fix(slack-search): stream task progress in plan mode

[TheodoreSpeaks]

Summary

Sim Search currently displays Slack search/read progress as individual timeline cards. Set its chat.startStream display mode to plan so those task updates appear together in a plan block, as described in Slack's API reference.

Update existing tests for streams starting with task progress or public answer text. Task IDs, completion/error updates, citations, thread identity, cancellation cleanup, and private-text filtering retain their existing behavior. Workflow Slack streaming keeps its configurable display mode.

Type of Change

• Bug fix

Testing

All checks passed:

• From apps/sim: bunx vitest run lib/slack-search lib/knowledge/application/slack-search lib/webhooks/slack-agent-api.test.ts lib/webhooks/slack-execution-stream.test.ts lib/webhooks/slack-stream-config.test.ts --maxWorkers=4 — 473 tests across 32 files.
• From apps/sim: bun run type-check.
• bun run check:api-validation.
• bunx biome check apps/sim/lib/slack-search/assistant-stream.ts apps/sim/lib/slack-search/assistant-stream.test.ts.
• git diff --check.

No live Slack messages were sent; rendering has not been manually verified in Slack.

Deployment

Base: staging. Merging triggers the staging deployment pipeline via ECR tag promotion. Production uses a separate main push and latest tag promotion. This PR is prepared for review only; merge and production release each require explicit approval.

[vercel]

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1 Skipped Deployment

Project	Deployment	Actions	Updated
docs	Skipped		Sep 24, 2026 1:44am UTC

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge, with no concrete correctness, security, or repository-rule violations identified.

Summary

This PR changes Slack Search assistant streams from timeline display to plan display so task progress is grouped into a plan block.

• Passes plan to chat.startStream for Slack Search streams.
• Updates task-first and answer-first tests to assert the new display mode.
• Leaves workflow Slack streaming configuration and stream lifecycle behavior unchanged.

_{Reviews (1) · Last reviewed commit: "fix(slack-search): stream task progress ..."}

[cubic-dev-ai]

No issues found across 2 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Re-trigger cubic}