feat(ui): add thinking ui to mothership

[TheodoreSpeaks]

Summary

Added thinking blocks. This allows users to understand llm's thinking process and also let them be assured we're actually running stuff in the background when thinking is displayed.

Thinking blocks are only displayed after 3 seconds of thinking.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation
• Other: ___________

Testing

• Tested with refresh, subagent thinking, long pauses, short pauses, aborts.

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

Screenshots/Videos

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		Apr 22, 2026 10:08pm

[cursor]

PR Summary

Medium Risk
Adds new content-block types and timing fields that flow through streaming, persistence, stop/cancel behavior, and rendering; mistakes could cause incorrect transcript ordering or cancelled state/timestamps in saved chats.

Overview
Adds a new Thinking UI panel for both main assistant and subagents, including collapse/expand behavior, auto-scroll support during height animations, and a 3s visibility threshold (hide short completed thinking, delay showing active thinking until it exceeds the threshold).

Extends content blocks end-to-end to carry timestamp/endedAt and introduces thinking/subagent_thinking blocks. Streaming now stamps boundaries when switching between text/thinking/tools/subagent spans, persists timing on /chat/stop, and avoids corrupting historical messages by only marking the active in-flight assistant message as stopped.

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[greptile-apps]

Greptile Summary

This PR introduces a collapsible thinking-block UI that surfaces LLM reasoning to users during and after streaming. Timestamps are threaded through the full content-block lifecycle — streaming context, persistence, and display — so elapsed time can be calculated and blocks shorter than 3 seconds can be suppressed as visual noise.

Confidence Score: 5/5

Safe to merge; only P2 style findings remain

All remaining findings are P2 (a stale comment that says "5s" while the constant is 3000 ms, and overflow-y-scroll vs overflow-y-auto). No logic errors, data-loss risks, or broken code paths were found. Timing propagation, flush ordering, and auto-scroll extension all look correct.

thinking-block.tsx — stale "5s" comment and overflow-y-scroll style choice

Important Files Changed

Filename	Overview
apps/sim/app/workspace/[workspaceId]/home/components/message-content/components/thinking-block/thinking-block.tsx	New component; minor stale comment ("5s" vs 3 s constant) and prefer overflow-y-auto over overflow-y-scroll
apps/sim/app/workspace/[workspaceId]/home/components/message-content/message-content.tsx	Correctly parses thinking/subagent_thinking blocks into segments and applies the 3 s filter before rendering ThinkingBlock
apps/sim/app/workspace/[workspaceId]/home/hooks/use-chat.ts	Adds ensureThinkingBlock, stampBlockEnd helpers and timestamps thinking/tool/compaction/subagent lifecycle blocks correctly through the stream
apps/sim/hooks/use-auto-scroll.ts	Adds animationstart listener that drives 500 ms RAF follow-scroll window for CSS height animations; cleanup is handled correctly
apps/sim/lib/copilot/request/go/stream.ts	Flushes open thinking blocks at subagent lifecycle boundaries and on abort/error, preventing ordering or silent-drop issues
apps/sim/lib/copilot/chat/display-message.ts	Correctly maps persisted lane+channel combinations to subagent_thinking/thinking/text content block types
apps/sim/lib/copilot/request/handlers/types.ts	Adds stampBlockEnd helper and wires it into flushThinkingBlock/flushSubagentThinkingBlock to close open blocks before persisting
apps/sim/lib/copilot/chat/persisted-message.ts	Propagates timestamp/endedAt through mapContentBlock and normalizeBlock for both canonical and legacy persisted blocks

Sequence Diagram

sequenceDiagram
    participant Stream as Stream (go/stream.ts)
    participant Handler as tool.ts / handlers
    participant Context as StreamingContext
    participant UseChat as use-chat.ts
    participant MsgContent as message-content.tsx
    participant ThinkBlock as ThinkingBlock

    Stream->>Context: text event (channel=thinking) → ensureThinkingBlock()
    Note over Context: currentThinkingBlock accumulates content + timestamp
    Stream->>Handler: tool or subagent lifecycle event
    Handler->>Context: flushThinkingBlock() — stampBlockEnd + push to contentBlocks
    UseChat->>UseChat: toRawPersistedContentBlockBody (type=text, channel=thinking)
    UseChat->>UseChat: withBlockTiming adds timestamp/endedAt
    UseChat-->>DB: persist contentBlocks with timing
    Note over DB: On reload
    DB-->>UseChat: PersistedContentBlock (lane, channel, timestamp, endedAt)
    UseChat->>MsgContent: toDisplayBlock → ContentBlockType.thinking
    MsgContent->>MsgContent: parseBlocks → ThinkingSegment (startedAt, endedAt)
    MsgContent->>MsgContent: elapsedMs ≤ 3000ms? → return null
    MsgContent->>ThinkBlock: render ThinkingBlock(isActive, isStreaming, startedAt, endedAt)
    ThinkBlock->>ThinkBlock: thresholdReached gate (3 s for active blocks)
    ThinkBlock->>ThinkBlock: rAF expand animation once threshold hit

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