diff --git a/docs/security/security.md b/docs/security/security.md
index 046364b..8dc17ec 100644
--- a/docs/security/security.md
+++ b/docs/security/security.md
@@ -449,10 +449,11 @@ Even with your own Issue fingerprint, you want GitHub alerts to remain stable:
 
 ## Current implementation status
 
-As of 2026-02, `promote_alerts.py` implements the fingerprint-based sync loop described above:
+As of 2026-03, `promote_alerts.py` implements the fingerprint-based sync loop described above:
 
 - Matches issues strictly by `secmeta.fingerprint` (from the alert message `Alert hash: ...`)
 - Ensures a parent issue per `rule_id` (`secmeta.type=parent`) and links child issues under the parent using GitHub sub-issues
+- Closes an open parent issue when all known child issues for the same `rule_id` are already closed
 - Writes/updates `secmeta` on child issues, including `gh_alert_numbers`, `first_seen`, `last_seen`, `last_seen_commit`, and occurrence tracking
 - Reopens a closed matching Issue when an alert is open again
 - Adds `[sec-event]` comments only for meaningful events (reopen, new occurrence)
diff --git a/src/security/collect_alert.py b/src/security/collect_alert.py
index 32cc5a4..63d7f75 100644
--- a/src/security/collect_alert.py
+++ b/src/security/collect_alert.py
@@ -59,13 +59,15 @@ def _snake_case(name: str) -> str:
     return name.strip().lower().replace(" ", "_")
 
 
-def _help_value(rule_help: str, name: str) -> str | None:
+def _help_value(rule_help: str | None, name: str) -> str | None:
     """Extract a value from ``**Name:** value`` markup in the rule help text."""
+    if not rule_help:
+        return None
     m = re.search(rf"\*\*{re.escape(name)}:\*\*\s*([^\n\r]+)", rule_help, re.IGNORECASE)
     return m.group(1) if m else None
 
 
-def _parse_rule_details(rule_help: str) -> dict[str, str | None]:
+def _parse_rule_details(rule_help: str | None) -> dict[str, str | None]:
     """Extract known rule detail fields from ``**Key:** value`` markup in rule help."""
     return {_snake_case(key): _help_value(rule_help, key) for key in RULE_DETAIL_KEYS}
 
@@ -118,7 +120,7 @@ def _normalise_alert(alert: dict) -> dict:
     instance = alert.get("most_recent_instance") or {}
     location = instance.get("location") or {}
     message_text = (instance.get("message") or {}).get("text", "")
-    rule_help = rule.get("help") or ""
+    rule_help = rule.get("help", "")
 
     return {
         "metadata": {
diff --git a/src/security/utils/alert_parser.py b/src/security/utils/alert_parser.py
index 4cbedbf..f593296 100644
--- a/src/security/utils/alert_parser.py
+++ b/src/security/utils/alert_parser.py
@@ -101,7 +101,7 @@ def load_open_alerts_from_file(path: str) -> LoadedAlerts:
     alerts = data.get("alerts", [])
     logging.info(f"Loaded {len(alerts)} alerts from {path} (repo={repo_full})")
 
-    open_alerts = [a for a in alerts if str((a.get("metadata") or {}).get("state") or "").lower() == "open"]
+    open_alerts = [a for a in alerts if str(a.get("metadata", {}).get("state", "")).lower() == "open"]
     logging.info(f"Found {len(open_alerts)} open alerts")
 
     open_by_number: dict[int, Alert] = {}
diff --git a/src/security/utils/issue_sync.py b/src/security/utils/issue_sync.py
index 87330b1..21429b9 100644
--- a/src/security/utils/issue_sync.py
+++ b/src/security/utils/issue_sync.py
@@ -71,13 +71,13 @@ def build_issue_index(issues: dict[int, Issue]) -> IssueIndex:
 
     for issue in issues.values():
         secmeta = load_secmeta(issue.body)
-        secmeta_type = (secmeta.get("type") or "").strip().lower()
+        secmeta_type = secmeta.get("type", "").strip().lower()
         if secmeta_type == SECMETA_TYPE_PARENT:
-            rule_id = (secmeta.get("rule_id") or "").strip()
+            rule_id = secmeta.get("rule_id", "").strip()
             if rule_id:
                 parent_by_rule_id.setdefault(rule_id, issue)
 
-        fp = (secmeta.get("fingerprint") or "").strip() or (secmeta.get("alert_hash") or "").strip()
+        fp = secmeta.get("fingerprint", "").strip() or secmeta.get("alert_hash", "").strip()
         if fp and secmeta_type != SECMETA_TYPE_PARENT:
             by_fingerprint.setdefault(fp, issue)
 
