[esp32_ble_tracker] Scan at the default window while a GATT connection is active (#18609)

tests/component_tests/esp32_ble_tracker/config/scan_window_explicit.yaml

@@ -0,0 +1,19 @@
+esphome:
+  name: scan-window-explicit
+
+esp32:
+  board: esp32dev
+  framework:
+    type: esp-idf
+
+wifi:
+  ssid: MySSID
+
+esp32_ble_tracker:
+  scan_parameters:
+    window: 30ms
+
+bluetooth_proxy:
+  active: true
+
+api:

tests/component_tests/esp32_ble_tracker/config/scan_window_raised.yaml

@@ -0,0 +1,17 @@
+esphome:
+  name: scan-window-raised
+
+esp32:
+  board: esp32dev
+  framework:
+    type: esp-idf
+
+wifi:
+  ssid: MySSID
+
+esp32_ble_tracker:
+
+bluetooth_proxy:
+  active: true
+
+api:

tests/component_tests/esp32_ble_tracker/config/scan_window_scan_only.yaml

@@ -0,0 +1,12 @@
+esphome:
+  name: scan-window-scan-only
+
+esp32:
+  board: esp32dev
+  framework:
+    type: esp-idf
+
+wifi:
+  ssid: MySSID
+
+esp32_ble_tracker:

tests/component_tests/esp32_ble_tracker/config/scan_window_user_set_scan_only.yaml

@@ -0,0 +1,14 @@
+esphome:
+  name: scan-window-user-scan-only
+
+esp32:
+  board: esp32dev
+  framework:
+    type: esp-idf
+
+wifi:
+  ssid: MySSID
+
+esp32_ble_tracker:
+  scan_parameters:
+    connection_scan_window: 20ms

tests/component_tests/esp32_ble_tracker/test_scan_window_default.py

@@ -12,11 +12,12 @@ arbiter a full-duty scan would starve wifi, so the 30 ms default is kept.
 from __future__ import annotations
 
 from collections.abc import Callable
+from pathlib import Path
 
 import pytest
 
 from esphome import config_validation as cv
-from esphome.components.ble_device_base import to_ble_units
+from esphome.components.ble_device_base import CONF_CONNECTION_SCAN_WINDOW, to_ble_units
 from esphome.components.const import CONF_SCAN_PARAMETERS, CONF_WINDOW
 from esphome.components.esp32 import KEY_IDF_VERSION
 from esphome.components.esp32_ble_tracker import (
@@ -120,3 +121,103 @@ def test_short_interval_without_window_still_rejected(
     stage_esp32("5.5.5", wifi=True)
     with pytest.raises(cv.Invalid, match="needs to be smaller than scan interval"):
         _scan_params({"scan_parameters": {"interval": "20ms"}})
+
+
+# The connection-time fallback window: while a GATT connection is active the
+# scanner drops from a raised full-duty window back to this value so the
+# connection gets guaranteed airtime.
+
+
+def test_raise_arms_connection_scan_window_default(
+    stage_esp32: Callable[..., None],
+) -> None:
+    stage_esp32("5.5.5", wifi=True)
+    params = _scan_params({})
+    assert params[CONF_WINDOW] == params[CONF_INTERVAL]
+    assert to_ble_units(params[CONF_CONNECTION_SCAN_WINDOW]) == 48
+
+
+def test_user_connection_scan_window_survives_raise(
+    stage_esp32: Callable[..., None],
+) -> None:
+    stage_esp32("5.5.5", wifi=True)
+    params = _scan_params({"scan_parameters": {"connection_scan_window": "60ms"}})
+    assert params[CONF_WINDOW] == params[CONF_INTERVAL]
+    assert to_ble_units(params[CONF_CONNECTION_SCAN_WINDOW]) == 96
+
+
+def test_unraised_window_gets_no_connection_scan_window_default(
+    stage_esp32: Callable[..., None],
+) -> None:
+    stage_esp32("5.5.4", wifi=True)
+    assert CONF_CONNECTION_SCAN_WINDOW not in _scan_params({})
+
+
+def test_connection_scan_window_above_interval_rejected(
+    stage_esp32: Callable[..., None],
+) -> None:
+    stage_esp32("5.5.5", wifi=True)
+    with pytest.raises(
+        cv.Invalid, match="connection_scan_window .* needs to be smaller"
+    ):
+        _scan_params({"scan_parameters": {"connection_scan_window": "400ms"}})
+
+
+def test_connection_scan_window_above_window_rejected(
+    stage_esp32: Callable[..., None],
+) -> None:
+    """A connection window above the (post-raise) window would widen the scan
+    during connections; the reject runs after the raise so a fallback below a
+    raised window still validates (covered by the survives-raise test)."""
+    stage_esp32("5.5.5", wifi=True)
+    with pytest.raises(
+        cv.Invalid, match="connection_scan_window .* needs to be smaller"
+    ):
+        _scan_params(
+            {"scan_parameters": {"window": "30ms", "connection_scan_window": "300ms"}}
+        )
+
+
+def test_connection_scan_window_truncation_collapse_rejected(
+    stage_esp32: Callable[..., None],
+) -> None:
+    """A connection window that truncates into the interval's 0.625 ms unit
+    would silently program a full-duty scan during connections."""
+    stage_esp32("5.5.5", wifi=True)
+    with pytest.raises(cv.Invalid, match="connection_scan_window .* both truncate"):
+        _scan_params(
+            {
+                "scan_parameters": {
+                    "interval": "320.5ms",
+                    "connection_scan_window": "320.2ms",
+                }
+            }
+        )
+
+
+@pytest.mark.parametrize(
+    ("config_file", "window_call", "connection_call", "warns"),
+    [
+        # Raised window with GATT clients: the injected fallback is emitted.
+        ("scan_window_raised.yaml", "set_scan_window(512)", True, False),
+        # Explicit window: nothing injected.
+        ("scan_window_explicit.yaml", "set_scan_window(48)", False, False),
+        # Scan-only build compiles the path out: the injected default is
+        # dropped silently, a user-set value warns.
+        ("scan_window_scan_only.yaml", "set_scan_window(512)", False, False),
+        ("scan_window_user_set_scan_only.yaml", "set_scan_window(512)", False, True),
+    ],
+)
+def test_connection_scan_window_codegen(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+    caplog: pytest.LogCaptureFixture,
+    config_file: str,
+    window_call: str,
+    connection_call: bool,
+    warns: bool,
+) -> None:
+    main_cpp = generate_main(component_config_path(config_file))
+    assert window_call in main_cpp
+    assert ("set_connection_scan_window(48)" in main_cpp) == connection_call
+    assert ("'connection_scan_window' has no effect" in caplog.text) == warns