v0.4.3

Prepare owner-approved npm release 0.4.3 (2026-10-19), following release PR #1746. This PR does not publish; the orchestrator owns merge and release dispatch.

• Set all seven packages, root/lockfile versions, internal dependency ranges and registry pins to 0.4.3; regenerate public/r with no stale 0.4.2 references.
• Consolidate MIGRATING.md into “Migrating to 0.4.3”, preserving diagram/comment pins, blob/video support, self-hosted canvas assets, sandboxed mock-ups, board-viewer and workspace/installer changes.
• Document new consumer dependencies: diagram-viewer and mockup-viewer items; shadcn toggle, tooltip and progress; tailwindcss@4.3.3 and zod@^4.6.5 for mock-ups; optional board tldraw@5.5.2/lucide-react@1.51.0 and self-hosted @tldraw/assets@5.5.2.

Local validation passed through the capped wrapper, serially in the foreground: check, typecheck, npm test (2,061 passed), verify including Chromium design audits, check:pack, release:preflight (exit 0), and registry consumers (Markdown, HTML, task-list, app including installed PDF rendering in Chromium, and pi-chat). Eleven deferred proofs remain unchanged backlog. No runtime behavior or tests changed; this repository uses migration notes rather than a separate changelog.

CI passed on the release head: verify, isolated package consumers, Studio scripted journeys, public demo Worker bundle and secret scan. No reruns or fixes were needed.

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