@@ -146,6 +146,61 @@ def maybe_reopen_parent_issue(
         )
 
 
+def _close_resolved_parent_issues(
+    issues: dict[int, Issue],
+    index: IssueIndex,
+    *,
+    dry_run: bool,
+) -> None:
+    """Close open parent issues whose known child issues are all closed."""
+    child_issues_by_rule_id: dict[str, list[Issue]] = {}
+
+    for issue in issues.values():
+        secmeta = load_secmeta(issue.body)
+        if secmeta.get("type", "").strip().lower() != SECMETA_TYPE_CHILD:
+            continue
+
+        rule_id = secmeta.get("rule_id", "").strip()
+        if not rule_id:
+            continue
+
+        child_issues_by_rule_id.setdefault(rule_id, []).append(issue)
+
+    for rule_id, parent_issue in index.parent_by_rule_id.items():
+        if parent_issue.state.lower() == "closed":
+            continue
+
+        child_issues = child_issues_by_rule_id.get(rule_id, [])
+        if not child_issues:
+            continue
+
+        if any(child_issue.state.lower() != "closed" for child_issue in child_issues):
+            continue
+
+        parent_secmeta = load_secmeta(parent_issue.body)
+        repo = parent_secmeta.get("repo", "").strip()
+        if not repo and child_issues:
+            repo = load_secmeta(child_issues[0].body).get("repo", "").strip()
+        if not repo:
+            logging.debug(f"Skip closing parent issue #{parent_issue.number}: no repo in secmeta")
+            continue
+
+        if dry_run:
+            logging.info(
+                f"DRY-RUN: would close parent issue #{parent_issue.number} (rule_id={rule_id}) "
+                f"because all {len(child_issues)} child issue(s) are closed"
+            )
+            parent_issue.state = "closed"
+            continue
+
+        if gh_issue_edit_state(repo, parent_issue.number, "closed"):
+            logging.info(
+                f"Closed parent issue #{parent_issue.number} (rule_id={rule_id}) "
+                f"because all {len(child_issues)} child issue(s) are closed"
+            )
+            parent_issue.state = "closed"
+
+
 def ensure_parent_issue(
     alert: Alert,
     issues: dict[int, Issue],
@@ -508,7 +563,7 @@ def _merge_child_secmeta(
     if str(ctx.alert_number) not in existing_alerts:
         existing_alerts.append(str(ctx.alert_number))
 
-    last_occ_fp = secmeta.get("last_occurrence_fp") or ""
+    last_occ_fp = secmeta.get("last_occurrence_fp", "")
     occurrence_count = int(secmeta.get("occurrence_count") or "0" or 0)
     new_occurrence = bool(ctx.occurrence_fp and ctx.occurrence_fp != last_occ_fp)
     if occurrence_count <= 0:
@@ -880,5 +935,6 @@ def sync_alerts_and_issues(
         priority_sync.flush()
 
     _label_orphan_issues(alerts, index, dry_run=dry_run)
+    _close_resolved_parent_issues(issues, index, dry_run=dry_run)
 
     return SyncResult(notifications=notifications, severity_changes=severity_changes)
diff --git a/src/security/utils/models.py b/src/security/utils/models.py
index 1cd6cb8..c495db7 100644
--- a/src/security/utils/models.py
+++ b/src/security/utils/models.py
@@ -143,7 +143,7 @@ def from_dict(cls, d: dict[str, Any], *, repo: str = "") -> "Alert":
             metadata=AlertMetadata(**{k: v for k, v in md.items() if k in AlertMetadata.__dataclass_fields__}),
             alert_details=AlertDetails(**{k: v for k, v in ad.items() if k in AlertDetails.__dataclass_fields__}),
             rule_details=RuleDetails(**{k: v for k, v in rd.items() if k in RuleDetails.__dataclass_fields__}),
-            repo=repo or str(d.get("_repo") or ""),
+            repo=repo or str(d.get("_repo", "")),
         )
 
 
diff --git a/src/shared/github_issues.py b/src/shared/github_issues.py
index 8edf70a..00a5604 100644
--- a/src/shared/github_issues.py
+++ b/src/shared/github_issues.py
@@ -118,9 +118,9 @@ def gh_issue_list_by_label(repo: str, label: str) -> dict[int, Issue]:
         label_names = [str(lbl.get("name") or lbl) if isinstance(lbl, dict) else str(lbl) for lbl in raw_labels]
         issues[number] = Issue(
             number=number,
-            state=str(obj.get("state") or ""),
-            title=str(obj.get("title") or ""),
-            body=str(obj.get("body") or ""),
+            state=str(obj.get("state", "")),
+            title=str(obj.get("title", "")),
+            body=str(obj.get("body", "")),
             labels=label_names,
         )
 
