diff --git a/ebuild/cli/commands.py b/ebuild/cli/commands.py
index ad039bbb..53765193 100644
--- a/ebuild/cli/commands.py
+++ b/ebuild/cli/commands.py
@@ -2281,6 +2281,9 @@ def new(log: Logger, project_name: str, template_name: str, board_name: str,
         "build.yaml.template": project_dir / "build.yaml",
         "eos.yaml.template": project_dir / "eos.yaml",
         "README.md.template": project_dir / "README.md",
+        # Every template's build.yaml declares a test target built from
+        # tests/test_main.c; without this file `ebuild build` fails at once.
+        "test_main.c.template": project_dir / "tests" / "test_main.c",
     }
 
     for template_file, output_path in file_mapping.items():
@@ -2293,6 +2296,7 @@ def new(log: Logger, project_name: str, template_name: str, board_name: str,
         for key, val in replacements.items():
             content = content.replace(key, val)
 
+        output_path.parent.mkdir(parents=True, exist_ok=True)
         output_path.write_text(content, encoding="utf-8")
         log.success(f"  {output_path.relative_to(parent)}")
 
diff --git a/templates/safety-critical/build.yaml.template b/templates/safety-critical/build.yaml.template
index 01317eb0..3222e520 100644
--- a/templates/safety-critical/build.yaml.template
+++ b/templates/safety-critical/build.yaml.template
@@ -24,12 +24,6 @@ targets:
       - eos
     depends: []
 
-firmware:
-  board: {{BOARD_NAME}}
-  core: {{CORE}}
-  tick_rate: 1000
-  watchdog_ms: 100
-
   - name: test_{{PROJECT_NAME}}
     type: test
     sources:
@@ -39,3 +33,9 @@ firmware:
     uses:
       - eos
     depends: []
+
+firmware:
+  board: {{BOARD_NAME}}
+  core: {{CORE}}
+  tick_rate: 1000
+  watchdog_ms: 100
diff --git a/tests/unit/test_new_scaffold.py b/tests/unit/test_new_scaffold.py
new file mode 100644
index 00000000..385a0809
--- /dev/null
+++ b/tests/unit/test_new_scaffold.py
@@ -0,0 +1,26 @@
+"""`ebuild new` must write every source its generated build.yaml declares."""
+from pathlib import Path
+
+import pytest
+import yaml
+from click.testing import CliRunner
+
+from ebuild.cli.commands import cli
+
+TEMPLATES = ["bare-metal", "ble-sensor", "rtos-app", "linux-app",
+             "secure-boot", "safety-critical"]
+
+
+@pytest.mark.parametrize("template", TEMPLATES)
+def test_new_writes_every_declared_source(tmp_path: Path, template: str) -> None:
+    result = CliRunner().invoke(
+        cli, ["new", "proj", "--template", template, "--board", "stm32f4",
+              "--output-dir", str(tmp_path)])
+    assert result.exit_code == 0, result.output
+    project = tmp_path / "proj"
+    config = yaml.safe_load((project / "build.yaml").read_text(encoding="utf-8"))
+    declared = [src for target in config["targets"] for src in target.get("sources", [])]
+    assert declared, "template declares no sources"
+    missing = [src for src in declared if not (project / src).is_file()]
+    assert not missing, f"{template}: build.yaml declares missing sources {missing}"
+    assert "{{" not in (project / "tests" / "test_main.c").read_text(encoding="utf-8")