feat(coding-agent): added mode-aware streaming preview for edit outputs
- Added mode-aware streaming mode resolution and strategy registration in tool execution flow.
- Changed edit rendering to propagate mode and file-scoped diff previews across edit/vim tool outputs.
- Added chunk-mode streaming helpers (`loadChunkSource`, `computeChunkDiff`, `dropIncompleteLastEdit`) with abort-aware error fallbacks.
- Added strategy-specific streaming preview support for replace, patch, hashline, apply_patch, and vim modes.
- Fixed streaming previews by dropping incomplete trailing edits and handling invalid chunk or aborted inputs.
- Expanded streaming and chunk-diff tests for partial JSON, open edits, empty paths, abort signals, and file loading checks.
can1357
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