[core] Prefetch tool-scons by PlatformIO's core spec (#18831)

esphome/platformio/prefetch.py

@@ -832,16 +832,16 @@ def _prefetch(build_dir: Path, env: str) -> None:
         for name, opts in p.packages.items()
         if not opts.get("optional")
     ]
-    # PIO's build engine installs outside the platform package list;
-    # skipped when the platform lists it itself
-    if not any(s.name == "tool-scons" for s in specs):
-        specs.append(
-            PackageSpec(
-                owner="platformio",
-                name="tool-scons",
-                requirements=get_core_dependencies()["tool-scons"],
-            )
+    # PIO's build engine installs tool-scons by its own registry spec at build
+    # start; a platform URL copy has no owner to match it, so prefetch that spec
+    specs = [s for s in specs if s.name != "tool-scons"]
+    specs.append(
+        PackageSpec(
+            owner="platformio",
+            name="tool-scons",
+            requirements=get_core_dependencies()["tool-scons"],
         )
+    )
     lib_deps = config.get(f"env:{env}", "lib_deps", [])
     # pio run's storage dir for this env, with its compatibility
     # qualifiers: an unqualified library install could land a different

tests/unit_tests/test_platformio_prefetch.py

@@ -13,6 +13,7 @@ from types import SimpleNamespace
 from unittest.mock import MagicMock, patch
 
 from filelock import Timeout
+from platformio.dependencies import get_core_dependencies
 from platformio.package.manager._install import PackageManagerInstallMixin
 from platformio.package.manager.base import BasePackageManager
 from platformio.package.manager.library import LibraryPackageManager
@@ -1728,30 +1729,31 @@ def test_preinstall_unlocks_even_when_pool_fails(tmp_path: Path) -> None:
     m.unlock.assert_called_once_with()
 
 
-def test_prefetch_skips_duplicate_tool_scons(tmp_path: Path) -> None:
-    """A platform that lists tool-scons itself does not get it appended."""
+def test_prefetch_replaces_platform_tool_scons_with_core_spec(tmp_path: Path) -> None:
+    """A platform's own tool-scons spec gives way to the core's registry spec."""
     _write_ini(tmp_path, "[env:testenv]\nplatform = fake/p@1\n")
     fake_platform = MagicMock()
     fake_platform.packages = {"tool-scons": {"optional": False}}
     fake_platform.get_package_spec.side_effect = lambda name: _FakeSpec(
-        uri=None, name=name
+        uri="https://x/scons.zip", name=name, owner=None
     )
     config = _fake_config(tmp_path, {"platform": "fake/p@1"})
     modules = _pio_modules(tmp_path, fake_platform, MagicMock(), config)
-    batches: list[list[str]] = []
+    batches: list[list] = []
     with (
         patch.dict("sys.modules", modules),
         patch.object(
             pf,
             "_registry_jobs",
             side_effect=lambda mgr, specs, seen: (
-                batches.append([s.name for s in specs]) or ([], 0, [])
+                batches.append(list(specs)) or ([], 0, [])
             ),
         ),
         patch.object(pf, "_uri_jobs", return_value=([], 0, [])),
     ):
         pf._prefetch(tmp_path, "testenv")
-    assert batches[0] == ["tool-scons"]
+    (spec,) = batches[0]
+    assert (spec.name, spec.owner, spec.uri) == ("tool-scons", "platformio", None)
 
 
 def test_platformio_private_api_contract() -> None:
@@ -1784,6 +1786,8 @@ def test_platformio_private_api_contract() -> None:
         assert callable(getattr(BasePackageManager, name))
     # The dependency wave mirrors install_dependency's builtin skip
     assert callable(LibraryPackageManager.is_builtin_lib)
+    # The prefetch keys tool-scons on this core dependency
+    assert "tool-scons" in get_core_dependencies()
     # The pre-install passes these positionally / by keyword
     assert "compatibility" in inspect.signature(BasePackageManager.__init__).parameters
     lib_params = inspect.signature(LibraryPackageManager.__init__).parameters