feat: add .mcp.json support to scaffold for mock MCP servers

scripts/scaffold.py

@@ -52,6 +52,12 @@ def _build_template_context(
     tags = metadata.tags or []
     has_llm_judge = (submission_dir / "tests" / "llm_judge.py").is_file()
 
+    # .mcp.json can be at root or inside supportive/ (legacy location)
+    has_mcp_json = (
+        (submission_dir / ".mcp.json").is_file()
+        or (submission_dir / "supportive" / ".mcp.json").is_file()
+    )
+
     base_context = {
         "submission_name": metadata.name,
         "persona": metadata.persona or "general",
@@ -62,6 +68,7 @@ def _build_template_context(
         "has_supportive": (submission_dir / "supportive").is_dir(),
         "has_scripts": (submission_dir / "scripts").is_dir(),
         "has_claude_md": (submission_dir / "CLAUDE.md").is_file(),
+        "has_mcp_json": has_mcp_json,
         "has_llm_judge": has_llm_judge,
         # These were formerly ad-hoc dict reads from raw metadata; they are
         # not SubmissionMetadata fields (extra="forbid" rejects them), so the
@@ -135,13 +142,20 @@ def _copy_submission_files(
 
     _copy_supportive(submission_dir, build_context_dir, variant)
 
-    # Treatment-only assets: CLAUDE.md, scripts/, docs, and skills are
+    # Treatment-only assets: CLAUDE.md, .mcp.json, scripts/, docs, and skills are
     # skill knowledge that only the treatment variant should receive.
     if variant == "treatment":
         claude_md = submission_dir / "CLAUDE.md"
         if claude_md.is_file():
             shutil.copy2(claude_md, build_context_dir / "CLAUDE.md")
 
+        # .mcp.json: check root first, fall back to supportive/ (legacy location)
+        mcp_json = submission_dir / ".mcp.json"
+        if not mcp_json.is_file():
+            mcp_json = submission_dir / "supportive" / ".mcp.json"
+        if mcp_json.is_file():
+            shutil.copy2(mcp_json, build_context_dir / ".mcp.json")
+
         scripts_src = submission_dir / "scripts"
         if scripts_src.is_dir():
             shutil.copytree(
@@ -210,11 +224,12 @@ def scaffold_submission(
             strategy,
         )
         # Control is a vanilla agent: no supportive files, no scripts,
-        # no CLAUDE.md. Only instruction.md and tests are shared.
+        # no CLAUDE.md, no .mcp.json. Only instruction.md and tests are shared.
         if variant == "control":
             context["has_supportive"] = False
             context["has_scripts"] = False
             context["has_claude_md"] = False
+            context["has_mcp_json"] = False
         rendered = _render_templates(jinja_env, context)
 
         target_dir.mkdir(parents=True, exist_ok=True)

templates/Dockerfile.j2

@@ -6,6 +6,9 @@ COPY tests/ /tests/
 {% if has_claude_md %}
 COPY CLAUDE.md /workspace/CLAUDE.md
 {% endif %}
+{% if has_mcp_json %}
+COPY .mcp.json /workspace/.mcp.json
+{% endif %}
 {% if has_supportive %}
 COPY supportive/ /workspace/supportive/
 {% endif %}

tests/test_scaffold.py

@@ -274,6 +274,83 @@ def test_no_supportive_in_dockerfile_when_absent(self, valid_submission: Path, t
         content = (treatment / "environment" / "Dockerfile").read_text()
         assert "COPY supportive/" not in content
 
