Fix/slack pre auth media download

[necoweb3]

Summary

This rejects unauthorized Slack message events before the adapter performs file metadata fetches or media processing.

The gateway runner performs the final _is_user_authorized check after the adapter has already constructed a MessageEvent. For Slack messages with files, that meant an unauthorized sender could still trigger Slack files_info calls and file-processing work before the runner rejected the event.

Changes

• Reuse the bound gateway runner auth check at the start of _handle_slack_message().
• Return before thread lookup, user resolution, files_info, or file download work when the sender is unauthorized.
• Preserve existing behavior when the adapter is used without a bound gateway runner.
• Add a regression test proving unauthorized Slack file messages do not call files_info.

Tests

python -m pytest tests/gateway/test_slack.py -k "unauthorized_message_does_not_fetch_file_info or file_shared_video_fallback_fetches_file_info" -q --timeout-method=thread
2 passed

[alt-glitch]

This was generated by AI during triage.

Related: #54213 (Teams) and #52353 (Telegram) apply the same pre-auth side-effect hardening pattern — reject the unauthorized sender before attachment metadata fetch / media download — to their respective platform adapters. This is the Slack counterpart (plugins/platforms/slack/adapter.py); not a duplicate (different adapter, different file).

[tonydwb]

Code Review Summary

Verdict: LGTM

Same pattern as Discord early-auth fix (PR #55273). Rejects unauthorized Slack message events before file metadata fetches or media processing.

• Consistent with Discord adapter pattern
• Clean early-auth gate
• Well-scoped: 2 files, 65 additions

Reviewed 2 files, 65 additions. Approved.

[teknium1]

Thanks for targeting a real pre-auth side-effect boundary. The normal Slack message path still fetches file metadata/media before the runner receives the constructed event (plugins/platforms/slack/adapter.py:2923, :2963, :3214, :3236; runner auth is at gateway/run.py:8958).

Problems

• The proposed __self__ lookup is not reliable on current main. Profile multiplexing installs a nested handler closure at gateway/run.py:8604-8606, created at :8629-8638; it has no bound runner __self__, so the early gate would be skipped.
• file_shared remains ungated: its registered handler reaches plugins/platforms/slack/adapter.py:2511, which calls files.info at :2528 before it delegates at :2587.

Suggested changes

• Use main's existing BasePlatformAdapter._is_sender_authorized() (gateway/platforms/base.py:2852-2874), which GatewayRunner wires in all startup paths (gateway/run.py:7068, :8611). Reject only an explicit False result.
• Apply the same gate before file_shared calls files.info, with regression coverage for that ingress and for a wrapped profile handler.

Automated hermes-sweeper review.

[teknium1]

Merged via #69482 — your commit was cherry-picked/reapplied onto current main with your authorship preserved in git history: your pre-auth media gating was cherry-picked directly.

Thanks for the contribution!