Add regression tests for cargo subdirectory manifest discovery

Cover a Tauri style layout where the manifest lives one level down and
must still be found, a discovered workspace manifest whose own
members resolve relative to its own directory rather than the outer
scan root, a decoy manifest inside a dependency install folder that
must never be searched into, and a manifest nested past the discovery
depth cap that is correctly left unfound.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017qfdzgbA5KedGEjD1AayNh

tests/test_cargo_introspect.py

@@ -455,3 +455,113 @@ tokio_rt = { version = "1", package = "tokio" }
 
     assert {node["id"] for node in result["nodes"]} == {"crate:app"}
     assert result["edges"] == []
+
+
+def test_cargo_introspect_discovers_a_manifest_in_a_subdirectory(tmp_path):
+    """#3678: a Tauri-style layout keeps Cargo.toml in src-tauri/, not at the
+    scan root. introspect_cargo must find it rather than erroring as if no
+    crate existed at all."""
+    tauri = tmp_path / "src-tauri"
+    tauri.mkdir()
+    _write_manifest(
+        tauri / "Cargo.toml",
+        """
+[package]
+name = "app"
+version = "0.1.0"
+edition = "2021"
+""",
+    )
+
+    result = introspect_cargo(tmp_path)
+
+    assert {node["id"] for node in result["nodes"]} == {"crate:app"}
+    node = next(n for n in result["nodes"] if n["id"] == "crate:app")
+    assert node["source_file"] == "src-tauri/Cargo.toml", (
+        f"the discovered manifest's source_file should stay relative to the "
+        f"scan root, not the crate subdirectory; got {node['source_file']!r}"
+    )
+
+
+def test_cargo_introspect_discovery_resolves_workspace_members_from_the_manifest(tmp_path):
+    """A discovered workspace manifest's own members are still resolved
+    relative to ITS directory, not the outer scan root (#3678)."""
+    tauri = tmp_path / "src-tauri"
+    tauri.mkdir()
+    _write_manifest(
+        tauri / "Cargo.toml",
+        """
+[workspace]
+members = ["core"]
+""",
+    )
+    core = tauri / "core"
+    core.mkdir()
+    _write_manifest(
+        core / "Cargo.toml",
+        """
+[package]
+name = "core"
+version = "0.1.0"
+edition = "2021"
+""",
+    )
+
+    result = introspect_cargo(tmp_path)
+
+    assert {node["id"] for node in result["nodes"]} == {"crate:core"}
+    node = next(n for n in result["nodes"] if n["id"] == "crate:core")
+    assert node["source_file"] == "src-tauri/core/Cargo.toml"
+
+
+def test_cargo_introspect_discovery_skips_noise_directories(tmp_path):
+    """A Cargo.toml sitting inside node_modules/ (a vendored or example crate
+    pulled in by an npm dependency) must never win over a real, non-noise
+    subdirectory (#3678)."""
+    noise = tmp_path / "node_modules" / "some-pkg"
+    noise.mkdir(parents=True)
+    _write_manifest(
+        noise / "Cargo.toml",
+        """
+[package]
+name = "decoy"
+version = "0.1.0"
+edition = "2021"
+""",
+    )
+    real = tmp_path / "src-tauri"
+    real.mkdir()
+    _write_manifest(
+        real / "Cargo.toml",
+        """
+[package]
+name = "app"
+version = "0.1.0"
+edition = "2021"
+""",
+    )
+
+    result = introspect_cargo(tmp_path)
+
+    assert {node["id"] for node in result["nodes"]} == {"crate:app"}, (
+        "discovery must never search into node_modules/"
+    )
+
+
+def test_cargo_introspect_discovery_does_not_search_past_the_depth_cap(tmp_path):
+    """A manifest nested deeper than the discovery cap is left unfound rather
+    than searched for indefinitely (#3678)."""
+    deep = tmp_path / "a" / "b" / "c" / "d"
+    deep.mkdir(parents=True)
+    _write_manifest(
+        deep / "Cargo.toml",
+        """
+[package]
+name = "too_deep"
+version = "0.1.0"
+edition = "2021"
+""",
+    )
+
+    with pytest.raises(FileNotFoundError):
+        introspect_cargo(tmp_path)