[mtskf]

Summary

When the host rejects an edit ("Cannot save" banner), the draft stays on screen only. If another writer then changed the file, the editor swapped in the new content and dropped both the draft and the banner without telling the user. The editor now shows the existing "local edit discarded" notice in that case.

Changes

• src/webview/editor.ts (applyDocument): raise the existing discard notice when a reseed replaces a rejected draft. The predicate is computed before the replace, because the shell clears serializeError right after the snapshot is applied.
  • Not raised while edit-sync still holds the bytes on a leading lineage (a readonly Document only rewinds the view; the buffer is restored and re-sent on re-grant).
  • Not raised when the incoming text differs in line endings only.
  • The notifier call is wrapped in try/catch, matching the existing call site in cm/edit-sync.ts, so a throwing notifier cannot leave the reducer behind the view.
• test/webview/shell.test.ts: the real-host harness gains a failing-validator switch, edit-rejected delivery, an external write, and a way to mark a posted Edit as lost. No new message or notice kind.

Related

• TODO: ARCH-03a
• Known residual, not handled here (recorded under ARCH-05): if a draft Document is re-sent to a fresh webview and only the separate edit-rejected delivery fails, the webview has neither a holder nor serializeError, so this notice does not fire. Dropping the serializeError condition would mis-announce ordinary external updates.

Test Plan

• New real-host test: parse-failed Edit, then an external write → exactly one discard notice (red before the fix, green after)
• Negative pin: rejected draft + same text with CRLF → no notice, text unchanged (goes red when the EOL conjunct is removed)
• Negative pin: failed send, then a readonly Document → no notice, buffer reaches the host on re-grant (goes red when the leading-lineage conjunct is removed)
• pnpm compile, pnpm lint, full pnpm vitest run green
• Not verified in a real VS Code window or E2E — in-memory (happy-dom + real host reducer) only