Beagle SCM

BLAME-006b: commit:?<root> token-diffs the whole initial tree (O(repo), seconds)

Loading the parentless ROOT commit (commit:?c7184818) takes ~4.4s because it token-level weave-diffs the ENTIRE initial-import tree as all-INS, where a one-sided (vs-empty) diff should be a cheap raw all-add. Split from BLAME-006 (the perf half). Method: Issues.

Input

Context

• Timing: root commit 4.35s / 3853 lines; a typical commit 0.16s / 183.
• Path: be commit:?<sha> (beagle/BE.cli.c:332 + relay :453-459) runs graf diff:?<sha>; graf_first_parent_hex returns GRAFNONE for the parentless root (GRAF.exe.c:75), so it falls to GRAF.exe.c:505 → GRAFDiffTreeRefs (graf/DIFFREF.c:564) which TOKEN-diffs every one of the 291 initial-import files as all-INS (@@ -1,0 +1,N @@) — O(repo), tokenizing+weave-diffing all.
• Semantically a root "commit show" IS the whole tree (diff vs empty); the win is to make whole-tree all-INS CHEAP, not to change what's shown.

Goals

• commit:?<root> (and any one-sided / vs-empty diff) loads in time proportional to the commit, not the repo — emit raw all-add without token-level weave diff when one side is empty.

Constraints

• Output unchanged (same all-add lines, same hunks); only the cost drops. graf change gates for review. Add a timing/shape test.

WIP

Design decisions

• At the diff entry (DIFFREF.c:564 / the WEAVE diff core), detect a one-empty-side diff and short-circuit to a raw all-INS emit (skip tokenize+LCS) for each file.

TODOs

• Repro: time be commit:?<root> vs a normal commit; confirm O(repo) hot path in GRAFDiffTreeRefs.
• Fix: empty-side short-circuit (raw all-add) in the tree-diff/weave path.
• Test: root/whole-tree commit-show is bounded; output byte-identical to before.

Blockers and bummers

• Pairs with BLAME-006a (the correctness half) — independent; land separately.

Outcome

• LANDED 8d66369c (FF child of 3dc19b0a; msg BLAME-006b: skip token-diff of binary blobs). Scan's "291-file all-INS" premise was wrong — the 4.35s was one 9.5 MB binary (dog/dogs.png) tokenized in 3.17s. Fix (graf): WEAVEFromBlobRm (one-sided/vs-empty short-circuit to raw all-add) + diffref_is_binary (git's NUL-in-first-8000 heuristic) so binaries are never token-diffed; root commit-show 4.35s→1.52s, text output byte-identical. Test: Case I in beagle/test/be-diff-projector.sh. 302/302. NB landing: reconciled a graf/DIFFREF.c overlap with DIFF-002 (both survive, verified on trunk); the POSTCFLCT marker false-positive on graf/WEAVE.c required the documented --force conflict-scan bypass (see POST-006/POST-017).