[u7-u7]

Change Summary

Prevent Markdown-to-HTML exports from silently replacing one report image with another. Current document-local numbered asset names collide across reports sharing an output directory, and repeated references within a report can also cause a later same-basename image to overwrite an earlier one.

Use streamed SHA-256 source-content filenames plus extension, and reuse repeated references. Distinct source images retain distinct assets across documents and repeated exports; identical bytes may share an asset. Existing resizing, compression, non-raster copying and resolution behavior remain unchanged.

Related issue number

No matching existing PR found in all-state searches for markdown/images, image/overwrite and markdown_converter. No issue automatically closed.

Validation

• Unchanged main: both original regression cases fail. Tests resolve generated HTML references and inspect actual exported PNG pixels.
• Fixed: 4 focused tests pass, covering repeated references, shared-folder exports, changed-source re-export without altering older reports, identical-content reuse and SVG copying.
• tests/utils: 151 passed, 30 subtests passed, 1 existing failure: transcript fixture expects subagents/worker-1.jsonl instead of .ms_agent/subagents/worker-1.jsonl, reproduced with unchanged converter.
• Changed-file pre-commit hooks, compilation and git diff --check pass. Full-repository hooks report baseline formatting/lint issues; unrelated automatic edits restored.

Not tested: browser visual rendering, PDF/DOCX/PPT export, other platforms/Python versions, concurrent source mutation or the full repository suite. Generated filenames change; callers should follow HTML references rather than assume numbered filenames. No live models or external services used.

Checklist

• Title summarizes the change.
• Regression tests cover the change.
• Full-repository pre-commit passes (baseline issues above).
• API unchanged; filename rationale documented inline.

AI assistance: implemented and tested with OpenAI Codex; automated review only, no human-review attestation. Submitted as a draft without requesting reviewers.