ADR numbering collision: three files share 00018 in docs/developing/decisions/

[theRTC204]

docs/developing/decisions/README.md states ADRs are "append-only and numbered sequentially," but three files currently share the number 00018:

• 00018-external-instance-directory-registry.md
• 00018-fragment-metadata-on-s3-objects.md
• 00018-view-independent-merges-and-subtree-grafting.md

These landed in commits 243e52b, fe4f4e5, and 1fe7e28 respectively — apparently three parallel changes each independently incremented from the last number they saw (00017) without knowing about the others, and merged without renumbering.

Since ADRs are append-only, renaming these already-published files seems wrong (it would break any existing links/citations to "ADR-00018" and rewrite merged history). Filing this so a maintainer can decide the right fix — e.g. renumber two of the three going forward, or accept the collision and just document which 00018 is which.

Note: 00019 and 00020 are currently unused, so new ADRs can continue sequentially from 00019 without conflict in the meantime.

[vys1n]

i would like to take up this issue but donkt know how to proceed

[vys1n]

I see that this file "00018-fragment-metadata-on-s3-objects.md" is the one being used as ADR 00018, and the other 2 named ADR 00018 haven't been mentioned anywhere (not sure about being in use in the codebase or architecturally)

If wanted I can rename them in any order(19, 20) or remove them if not in use.