fix: read saving session available_events from configured entity, not rewritten one

[springfall2008]

Summary

Fixes #4573.

The octopus_saving_session binary_sensor -> event entity rewrite (a fallback for legacy configs) rebound entity_id unconditionally whenever joined_events was empty on the configured entity. The following available_events read then used the rewritten entity name instead of the one the user configured. If the rewritten entity didn't exist (e.g. custom entity names with no _sessions substring, or the newer flexibility API naming), available_events came back empty and saving-session auto-join silently stopped working - with nothing logged, since the "auto-join is disabled" message also requires available_events to be truthy.

Fix

available_events and joined_events are now both read from the configured entity first. The rewrite to the event.* entity is only attempted - and only adopted - when the configured entity has neither attribute and the rewritten entity actually returns data. This preserves the legacy binary_sensor path (where entity_id genuinely needs to be rebound so a later join-service call targets the correct entity) while fixing the case where the configured entity already has the data needed.

Test plan

• Added test_saving_session_custom_entity_no_rewrite_match, reproducing the issue's scenario (custom entity name, empty joined_events, populated available_events, no matching rewritten entity). Confirmed it fails on the pre-fix code (0 join calls) and passes with the fix.
• All existing saving-session tests still pass (saving_session, saving_session_null, saving_session_notify, saving_session_default_rate, saving_session_axle_conflict, saving_session_auto_join_toggle).
• Full ./run_all --quick suite passes.
• pre-commit (ruff, black, cspell) passes on changed files.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Fixes a regression in Octopus Saving Session auto-join by ensuring available_events is read from the user-configured saving-session entity, and only falling back to the legacy binary_sensor.*_sessions -> event.*_session_events rewrite when the configured entity provides no relevant attributes.

Changes:

• Read both joined_events and available_events from the configured octopus_saving_session entity before attempting any entity-id rewrite.
• Gate the entity-id rewrite so it’s only adopted when the rewritten entity actually returns usable data.
• Add a regression test covering custom entity names that do not match the rewrite pattern.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
apps/predbat/octopus.py	Fixes saving-session attribute reads so available_events isn’t accidentally read from a rewritten/nonexistent entity.
apps/predbat/tests/test_saving_session.py	Adds regression coverage for a custom configured entity name where rewrite would not resolve.
apps/predbat/unit_test.py	Registers the new saving-session regression test in the test runner.

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