diff --git a/esphome/arduino8266/component.py b/esphome/arduino8266/component.py
index 73121bee87..42f2b72c77 100644
--- a/esphome/arduino8266/component.py
+++ b/esphome/arduino8266/component.py
@@ -31,6 +31,8 @@ from esphome.platformio.library import (
     collect_filtered_files,
     convert_libraries,
     ensure_list,
+    is_lib_ignored,
+    lib_ignore_set,
     normalize_dependencies,
     parse_library_properties,
 )
@@ -134,12 +136,9 @@ def resolve_libraries(framework_path: Path) -> list[ArduinoLibrary]:
     external: list[Library] = []
     # PlatformIO's lib_ignore covers framework-bundled libraries too; the
     # shared converter only filters the registry/git ones.
-    lib_ignore = {
-        ignore.split("/")[-1].lower()
-        for ignore in CORE.platformio_options.get("lib_ignore", [])
-    }
+    lib_ignore = lib_ignore_set()
     for library in CORE.platformio_libraries.values():
-        if library.name and library.name.split("/")[-1].lower() in lib_ignore:
+        if is_lib_ignored(library.name, lib_ignore):
             continue
         # A version pin means a registry package ("pngle@1.1.0"), never a
         # framework-bundled library.
@@ -174,7 +173,7 @@ def resolve_libraries(framework_path: Path) -> list[ArduinoLibrary]:
                 or not (framework_path / "libraries" / name).is_dir()
             ):
                 continue
-            if name.lower() in lib_ignore:
+            if is_lib_ignored(name, lib_ignore):
                 continue
             try:
                 check_library_data(dep, ESP8266_PLATFORM, "arduino")
diff --git a/esphome/arduino8266/framework.py b/esphome/arduino8266/framework.py
index e75ef892f3..73197ae72c 100644
--- a/esphome/arduino8266/framework.py
+++ b/esphome/arduino8266/framework.py
@@ -121,9 +121,7 @@ def _pio_system() -> str:
     return "linux_x86_64"
 
 
-def _registry_download(
-    package: str, version: str
-) -> tuple[str, str | None, int | None]:
+def _registry_download(package: str, version: str) -> tuple[str, str, int | None]:
     """Resolve a package's download URL, sha256, and size via the PIO registry."""
     import requests
 
diff --git a/esphome/build_gen/arduino8266.py b/esphome/build_gen/arduino8266.py
index 65e184e127..9274198f42 100644
--- a/esphome/build_gen/arduino8266.py
+++ b/esphome/build_gen/arduino8266.py
@@ -493,10 +493,9 @@ def write_project(paths: dict[str, Path]) -> bool:
     # as under PlatformIO (a silently ignored ``build_unflags: -Os`` would
     # diverge between the toolchains).
     unflags = set(CORE.build_unflags)
-    if unflags:
-        cflags = [f for f in cflags if f not in unflags]
-        cxxflags = [f for f in cxxflags if f not in unflags]
-        asflags = [f for f in asflags if f not in unflags]
+    cflags = [f for f in cflags if f not in unflags]
+    cxxflags = [f for f in cxxflags if f not in unflags]
+    asflags = [f for f in asflags if f not in unflags]
 
     link_flags = [f for f in _LINKFLAGS if f not in unflags]
     if esp8266_data.get(KEY_SCANF_FLOAT):
@@ -522,6 +521,10 @@ def write_project(paths: dict[str, Path]) -> bool:
     build_tool = Path(__file__).parent.parent / "arduino8266" / "build_tool.py"
     ccache = ccache_path()
 