diff --git a/src/shared/github_projects.py b/src/shared/github_projects.py
index 0195379..2a2ec4a 100644
--- a/src/shared/github_projects.py
+++ b/src/shared/github_projects.py
@@ -233,7 +233,7 @@ def _prefetch_items(self) -> None:
                 if item_id and content_id:
                     self._content_to_item[content_id] = item_id
                 fv = node.get("fieldValueByName") or {}
-                current_opt = fv.get("optionId") or ""
+                current_opt = fv.get("optionId", "")
                 if item_id:
                     self._item_current_option[item_id] = current_opt
             total += len(nodes)
diff --git a/tests/security/utils/test_issue_sync.py b/tests/security/utils/test_issue_sync.py
index 9a502c5..5fa7422 100644
--- a/tests/security/utils/test_issue_sync.py
+++ b/tests/security/utils/test_issue_sync.py
@@ -26,6 +26,7 @@
 from shared.models import Issue
 from utils.issue_sync import (
     _append_notification,
+    _close_resolved_parent_issues,
     _comment_child_event,
     _flush_parent_body_updates,
     _handle_existing_child_issue,
@@ -811,6 +812,50 @@ def test_label_orphan_no_repo_in_secmeta() -> None:
     _label_orphan_issues({}, index, dry_run=False)
 
 
+# =====================================================================
+# _close_resolved_parent_issues
+# =====================================================================
+
+
+def test_close_resolved_parent_issue(mocker: MockerFixture) -> None:
+    """Closes an open parent when all known children are closed."""
+    mock_edit = mocker.patch("utils.issue_sync.gh_issue_edit_state", return_value=True)
+    parent = _issue_with_secmeta(10, {
+        "type": "parent", "rule_id": "R1", "repo": "org/repo",
+    })
+    child_one = _issue_with_secmeta(11, {
+        "type": "child", "rule_id": "R1", "fingerprint": "fp1", "repo": "org/repo",
+    }, state="closed")
+    child_two = _issue_with_secmeta(12, {
+        "type": "child", "rule_id": "R1", "fingerprint": "fp2", "repo": "org/repo",
+    }, state="closed")
+    issues = {10: parent, 11: child_one, 12: child_two}
+    index = build_issue_index(issues)
+
+    _close_resolved_parent_issues(issues, index, dry_run=False)
+
+    mock_edit.assert_called_once_with("org/repo", 10, "closed")
+    assert parent.state == "closed"
+
+
+def test_close_resolved_parent_skips_open_child(mocker: MockerFixture) -> None:
+    """Leaves the parent open when any child is still open."""
+    mock_edit = mocker.patch("utils.issue_sync.gh_issue_edit_state", return_value=True)
+    parent = _issue_with_secmeta(10, {
+        "type": "parent", "rule_id": "R1", "repo": "org/repo",
+    })
+    child = _issue_with_secmeta(11, {
+        "type": "child", "rule_id": "R1", "fingerprint": "fp1", "repo": "org/repo",
+    }, state="open")
+    issues = {10: parent, 11: child}
+    index = build_issue_index(issues)
+
+    _close_resolved_parent_issues(issues, index, dry_run=False)
+
+    mock_edit.assert_not_called()
+    assert parent.state == "open"
+
+
 # =====================================================================
 # ensure_issue (end-to-end orchestration per alert)
 # =====================================================================
@@ -947,6 +992,24 @@ def test_sync_severity_change_detected(sast_alert: Alert) -> None:
     assert result.severity_changes[0].new_severity == "high"
 
 
+def test_sync_closes_parent_when_all_children_closed(mocker: MockerFixture) -> None:
+    """Closes a parent during sync when its children are already closed."""
+    mock_edit = mocker.patch("utils.issue_sync.gh_issue_edit_state", return_value=True)
+    parent = _issue_with_secmeta(10, {
+        "type": "parent", "rule_id": "R1", "repo": "org/repo",
+    })
+    child = _issue_with_secmeta(11, {
+        "type": "child", "rule_id": "R1", "fingerprint": "fp1", "repo": "org/repo",
+    }, state="closed")
+    issues = {10: parent, 11: child}
+
+    result = sync_alerts_and_issues({}, issues, dry_run=False)
+
+    assert result.notifications == []
+    mock_edit.assert_called_once_with("org/repo", 10, "closed")
+    assert parent.state == "closed"
+
+
 # =====================================================================
 # _init_priority_sync
 # =====================================================================