fix: remove unsupported mode: frontmatter from Copilot skills mode (fixes #2799) (#2819)

VS Code Copilot Agent Skills do not support the `mode:` frontmatter field.
The generated SKILL.md files included `mode: speckit.<stem>` injected by
CopilotIntegration.post_process_skill_content(), which had no effect in
VS Code and could cause confusion. Simplify post_process_skill_content to
delegate directly to _CopilotSkillsHelper without injecting mode:.

Update tests to assert mode: is absent from generated skill frontmatter.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

src/specify_cli/integrations/copilot/__init__.py

@@ -283,58 +283,13 @@ class CopilotIntegration(IntegrationBase):
         return f"speckit.{template_name}.agent.md"
 
     def post_process_skill_content(self, content: str) -> str:
-        """Inject shared hook guidance and Copilot ``mode:`` frontmatter.
+        """Inject shared hook guidance into Copilot skill content.
 
-        Inserts ``mode: speckit.<stem>`` before the closing ``---`` so
-        Copilot can associate the skill with its agent mode.
+        Delegates to :class:`_CopilotSkillsHelper` for shared post-processing.
+        The ``mode:`` frontmatter field is intentionally omitted: VS Code
+        Copilot Agent Skills do not support it (see issue #2799).
         """
-        updated = _CopilotSkillsHelper().post_process_skill_content(content)
-        lines = updated.splitlines(keepends=True)
-
-        # Extract skill name from frontmatter to derive the mode value
-        dash_count = 0
-        skill_name = ""
-        for line in lines:
-            stripped = line.rstrip("\n\r")
-            if stripped == "---":
-                dash_count += 1
-                if dash_count == 2:
-                    break
-                continue
-            if dash_count == 1:
-                if stripped.startswith("mode:"):
-                    return updated  # already present
-                if stripped.startswith("name:"):
-                    # Parse: name: "speckit-plan" → speckit.plan
-                    val = stripped.split(":", 1)[1].strip().strip('"').strip("'")
-                    # Convert speckit-plan → speckit.plan
-                    if val.startswith("speckit-"):
-                        skill_name = "speckit." + val[len("speckit-"):]
-                    else:
-                        skill_name = val
-
-        if not skill_name:
-            return updated
-
-        # Inject mode: before the closing --- of frontmatter
-        out: list[str] = []
-        dash_count = 0
-        injected = False
-        for line in lines:
-            stripped = line.rstrip("\n\r")
-            if stripped == "---":
-                dash_count += 1
-                if dash_count == 2 and not injected:
-                    if line.endswith("\r\n"):
-                        eol = "\r\n"
-                    elif line.endswith("\n"):
-                        eol = "\n"
-                    else:
-                        eol = ""
-                    out.append(f"mode: {skill_name}{eol}")
-                    injected = True
-            out.append(line)
-        return "".join(out)
+        return _CopilotSkillsHelper().post_process_skill_content(content)
 
     def setup(
         self,

tests/integrations/test_integration_copilot.py

@@ -426,8 +426,8 @@ class TestCopilotSkillsMode:
 
     # -- Copilot-specific post-processing ---------------------------------
 
-    def test_post_process_skill_content_injects_mode(self):
-        """post_process_skill_content() should inject mode: field."""
+    def test_post_process_skill_content_does_not_inject_mode(self):
+        """post_process_skill_content() must NOT inject mode: — VS Code Copilot does not support it."""
         copilot = self._make_copilot()
         content = (
             "---\n"
@@ -437,10 +437,10 @@ class TestCopilotSkillsMode:
             "\nBody content\n"
         )
         updated = copilot.post_process_skill_content(content)
-        assert "mode: speckit.plan" in updated
+        assert "mode:" not in updated
 
     def test_post_process_skill_content_injects_hook_note(self):
-        """post_process_skill_content() should inject shared hook guidance."""
+        """post_process_skill_content() should inject shared hook guidance but not mode:."""
         copilot = self._make_copilot()
         content = (
             "---\n"
@@ -451,7 +451,7 @@ class TestCopilotSkillsMode:
         )
         updated = copilot.post_process_skill_content(content)
         assert "replace dots" in updated
-        assert "mode: speckit.specify" in updated
+        assert "mode:" not in updated
 
     def test_post_process_idempotent(self):
         """post_process_skill_content() must be idempotent."""
@@ -467,8 +467,8 @@ class TestCopilotSkillsMode:
         second = copilot.post_process_skill_content(first)
         assert first == second
 
-    def test_skills_have_mode_in_frontmatter(self, tmp_path):
-        """Generated SKILL.md files should have mode: field from post-processing."""
+    def test_skills_do_not_have_mode_in_frontmatter(self, tmp_path):
+        """Generated SKILL.md files must NOT contain mode: — VS Code Copilot does not support it."""
         copilot = self._make_copilot()
         created, _ = self._setup_skills(copilot, tmp_path)
         skill_files = [f for f in created if f.name == "SKILL.md"]
@@ -477,11 +477,7 @@ class TestCopilotSkillsMode:
             content = f.read_text(encoding="utf-8")
             parts = content.split("---", 2)
             fm = yaml.safe_load(parts[1])
-            assert "mode" in fm, f"{f} frontmatter missing 'mode'"
-            # mode should be speckit.<stem>
-            skill_dir_name = f.parent.name
-            stem = skill_dir_name.removeprefix("speckit-")
-            assert fm["mode"] == f"speckit.{stem}"
+            assert "mode" not in fm, f"{f} frontmatter must not contain unsupported 'mode' field"
 
     def test_skills_hook_sections_explain_dotted_command_conversion(self, tmp_path):
         """Generated skills with hook sections should include shared hook guidance."""

tests/integrations/test_integration_subcommand.py

@@ -898,11 +898,10 @@ class TestIntegrationSwitch:
         assert copilot_git_feature.exists(), "Git extension skill should exist for Copilot skills mode"
         assert not copilot_agent_file.exists(), "Copilot skills mode should not create extension .agent.md files"
 
-        # Verify Copilot-specific frontmatter: mode field should map from
-        # skill name (speckit-git-feature) back to dot notation (speckit.git-feature)
+        # Verify Copilot skill frontmatter does NOT contain mode: — VS Code Copilot does not support it
         skill_content = copilot_git_feature.read_text(encoding="utf-8")
-        assert "mode: speckit.git-feature" in skill_content, (
-            "Copilot skill frontmatter should contain mode mapped from skill name"
+        assert "mode:" not in skill_content, (
+            "Copilot skill frontmatter must not contain unsupported 'mode' field"
         )
 
         registry = json.loads(