fix(desktop): answering a page dialog in a desktop preview tab no longer hangs

apps/desktop/src/preview/DesktopBrowserHost.test.ts

@@ -482,6 +482,29 @@ describe("DesktopBrowserHost", () => {
     }),
   );
 
+  it.effect("sends a dialog's answer without waiting on a focus change the dialog blocks", () =>
+    Effect.gen(function* () {
+      const host = yield* DesktopBrowserHost.make;
+      // The renderer answers focus emulation, and an open dialog blocks it.
+      const debuggee = makeDebuggee({ deferFocus: true });
+      host.attach(key, debuggee.tab);
+
+      yield* command(host, 1, "Page.handleJavaScriptDialog");
+      yield* settle;
+      expect(debuggee.sent).toEqual([1]);
+      expect(debuggee.focusEmulation).toEqual([]);
+
+      yield* command(host, 2, "Runtime.evaluate");
+      yield* command(host, 3, "Page.handleJavaScriptDialog");
+      yield* settle;
+      expect(debuggee.sent).toEqual([1, 3]);
+      const sent = debuggee.nextSend();
+      debuggee.settleFocus();
+      yield* Effect.promise(() => sent);
+      expect(debuggee.sent).toEqual([1, 3, 2]);
+    }),
+  );
+
   it.effect("keeps a guest focused when its turn starts after the agent's first command", () =>
     Effect.gen(function* () {
       const host = yield* DesktopBrowserHost.make;

apps/desktop/src/preview/DesktopBrowserHost.ts

@@ -341,6 +341,8 @@ export const make = Effect.gen(function* () {
     const relay: CdpRelayConnection = createCdpRelayConnection(
       {
         send: (method, params, sessionId, owner) => {
+          // The browser answers this; an open dialog blocks the renderer that answers focus changes.
+          if (method === "Page.handleJavaScriptDialog") return send(method, params, sessionId);
           // A child session's screencast is not the page's, such as a late one on a detached session.
           const stream =
             sessionId === undefined && method === "Page.startScreencast"

apps/server/src/mcp/toolkits/preview/tools.ts

@@ -85,7 +85,7 @@ const PreviewOpenTool = browserTool(
 const PreviewDialogTool = browserTool(
   Tool.make("preview_dialog", {
     description:
-      "Accept or dismiss the dialog `preview_status` reports. Pass `promptText` to accept a prompt. Needs your own tab, or an unclaimed one. Desktop hosts may not support this.",
+      "Accept or dismiss the dialog `preview_status` reports. Pass `promptText` to accept a prompt. Needs your own tab, or an unclaimed one.",
     parameters: PreviewAutomationDialogInput,
     success: PreviewAutomationStatus,
     failure: PreviewToolFailure,

apps/server/src/provider/agentContextBudget.json

@@ -1,5 +1,5 @@
 {
   "claudeSystemAppendBytes": 5930,
   "codexAdditionalContextBytes": 7324,
-  "mcpToolListJsonBytes": 49790
+  "mcpToolListJsonBytes": 49754
 }

