Summary

PlatformConfig.gateway_restart_notification has been a no-op when set under the user-friendly top-level platform section (e.g. telegram:) in config.yaml. The bridge loop in load_gateway_config (gateway/config.py:758) only forwarded a fixed allowlist of keys, and gateway_restart_notification wasn't on the list, so:

1. telegram.gateway_restart_notification: false never reached the platforms data dict.
2. PlatformConfig.from_dict() read the safe default (True) every time.
3. The suppression check at gateway/run.py:2767 always evaluated to truthy → shutdown/restart notifications were always sent.

Fix

The issue's suggested fix (route the key through bridged) is not quite right — extra.update(bridged) would land it in extra, where PlatformConfig.from_dict() never looks (it reads data.get(\"gateway_restart_notification\") from the top level, see gateway/config.py:313). enabled already solves the same problem by writing directly to plat_data at the top level. This PR mirrors that path:

restart_notify_was_explicit = (
    \"gateway_restart_notification\" in platform_cfg
)
if not bridged and not enabled_was_explicit and not restart_notify_was_explicit:
    continue
...
if restart_notify_was_explicit:
    plat_data[\"gateway_restart_notification\"] = platform_cfg[
        \"gateway_restart_notification\"
    ]

Including the key in the early-continue guard matters: without it, sections that only set gateway_restart_notification (no other bridgeable keys, no explicit enabled) would fall through to continue and never even materialise an entry in platforms_data.

Test plan

• test_bridges_gateway_restart_notification_from_telegram_section — telegram.gateway_restart_notification: false round-trips to False (the reported case).
• test_bridges_gateway_restart_notification_true_explicit — explicit true under discord: also bridges (proves the bridge isn't accidentally swallowing values that match the default).
• test_gateway_restart_notification_defaults_true_when_unset — omitting the key keeps True so existing configs are unaffected.
• All 43 existing tests in tests/gateway/test_config.py still pass.

Without the fix, the two assertions targeting Platform.DISCORD / Platform.TELEGRAM fail with KeyError because the platform entry isn't even created (verified by reverting the fix locally).

Fixes #24644