Profile convert to metadata format is O(n²) per tag in mergeProfiles (13.8.3+), blocks the event loop for minutes on large profiles #3681

Versions: @salesforce/source-deploy-retrieve 13.10.1 (same mergeProfiles loop since 13.8.3, when ProfileMetadataFinalizer was added; 13.8.2 and earlier copied profile files as-is). Node 26.0.0, macOS.

Repro: a project with 73 profiles in one package directory (103 MB of *.profile-meta.xml, large fieldPermissions / objectPermissions lists). ComponentSet.fromSource(profilesDir) then new MetadataConverter().convert(cs, 'metadata', { type: 'zip' }):

Output is byte-identical in all three (per-entry sha256 of the zip match).

Root cause: src/convert/convertContext/profileMetadataFinalizer.ts, mergeProfiles, line 235:

if (mergedValues.some((existing) => isDeepStrictEqual(existing, entry))) continue;

Every entry is compared with every entry already merged for that tag, synchronously, so a tag with n entries costs n²/2 isDeepStrictEqual calls. This runs even when a profile has only one source file, where there is nothing to merge.

Proposed fix: (1) when profiles.length === 1, return the single profile's entries as-is (root attributes built the same way); (2) for several pieces, dedupe with a Set keyed by a deterministic serialization of each entry (sorted object keys) instead of the linear scan. The singleton-conflict check is unchanged.

Behavior note: with (1), exact duplicate entries inside one profile file are kept, as in 13.8.2 and earlier; 13.8.3-13.10.1 drop them. Duplicates across pieces are still removed.

The remaining ~6 s block after the fix is fast-xml-parser parsing all profiles back to back in parseXml (~4 s) plus JsToXml (~1.3 s), from the finalizer parsing and re-serializing profiles that 13.8.2 streamed unchanged. Not addressed here.