fix: backfill base_url on migration so pre-base_url entries still load

async_setup_entry does entry.data[CONF_BASE_URL] as a hard index, but
base_url is this fork's own addition: an entry created by a build from
before the base_url commits (48195c9 era, version 2 minor 7) has no such
key. On restart, setup raises KeyError: 'base_url' and the integration
fails to load -- reproduced in test first, where async_setup returns
False with that KeyError in the log.

Fixed with a migration step rather than a defensive .get(), matching the
pattern the rest of async_migrate_entry already uses, so the invariant
"a loaded entry has base_url" holds for every caller instead of each
call site guarding itself:

- new step 2.7 -> 2.8 backfills DEFAULT_BASE_URL via dict.setdefault, so
  an entry that already has a base_url keeps its own endpoint and only a
  missing one is filled. An install from before this feature was
  implicitly using api.openai.com, which is exactly DEFAULT_BASE_URL, so
  the backfill preserves existing behavior rather than repointing anyone.
- config_flow MINOR_VERSION 7 -> 8, otherwise the step never runs.

test_client_built_with_base_url now also covers the preserve path, since
its entry starts at minor 7 with a base_url set and must still reach the
client unchanged after migrating.

Also updated test_form's `minor_version == 7` assertion to 8; it pins
the version new entries are created at, so the bump is expected. The
reauth test's MockConfigEntry stays at minor 7 on purpose -- it stands
in for an already-existing entry.

Local: 138 passed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NxJYWgGJtCw13qUHZtG8ki

custom_components/openai_compatible/__init__.py

@@ -49,6 +49,7 @@ from .const import (
     CONF_TEMPERATURE,
     CONF_TOP_P,
     DEFAULT_AI_TASK_NAME,
+    DEFAULT_BASE_URL,
     DEFAULT_NAME,
     DEFAULT_STT_NAME,
     DEFAULT_TTS_NAME,
@@ -489,6 +490,16 @@ async def async_migrate_entry(hass: HomeAssistant, entry: OpenAIConfigEntry) ->
                     )
         hass.config_entries.async_update_entry(entry, minor_version=7)
 
+    if entry.version == 2 and entry.minor_version == 7:
+        # base_url is this fork's addition, so an entry written by a build
+        # from before it existed has no such key, and async_setup_entry's
+        # lookup raises KeyError. Such an install was implicitly talking to
+        # OpenAI, which is what DEFAULT_BASE_URL is, so backfilling it keeps
+        # the endpoint it was already using.
+        data = dict(entry.data)
+        data.setdefault(CONF_BASE_URL, DEFAULT_BASE_URL)
+        hass.config_entries.async_update_entry(entry, data=data, minor_version=8)
+
     LOGGER.debug(
         "Migration to version %s:%s successful", entry.version, entry.minor_version
     )