[packages] Improve error messages with include stack and fix missing path propagation (#15844)

Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>
Co-authored-by: J. Nick Koston <nick@home-assistant.io>
Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

tests/unit_tests/test_substitutions.py

@@ -14,6 +14,7 @@ from esphome.components.packages import (
     do_packages_pass,
     merge_packages,
 )
+from esphome.components.substitutions.jinja import UndefinedError
 from esphome.config import resolve_extend_remove
 from esphome.config_helpers import Extend, merge_config
 import esphome.config_validation as cv
@@ -675,6 +676,39 @@ def test_include_filename_substitution_undefined_var(tmp_path: Path) -> None:
         substitutions.do_substitution_pass(config)
 
 
+def test_raise_first_undefined_logs_extras_at_debug(
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    """Only the first undefined error is raised; extras are logged at debug."""
+    errors: substitutions.ErrList = [
+        (UndefinedError("'a' is undefined"), ["url"], None),
+        (UndefinedError("'b' is undefined"), ["ref"], None),
+        (UndefinedError("'c' is undefined"), ["path"], None),
+    ]
+
+    with (
+        caplog.at_level(logging.DEBUG, logger="esphome.components.substitutions"),
+        pytest.raises(cv.Invalid) as exc_info,
+    ):
+        substitutions.raise_first_undefined(errors, None, "package definition")
+
+    # First error is surfaced as the cv.Invalid message.
+    raised = str(exc_info.value)
+    assert "'a' is undefined" in raised
+    assert "'b' is undefined" not in raised
+    assert "'c' is undefined" not in raised
+
+    # Remaining errors are captured via debug logging for troubleshooting.
+    assert "Additional undefined variables in package definition" in caplog.text
+    assert "'b' is undefined at 'ref'" in caplog.text
+    assert "'c' is undefined at 'path'" in caplog.text
+
+
+def test_raise_first_undefined_noop_on_empty() -> None:
+    """An empty errors list is a no-op — no exception, no log."""
+    substitutions.raise_first_undefined([], None, "package definition")
+
+
 def test_do_substitution_pass_included_substitutions_must_be_mapping(
     tmp_path: Path,
 ) -> None: