* Bound diagnostic config read with size cap
* fix: use buffer.toString for readRegularFileSync result in diagnostic export
* test: verify normal and oversized diagnostic config export behavior
PR #110591 — Add focused regression coverage for the bounded diagnostic config read:
- Test: normal config file (<8MB) produces parseOk: true in config/shape.json
- Test: oversized config file (>8MB) produces parseOk: false with graceful error handling
- Both tests verify the support bundle zip is still written with all expected contents
* refactor(logging): clarify support export config limit
Co-authored-by: 陈宪彪0668000387 <chen.xianbiao@xydigit.com>
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Co-authored-by: Peter Steinberger <steipete@gmail.com>
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