Summary

• add Slack draft-stream previews that post once and update via chat.update
• add configurable streaming modes so teams can pick UX behavior:
  • replace: in-place replacement updates
  • status_final: stable status updates + separate final answer
  • append: append-only growth (never replaces earlier text)
• add draft preview lifecycle hardening (clear, media/no-final cleanup)
• keep multi-account safety by using explicit token: ctx.botToken on updates

Why

Different teams prefer different streaming UX patterns. This change allows Slack users to choose the style that fits them while preventing stale draft artifacts and preserving safe fallback behavior.

Changes

• Streaming runtime:
  • src/slack/draft-stream.ts
  • src/slack/stream-mode.ts
  • src/slack/monitor/message-handler/dispatch.ts
• Config surface:
  • src/config/types.slack.ts
  • src/config/zod-schema.providers-core.ts
  • src/config/schema.help.ts
  • src/config/schema.labels.ts
• Tests:
  • src/slack/draft-stream.test.ts
  • src/slack/stream-mode.test.ts

Dependency

Depends on Slack Block Kit foundation stack (starting at #18180 through #18500).
If reviewing before dependencies merge, review tip commit: 865918d96.

Validation

• pnpm vitest run src/slack/stream-mode.test.ts src/slack/draft-stream.test.ts src/slack/monitor/slash.test.ts src/slack/monitor/events/interactions.test.ts
• pnpm tsgo
• pnpm check

Notes

• Slack-only scope; no Discord/webchat streaming behavior changes.