diff --git a/tests/browser/workspace.spec.mjs b/tests/browser/workspace.spec.mjs
index 117a580..65df3fd 100644
--- a/tests/browser/workspace.spec.mjs
+++ b/tests/browser/workspace.spec.mjs
@@ -630,3 +630,55 @@ test('the footer is the concept app footer with production copy', async ({ page
     }
 });
 
+// #164: the maintainer serves ComfyUI behind a proxy prefix. Everything, the ComfyUI link included, stays on that mount.
+const PROXY_MOUNT = '/ComfyBackendDirect';
+async function serveUnderProxyMount(page) {
+    const escaped = [];
+    page.on('request', item => {
+        const { pathname } = new URL(item.url());
+        if (pathname.startsWith('/prompt_manager/')) escaped.push(pathname);
+    });
+    await page.route(url => url.pathname.startsWith(`${PROXY_MOUNT}/`), async route => {
+        const url = new URL(route.request().url());
+        url.pathname = url.pathname.slice(PROXY_MOUNT.length);
+        const response = await route.fetch({ url: url.href });
+        await route.fulfill({ response });
+    });
+    return escaped;
+}
+
+test('the ComfyUI link points to the root of a non-standard proxy mount', async ({ page }) => {
+    const escaped = await serveUnderProxyMount(page);
+    for (const route of ['overview', 'library', 'tags']) {
+        await page.goto(`${PROXY_MOUNT}${workspace}#/${route}`);
+        await expect(page.locator('#workspace-main > .heading h1')).toBeVisible();
+        const link = page.getByRole('link', { name: 'ComfyUI', exact: true });
+        await expect(link).toHaveAttribute('href', `${PROXY_MOUNT}/`);
+        expect(await link.evaluate(node => node.href)).toBe(new URL(`${PROXY_MOUNT}/`, page.url()).href);
+    }
+    await expect(navCount(page, 'library')).toHaveCount(1);
+    expect(escaped).toEqual([]);
+});
+
+test('a resolver failure for the ComfyUI link never stops the shell from mounting', async ({ page }) => {
+    await serveUnderProxyMount(page);
+    // Wrap the shared client as it loads so only the topbar's canvas-root lookup throws (the sender reads the same root).
+    await page.addInitScript(() => {
+        let client;
+        Object.defineProperty(window, 'ApiClient', { configurable: true, get: () => client, set(value) {
+            client = { ...value, resolveUrl: (url, ...rest) => {
+                if (url === '/prompt_manager/' && /topbar\.mjs/.test(new Error().stack)) throw new Error('resolver unavailable');
+                return value.resolveUrl(url, ...rest);
+            } };
+        } });
+    });
+    const warnings = [];
+    page.on('console', message => { if (message.type() === 'warning') warnings.push(message.text()); });
+    await page.goto(`${PROXY_MOUNT}${workspace}#/overview`);
+    await expect(page.locator('#workspace-main h1')).toHaveText('Overview');
+    await expect(sidebarLinks(page)).toHaveCount(routes.length);
+    expect(warnings.filter(text => text.includes('the ComfyUI link falls back to the page mount'))).toHaveLength(1);
+    await expect(page.getByRole('link', { name: 'ComfyUI', exact: true })).toHaveAttribute('href', `${PROXY_MOUNT}/`);
+    await sidebarLink(page, 'Prompt library').click();
+    await expect(page.locator('#workspace-main h1')).toHaveText('Prompt library');
+});
diff --git a/tests/js/workspace-topbar.test.js b/tests/js/workspace-topbar.test.js
index bdf797e..4255955 100644
--- a/tests/js/workspace-topbar.test.js
+++ b/tests/js/workspace-topbar.test.js
@@ -1,6 +1,6 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
-import { canvasRoot, bindCanvasLink } from '../../web/js/workspace/topbar.mjs';
+import { canvasRoot, canvasHref, bindCanvasLink } from '../../web/js/workspace/topbar.mjs';
 
 // The shared mount-aware resolver (#164), as api-client.js implements it.
 const resolverAt = pathname => url => {
@@ -27,6 +27,33 @@ test('the canvas root is the ComfyUI root under the page mount', () => {
     assert.throws(() => canvasRoot(() => 'https://elsewhere.example/'), /canvas/i);
 });
 
