diff --git a/apps/api/src/companion-agent-tools.ts b/apps/api/src/companion-agent-tools.ts
index a9d8dca0..c82a0175 100644
--- a/apps/api/src/companion-agent-tools.ts
+++ b/apps/api/src/companion-agent-tools.ts
@@ -54,7 +54,7 @@ const TOOL_HINTS: Record<string, string> = {
   search_memos: " Searches note titles and bodies, not notebook names. query is optional. For recently created or added notes, pass createdAfter (YYYY-MM-DD or ISO date-time) and omit query; never put this week/最近/新增 in query. For recently edited notes, use updatedAfter. Do not pass notebookId unless find_notebooks or list_notebooks returned it. For notes in a named notebook, find_notebooks then list_memos. If hasMore is true, say the list is incomplete.",
   list_tags: " Use this when the user names a tag.",
   create_memo: " For prose Markdown notes only. Never use this for 思维导图/mind maps, 流程图/flowcharts, or 架构图; use create_diagram_memo.",
-  create_diagram_memo: " Create an editable visual diagram note. kind=mind-map for 思维导图/mind map, flowchart for 流程图, architecture for 架构图. For mind maps, give a root and children with parentId; omit node type. If the user did not name a notebook, use the open notebook id from Focus DATA. Build nodes from the open note body in Focus DATA when the user refers to this note.",
+  create_diagram_memo: " Create an editable visual diagram note. kind=mind-map for 思维导图/mind map, flowchart for 流程图, architecture for 架构图. Omit edge ids; EdgeEver generates them. For mind maps, give a root and children with parentId; omit node type. If the user did not name a notebook, use the open notebook id from Focus DATA. Build nodes from the open note body in Focus DATA when the user refers to this note.",
   get_diagram: " Read an existing editable diagram as a semantic graph. Call this before update_diagram. Do not use get_memo when you only need the diagram structure.",
   update_diagram: " Edit an existing diagram after get_diagram. Pass expectedRevision from get_diagram. Use add_node, update_node, remove_node, add_edge, update_edge, or remove_edge. Do not create a new diagram unless the user asked for a new note.",
   use_note_template: " Create a new memo from a template. If the user did not name a notebook, use the open notebook id from Focus DATA.",
diff --git a/apps/api/src/companion-tool-actions.test.mjs b/apps/api/src/companion-tool-actions.test.mjs
index 7b1120c7..5f47360b 100644
--- a/apps/api/src/companion-tool-actions.test.mjs
+++ b/apps/api/src/companion-tool-actions.test.mjs
@@ -219,6 +219,29 @@ describe("shared companion MCP adapter", () => {
       .toContain("eval");
     expect(f.sqlite.query("SELECT COUNT(*) AS n FROM companion_actions").get().n).toBe(0);
   });
+  test("create_diagram_memo keeps generated edge IDs out of Agent input", async () => {
+    const f = await setup();
+    const tools = createCompanionTools({ ...f, scope, signal: new AbortController().signal, assertActive: async () => {}, sources: [] });
+    const input = {
+      notebookId: "ideas",
+      title: "Service architecture",
+      kind: "architecture",
+      nodes: [
+        { id: "web", label: "Web", type: "frontend" },
+        { id: "api", label: "API", type: "service" },
+      ],
+      edges: [{ source: "web", target: "api", type: "request" }],
+    };
+    expect(() => validateCompanionTool("create_diagram_memo", {
+      ...input,
+      edges: [{ id: "edge-1", source: "web", target: "api", type: "request" }],
+    })).toThrow();
+    const created = await tools.create_diagram_memo.execute(input);
+    expect(created).toMatchObject({ applied: true, diagramKind: "architecture", nodeCount: 2 });
+    const diagram = parseDiagramDocument((await getMemoDetail(f.db, scope.workspaceId, created.id)).contentMarkdown);
+    expect(diagram.edges).toMatchObject([{ source: "web", target: "api", kind: "request" }]);
+    expect(diagram.edges[0].id).toBeTruthy();
+  });
   test("note templates and AI instructions execute immediately including deletes", async () => {
     const f = await setup();
     const tools = createCompanionTools({ ...f, scope, signal: new AbortController().signal, assertActive: async () => {}, sources: [] });
diff --git a/apps/api/src/mcp-tools.test.mjs b/apps/api/src/mcp-tools.test.mjs
index 86cffe8b..467dc456 100644
--- a/apps/api/src/mcp-tools.test.mjs
+++ b/apps/api/src/mcp-tools.test.mjs
@@ -66,6 +66,7 @@ describe("MCP tool catalog", () => {
     });
     expect(byName.get("create_diagram_memo")?.inputSchema.properties.nodes.items.properties.x).toBeUndefined();
     expect(byName.get("create_diagram_memo")?.inputSchema.properties.nodes.items.properties.width).toBeUndefined();
+    expect(byName.get("create_diagram_memo")?.inputSchema.properties.edges.items.properties.id).toBeUndefined();
     expect(byName.get("get_diagram")?.annotations).toMatchObject({
       readOnlyHint: true,
       destructiveHint: false,
@@ -98,6 +99,8 @@ describe("MCP tool catalog", () => {
     });
     expect(byName.get("update_diagram")?.inputSchema.properties.operations.items.oneOf).toBeUndefined();
     expect(byName.get("update_diagram")?.inputSchema.properties.operations.items.properties.op.const).toBeUndefined();
+    expect(byName.get("update_diagram")?.inputSchema.properties.operations.items.properties.edge.properties.id)
+      .toEqual({ type: "string", minLength: 1, maxLength: 100 });
     expect(byName.get("rename_notebook")?.annotations).toMatchObject({
       readOnlyHint: false,
       destructiveHint: false,
diff --git a/apps/api/src/mcp-tools.ts b/apps/api/src/mcp-tools.ts
index d82ebc62..af358563 100644
--- a/apps/api/src/mcp-tools.ts
+++ b/apps/api/src/mcp-tools.ts
@@ -33,17 +33,26 @@ const diagramNodeSchema = {
   properties: diagramNodeProperties,
 };
 
+const diagramEdgeProperties = {
+  source: { type: "string", minLength: 1, maxLength: 100 },
+  target: { type: "string", minLength: 1, maxLength: 100 },
+  label: { type: "string", maxLength: 500 },
+  type: { type: "string", enum: ["dependency", "request", "async", "data"] },
+  bidirectional: { type: "boolean" },
+};
+
 const diagramEdgeSchema = {
   type: "object",
   required: ["source", "target"],
   additionalProperties: false,
+  properties: diagramEdgeProperties,
+};
+
+const mutableDiagramEdgeSchema = {
+  ...diagramEdgeSchema,
   properties: {
     id: { type: "string", minLength: 1, maxLength: 100 },
-    source: { type: "string", minLength: 1, maxLength: 100 },
-    target: { type: "string", minLength: 1, maxLength: 100 },
-    label: { type: "string", maxLength: 500 },
-    type: { type: "string", enum: ["dependency", "request", "async", "data"] },
-    bidirectional: { type: "boolean" },
+    ...diagramEdgeProperties,
   },
 };
 
@@ -201,7 +210,7 @@ const MCP_TOOL_DEFINITIONS = [
               },
               node: diagramNodeSchema,
               nodeId: { type: "string", minLength: 1 },
-              edge: diagramEdgeSchema,
+              edge: mutableDiagramEdgeSchema,
               edgeId: { type: "string", minLength: 1 },
               changes: {
                 type: "object",