[image] Only migrate recognised legacy image configs

Guard the legacy `image:` migration so it only rewrites shapes the
pre-platform schema actually accepted. A list with a non-dict or
already-platform-tagged entry, or a dict with no recognised image keys
(e.g. `image: ["bad"]`, `image: {foo: 1}`), now returns None from the
migration hook, so normal platform validation surfaces a proper error
instead of the migration silently dropping the input.

esphome/components/image/__init__.py

@@ -487,6 +487,32 @@ def _is_new_image_format(config: object) -> bool:
     )
 
 
+def _is_legacy_image_format(config: object) -> bool:
+    """True when ``config`` matches a shape the pre-platform schema accepted.
+
+    Only these shapes are migrated. Anything else -- a list containing a
+    non-dict (or already platform-tagged) entry, or a dict with no recognised
+    image keys -- is left untouched so the platform validation surfaces a
+    proper error instead of the migration silently dropping the input.
+    """
+    if isinstance(config, list):
+        # A bare list of (not-yet-platform-tagged) image dicts.
+        return bool(config) and all(
+            isinstance(entry, dict) and CONF_PLATFORM not in entry for entry in config
+        )
+    if not isinstance(config, dict):
+        return False
+    # A single image dict, or the grouped `defaults:`/`images:`/type-key form.
+    return (
+        CONF_ID in config
+        or CONF_FILE in config
+        or any(
+            key in (CONF_DEFAULTS, CONF_IMAGES) or key.upper() in IMAGE_TYPE
+            for key in config
+        )
+    )
+
+
 def _flatten_legacy_image_config(config: object) -> list[dict]:
     """Structurally flatten a legacy ``image:`` config into image dicts.
 
@@ -543,8 +569,13 @@ def _flatten_legacy_image_config(config: object) -> list[dict]:
 
 
 def _migrate_legacy_image_config(config: object) -> list[dict] | None:
-    """Rewrite a legacy ``image:`` config into the ``platform: file`` list."""
-    if _is_new_image_format(config):
+    """Rewrite a legacy ``image:`` config into the ``platform: file`` list.
+
+    Returns None for the already-migrated platform form and for any shape the
+    pre-platform schema never accepted, so normal platform validation can
+    surface a proper error instead of the migration silently discarding input.
+    """
+    if _is_new_image_format(config) or not _is_legacy_image_format(config):
         return None
     migrated = [
         {CONF_PLATFORM: PLATFORM_FILE, **entry}

tests/component_tests/image/test_init.py

@@ -22,6 +22,7 @@ from esphome.components.image import (
     CONF_TRANSPARENCY,
     PLATFORM_FILE,
     _flatten_legacy_image_config,
+    _is_legacy_image_format,
     _is_new_image_format,
     _migrate_legacy_image_config,
     get_all_image_metadata,
@@ -323,6 +324,49 @@ def test_migrate_legacy_warns_and_prepends_platform(
     assert f"platform: {PLATFORM_FILE}" in caplog.text
 
 
+@pytest.mark.parametrize(
+    ("config", "expected"),
+    [
+        # Recognised legacy shapes -> migrate.
+        pytest.param([{"id": "a", "file": "x.png"}], True, id="bare_list_of_dicts"),
+        pytest.param({"id": "a", "file": "x.png"}, True, id="single_image_dict"),
+        pytest.param({"file": "x.png"}, True, id="single_dict_file_only"),
+        pytest.param({"defaults": {}, "images": []}, True, id="defaults_images"),
+        pytest.param({"rgb565": [{"id": "a"}]}, True, id="type_grouped"),
+        # Shapes the legacy schema never accepted -> not migrated.
+        pytest.param([], False, id="empty_list"),
+        pytest.param(["bad"], False, id="list_with_non_dict"),
+        pytest.param([{"id": "a"}, "bad"], False, id="list_mixed_dict_and_non_dict"),
+        pytest.param(
+            [{CONF_PLATFORM: "file", "id": "a"}], False, id="already_platform_tagged"
+        ),
+        pytest.param({"foo": 1}, False, id="dict_unknown_keys"),
+        pytest.param("a string", False, id="scalar"),
+    ],
+)
+def test_is_legacy_image_format(config: object, expected: bool) -> None:
+    assert _is_legacy_image_format(config) is expected
+
+
+@pytest.mark.parametrize(
+    "config",
+    [
+        pytest.param(["bad"], id="list_with_non_dict"),
+        pytest.param([{"id": "a"}, "bad"], id="list_mixed"),
+        pytest.param({"foo": 1}, id="dict_unknown_keys"),
+    ],
+)
+def test_migrate_returns_none_for_invalid_legacy_shapes(
+    config: object, caplog: pytest.LogCaptureFixture
+) -> None:
+    """Unrecognised shapes are not migrated (and emit no warning) so normal
+    platform validation surfaces a proper error instead of silently dropping
+    the offending input."""
+    with caplog.at_level(logging.WARNING):
+        assert _migrate_legacy_image_config(config) is None
+    assert "deprecated" not in caplog.text
+
+
 # --------------------------- end legacy migration --------------------------