diff --git a/esphome/arduino8266/framework.py b/esphome/arduino8266/framework.py
index cded1438c4..b27744cb20 100644
--- a/esphome/arduino8266/framework.py
+++ b/esphome/arduino8266/framework.py
@@ -75,6 +75,14 @@ def framework_package_version(ver: Version) -> str:
             f"Arduino core {ver} is not supported yet; "
             "the newest known core series is 3.x"
         )
+    if ver < Version(2, 6, 3):
+        # Older cores use the 1.x/2.x package-major encodings, which the
+        # PlatformIO path handles before delegating here; never encode them
+        # wrongly for a caller that skipped that guard
+        raise EsphomeError(
+            f"Arduino core {ver} predates the package encoding this helper "
+            "implements (2.6.3 and newer)"
+        )
     return f"3.{ver.major}{ver.minor:02d}{ver.patch:02d}.0"
 
 
@@ -133,7 +141,13 @@ def check_and_install(framework_version: Version) -> InstalledPaths:
 
 def get_build_env(toolchain_path: Path) -> dict[str, str]:
     env = os.environ.copy()
-    env["PATH"] = str(toolchain_path / "bin") + os.pathsep + env.get("PATH", "")
+    # Drop empty entries: a trailing separator from an absent PATH would
+    # make the shell search the current directory for tools
+    parts = [
+        str(toolchain_path / "bin"),
+        *filter(None, env.get("PATH", "").split(os.pathsep)),
+    ]
+    env["PATH"] = os.pathsep.join(parts)
     env.update(ccache_env())
     return env
 
diff --git a/esphome/components/esp8266/__init__.py b/esphome/components/esp8266/__init__.py
index 47b122afb8..dafb9b3cc6 100644
--- a/esphome/components/esp8266/__init__.py
+++ b/esphome/components/esp8266/__init__.py
@@ -194,7 +194,7 @@ def _format_framework_arduino_version(ver: cv.Version) -> str:
     except EsphomeError as err:
         # Anchor the 4.x rejection to the framework version line instead of
         # aborting with a bare traceback-level error
-        raise cv.Invalid(str(err)) from err
+        raise cv.Invalid(str(err), path=[CONF_VERSION]) from err
 
 
 # NOTE: Keep this in mind when updating the recommended version:
diff --git a/tests/unit_tests/test_arduino8266_framework.py b/tests/unit_tests/test_arduino8266_framework.py
index 56d89cc37d..cdd1ae0417 100644
--- a/tests/unit_tests/test_arduino8266_framework.py
+++ b/tests/unit_tests/test_arduino8266_framework.py
@@ -27,6 +27,10 @@ def test_framework_package_version() -> None:
     # A future major bump needs its own encoding, not a doomed registry lookup
     with pytest.raises(EsphomeError, match="not supported yet"):
         framework.framework_package_version(cv.Version(4, 0, 0))
+    # The pre-2.6.3 eras use other encodings; the helper is total, not wrong
+    with pytest.raises(EsphomeError, match="predates the package encoding"):
+        framework.framework_package_version(cv.Version(2, 6, 2))
+    assert framework.framework_package_version(cv.Version(2, 6, 3)) == "3.20603.0"
 
 
 def test_format_framework_arduino_version_pins_all_series() -> None:
@@ -39,8 +43,9 @@ def test_format_framework_arduino_version_pins_all_series() -> None:
     assert fmt(cv.Version(2, 7, 4)) == "~3.20704.0"
     assert fmt(cv.Version(3, 1, 2)) == "~3.30102.0"
     # Anchored to the framework version line, not a bare EsphomeError
-    with pytest.raises(cv.Invalid, match="not supported yet"):
+    with pytest.raises(cv.Invalid, match="not supported yet") as excinfo:
         fmt(cv.Version(4, 0, 0))
+    assert excinfo.value.path == ["version"]
 
 
 def test_tools_path_default_and_prefix(tmp_path: Path) -> None:
@@ -125,3 +130,22 @@ def test_check_and_install_rejects_old_core(tmp_path: Path) -> None:
     """Calling the installer below the floor fails before any download."""
     with pytest.raises(EsphomeError, match=">= 3.1.1"):
         framework.check_and_install(cv.Version(3, 0, 2))
+
+
+def test_get_build_env_without_path_has_no_empty_entry(tmp_path: Path) -> None:
+    """An absent PATH must not leave a trailing separator (an empty entry
+    means the current directory to the shell)."""
+    with (
+        patch.dict(os.environ, {}, clear=True),
+        patch.object(framework, "ccache_env", return_value={}),
+    ):
+        env = framework.get_build_env(tmp_path)
+    assert env["PATH"] == str(tmp_path / "bin")
+    with (
+        patch.dict(
+            os.environ, {"PATH": f"/usr/bin{os.pathsep}{os.pathsep}/bin"}, clear=True
+        ),
+        patch.object(framework, "ccache_env", return_value={}),
+    ):
+        env = framework.get_build_env(tmp_path)
+    assert env["PATH"].split(os.pathsep) == [str(tmp_path / "bin"), "/usr/bin", "/bin"]