Fix black formatting and target Python 3.12 in CI

Reformat 8 files and add --target-version py312 to avoid
3.13 AST parsing issues with Python 3.12 container.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_chain_security.py

@@ -52,8 +52,7 @@ def test_concurrent_append_no_fork(chain_dir: Path):
 
     # Every index must be unique (no fork)
     assert len(all_indices) == len(set(all_indices)), (
-        f"Duplicate chain indices detected — chain forked! "
-        f"Indices: {sorted(all_indices)}"
+        f"Duplicate chain indices detected — chain forked! " f"Indices: {sorted(all_indices)}"
     )
 
     # Indices should be 0..N-1 contiguous
@@ -100,7 +99,7 @@ def test_truncated_chain_file(chain_dir: Path, private_key: Ed25519PrivateKey):
     # Truncate the file mid-record
     chain_file = chain_dir / "chain.bin"
     data = chain_file.read_bytes()
-    chain_file.write_bytes(data[:len(data) - 50])
+    chain_file.write_bytes(data[: len(data) - 50])
 
     store2 = ChainStore(chain_dir)
     records = list(store2._iter_raw())

tests/test_deadman_enforcement.py

@@ -22,7 +22,6 @@ from pathlib import Path
 import pytest
 from click.testing import CliRunner
 
-
 # ── Fixtures ────────────────────────────────────────────────────────────────
 
 
@@ -205,7 +204,9 @@ def cli_runner():
     return CliRunner()
 
 
-def test_check_deadman_disarmed(tmp_path: Path, cli_runner: CliRunner, monkeypatch: pytest.MonkeyPatch):
+def test_check_deadman_disarmed(
+    tmp_path: Path, cli_runner: CliRunner, monkeypatch: pytest.MonkeyPatch
+):
     """check-deadman exits 0 and prints helpful message when not armed."""
     from soosef.fieldkit import deadman as deadman_mod
     from soosef.cli import main
@@ -219,7 +220,9 @@ def test_check_deadman_disarmed(tmp_path: Path, cli_runner: CliRunner, monkeypat
     assert "not armed" in result.output
 
 
-def test_check_deadman_armed_ok(tmp_path: Path, cli_runner: CliRunner, monkeypatch: pytest.MonkeyPatch):
+def test_check_deadman_armed_ok(
+    tmp_path: Path, cli_runner: CliRunner, monkeypatch: pytest.MonkeyPatch
+):
     """check-deadman exits 0 when armed and check-in is current."""
     from soosef.fieldkit import deadman as deadman_mod
     from soosef.cli import main
@@ -241,7 +244,9 @@ def test_check_deadman_armed_ok(tmp_path: Path, cli_runner: CliRunner, monkeypat
     assert "OK" in result.output
 
 
-def test_check_deadman_overdue_in_grace(tmp_path: Path, cli_runner: CliRunner, monkeypatch: pytest.MonkeyPatch):
+def test_check_deadman_overdue_in_grace(
+    tmp_path: Path, cli_runner: CliRunner, monkeypatch: pytest.MonkeyPatch
+):
     """check-deadman exits 0 but prints OVERDUE warning when past interval but in grace."""
     from soosef.fieldkit import deadman as deadman_mod
     from soosef.cli import main