7c59972bb1
Fix 6 bugs discovered during MCP tool usage: 1. syncToCanvas error handling: Distinguish network errors (return null) from API errors (re-throw with actual message). Fixes misleading "HTTP server unavailable" on batch_create_elements. 2. USER_PREFS fallbacks: create_element and batch_create_elements now apply fontFamily/roughness/fontSize/strokeWidth from preferences.json when not explicitly provided by the caller. 3. Hello handshake: Frontend sends `hello` on tenant_switched and handles `hello_ack`. Server resolves projectId from tenantId when absent. Fixes WS connections being registered under wrong scope. 4. Serialized broadcasts: Add serializedBroadcastWithAck() that queues broadcasts per tenant/project scope. Prevents race condition where parallel MCP create_element calls produce overlapping WS messages that clobber each other in the frontend. 5. Viewport screenshot: get_canvas_screenshot passes captureViewport=true, frontend captures DOM canvas via toDataURL() instead of exportToBlob() which always rendered the full scene bounding box. 6. Viewport animate:false: set_viewport uses animate:false for instant positioning, preventing mid-animation screenshot captures. Tests: 14 new tests (8 API, 6 WS) + 9 E2E specs covering all fixes. Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>