diff --git a/esphome/framework_helpers.py b/esphome/framework_helpers.py
index b1c34fed36..7e889a2d1d 100644
--- a/esphome/framework_helpers.py
+++ b/esphome/framework_helpers.py
@@ -779,15 +779,25 @@ def run_batch_downloads(
     collected (list.append is atomic under the GIL) and returned after the
     bar is done, so the caller's warnings never land on the bar's row; a
     failed job credits its tracker 0 so the bar can still complete. Ctrl-C
-    drops queued jobs instead of downloading them all before the process
-    can exit; in-flight ones still finish. ``jobs`` must be non-empty.
+    drops queued jobs and aborts in-flight ones at their next progress
+    tick; resumable ``.part`` files keep the bytes already fetched.
+    ``jobs`` must be non-empty.
     """
     failures: list[tuple[str, Exception]] = []
+    cancelled = threading.Event()
 
     def _run(name: str, fetch: Callable[[Callable[[int], None]], None]) -> None:
         tracker = progress.tracker()
+
+        def checked(done: int) -> None:
+            if cancelled.is_set():
+                raise _BatchDownloadCancelled
+            tracker(done)
+
         try:
-            fetch(tracker)
+            fetch(checked)
+        except _BatchDownloadCancelled:
+            tracker(0)
         except Exception as err:  # noqa: BLE001  # pylint: disable=broad-exception-caught
             failures.append((name, err))
             tracker(0)
@@ -796,12 +806,21 @@ def run_batch_downloads(
     try:
         for future in [ex.submit(_run, name, fetch) for name, fetch in jobs]:
             future.result()
+    except BaseException:
+        # Without this the non-daemon workers download to completion before
+        # the interpreter can exit, making Ctrl-C ineffective for minutes
+        cancelled.set()
+        raise
     finally:
         ex.shutdown(wait=True, cancel_futures=True)
         progress.done()
     return failures
 
 
+class _BatchDownloadCancelled(Exception):
+    """Raised inside a download job to abandon it after Ctrl-C."""
+
+
 class BatchDownloadProgress:
     """One progress bar across several concurrent ``download_with_resume`` calls.
 
diff --git a/esphome/platformio/library.py b/esphome/platformio/library.py
index e7ce437570..f3622ffc52 100644
--- a/esphome/platformio/library.py
+++ b/esphome/platformio/library.py
@@ -59,7 +59,8 @@ DEFAULT_BUILD_FLAGS = []
 # "asm" merges SCons's AS and ASPP sets: all compile as assembler-with-cpp.
 # The kind values drive the ESP8266 native ninja rules (later in this
 # chain); existing backends consume only the keys. Note .C/.C++ join the
-# suffix set here, matching PlatformIO's CXXSUFFIXES.
+# suffix set here per CXXSUFFIXES; SCons demotes .C to C on
+# case-insensitive filesystems, we always treat it as C++.
 SOURCE_KIND_FOR_SUFFIX: dict[str, str] = {
     ".c": "c",
     ".cpp": "cxx",
diff --git a/tests/unit_tests/test_espidf_framework.py b/tests/unit_tests/test_espidf_framework.py
index 6fbdd2fb19..cecf49325f 100644
--- a/tests/unit_tests/test_espidf_framework.py
+++ b/tests/unit_tests/test_espidf_framework.py
@@ -984,9 +984,13 @@ def test_prefetch_downloads_each_archive_with_resume(tmp_path: Path) -> None:
     kwargs = calls[("https://example.com/cmake.tar.gz", dist / "cmake-3.30.2.tar.gz")]
     assert kwargs["sha256"] == "ab" * 32
     assert kwargs["size"] == 123
-    # every archive reports into the one combined progress bar
+    # every archive reports into the one combined progress bar via the
+    # cancellation-checked wrapper; verify it delegates to the tracker
     progress_cls.assert_called_once_with("Downloading ESP-IDF tools", 123 + 45)
-    assert all(kw["progress"] is tracker for kw in calls.values())
+    before = tracker.call_count
+    for kw in calls.values():
+        kw["progress"](7)
+    assert tracker.call_count == before + len(calls)
 
 
 def test_prefetch_downloads_archives_concurrently(tmp_path: Path) -> None:
diff --git a/tests/unit_tests/test_framework_helpers.py b/tests/unit_tests/test_framework_helpers.py
index 6be152144a..f88bcc2170 100644
--- a/tests/unit_tests/test_framework_helpers.py
+++ b/tests/unit_tests/test_framework_helpers.py
@@ -1158,6 +1158,40 @@ class TestDownloadWithResume:
         assert seen == [8]
 
 
+def test_run_batch_downloads_ctrl_c_aborts_in_flight_jobs() -> None:
+    """Ctrl-C cancels in-flight downloads at their next tick instead of
+    letting non-daemon workers download to completion."""
+    import threading
+    import time
+
+    from esphome.framework_helpers import BatchDownloadProgress, run_batch_downloads
+
+    started = threading.Event()
+    ticks: list[int] = []
+
+    def interrupter(tracker) -> None:
+        started.wait(5)
+        raise KeyboardInterrupt
+
+    def slow_download(tracker) -> None:
+        started.set()
+        for i in range(500):
+            tracker(i)
+            ticks.append(i)
+            time.sleep(0.01)
+
+    t0 = time.monotonic()
+    with pytest.raises(KeyboardInterrupt):
+        run_batch_downloads(
+            BatchDownloadProgress("Downloading", 0),
+            [("boom", interrupter), ("slow", slow_download)],
+            max_workers=2,
+        )
+    # Uncancelled, slow_download alone takes ~5s
+    assert time.monotonic() - t0 < 3
+    assert len(ticks) < 500
+
+
 class TestBatchDownloadProgress:
     def test_sums_trackers_into_one_bar(self) -> None:
         with patch("esphome.framework_helpers.ProgressBar") as bar_cls:
diff --git a/tests/unit_tests/test_platformio_library.py b/tests/unit_tests/test_platformio_library.py
index e1defb0710..0abba6d71c 100644
--- a/tests/unit_tests/test_platformio_library.py
+++ b/tests/unit_tests/test_platformio_library.py
@@ -276,6 +276,8 @@ def test_wave_requirement_growth_defers_the_superseded_download(tmp_path, monkey
         (self.path / "library.json").write_text(json.dumps(manifests[self.name]))
 
     monkeypatch.setattr(ConvertedLibrary, "download", fake_download)
+    # Hermetic: unknown sizes take the sequential path instead of real HEADs
+    monkeypatch.setattr(lib, "_content_lengths", lambda urls: [None] * len(urls))
     _patch_registry_resolve(monkeypatch)
     top = convert_libraries(
         [Library("esphome/A", "1.0.0", None), Library("esphome/B", None, None)],
@@ -710,9 +712,7 @@ def test_content_lengths_head_requests(monkeypatch: pytest.MonkeyPatch) -> None:
             return SimpleNamespace(ok=True, headers={"content-length": "123, 123"})
         return SimpleNamespace(ok=True, headers={"content-length": "123"})
 
-    monkeypatch.setattr(
-        lib.requests if hasattr(lib, "requests") else requests, "head", fake_head
-    )
+    monkeypatch.setattr(requests, "head", fake_head)
     # None marks an unknown size (probe failure or non-2xx), distinct
     # from a genuine zero
     assert lib._content_lengths(