修复 Discord 私聊 reaction 被静默丢弃（PR #10418）

• You already run Discord integration and rely on reaction events for automations/workflows.
• Gateway runtime can be upgraded to include PR #10418.

1. Upgrade to a build that includes PR #10418, then restart gateway.
2. Create two reaction canaries: one in server channel and one in DM/group DM.
3. Trigger reaction events and verify DM paths are no longer dropped by guild-only guards.
4. Inspect logs/peer metadata and ensure DM uses `kind=dm` with user ID, group DM uses group path.
5. Keep one regression test for guild reactions to ensure no channel-side regression.

• Discord permission and intent settings can still block events even after this fix.
• The PR description references specific tests; local environment behavior should still be re-validated（需验证）。

This tip is aggregated from community/public sources and preserved with attribution.