diff --git a/.gitignore b/.gitignore
index b7022dd..0b5a2cd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,4 +4,5 @@ dist
 out
 .env
 extension.js
+extension.css
 extension.js.LICENSE.txt
diff --git a/scripts/dev.ts b/scripts/dev.ts
index 3b5e789..e2a21a9 100644
--- a/scripts/dev.ts
+++ b/scripts/dev.ts
@@ -1,5 +1,7 @@
 import esbuild from "esbuild";
 import dotenv from "dotenv";
+import fs from "fs";
+import path from "path";
 import { compile, args } from "./compile";
 
 dotenv.config();
@@ -9,8 +11,33 @@ const dev = () => {
   return new Promise<number>((resolve) => {
     compile({
       opts: args,
-      builder: (opts: esbuild.BuildOptions) =>
-        esbuild.context(opts).then((esb) => esb.watch()),
+      builder: (opts: esbuild.BuildOptions) => {
+        const outFile = path.join(process.cwd(), "dist", "extension.js");
+        const rootFile = path.join(process.cwd(), "extension.js");
+        const outCssFile = path.join(process.cwd(), "dist", "extension.css");
+        const rootCssFile = path.join(process.cwd(), "extension.css");
+        // Keep a root extension.js so Roam dev loading can target tldraw/ instead of tldraw/dist/.
+        const copyOutputPlugin: esbuild.Plugin = {
+          name: "copy-output-to-root",
+          setup(build) {
+            build.onEnd((result) => {
+              if (result.errors.length) return;
+              if (fs.existsSync(outFile)) {
+                fs.cpSync(outFile, rootFile);
+              }
+              if (fs.existsSync(outCssFile)) {
+                fs.cpSync(outCssFile, rootCssFile);
+              }
+            });
+          },
+        };
+        return esbuild
+          .context({
+            ...opts,
+            plugins: [...(opts.plugins || []), copyOutputPlugin],
+          })
+          .then((esb) => esb.watch());
+      },
     });
     process.on("exit", resolve);
   });
diff --git a/src/components/canvas/Tldraw.tsx b/src/components/canvas/Tldraw.tsx
index 56b587c..c72d7bd 100644
--- a/src/components/canvas/Tldraw.tsx
+++ b/src/components/canvas/Tldraw.tsx
@@ -1,6 +1,7 @@
 import React, { useEffect, useMemo, useState, useRef } from "react";
 import { OnloadArgs } from "roamjs-components/types";
 import renderWithUnmount from "roamjs-components/util/renderWithUnmount";
+import renderToast from "roamjs-components/components/Toast";
 import getPageUidByPageTitle from "roamjs-components/queries/getPageUidByPageTitle";
 import getUids from "roamjs-components/dom/getUids";
 import {
@@ -662,8 +663,32 @@ const renderTldrawCanvasHelper = ({
   if (!childFromRoot?.parentElement) return () => {};
 
   const parentEl = childFromRoot.parentElement;
-  if (parentEl.querySelector(".roamjs-tldraw-canvas-container"))
-    return () => {};
+  const hasExistingCanvasByClass = !!parentEl.querySelector(
+    ".roamjs-tldraw-canvas-container",
+  );
+  // Query Builder uses this id for the canvas mount.
+  const hasExistingCanvasById = !!parentEl.querySelector(
+    "#roamjs-tldraw-canvas-container",
+  );
+  const hasExistingCanvas = hasExistingCanvasByClass || hasExistingCanvasById;
+  // Query Builder tags rm-block-children with this attribute when it owns the canvas mount.
+  const hasQueryBuilderCanvasOwner = childFromRoot.hasAttribute(
+    "data-roamjs-discourse-playground",
+  );
+  if (
+    hasQueryBuilderCanvasOwner &&
+    !parentEl.hasAttribute("data-roamjs-tldraw-qb-warning-shown")
+  ) {
+    parentEl.setAttribute("data-roamjs-tldraw-qb-warning-shown", "true");
+    renderToast({
+      id: "tldraw-query-builder-canvas-conflict",
+      intent: "warning",
+      content: `Multiple canvases have been detected on this page.  This may cause unexpected behavior.
+
+Either disable the tldraw extension or disable the Query Builder Discourse Graph flag.`,
+    });
+  }
+  if (hasExistingCanvas || hasQueryBuilderCanvasOwner) return () => {};
 
   const canvasWrapperEl = document.createElement("div");
   parentEl.appendChild(canvasWrapperEl);