+    # $in/$out stay unquoted in the rule commands: ninja shell-escapes its
+    # built-in path variables itself when expanding a command (POSIX and
+    # Windows), so adding quotes would wrap ninja's own quoting and break
+    # space-containing paths. Only literal paths need _q().
     lines = [
         "# Auto-generated by ESPHome",
         "ninja_required_version = 1.5",
@@ -532,35 +535,35 @@ def write_project(paths: dict[str, Path]) -> bool:
         f"ccache = {_q(ccache) if ccache else ''}",
         "",
         "rule cc",
-        '  command = $ccache $cc -MMD -MF "$out.d" $cflags $flags -c "$in" -o "$out"',
+        "  command = $ccache $cc -MMD -MF $out.d $cflags $flags -c $in -o $out",
         "  depfile = $out.d",
         "  deps = gcc",
         "  description = CC $out",
         "rule cxx",
-        '  command = $ccache $cxx -MMD -MF "$out.d" $cxxflags $flags -c "$in" -o "$out"',
+        "  command = $ccache $cxx -MMD -MF $out.d $cxxflags $flags -c $in -o $out",
         "  depfile = $out.d",
         "  deps = gcc",
         "  description = CXX $out",
         "rule asm",
-        '  command = $ccache $cc -MMD -MF "$out.d" -x assembler-with-cpp $asflags $flags -c "$in" -o "$out"',
+        "  command = $ccache $cc -MMD -MF $out.d -x assembler-with-cpp $asflags $flags -c $in -o $out",
         "  depfile = $out.d",
         "  deps = gcc",
         "  description = AS $out",
         "rule ar",
-        f'  command = $python $buildtool ar {_q(toolchain_bin / "xtensa-lx106-elf-ar")} "$out" "$out.rsp"',
+        f"  command = $python $buildtool ar {_q(toolchain_bin / 'xtensa-lx106-elf-ar')} $out $out.rsp",
         "  rspfile = $out.rsp",
         "  rspfile_content = $in_newline",
         "  description = AR $out",
         "rule link",
-        '  command = $cxx -o "$out" $linkflags @"$out.rsp" $libdirflags -Wl,--start-group $archives $libflags -Wl,--end-group',
+        "  command = $cxx -o $out $linkflags @$out.rsp $libdirflags -Wl,--start-group $archives $libflags -Wl,--end-group",
         "  rspfile = $out.rsp",
         "  rspfile_content = $in_newline",
         "  description = LINK $out",
         "rule elf2bin",
-        f'  command = $python {_q(framework / "tools" / "elf2bin.py")} --eboot {_q(framework / "bootloaders" / "eboot" / "eboot.elf")} --app "$in" --flash_mode {esp8266_data[KEY_FLASH_MODE]} --flash_freq 40 --flash_size {_flash_size_str(flash_ld_name)} --path {_q(toolchain_bin)} --out "$out"',
+        f"  command = $python {_q(framework / 'tools' / 'elf2bin.py')} --eboot {_q(framework / 'bootloaders' / 'eboot' / 'eboot.elf')} --app $in --flash_mode {esp8266_data[KEY_FLASH_MODE]} --flash_freq 40 --flash_size {_flash_size_str(flash_ld_name)} --path {_q(toolchain_bin)} --out $out",
         "  description = BIN $out",
         "rule copy",
-        '  command = $python $buildtool copy "$in" "$out"',
+        "  command = $python $buildtool copy $in $out",
         "  description = COPY $out",
         "",
         f"cflags = {' '.join(cflags)}",
diff --git a/esphome/platformio/library.py b/esphome/platformio/library.py
index 22a86af34f..c8896d9202 100644
--- a/esphome/platformio/library.py
+++ b/esphome/platformio/library.py
@@ -688,6 +688,24 @@ def _node_key(
     return name, "registry", (owner, pkgname)
 
 
+def lib_ignore_set() -> set[str]:
+    """The ``lib_ignore`` names from ``esphome->platformio_options``,
+    normalized to lowercase short names (the part after the ``/``)."""
+    return {
+        name.split("/")[-1].lower()
+        for name in CORE.platformio_options.get("lib_ignore", [])
+    }
+
+
+def is_lib_ignored(name: str | None, lib_ignore: set[str]) -> bool:
+    """Whether ``name`` matches the normalized ``lib_ignore`` set."""
+    return (
+        bool(lib_ignore)
+        and name is not None
+        and (name.split("/")[-1].lower() in lib_ignore)
+    )
+
+
 def convert_libraries(
     libraries: list[Library], backend: LibraryBackend
 ) -> list[ConvertedLibrary]:
@@ -713,10 +731,7 @@ def convert_libraries(
     """
     nodes: dict[str, _LibNode] = {}
 
-    lib_ignore = {
-        name.split("/")[-1].lower()
-        for name in CORE.platformio_options.get("lib_ignore", [])
-    }
+    lib_ignore = lib_ignore_set()
 
     # The generated build files inside the shared cache bake in the dependency
     # wiring, which lib_ignore changes; salt the cache path so configs with
@@ -729,9 +744,7 @@ def convert_libraries(
     )
 
     def is_ignored(name: str | None) -> bool:
-        if not lib_ignore or name is None:
-            return False
-        return name.split("/")[-1].lower() in lib_ignore
+        return is_lib_ignored(name, lib_ignore)
 
     def add_spec(name: str | None, version: str | None, repository: str | None) -> str:
         key, kind, locator = _node_key(name, version, repository)
diff --git a/tests/unit_tests/build_gen/test_arduino8266.py b/tests/unit_tests/build_gen/test_arduino8266.py
index 1d51830c9b..813743c7fa 100644
--- a/tests/unit_tests/build_gen/test_arduino8266.py
+++ b/tests/unit_tests/build_gen/test_arduino8266.py
@@ -249,9 +249,13 @@ def test_write_project_link_line_and_exclusions(tmp_path: Path) -> None:
     assert "-T eagle.flash.4m.ld" in content
     # scanf float disabled: the forced-link flag must not appear
     assert "_scanf_float" not in content
-    # Compile inputs and outputs are quoted (space-containing cache paths)
-    assert '-c "$in" -o "$out"' in content
-    assert '--app "$in"' in content
+    # $in/$out must stay UNQUOTED: ninja shell-escapes its built-in path
+    # variables itself, so added quotes would wrap ninja's quoting and break
+    # space-containing paths.
+    assert "-c $in -o $out" in content
+    assert "--app $in --flash_mode" in content
+    assert '"$in"' not in content
+    assert '"$out"' not in content
     # -L/-l from esphome build_flags reach the link line, not the compiles
     assert '-L"/opt/blobs"' in content
     assert "-luser_blob" in content