Fix collapse-all trigger causing newly mounted items to auto-collapse

[everpcpc]

Summary

When clicking "Collapse Diff" or "Collapse All", the collapseAllTrigger counter increments. Components checked collapseAllTrigger > 0 in a useEffect to decide whether to collapse. However, when new items (diffs, tool calls, thinking blocks) mounted after the button was clicked, they saw the trigger was already > 0 and auto-collapsed on mount.

Fixed by capturing the trigger value at mount time via useRef and only reacting to values greater than the initial one. This makes collapse a one-time operation that only affects currently mounted items.

Files changed:

• InlineDiffViewer.tsx — inline diffs in timeline
• ToolCallMessage.tsx — tool call entries
• ThinkingMessage.tsx — thinking blocks
• TimelineView.tsx — AgentResponse component

Tests

• No Test - UI interaction bug, verified by code inspection

Type of change

• Bug Fix (non-breaking change which fixes an issue)