[pathanin]

Fixes every finding of the 2026-10-21 code review (docs/code-review-2026-10-21.md), plus the 3 history.js checks that failed on Chrome for Mac.

What changed

Work that waits no longer lands on a newer document (findings 1–3, c56df80)

• A save, resize or Open still running when New or Open replaces the document is cancelled or dropped. A new S.docId tells documents apart.
• ⌘E on a selection keeps marks that clear (Transparent strokes, patches, fills that replace pixels) as objects. Before, it brought the cleared pixels back.

The rest of the review (findings 4–12)

• 4: the "nothing seen changes" claim for ⌘E on a selection now notes anti-aliasing shifts on nearby paths.
• 5: Open after a slow "Discard unsaved changes?" offers the picker from a toast button. It used to fail with "permission was denied".
• 6: PNG CRCs are computed only for the chunk that is read.
• 7: a colour pick restyles only what the selected kind draws with. No more undo steps that change nothing.
• 8: Cut deletes only after the clipboard write succeeds, and only what it copied.
• 9: box-select and pan release toolbar focus, so Delete and the arrows reach the selection.
• 10: [ / ] move an odd size above 10 onto the even grid.
• 11: png-worker.js reads a transferred snapshot back. The page no longer calls getImageData on #image. The worker still accepts the old {raw} message.
• 12:
  • encodeBlob falls back to toBlob when the snapshot fails.
  • A PNG's scene chunk is validated (Core.validObj). A bad one opens as plain pixels.
  • No Math.max(...) over object lists (Core.unionBox).
  • A brush's frame is its ink.
  • paintLater skips an empty pass.
• Also: copying the whole image won't put an image edited mid-copy on the clipboard, and ⌘E on a lone image adds no undo step.

history.js on Chrome for Mac

• Cause: a live pencil stroke left the anti-aliased edges of objects under it (text, scaled images) up to 4 levels off a fresh render. The stroke's rects were drawn in a later GPU batch than those objects.
• Fix: when the stroke joins, its tiles that hold other objects are composed again (rejoin, scene.js).
• Cost, measured on the M4 at 4000×3000:
  • ~9 ms more main-thread time on release (pencil over 5k: inpMain 1.2 → 10.2 ms; no interaction over 200 ms).
  • The GPU process settles ~50 MB higher. Over 60 strokes it levels off, so it's not a leak. The bench's after edits memory row shows +120 MB.

Decisions for you

These are the agent's defaults. They're also listed in task.md under Open.

• An Open superseded by a later Open, drop or New is dropped silently.
• An edit made while an Open loads, or while its Open… toast waits, brings a second discard prompt.
• New messages:
  • "Save cancelled: a different image is open now"
  • "Discard confirmed. Choose the file to open" (with an Open… button)
  • "Copied: the selection changed, so nothing was cut"
  • "Copy failed: the image changed while it was copied. Copy again"
• ⌘E keeps marks that clear as objects, with a toast saying why.
• ⌘E on a selection that is already one image does nothing, with no message.
• One test now expects different behaviour. Pressing X on a selected line used to swap both colours, but a line never draws its colour 2 (alt). The check now expects only the line's colour to change.

Verification (this Mac)

• Unit: 95 passed.
• Chrome: smoke 332, history 86, preview 40, filledge 13, objects 236, alpha 114, libs 75, pwa 16. All passed.
• WebKit: smoke 331, history 86, preview 40, filledge 13, objects 233, alpha 114, libs 75. All passed.
• Each new check was run without its fix and failed.
• Not done: the fourth review round of c56df80 was interrupted before it reported. Firefox and real Safari remain untested, as before.