[Feat] Deliver destinationless automation results by chat or Email

[roomote-roomote]

​Opened on behalf of @mrubens. View the task or mention @roomote-roomote for follow-up asks.

What changed

• resolves destinationless custom automations to the creator's first usable linked chat DM
• falls back to the creator's current verified Email identity when no connected chat DM is available
• routes Email fallback through the existing durable AgentMail automation conversation, including Fast runs and startup failures
• preserves direct-message routing for Discord fallbacks instead of treating DM channel IDs as guild channels
• preserves configured destinations and keeps the synthetic stored Session when no fallback route is usable

Why this change was made

Custom automations without a configured destination could complete successfully while their result remained only in a stored Session. Verified Email automation destinations now provide an ultimate delivery route after linked chat DMs have been exhausted.

Impact

Creators receive destinationless automation results through chat when possible and verified Email otherwise, without duplicate cross-channel delivery or silent substitution of an unavailable explicit destination. Focused automation tests pass all 49 cases, including a Discord-only DM fallback regression; SDK type checking, repository pre-push lint and type checks, and knip also pass.

[roomote-community]

No new code issues found. See task

• Discord DM fallbacks are treated as guild channels and fail to launch.

_{Reviewed 382cab9}

[roomote-roomote]

Fixed the Discord DM fallback classification in 382cab95. Destinationless Discord automations now use the DM conversation path instead of guild-channel lookup, with a focused regression added; 49 automation tests and SDK type checking pass. See task