+test('the canvas root follows a non-standard proxy mount', () => {
+    assert.equal(canvasRoot(resolverAt('/ComfyBackendDirect/prompt_manager/workspace')), '/ComfyBackendDirect/');
+    assert.equal(canvasHref(resolverAt('/ComfyBackendDirect/prompt_manager/workspace'), '/ComfyBackendDirect/prompt_manager/workspace'),
+        '/ComfyBackendDirect/');
+});
+
+// A4 review: a resolver failure must never stop the shell from mounting, and the fallback stays on the page's mount.
+test('a resolver failure falls back to the page mount and never to another origin', () => {
+    const warn = console.warn;
+    const warnings = [];
+    console.warn = (...args) => warnings.push(args);
+    try {
+        const broken = () => { throw new Error('resolver unavailable'); };
+        assert.equal(canvasHref(broken, '/ComfyBackendDirect/prompt_manager/workspace'), '/ComfyBackendDirect/');
+        assert.equal(canvasHref(broken, '/ComfyBackendDirect/prompt_manager/workspace/'), '/ComfyBackendDirect/');
+        assert.equal(canvasHref(broken, '/prompt_manager/workspace'), '/');
+        assert.equal(canvasHref(() => 'https://elsewhere.example/prompt_manager/', '/a/prompt_manager/workspace'), '/a/');
+        assert.equal(canvasHref(broken, '//elsewhere.example/prompt_manager/workspace'), '/');
+        assert.equal(canvasHref(broken, '/workspace'), '/');
+        assert.equal(canvasHref(broken, undefined), '/');
+        assert.equal(canvasHref(undefined, '/a/prompt_manager/workspace'), '/a/');
+        assert.equal(warnings.length, 8);
+    } finally {
+        console.warn = warn;
+    }
+});
+
 test('ComfyUI link follows its href unless a resolved pair is selected', () => {
     const node = link();
     const opened = [];
diff --git a/tools/vendor/frontend-coverage-baseline.json b/tools/vendor/frontend-coverage-baseline.json
index fcdbfb2..747366b 100644
--- a/tools/vendor/frontend-coverage-baseline.json
+++ b/tools/vendor/frontend-coverage-baseline.json
@@ -302,7 +302,7 @@
   "workspace/topbar.mjs": {
     "lines": 98,
     "branches": 98,
-    "functions": 81,
+    "functions": 83,
     "statements": 98
   },
   "workspace/viewer-state.mjs": {
diff --git a/web/js/workspace/index.mjs b/web/js/workspace/index.mjs
index b725a03..b57de5f 100644
--- a/web/js/workspace/index.mjs
+++ b/web/js/workspace/index.mjs
@@ -6,7 +6,7 @@ import { mountImages } from './images.mjs';
 import { mountLibrary, mountNewPromptAction, onLibraryWrite } from './library.mjs';
 import { mountVocabulary } from './vocabulary.mjs';
 import { createWorkspaceIcon } from './icons.mjs';
-import { bindCanvasLink, canvasRoot } from './topbar.mjs';
+import { bindCanvasLink, canvasHref } from './topbar.mjs';
 import { renderHeading } from './heading.mjs';
 
 const { createApiClient, resolveUrl } = window.ApiClient;
@@ -42,7 +42,7 @@ function mountWorkspace() {
     // D6: ComfyUI ↗ opens the canvas; on Images with a resolved selection it sends that pair (D5: no Activity).
     let images = null;
     scope.cleanup(bindCanvasLink(document.querySelector('.topbar .canvas-link'), {
-        href: canvasRoot(resolveUrl),
+        href: canvasHref(resolveUrl, window.location.pathname),
         getSelectedPair: () => images?.selectedPair?.() ?? null,
         sender: {open: (roles, trigger) => images?.sender.open(roles, trigger)},
     }));
diff --git a/web/js/workspace/topbar.mjs b/web/js/workspace/topbar.mjs
index 45e500c..ea66eba 100644
--- a/web/js/workspace/topbar.mjs
+++ b/web/js/workspace/topbar.mjs
@@ -11,6 +11,23 @@ export function canvasRoot(resolve) {
     return root.replace(PROMPT_MANAGER, '');
 }
 
+const PAGE_MOUNT = /^(.*\/)prompt_manager(?:\/|$)/;
+
+/**
+ * The canvas link's href. A resolver failure must never stop the shell from mounting, so it falls back to the
+ * ComfyUI root read from the page's own path (the #164 proxy mount), and to the origin root when even that is not a
+ * same-origin root-relative path.
+ */
+export function canvasHref(resolve, pathname) {
+    try {
+        return canvasRoot(resolve);
+    } catch (error) {
+        console.warn('Prompt Manager: the ComfyUI link falls back to the page mount.', error);
+        const mount = typeof pathname === 'string' ? pathname.match(PAGE_MOUNT)?.[1] : undefined;
+        return mount && !mount.startsWith('//') ? mount : '/';
+    }
+}
+
 const plainClick = event => event.button === 0 && !event.metaKey && !event.ctrlKey && !event.shiftKey && !event.altKey;
 const isPair = roles => roles !== null && typeof roles === 'object' &&
     typeof roles.positive === 'string' && typeof roles.negative === 'string';