+    def test_mcp_json_at_root_copied_only_for_treatment(self, tmp_path: Path):
+        """.mcp.json at submission root is copied only for treatment."""
+        sub = tmp_path / "mcp-skill"
+        sub.mkdir()
+        (sub / "instruction.md").write_text("Do it.\n")
+        (sub / "skills").mkdir()
+        (sub / "skills" / "SKILL.md").write_text("# Skill\n")
+        (sub / "tests").mkdir()
+        (sub / "tests" / "test_outputs.py").write_text("def test(): pass\n")
+        (sub / ".mcp.json").write_text('{"mcpServers": {}}\n')
+        (sub / "metadata.yaml").write_text(yaml.dump({"name": "mcp-skill"}))
+
+        output = tmp_path / "output"
+        treatment, control = scaffold_submission(sub, output, TEMPLATES_DIR)
+        assert (treatment / "environment" / ".mcp.json").is_file()
+        assert not (control / "environment" / ".mcp.json").exists()
+
+    def test_mcp_json_in_supportive_copied_only_for_treatment(self, tmp_path: Path):
+        """.mcp.json in supportive/ (legacy location) is copied only for treatment."""
+        sub = tmp_path / "mcp-skill-legacy"
+        sub.mkdir()
+        (sub / "instruction.md").write_text("Do it.\n")
+        (sub / "skills").mkdir()
+        (sub / "skills" / "SKILL.md").write_text("# Skill\n")
+        (sub / "tests").mkdir()
+        (sub / "tests" / "test_outputs.py").write_text("def test(): pass\n")
+        supportive = sub / "supportive"
+        supportive.mkdir()
+        (supportive / ".mcp.json").write_text('{"mcpServers": {}}\n')
+        (sub / "metadata.yaml").write_text(yaml.dump({"name": "mcp-skill-legacy"}))
+
+        output = tmp_path / "output"
+        treatment, control = scaffold_submission(sub, output, TEMPLATES_DIR)
+        assert (treatment / "environment" / ".mcp.json").is_file()
+        assert not (control / "environment" / ".mcp.json").exists()
+
+    def test_dockerfile_includes_mcp_json_for_treatment(self, tmp_path: Path):
+        """Dockerfile includes COPY .mcp.json when present."""
+        sub = tmp_path / "mcp-skill"
+        sub.mkdir()
+        (sub / "instruction.md").write_text("Do it.\n")
+        (sub / "skills").mkdir()
+        (sub / "skills" / "SKILL.md").write_text("# Skill\n")
+        (sub / "tests").mkdir()
+        (sub / "tests" / "test_outputs.py").write_text("def test(): pass\n")
+        (sub / ".mcp.json").write_text('{"mcpServers": {}}\n')
+        (sub / "metadata.yaml").write_text(yaml.dump({"name": "mcp-skill"}))
+
+        output = tmp_path / "output"
+        treatment, _ = scaffold_submission(sub, output, TEMPLATES_DIR)
+        content = (treatment / "environment" / "Dockerfile").read_text()
+        assert "COPY .mcp.json /workspace/.mcp.json" in content
+
+    def test_dockerfile_excludes_mcp_json_for_control(self, tmp_path: Path):
+        """Dockerfile excludes .mcp.json for control variant."""
+        sub = tmp_path / "mcp-skill"
+        sub.mkdir()
+        (sub / "instruction.md").write_text("Do it.\n")
+        (sub / "skills").mkdir()
+        (sub / "skills" / "SKILL.md").write_text("# Skill\n")
+        (sub / "tests").mkdir()
+        (sub / "tests" / "test_outputs.py").write_text("def test(): pass\n")
+        (sub / ".mcp.json").write_text('{"mcpServers": {}}\n')
+        (sub / "metadata.yaml").write_text(yaml.dump({"name": "mcp-skill"}))
+
+        output = tmp_path / "output"
+        _, control = scaffold_submission(sub, output, TEMPLATES_DIR)
+        content = (control / "environment" / "Dockerfile").read_text()
+        assert "COPY .mcp.json" not in content
+
+    def test_no_mcp_json_in_dockerfile_when_absent(self, valid_submission: Path, tmp_path: Path):
+        """Dockerfile excludes .mcp.json when not present in submission."""
+        output = tmp_path / "output"
+        treatment, _ = scaffold_submission(valid_submission, output, TEMPLATES_DIR)
+        content = (treatment / "environment" / "Dockerfile").read_text()
+        assert "COPY .mcp.json" not in content
+
     def test_test_sh_includes_llm_judge_when_present(self, full_submission: Path, tmp_path: Path):
         output = tmp_path / "output"
         treatment, _ = scaffold_submission(full_submission, output, TEMPLATES_DIR)