fix: persist canvas agent media provenance

docs/无限画布对话框Agent模式升级开发文档-借鉴Cowart-2026-06-22.md

@@ -1434,6 +1434,7 @@ metadata: {
 metadata: {
   generatedByAgent: true,
   revisionOf: sourceNodeId,
+  sourceNodeId,
   sourceNodeIds: [...],
   prompt,
   model,

lib/canvas/agent-mutations.ts

@@ -131,6 +131,13 @@ function buildMediaNode(params: {
   const sourceMessageId = String(
     itemMetadata.messageId || planMetadata.messageId || ""
   ).trim();
+  const sourcePrompt = String(
+    params.item.prompt || itemMetadata.prompt || planMetadata.prompt || ""
+  ).trim();
+  const sourceModel = String(itemMetadata.model || planMetadata.model || "").trim();
+  const primarySourceNodeId = String(
+    itemMetadata.sourceNodeId || planMetadata.sourceNodeId || params.sourceNodeIds[0] || ""
+  ).trim();
   const metadata = {
     ...planMetadata,
     ...itemMetadata,
@@ -140,6 +147,10 @@ function buildMediaNode(params: {
     canvasAgentMediaItemId: params.item.mediaItemId,
     canvasAgentPlacement: params.plan.placement,
     canvasAgentPlacementStrategy: params.plan.placementStrategy,
+    messageId: sourceMessageId || undefined,
+    prompt: sourcePrompt || undefined,
+    model: sourceModel || undefined,
+    sourceNodeId: primarySourceNodeId || undefined,
     sourceMessageId: sourceMessageId || undefined,
     sourceImageKey: type === "image" && sourceMessageId ? params.item.url : undefined,
     sourceNodeIds: params.sourceNodeIds,

tests/routes/canvas-chat-helpers.test.ts

@@ -1404,6 +1404,7 @@ test.describe("canvas chat pure helpers", () => {
             prompt: "换成白底",
             metadata: {
               messageId: "assistant-append-1",
+              model: "test-image-model",
             },
           },
         ],
@@ -1428,6 +1429,11 @@ test.describe("canvas chat pure helpers", () => {
           canvasAgentOperationId: "op-append-1",
           canvasAgentMediaItemId: "media-append-1",
           revisionOf: "image-1",
+          sourceNodeId: "image-1",
+          sourceNodeIds: ["image-1"],
+          prompt: "换成白底",
+          model: "test-image-model",
+          messageId: "assistant-append-1",
           sourceMessageId: "assistant-append-1",
           sourceImageKey: "https://cdn.example.com/revision.png",
         },