researcher', 'planner', 'checker'],
-    coreArtifacts: {
-      produces: ['PLAN.md'],
-      consumes: ['CONTEXT.md'],
-    },
-  },
-  {
-    step: 'execute',
-    points: ['execute:pre', 'execute:wave:pre', 'execute:wave:post', 'execute:post'],
-    agentRoles: ['executor', 'verifier'],
-    coreArtifacts: {
-      produces: ['SUMMARY.md'],
-      consumes: ['PLAN.md'],
-    },
-  },
-  {
-    step: 'verify',
-    points: ['verify:pre', 'verify:post'],
-    agentRoles: ['orchestrator'],
-    coreArtifacts: {
-      produces: ['UAT.md'],
-      consumes: ['SUMMARY.md'],
-    },
-  },
-  {
-    step: 'ship',
-    points: ['ship:pre', 'ship:post'],
-    agentRoles: ['orchestrator'],
-    coreArtifacts: {
-      produces: [],
-      consumes: ['UAT.md'],
-    },
-  },
-];
+// Generated from workflow markers by scripts/gen-loop-host-contract.cjs (ADR-894 §3).
+// Require the committed gsd-core/bin/lib/loop-host-contract.cjs artifact so the
+// registry generator and the loop-host-contract generator share one source of truth.
+const { LOOP_HOST_CONTRACT } = require('../gsd-core/bin/lib/loop-host-contract.cjs');
 
 // Canonical point order — explicit constant (do NOT rely on Set insertion order).
 // Used for point-ordering semantics in consumes-satisfiability validation and topo-sort.