diff --git a/.github/workflows/agents-issue-format-guard.yml b/.github/workflows/agents-issue-format-guard.yml
index 1a6d216a1..ebf03c9c0 100644
--- a/.github/workflows/agents-issue-format-guard.yml
+++ b/.github/workflows/agents-issue-format-guard.yml
@@ -61,6 +61,14 @@ jobs:
           jq -r '.body // ""' issue.json > body.md
           exempt=false
           held=false
+          # A closed issue has nothing left to format. Routing one to the optimizer
+          # produces a body edit, that edit re-fires this guard, and the pair loops
+          # against work that is already delivered — see Fine-Art-Archive#464, which
+          # kept formatting for 17.5 hours after it was closed.
+          if [[ "$(jq -r '.state // "" | ascii_downcase' issue.json)" == "closed" ]]; then
+            echo "Issue is closed — nothing to format."
+            exempt=true
+          fi
           if jq -e '[.labels[].name] | any(. == "tracker:durable" or . == "wontfix")' issue.json >/dev/null; then exempt=true; fi
           if jq -e '[.labels[].name] | any(. == "agents:auto-pilot-pause" or . == "needs-human")' issue.json >/dev/null; then held=true; fi
           if jq -er '.author.login // ""' issue.json | grep -qiE '(\[bot\]|^renovate$|^dependabot$)'; then exempt=true; fi
diff --git a/langsmith-fleet-worker-attempt.json b/langsmith-fleet-worker-attempt.json
index 5c8ce841b..65173a280 100644
--- a/langsmith-fleet-worker-attempt.json
+++ b/langsmith-fleet-worker-attempt.json
@@ -1,13 +1,13 @@
 {
   "agent": "codex",
   "cli_version": "0.144.1",
-  "emitted_at": "2026-08-08T15:51:23.873676Z",
+  "emitted_at": "2026-08-08T23:54:44.735714Z",
   "execution_profile": "codex-default",
   "fallback_models": [
     "gpt-5.5"
   ],
   "operation_role": "worker",
-  "pr_number": "2985",
+  "pr_number": "2997",
   "requested_model": "gpt-5.6-terra",
   "runner": "reusable-codex-run",
   "schema": "langsmith-fleet/v1",
diff --git a/templates/consumer-repo/.github/workflows/agents-issue-format-guard.yml b/templates/consumer-repo/.github/workflows/agents-issue-format-guard.yml
index 1a6d216a1..ebf03c9c0 100644
--- a/templates/consumer-repo/.github/workflows/agents-issue-format-guard.yml
+++ b/templates/consumer-repo/.github/workflows/agents-issue-format-guard.yml
@@ -61,6 +61,14 @@ jobs:
           jq -r '.body // ""' issue.json > body.md
           exempt=false
           held=false
+          # A closed issue has nothing left to format. Routing one to the optimizer
+          # produces a body edit, that edit re-fires this guard, and the pair loops
+          # against work that is already delivered — see Fine-Art-Archive#464, which
+          # kept formatting for 17.5 hours after it was closed.
+          if [[ "$(jq -r '.state // "" | ascii_downcase' issue.json)" == "closed" ]]; then
+            echo "Issue is closed — nothing to format."
+            exempt=true
+          fi
           if jq -e '[.labels[].name] | any(. == "tracker:durable" or . == "wontfix")' issue.json >/dev/null; then exempt=true; fi
           if jq -e '[.labels[].name] | any(. == "agents:auto-pilot-pause" or . == "needs-human")' issue.json >/dev/null; then held=true; fi
           if jq -er '.author.login // ""' issue.json | grep -qiE '(\[bot\]|^renovate$|^dependabot$)'; then exempt=true; fi
diff --git a/tests/workflows/test_issue_format_guard_closed_issues.py b/tests/workflows/test_issue_format_guard_closed_issues.py
new file mode 100644
index 000000000..402aada60
--- /dev/null
+++ b/tests/workflows/test_issue_format_guard_closed_issues.py
@@ -0,0 +1,123 @@
+"""The format guard must not process closed issues.
+
+These tests execute the guard's real "Resolve issue" step, lifted straight out of
+the workflow YAML, against a fixture issue payload. A closed issue routed to the
+optimizer produces a body edit, that edit re-fires the guard, and the pair loops
+against already-delivered work: Fine-Art-Archive#464 kept formatting for 17.5
+hours after it was closed.
