fix(cli): reject duplicate --side names with a clear error

src/pf1e_simulator/cli.py

@@ -108,6 +108,18 @@ def _build_spec(args: argparse.Namespace) -> EncounterSpec:
     map_spec = load_map(args.map)
     provided = [tuple(raw) for raw in args.side]
     provided_names = {raw[0] for raw in provided}
+    seen_names: set[str] = set()
+    duplicates: set[str] = set()
+    for raw in provided:
+        if raw[0] in seen_names:
+            duplicates.add(raw[0])
+        seen_names.add(raw[0])
+    if duplicates:
+        msg = (
+            "duplicate --side names (each camp must be provided exactly "
+            f"once): {', '.join(sorted(duplicates))}"
+        )
+        raise CliError(msg)
     missing = sorted(set(map_spec.deployment) - provided_names)
     if missing:
         msg = f"sides in map deployment without --side: {', '.join(missing)}"

tests/test_cli.py

@@ -60,6 +60,30 @@ def test_cli_rejects_missing_deployment_side(capsys: pytest.CaptureFixture[str])
     assert "monsters" in capsys.readouterr().err
 
 
+def test_cli_rejects_duplicate_side_names(capsys: pytest.CaptureFixture[str]) -> None:
+    rc = main(
+        [
+            "--map",
+            str(MAP),
+            "--side",
+            "players",
+            str(GOBLIN),
+            "--side",
+            "players",
+            str(ORC),
+            "--side",
+            "monsters",
+            str(ORC),
+            "--runs",
+            "10",
+        ]
+    )
+    assert rc == 2
+    err = capsys.readouterr().err
+    assert "duplicate --side names" in err
+    assert "players" in err
+
+
 def test_cli_transcript_prints_first_battle_log(capsys: pytest.CaptureFixture[str]) -> None:
     rc = main(
         [