diff --git a/esphome/build_gen/arduino8266.py b/esphome/build_gen/arduino8266.py
index 1dd5eb9aba..8dc1a6c19e 100644
--- a/esphome/build_gen/arduino8266.py
+++ b/esphome/build_gen/arduino8266.py
@@ -1246,7 +1246,7 @@ def write_project(paths: InstalledPaths, ccache: str | None) -> bool:
                         flags_id,
                     ),
                 )
-        except OSError as err:
+        except (OSError, UnicodeError) as err:
             # Identity unknown: a stale cache entry must never be served
             _LOGGER.warning(
                 "Could not establish the pch identity; compiling without it: %s", err
diff --git a/esphome/build_helpers/pch.py b/esphome/build_helpers/pch.py
index 778e647a5b..4e74333f19 100644
--- a/esphome/build_helpers/pch.py
+++ b/esphome/build_helpers/pch.py
@@ -170,7 +170,7 @@ def pch_checksum(
         digest.update(closure[name])
         digest.update(b"\0")
     for item in extra:
-        digest.update(item.encode())
+        digest.update(item.encode(errors="surrogateescape"))
         digest.update(b"\0")
     return digest.hexdigest()
 
@@ -317,7 +317,7 @@ def prepare_pch(
                 cmd_id,
             ),
         )
-    except OSError as err:
+    except (OSError, UnicodeError) as err:
         # Identity unknown: a stale cache entry must never be served
         _LOGGER.warning(
             "Could not establish the pch identity; compiling without it: %s", err
diff --git a/esphome/platformio/pch.py.script b/esphome/platformio/pch.py.script
index a09d1ebc64..38596333c4 100644
--- a/esphome/platformio/pch.py.script
+++ b/esphome/platformio/pch.py.script
@@ -158,20 +158,25 @@ def _setup_pch() -> None:
     # -include entries, so an unguarded user header folded here would be
     # included twice. An unfolded header simply stays consumer-only and
     # ccache hashes it directly off the command line.
-    folded = [name for name in include_headers if (src_dir / name).is_file()]
+    folded = [
+        name
+        for name in include_headers
+        # An absolute name would sneak past src_dir /: keep it consumer-only
+        if not Path(name).is_absolute() and (src_dir / name).is_file()
+    ]
     if unfolded := [n for n in include_headers if n not in folded]:
         print(f"ESPHome: not precompiling non-src force-includes: {unfolded}")
     content = "".join(f'#include "{name}"\n' for name in (*folded, _CORE_HEADER))
 
     digest = hashlib.sha256()
-    digest.update(content.encode())
-    digest.update(cxx.encode())
+    digest.update(content.encode(errors="surrogateescape"))
+    digest.update(cxx.encode(errors="surrogateescape"))
     # Mirror CCACHE_BASEDIR: strip the per-device build path so identical
     # configs produce identical .sum files and share cache entries
     flags_id = " ".join(flags)
     if basedir := os.environ.get("CCACHE_BASEDIR"):
         flags_id = flags_id.replace(basedir, "")
-    digest.update(flags_id.encode())
+    digest.update(flags_id.encode(errors="surrogateescape"))
     # GCC never validates a .gch against its source headers, and PlatformIO
     # package paths carry no version, so a package bump must invalidate here
     platform = env.PioPlatform()  # noqa: F821
diff --git a/tests/unit_tests/build_helpers/test_pch.py b/tests/unit_tests/build_helpers/test_pch.py
index a7c3c5b5dd..ec81226e4d 100644
--- a/tests/unit_tests/build_helpers/test_pch.py
+++ b/tests/unit_tests/build_helpers/test_pch.py
@@ -175,3 +175,9 @@ def test_include_closure_survives_non_utf8_include_name(tmp_path: Path) -> None:
     (tmp_path / "b.h").write_text("")
     closure = pch._include_closure(tmp_path, ["a.h"])
     assert set(closure) == {"a.h", "b.h"}
+
+
+def test_pch_checksum_survives_surrogate_extra(tmp_path: Path) -> None:
+    """Install paths from non-UTF-8 filesystems carry surrogates; hashing
+    them must not raise past the caller's identity-unknown guard."""
+    assert pch.pch_checksum(tmp_path, [], ["/opt/bad\udcff/framework"])
diff --git a/tests/unit_tests/test_platformio_pch_script.py b/tests/unit_tests/test_platformio_pch_script.py
index e9aafd3951..510fcbce97 100644
--- a/tests/unit_tests/test_platformio_pch_script.py
+++ b/tests/unit_tests/test_platformio_pch_script.py
@@ -175,6 +175,18 @@ def test_pch_script_preserves_spaced_flag_elements(tmp_path: Path) -> None:
     assert pch.splitlines()[0] == '#include "other.h"'
 
 
+def test_pch_script_leaves_absolute_force_includes_unfolded(
+    tmp_path: Path,
+) -> None:
+    """An absolute -include resolves through src_dir / name; it must still
+    stay consumer-only or the host path enters the .sum."""
+    outside = tmp_path / "outside.h"
+    outside.write_text("")
+    _run_script(tmp_path, flags=["-DX=1", "-include", str(outside)])
+    pch = (tmp_path / "dev" / "esphome_pch.h").read_text()
+    assert "outside.h" not in pch
+
+
 def test_pch_script_leaves_non_src_force_includes_unfolded(
     tmp_path: Path, capsys: pytest.CaptureFixture[str]
 ) -> None: