[Bug] Section blocks duplicated in streamed long assistant replies

Bug Description
section block duplicated 3× in long reply Title: Streaming render: section block in long assistant reply duplicated 3× in terminal output

Body:

## What happened

In a long assistant reply (a multi-section structured report — headers
the last ~4 sections rendered in the terminal three times in a row.

The model's actual generated content (verifiable from the conversation
transcript) contained each section exactly once. The duplication only
exists in the rendered terminal output — content above the duplicated
block (BLOCKER / MAJOR sections) appeared once and correctly.

## Reproduction context

• CLI: Claude Code, Opus 4.7 (1M context), fast mode
• macOS 25.5.0, zsh, Terminal/iTerm
• Reply was ~150 lines, streamed
• No tool calls between the duplicated sections — pure text streaming
• User reported "це вже не вперше" (this is not the first time) — so

this is a recurring intermittent issue, not a one-off

## Expected
Each section block rendered exactly once.

## Actual
Sections "Nice to fix (MINOR)" → "What went well (PRAISE)" →
"Commit messages" → "Summary" appeared three times consecutively in
the rendered output, with the third instance being truncated /
interleaved.

## Notes

• This breaks reading flow on long structured reports (code reviews,

audits) where users rely on section ordering.

• If this is a streaming-buffer / re-render bug, a small repro would

be: ask the assistant for a multi-section structured report >100
lines and watch for late-section duplication.

Environment Info

• Platform: darwin
• Terminal: intellij
• Version: 2.1.141
• Feedback ID: 7881c697-33b4-4751-b1ea-18001099193d

Errors

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