diff --git a/esphome/build_helpers/ccache.py b/esphome/build_helpers/ccache.py
index 6c9223e4cc..46483f0577 100644
--- a/esphome/build_helpers/ccache.py
+++ b/esphome/build_helpers/ccache.py
@@ -32,8 +32,8 @@ def _ccache_runs(ccache: str) -> bool:
             stdout=subprocess.DEVNULL,
             stderr=subprocess.DEVNULL,
             timeout=15,
-            # Repo-wide convention (posix_spawn fast path); pinned by
-            # tests/script/test_helpers.py
+            # Repo-wide convention (posix_spawn fast path); see the
+            # close_fds=False call sites across esphome/ and script/helpers.py
             close_fds=False,
         )
     except (OSError, subprocess.SubprocessError):
diff --git a/esphome/espidf/component.py b/esphome/espidf/component.py
index fd49c5df05..bd104dfe9a 100644
--- a/esphome/espidf/component.py
+++ b/esphome/espidf/component.py
@@ -93,7 +93,7 @@ def generate_cmakelists_txt(component: IDFComponent) -> str:
     )
     # PlatformIO shell-lexes each build.flags entry, so one entry can carry a
     # flag and its argument (e.g. "-include cp_custom_alloc.h"); bare
-    # -I/-L/-l tokens re-glue to their argument ("-I foo" -> "-Ifoo") so the
+    # -I/-L/-l/-D tokens re-glue to their argument ("-I foo" -> "-Ifoo") so
     # prefix classifiers below still route them.
     build_flags = lex_build_flags(build_flags, f"library {component.name}")
 
diff --git a/esphome/platformio/library.py b/esphome/platformio/library.py
index a7f7816887..7349c46144 100644
--- a/esphome/platformio/library.py
+++ b/esphome/platformio/library.py
@@ -23,7 +23,6 @@ import logging
 import os
 from pathlib import Path, PurePosixPath
 import re
-import shlex
 import tempfile
 from typing import Any
 from urllib.parse import urlsplit, urlunsplit
@@ -562,6 +561,11 @@ def _resolve_registry_version(
 
 def split_flag_entry(entry: Any, owner: str) -> list[str]:
     """``shlex.split`` with a clean error naming the offending flags entry."""
+    # Late import: this module loads with the esp32 platform on every
+    # validate/compile; shlex (and its linecache pull-in) is only needed
+    # when actually lexing flags
+    import shlex
+
     try:
         return shlex.split(entry)
     except (ValueError, AttributeError, TypeError) as err:
diff --git a/tests/unit_tests/test_platformio_extra_script.py b/tests/unit_tests/test_platformio_extra_script.py
index e1217a4006..3de9ced3d8 100644
--- a/tests/unit_tests/test_platformio_extra_script.py
+++ b/tests/unit_tests/test_platformio_extra_script.py
@@ -198,10 +198,14 @@ def test_apply_extra_script_no_script_and_no_flags(tmp_path) -> None:
     assert "flags" not in c.data["build"]
 
 
-def test_apply_extra_script_ignores_uncaptured_env_calls(tmp_path) -> None:
-    """Un-captured env vars and unsupported env methods are silent no-ops."""
+def test_apply_extra_script_ignores_uncaptured_env_calls(tmp_path, caplog) -> None:
+    """Un-captured env vars and unsupported env methods are skipped but
+    diagnosable from the build log."""
+    import logging
+
     from esphome.platformio.extra_script import apply_extra_script
 
+    caplog.set_level(logging.DEBUG)
     script = tmp_path / "extra.py"
     script.write_text(
         "env.Replace(CC='clang')\nenv.Append(UNCAPTURED=['x'], LIBS='single')\n"
@@ -211,6 +215,8 @@ def test_apply_extra_script_ignores_uncaptured_env_calls(tmp_path) -> None:
     c.data = {"build": {"extraScript": "extra.py"}}
     apply_extra_script(c, board_mcu=lambda: "esp8266", pio_platform="espressif8266")
     assert c.data["build"]["flags"] == ["-lsingle"]
+    assert "env.Append(UNCAPTURED=...) is not captured" in caplog.text
+    assert "env.Replace(...) is a no-op here" in caplog.text
 
 
 def test_apply_extra_script_swallows_script_errors(tmp_path, caplog) -> None:
diff --git a/tests/unit_tests/test_platformio_toolchain.py b/tests/unit_tests/test_platformio_toolchain.py
index 416deceadb..77d9ed436e 100644
--- a/tests/unit_tests/test_platformio_toolchain.py
+++ b/tests/unit_tests/test_platformio_toolchain.py
@@ -1975,3 +1975,12 @@ def test_run_platformio_cli_invokes_heal(
     with patch.object(toolchain, "heal_platformio_python_env") as mock_heal:
         toolchain.run_platformio_cli("test")
     mock_heal.assert_called_once()
+
+
+def test_ccache_probe_spawns_with_close_fds_false() -> None:
+    """The probe follows the repo-wide posix_spawn convention."""
+    from esphome.build_helpers import ccache
+
+    with patch("subprocess.run") as mock_run:
+        assert ccache._ccache_runs("/usr/bin/ccache") is True
+    assert mock_run.call_args.kwargs["close_fds"] is False