GET-056: merge gate keys on kind, must key on content — text weaves, binary/link/gitlink reset

Now: DONE

Input

Context

The D5 dirty-merge gate at be/verbs/get/get.js:1053 reads kind === "f", reusing checkout's leaf-kind (f/x/l/s) as a mergeability test. Two wrongs follow: a dirty EXECUTABLE text file (x) is clean-reset (its uncommitted edit silently dropped), and a dirty BINARY 644 file (f) is fed to weave3 as if it were text.

RULING (gritzko, 2026-07-28): symlink, gitlink or BINARY get reset; anything parseable (any text) gets MERGED.
kindOf() exists to tell checkout.materialise how to WRITE a leaf; mergeability is a property of the BYTES, not the mode bit.
The binary predicate already exists: isBinary at be/views/diff/diff.js:75 — git's heuristic, NUL in the first 8000 bytes — but it is file-private.

Goals

Gate becomes: regular file (f or x) AND no side of the 3-way (base, on-disk, target) is binary → weave3; everything else clean-resets exactly as l/s do today.
Export isBinary from be/views/diff/diff.js and reuse it — no second copy of the heuristic.
Repro tests FIRST, both directions: (a) dirty executable TEXT file across a get → must weave, edit preserved; (b) dirty BINARY 644 file across a get → must clean-reset, no fences/garbage.

Constraints

weave3 and checkout.materialise(..., {kind}) already pass kind through unchanged — nothing downstream needs touching.
No other tests edited; no commits (put + report only, per work).
Minimal diff: the gate condition + the isBinary export + the new tests.

WIP

Design decisions

Binary check covers base, on-disk and target bytes: weave3 output is only meaningful when all three sides are text.

TODOs

repro (a): dirty exec text file is clean-reset today (edit lost)
repro (b): dirty binary 644 file is woven today (garbage/fences)
export isBinary from views/diff/diff.js
gate: (kind === "f" || kind === "x") && !anySideBinary
full test run

Outcome

(pending)