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`remoteSha..localSha` is "everything new on this branch", which is not the
same as "everything new to the remote". Merge origin/main into a feature
branch and every commit main gained since that branch's last push becomes
an added line — content that is already published, already scanned, and
not this push's doing.
Two consequences, both observed:
· FALSE HIGH FINDINGS. A placeholder connection string in a fixture
someone else had already merged blocked an unrelated push as
db.url_with_password, telling the operator to rotate a credential
over a file they never touched. A guard that cries wolf on catch-up
merges is one people learn to bypass reflexively — which is exactly
how a real secret gets through.
· OVERSIZED SCANS. The SCAN_CHUNK_BYTES comment already records a
1,146,782-byte diff from "a feature branch catching up to a busy
main" blowing the engine's 1 MiB cap. Same root cause, treated there
as a size problem. Narrowing the range fixes the size too.
A two-dot range cannot express this: after merging main, neither the
remote tip nor the merge-base with main is an ancestor of the other, so
no single base excludes both.
The narrowed range is `rev-list localSha --not remoteSha --remotes`.
remoteSha STAYS the base — it is what git tells us the remote has, and is
authoritative in a way --remotes is not, since tracking refs can be
absent or stale. Using --remotes alone excludes nothing in a repo without
them, so every commit ever made reads as new. That is the same false
positive from the other direction, and it is what the existing test
"only NEW content is scanned (remote..local), not pre-existing" catches.
When excluding tracking refs changes nothing, this push has no catch-up
commits and the plain range already describes it exactly — so we defer to
it. That keeps every non-catch-up push on the original gitStrict diff
path, which is what #1946's fail-closed regression test exercises. A
narrowing that silently retired that test would be a worse trade than the
false positives it set out to fix.
Each commit is diffed alone. A merge's combined diff shows only content
present in no parent, so a secret introduced while resolving a conflict
is still caught while an ordinary merge contributes nothing.
Tests: 22/22 existing prepush tests still pass (two of them fail without
the remoteSha base and the defer-to-plain-range guard respectively —
verified by mutation). 5 new tests build real repositories on disk and
pin both directions: a catch-up merge no longer re-scans published
content, and secrets in new commits, in merge resolutions, and in
repos with no remote are all still scanned.
Absorbs PR #2592 by @Two-Six-Alpha-1115 (applied via git am -3; 5 new
tests pass in test/redact-prepush-scan-range.test.ts). Also narrows the
range for the rebased-force-push shape reported in #2573 — proven by the
follow-up regression test.
Co-authored-by: Scott <scott@peninsulaminerals.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>