fix(#1505): extract context_guard step to reference file; fix allow-test-rule see ref

- Extract execute-phase.md context_guard step prose to
  gsd-core/references/execute-phase-context-guard.md (@-ref lazy load),
  bringing execute-phase.md back under the ADR-857 phase-6 size ceiling
  (92914 < 93166 bytes)
- Fix allow-test-rule comment: add `see #1452` per ADR-456 lint rule
- Update feat-1452 tests to check the reference file for extracted content
- Register execute-phase-context-guard.md in INVENTORY-MANIFEST.json and
  INVENTORY.md Workflow References section
- Regenerate workflow-size-baseline.json after file shrinkage

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/INVENTORY-MANIFEST.json

@@ -214,6 +214,7 @@
       "edge-probe.md",
       "execute-mvp-tdd.md",
       "execute-phase-between-wave-reset.md",
+      "execute-phase-context-guard.md",
       "execute-phase-wave-guard.md",
       "executor-examples.md",
       "gate-prompts.md",

docs/INVENTORY.md

@@ -301,6 +301,7 @@ Full roster at `gsd-core/references/*.md`. References are shared knowledge docum
 |-----------|------|
 | `agent-contracts.md` | Formal interface between orchestrators and agents. |
 | `context-budget.md` | Context window budget allocation rules. |
+| `execute-phase-context-guard.md` | Context exhaustion guard step for `execute-phase` wave loop — `workflow.context_guard_mode` dispatch table (warn/auto/off) and POOR-tier pause-work trigger (#1452). |
 | `continuation-format.md` | Session continuation/resume format. |
 | `domain-probes.md` | Domain-specific probing questions for discuss-phase. |
 | `edge-probe.md` | Spec-phase edge-completeness probe — 8-category edge taxonomy, shape classification, and the `requirements → checks → verifier` resolution model (Step 5.5). |