Keep no-op rebuilds quiet

A -n dry-run probe answers 'no work to do' without the real ninja spawn,
and running with cwd instead of -C drops the 'Entering directory' banner
on real builds too.

esphome/arduino8266/toolchain.py

@@ -89,16 +89,33 @@ def run_compile(config: ConfigType, verbose: bool) -> int:
     if ninja_changed or not (build_dir / "compile_commands.json").is_file():
         _write_compile_commands(paths.ninja, build_dir, env)
 
-    cmd = [str(paths.ninja), "-C", str(build_dir)]
+    cmd = [str(paths.ninja)]
     if verbose:
         cmd.append("-v")
     if jobs := config[CONF_ESPHOME].get(CONF_COMPILE_PROCESS_LIMIT):
         cmd += ["-j", str(jobs)]
 
-    _LOGGER.debug("Running: %s", " ".join(cmd))
-    rc = subprocess.run(cmd, env=env, check=False, close_fds=False).returncode
-    if rc != 0:
-        return rc
+    # A dry-run probe keeps a no-op rebuild quiet: ninja would only print
+    # "no work to do". cwd instead of -C also drops the "Entering
+    # directory" banner on real builds.
+    probe = subprocess.run(
+        [str(paths.ninja), "-n"],
+        cwd=build_dir,
+        env=env,
+        capture_output=True,
+        text=True,
+        check=False,
+        close_fds=False,
+    )
+    if probe.returncode == 0 and "no work to do" in probe.stdout:
+        _LOGGER.debug("ninja: nothing to rebuild")
+    else:
+        _LOGGER.debug("Running: %s", " ".join(cmd))
+        rc = subprocess.run(
+            cmd, cwd=build_dir, env=env, check=False, close_fds=False
+        ).returncode
+        if rc != 0:
+            return rc
 
     _print_size_summary(build_dir, paths)
     try:

tests/unit_tests/test_arduino8266_toolchain.py

@@ -92,13 +92,41 @@ def test_run_compile_success(tmp_path: Path) -> None:
             {CONF_ESPHOME: {CONF_COMPILE_PROCESS_LIMIT: 4}}, verbose=False
         )
     assert rc == 0
-    cmd = mock_run.call_args[0][0]
+    # The -n probe runs first, then the real build (cwd, no -C banner)
+    ninja_calls = [c for c in mock_run.call_args_list if "ninja" in str(c[0][0][0])]
+    assert ninja_calls[0][0][0][-1] == "-n"
+    cmd = ninja_calls[1][0][0]
     assert cmd[-2:] == ["-j", "4"]
+    assert "-C" not in cmd
+    assert ninja_calls[1][1]["cwd"] is not None
     mock_compdb.assert_called_once()
     mock_size.assert_called_once()
     mock_idedata.assert_called_once()
 
 
+def test_run_compile_noop_skips_the_build_spawn(tmp_path: Path) -> None:
+    """A no-op rebuild stays quiet: the -n probe answers "no work to do"
+    and the real ninja spawn (and its banner) never happens."""
+    with (
+        patch.object(framework, "check_and_install", return_value=_paths(tmp_path)),
+        patch.object(framework, "get_build_env", return_value={}),
+        patch("esphome.build_gen.arduino8266.write_project"),
+        patch.object(
+            toolchain.subprocess,
+            "run",
+            return_value=MagicMock(returncode=0, stdout="ninja: no work to do.\n"),
+        ) as mock_run,
+        patch.object(toolchain, "_write_compile_commands"),
+        patch.object(toolchain, "_print_size_summary"),
+        patch.object(toolchain, "get_idedata"),
+    ):
+        rc = toolchain.run_compile({CONF_ESPHOME: {}}, verbose=False)
+    assert rc == 0
+    ninja_calls = [c for c in mock_run.call_args_list if "ninja" in str(c[0][0][0])]
+    assert len(ninja_calls) == 1
+    assert ninja_calls[0][0][0][-1] == "-n"
+
+
 def test_run_compile_warns_when_idedata_fails(
     tmp_path: Path, caplog: pytest.LogCaptureFixture
 ) -> None: