extract: refuse writes that would shrink an existing file unless --force #25

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1. adrianbrowning

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   on Sep 26, 2026
2. adrianbrowning commented on Oct 5, 2026

   

   adrianbrowning

   on Oct 5, 2026

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   This was generated by AI during triage.

   Triage note after #24 and #15:

   They don't cover this. Since #15, extract refuses ambiguous mappings before it writes anything: several blocks for one file without distinct region= values, broken markers in an existing target, unsafe paths. It never compares sizes, though. Two cases can still shrink a file with no check:

   • --force replacing an existing whole file with a shorter block, which is the case this issue asks about.
   • A region splice whose new body is shorter than the old one. This is normal when you edit code, so a guard here would need a threshold.

   What's still to decide:

   • Does --force cover this already? It's an explicit opt-in, so a shrink guard might mean a second flag (--allow-shrink) or a ratio threshold.
   • Should splices be included at all?
3. adrianbrowning commented on Oct 8, 2026

   

   adrianbrowning

   on Oct 8, 2026

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   This was generated by AI during triage.

   Closing as out of scope. The reasoning is recorded in .out-of-scope/extract-shrink-guard.md (added in #60).

   Checked on main (238c32e):

   • A region= block splices into the existing file. A file with an import, a region and an export kept the import and the export, and only the region body changed.
   • Without --force, an existing whole file is never overwritten. A 40-line src/whole.ts was skipped with "exists and has block(s) without region=. Use --force to overwrite." and extract exited 2.
   • extract --force is the only way left to shrink a file: the same src/whole.ts went from 40 lines to 1, exit 0. That is what --force asks for, so a guard would only add a second flag for the same intent.
   • mdcode extract --check --force (feat: extract --check and the check-sync GitHub Action (#28, 1/2) #57) previews it without writing: src/whole.ts differs from this block; extract would overwrite it.

   Splices that make a region shorter are ordinary edits, so a size threshold there would refuse normal changes.
4. adrianbrowning

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5. adrianbrowning

   closed this as not plannedon Oct 8, 2026
6. adrianbrowning

   added a commit that references this issue on Oct 8, 2026

   docs(triage): record the extract shrink guard as out of scope (#25) (#60

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