fix(install): stop hardcoding the global skill path in the Antigravity workflow (#2319)

`_ANTIGRAVITY_WORKFLOW` is shared by the global and project-scoped installs,
which write SKILL.md to different locations (~/.gemini/config/skills vs
.agents/skills). The template named the global path unconditionally, so
`install --project --platform antigravity` (and `antigravity install
--project`) emitted a workflow pointing at a file that scope never writes -
a dangling reference on any machine without a prior global install.

Refer to the skill by name rather than by location, matching what every
block in always_on/ already does. Antigravity resolves it from the
`name: graphify` frontmatter in either scope, so no path interpolation is
needed and neither scope can dangle.

The existing tests only asserted the workflow file exists, which is why this
shipped; add coverage that the generated workflow names no skill path, in
both project and global scope.

graphify/install.py

@@ -915,6 +915,9 @@ def vscode_uninstall(project_dir: Path | None = None) -> None:
         print(f"  {instructions}  ->  deleted (was empty after removal)")
 _ANTIGRAVITY_RULES_PATH = Path(".agents") / "rules" / "graphify.md"
 _ANTIGRAVITY_WORKFLOW_PATH = Path(".agents") / "workflows" / "graphify.md"
+# Names no SKILL.md location on purpose: this constant is shared by the global and
+# project-scoped installs, which put the skill in different places, so any hardcoded
+# path dangles for the other scope. Antigravity resolves the skill by frontmatter name.
 _ANTIGRAVITY_WORKFLOW = """\
 ---
 name: graphify
@@ -923,7 +926,7 @@ description: Turn any folder of files into a navigable knowledge graph
 
 # Workflow: graphify
 
-Follow the graphify skill installed at ~/.gemini/config/skills/graphify/SKILL.md to run the full pipeline.
+Follow the graphify skill to run the full pipeline.
 
 If no path argument is given, use `.` (current directory).
 """

tests/test_antigravity_install.py

@@ -20,6 +20,37 @@ def test_antigravity_project_install_writes_rules_and_workflows(tmp_path):
     assert skill.read_text(encoding="utf-8").startswith("---\n")
 
 
+def test_antigravity_workflow_names_no_skill_path(tmp_path):
+    """The workflow must not hardcode a SKILL.md location.
+
+    One constant serves both scopes, which install the skill to different places,
+    so naming either path dangles for the other: a project-scoped install used to
+    point at ~/.gemini/config/skills/graphify/SKILL.md, which it never writes.
+    """
+    m._project_install("antigravity", tmp_path)
+    body = (tmp_path / ".agents" / "workflows" / "graphify.md").read_text(encoding="utf-8")
+    assert ".gemini" not in body, "workflow must not reference the global skill dir"
+    assert "SKILL.md" not in body, "workflow must not name a skill path in any scope"
+    assert "~" not in body, "workflow must not reference a home directory"
+    assert "graphify skill" in body, "workflow should still point at the skill by name"
+
+
+def test_antigravity_global_install_workflow_names_no_skill_path(tmp_path, monkeypatch):
+    """Global install shares the constant, so it must stay path-free too."""
+    monkeypatch.setattr("pathlib.Path.home", lambda: tmp_path / "home")
+    monkeypatch.setenv("HOME", str(tmp_path / "home"))
+    m._antigravity_install(tmp_path)
+
+    # The skill really does land in the global dir the old text named ...
+    assert (
+        tmp_path / "home" / ".gemini" / "config" / "skills" / "graphify" / "SKILL.md"
+    ).exists()
+    # ... but the workflow still must not hardcode it.
+    body = (tmp_path / ".agents" / "workflows" / "graphify.md").read_text(encoding="utf-8")
+    assert ".gemini" not in body
+    assert "SKILL.md" not in body
+
+
 def test_antigravity_project_uninstall_clears_rules_and_workflows(tmp_path):
     m._project_install("antigravity", tmp_path)
     m._project_uninstall("antigravity", tmp_path)