+"""
+
+from __future__ import annotations
+
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+import yaml
+
+REPO_ROOT = Path(__file__).resolve().parents[2]
+GUARD_PATH = REPO_ROOT / ".github/workflows/agents-issue-format-guard.yml"
+CONSUMER_GUARD_PATH = (
+    REPO_ROOT / "templates/consumer-repo/.github/workflows/agents-issue-format-guard.yml"
+)
+GUARD_PATHS = (GUARD_PATH, CONSUMER_GUARD_PATH)
+
+JQ_AVAILABLE = shutil.which("jq") is not None
+skip_if_no_jq = pytest.mark.skipif(not JQ_AVAILABLE, reason="jq required by the guard step")
+
+
+def _resolve_step_script(path: Path) -> str:
+    workflow = yaml.safe_load(path.read_text(encoding="utf-8"))
+    for step in workflow["jobs"]["check"]["steps"]:
+        if step.get("name") == "Resolve issue":
+            return step["run"]
+    raise AssertionError(f"'Resolve issue' step not found in {path}")
+
+
+def _run_resolve_step(tmp_path: Path, script: str, issue_json: str) -> dict[str, str]:
+    """Run the real step with `gh` stubbed to return the fixture payload."""
+    bin_dir = tmp_path / "bin"
+    bin_dir.mkdir()
+    fixture = tmp_path / "fixture.json"
+    fixture.write_text(issue_json, encoding="utf-8")
+
+    # The step's only external call is `gh issue view … > issue.json`.
+    gh_stub = bin_dir / "gh"
+    gh_stub.write_text(f'#!/usr/bin/env bash\ncat "{fixture}"\n', encoding="utf-8")
+    gh_stub.chmod(0o755)
+
+    github_output = tmp_path / "github_output"
+    github_output.touch()
+
+    completed = subprocess.run(
+        ["bash", "-c", script],
+        cwd=tmp_path,
+        text=True,
+        capture_output=True,
+        env={
+            "PATH": f"{bin_dir}:{shutil.os.environ['PATH']}",
+            "GITHUB_OUTPUT": str(github_output),
+            "GITHUB_REPOSITORY": "stranske/Fine-Art-Archive",
+            "NUMBER": "464",
+            "GH_TOKEN": "stub",
+        },
+    )
+    assert completed.returncode == 0, f"step failed: {completed.stderr}"
+
+    outputs: dict[str, str] = {}
+    for line in github_output.read_text(encoding="utf-8").splitlines():
+        if "=" in line:
+            key, _, value = line.partition("=")
+            outputs[key] = value
+    return outputs
+
+
+# The #464 shape: closed, and carrying none of the pre-existing exemption signals.
+CLOSED_ISSUE = """
+{
+  "number": 464,
+  "state": "CLOSED",
+  "body": "## Tasks\\n- [ ] do a thing\\n\\n## Acceptance Criteria\\n- [ ] it is done\\n",
+  "labels": [{"name": "agents:format"}, {"name": "agents:formatted"}],
+  "author": {"login": "stranske"}
+}
+"""
+
+OPEN_ISSUE = CLOSED_ISSUE.replace('"state": "CLOSED"', '"state": "OPEN"')
+
+
+@skip_if_no_jq
+@pytest.mark.parametrize("guard_path", GUARD_PATHS, ids=lambda p: str(p.relative_to(REPO_ROOT)))
+def test_closed_issue_is_exempt(tmp_path: Path, guard_path: Path) -> None:
+    outputs = _run_resolve_step(tmp_path, _resolve_step_script(guard_path), CLOSED_ISSUE)
+    assert outputs["exempt"] == "true", (
+        "a closed issue must be exempt; otherwise the guard keeps routing it to the "
+        "optimizer and the pair loops against delivered work"
+    )
+
+
+@skip_if_no_jq
+@pytest.mark.parametrize("guard_path", GUARD_PATHS, ids=lambda p: str(p.relative_to(REPO_ROOT)))
+def test_open_issue_is_still_processed(tmp_path: Path, guard_path: Path) -> None:
+    """The exemption must be narrow: an equivalent open issue still gets validated."""
+    outputs = _run_resolve_step(tmp_path, _resolve_step_script(guard_path), OPEN_ISSUE)
+    assert outputs["exempt"] == "false"
+    assert outputs["held"] == "false"
+
+
+@skip_if_no_jq
+@pytest.mark.parametrize("guard_path", GUARD_PATHS, ids=lambda p: str(p.relative_to(REPO_ROOT)))
+def test_closed_state_is_matched_case_insensitively(tmp_path: Path, guard_path: Path) -> None:
+    """`gh` returns CLOSED; the REST API returns closed. Both must exempt."""
+    lowercase = CLOSED_ISSUE.replace('"state": "CLOSED"', '"state": "closed"')
+    outputs = _run_resolve_step(tmp_path, _resolve_step_script(guard_path), lowercase)
+    assert outputs["exempt"] == "true"
+
+
+def test_both_guard_copies_carry_the_closed_check() -> None:
+    """Root and consumer template must not drift on this check."""
+    for path in GUARD_PATHS:
+        assert "ascii_downcase" in _resolve_step_script(
+            path
+        ), f"{path} lacks the closed-state check"