[jameswillis99]

Summary

The merge reads only id, version and revisionId from the to and from head pkg versions, but getPkgVersion loads each whole row, including the project-sized model column (about 8 MB each on a project with a 4 MB main revision). A new private getPkgVersionHead reads them through the version-only mode from cb401ee18, which skips the model column.

_tryMergeBranch
  latestToPkgVersion    getPkgVersion(...)  ->  getPkgVersionHead(...)   no model column
  latestFromPkgVersion  getPkgVersion(...)  ->  getPkgVersionHead(...)   no model column

The version-only projection gains revisionId, which the merge compares with the latest revision id. getLatestPkgVersionNumber shares that projection, so its query selects one more small column. Same permission checks and not-found messages as getPkgVersion. The two prefill reads are not changed.

A new spec in branching.spec.ts checks that a merge preview reads one pkg version model row (the ancestor's) from the database instead of three.

Evidence

• Less data read: a merge preview now reads 1 pkg version model row from Postgres (the ancestor's, which the merge needs) instead of 3. On a project with a 4 MB main revision, that is 8.3 million fewer characters read per merge call. The new spec fails without the change.
• Less memory held: the two skipped head strings are about 8.3 MB each and no longer stay referenced through the publishes. In a replay with the Node heap capped at 640 MB, the heap left after the last full GC went from 386 MB to 369 MB (median of three runs, lower in all three paired runs).
• No behaviour change: 17 merge scenarios on real Postgres (preview, conflicts, picks, resolved bundle string, concurrent change, both auto-commits, app host mismatch, soft-deleted heads) and a replay of a real-size project (5 dependencies) give responses, write statements and rows identical to master.

Merge Danger

Door: two-way

Blast Radius: branch merge. The loader's version-only query selects one more small column (revisionId, 37 bytes a row). The head objects are typed as Pick<PkgVersion, "id" | "version" | "revisionId">, so a later edit that reads .model from them fails to compile.

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[sampullman]

Fixed in a4e0313.