diff --git a/WORKBOARD.yaml b/WORKBOARD.yaml
index 5c31e95..3c25484 100644
--- a/WORKBOARD.yaml
+++ b/WORKBOARD.yaml
@@ -486,3 +486,8 @@ items:
     status: validated
     source: docs/LEGACY-INGEST.md
     owner: ""
+  - id: CTO-WORK-098
+    title: Stage 5 Target Sandbox Stale State Gate
+    status: validated
+    source: docs/STAGE5-TARGET-SANDBOX-STALE-CASE-STATE.md
+    owner: ""
diff --git a/tools/validate_cto_child.py b/tools/validate_cto_child.py
index 1c6a94e..ddd8973 100644
--- a/tools/validate_cto_child.py
+++ b/tools/validate_cto_child.py
@@ -16,6 +16,7 @@ REQUIRED_FILES = [
     "WORKBOARD.yaml",
     "CONTEXT.md",
     "docs/LEGACY-INGEST.md",
+    "docs/STAGE5-TARGET-SANDBOX-STALE-CASE-STATE.md",
     ".sot/00-START/CTO-WORKSPACE-INTENT.md",
     ".sot/03-PROTOCOLS/CTO-CASE-BACKEND-BRIEF.md",
     ".sot/03-PROTOCOLS/CTO-ARCHITECTURE-BRIEF-CLOSEOUT-PRD.md",
@@ -904,6 +905,21 @@ REQUIRED_STAGE5_TARGET_FORBIDDEN_ACTIONS = [
     "cortex_core_mutation",
 ]
 
+REQUIRED_STAGE5_TARGET_STALE_STATE_PHRASES = [
+    "Local planning evidence only. Not Core authority. Not Runtime authority.",
+    "Status: stale-state-declared.",
+    "/home/svrnty/workspaces/cortex-os/cto-stage5-target-sandbox",
+    "The target sandbox is still not move-ready",
+    "`python3 -m pytest -q` in the target sandbox: `11 passed`.",
+    "`python3 tools/validate_cto_stage5_target_sandbox_child.py` in the target",
+    "`python3 tools/validate_cto_child.py` in CTO: `ok: true`.",
+    "No live process matched the target path",
+    "not archive-stable completion evidence",
+    "Do not edit the target sandbox only to make cleanup look cleaner.",
+    "Movement remains deferred until CTO replaces the absolute live path dependency",
+    "No hard delete, Core mutation, Harness rerun, Case rerun, provider",
+]
+
 REQUIRED_PROVIDER_ADMISSION_PRD_PHRASES = [
     "Local planning SOT only. Not a Core Protocol. Not active Core authority.",
     "https://github.com/workos/case.git",
@@ -2665,6 +2681,14 @@ def main() -> int:
             if key.lower() in {"api_key", "apikey", "access_token", "token", "secret", "password", "credential_value"}:
                 errors.append(f"stage5_target_admission_forbidden_secret_key:{key}")
 
+    stage5_target_stale_state = ROOT / "docs/STAGE5-TARGET-SANDBOX-STALE-CASE-STATE.md"
+    if stage5_target_stale_state.is_file():
+        text = stage5_target_stale_state.read_text(encoding="utf-8")
+        for phrase in REQUIRED_STAGE5_TARGET_STALE_STATE_PHRASES:
+            checked.append(f"stage5_target_stale_state_phrase:{phrase}")
+            if phrase not in text:
+                errors.append(f"missing_stage5_target_stale_state_phrase:{phrase}")
+
     stage6_prd = ROOT / ".sot/03-PROTOCOLS/CTO-CASE-STAGE6-CANDIDATE-DEFAULT-PRD.md"
     if stage6_prd.is_file():
         text = stage6_prd.read_text(encoding="utf-8")
@@ -2999,6 +3023,10 @@ def main() -> int:
             checked.append(f"workboard_id:{issue_id}")
             if issue_id not in text:
                 errors.append(f"missing_workboard_id:{issue_id}")
+        for issue_id in ["CTO-WORK-098"]:
+            checked.append(f"workboard_id:{issue_id}")
+            if issue_id not in text:
+                errors.append(f"missing_workboard_id:{issue_id}")
         expected_statuses = {
             "CTO-WORK-001": "validated",
             "CTO-WORK-002": "validated",
@@ -3094,6 +3122,7 @@ def main() -> int:
             "CTO-WORK-095": "validated",
             "CTO-WORK-096": "validated",
             "CTO-WORK-097": "validated",
+            "CTO-WORK-098": "validated",
         }
         for issue_id, expected in expected_statuses.items():
             checked.append(f"workboard_status:{issue_id}:{expected}")
@@ -3196,6 +3225,8 @@ def main() -> int:
             errors.append("workboard_missing_codex_retention_archive_source")
         if "docs/LEGACY-INGEST.md" not in text:
             errors.append("workboard_missing_legacy_ingest_source")
+        if "docs/STAGE5-TARGET-SANDBOX-STALE-CASE-STATE.md" not in text:
+            errors.append("workboard_missing_stage5_target_stale_state_source")
 
     payload = {
         "ok": not errors,