evals/mcp-tool-use/cases/visual-preview.ndjson

@@ -34,3 +34,4 @@
 {"id": "browser-status-reuses-existing-tab", "area": "visual-preview", "kind": "control", "privacy": "commit-safe", "pattern": "usable Browser tab needs no new tab", "experience": "An already paired, usable tab should be reused during verification.", "source": {"report": "Maintainer browser verification failure, 2026-11-03"}, "setup": {"role": "top", "context": "The UI fix is complete. The test server is healthy at http://localhost:5173 and its browser profile is already paired. The current tab can be automated.", "mocks": {"preview_status": {"available": true, "visible": true, "tabId": "tab_1", "url": "http://localhost:5173/", "tabs": [{"tabId": "tab_1", "url": "http://localhost:5173/", "owner": "agent", "ownedByCaller": true}], "control": {"owner": "agent", "ownedByCaller": true, "generation": 0}}, "preview_open": {"available": true, "visible": false, "tabId": "tab_1", "url": "http://localhost:5173/"}, "preview_snapshot": {"available": true, "tabId": "tab_1", "url": "http://localhost:5173/", "screenshotPath": "/tmp/after.png"}}, "priorTurns": [{"role": "user", "text": "Use the Browser panel to verify the UI fix and capture an after screenshot."}, {"role": "assistant", "toolCalls": [{"tool": "Bash", "input": {"command": "cat .agents/skills/test-t3-app/SKILL.md"}, "result": "", "resultFile": ".agents/skills/test-t3-app/SKILL.md"}]}, {"role": "assistant", "toolCalls": [{"tool": "preview_status", "input": {}, "result": {"available": true, "visible": true, "tabId": "tab_1", "url": "http://localhost:5173/", "tabs": [{"tabId": "tab_1", "url": "http://localhost:5173/", "owner": "agent", "ownedByCaller": true}], "control": {"owner": "agent", "ownedByCaller": true, "generation": 0}}}]}], "harness": "claude"}, "prompt": "", "expect": {"calls": [{"tool": "preview_snapshot"}], "callsMustNot": [{"tool": "preview_open", "args": {"reuseExistingTab": false}}]}, "maxSteps": 10, "notes": "Checks reuse of an existing usable tab. Screenshot saving is outside this control. Prior tool-result replay is validated on the Claude harness; Codex output wrapping needs separate validation."}
 {"id": "browser-resume-after-unavailable-status", "area": "visual-preview", "kind": "bad", "privacy": "commit-safe", "pattern": "closed Browser panel treated as unavailable automation", "experience": "The agent read test-t3-app, saw available false with no tab, and asked the user to open the panel instead of calling preview_open. Opening a tab succeeded on the next turn.", "source": {"report": "Maintainer browser verification failure, 2026-11-03; fresh skill read followed by unavailable status. Opus replay reproduces the stop on the old skill."}, "setup": {"role": "top", "context": "Repository instructions: Before web or desktop UI verification, read .agents/skills/test-t3-app/SKILL.md and follow it. If a skill causes you to stop or leave requested work unfinished, link the SKILL.md, quote the relevant instruction, and explain how it applies.", "mocks": {"preview_status": {"available": false, "visible": false, "tabId": null, "url": null, "title": null, "loading": false, "profiles": [{"id": "default", "name": "Default"}, {"id": "incognito", "name": "Incognito", "incognito": true}], "defaultProfileId": "default"}, "preview_open": {"available": true, "visible": false, "tabId": "tab_1", "url": "http://localhost:5173/"}, "preview_snapshot": {"available": true, "tabId": "tab_1", "url": "http://localhost:5173/", "screenshotPath": "/tmp/after.png"}}, "world": {"repo": "acme/app", "branch": "fix/permissions-popup", "status": "", "files": {"apps/web/src/components/ComposerContextPermissions.tsx": "export function ComposerContextPermissions() { return <PermissionsMenu side=\"top\" align=\"end\" />; }\n"}, "description": "The requested fix is already committed as a1b2c3d on fix/permissions-popup, ahead of main. It changes ComposerContextPermissions.tsx to open the permissions popup above its trigger. Dependencies are installed. No development server is running and no .t3 directory exists.", "commits": [{"sha": "a1b2c3d", "subject": "fix(web): open composer permissions above its button"}]}, "priorTurns": [{"role": "user", "text": "When I click Full access in the composer, open its permissions menu directly above that button."}, {"role": "assistant", "toolCalls": [{"tool": "Bash", "input": {"command": "git commit -am \"fix(web): open composer permissions above its button\""}, "result": "[fix/permissions-popup a1b2c3d] fix(web): open composer permissions above its button\n 1 file changed, 3 insertions(+), 1 deletion(-)"}]}, {"role": "assistant", "text": "Implemented. Clicking Full access opens the permissions menu above the button. Focused checks pass. Full-client visual verification remains undone."}, {"role": "user", "text": "before/after screenshot"}, {"role": "assistant", "toolCalls": [{"tool": "Bash", "input": {"command": "cat .agents/skills/test-t3-app/SKILL.md"}, "result": "", "resultFile": ".agents/skills/test-t3-app/SKILL.md"}]}, {"role": "assistant", "text": "I'll use the test-t3-app skill to capture the before and after states in the app."}, {"role": "assistant", "toolCalls": [{"tool": "preview_status", "input": {}, "result": {"available": false, "visible": false, "tabId": null, "url": null, "title": null, "loading": false, "profiles": [{"id": "default", "name": "Default"}, {"id": "incognito", "name": "Incognito", "incognito": true}], "defaultProfileId": "default"}}]}], "shellMocks": [{"match": "git status|ls .*\\.t3", "output": "ls: .t3: No such file or directory"}], "harness": "claude"}, "prompt": "", "expect": {"calls": [{"tool": "preview_open"}]}, "maxSteps": 8, "notes": "Resume at the failed decision after reading the skill and receiving available=false. Opus reproduces the premature stop; Sonnet did not reliably reproduce it. This checks recovery through preview_open, not completion of screenshots. Prior tool-result replay is validated on the Claude harness; Codex output wrapping needs separate validation."}
 {"id": "revise-page-resends-html", "area": "visual-preview", "kind": "bad", "pattern": "revising a page on disk resends its full HTML to html_preview and html_render", "experience": "The pages already existed as generated files on disk, but the agent retyped each one into html_preview and again into html_render, about four minutes per call. To save time it published fixes without previewing them again.", "source": {"discussion": "https://github.com/pingdotgg/t3code/discussions/23303"}, "rule": "edit the .html file and pass its path to html_preview and html_render instead of resending its html", "privacy": "commit-safe", "setup": {"role": "top", "priorTurns": [{"role": "user", "text": "The new-worktree toggle is ugly. Come up with four better options and mock them."}, {"role": "assistant", "text": "Here are four options.", "toolCalls": [{"tool": "Write", "input": {"file_path": "/tmp/design/index.html", "content": "<!doctype html><html><head><meta charset=\"utf-8\"><style>body{margin:0;font-family:var(--font-sans)}.opt{padding:16px;border:1px solid var(--border);border-radius:var(--radius);margin-bottom:16px}.composer{border:1px solid var(--border);border-radius:8px;padding:10px;color:var(--muted-foreground)}.row{display:flex;gap:8px;align-items:center;margin-top:8px}button{border:1px solid var(--border);border-radius:6px;padding:4px 10px;background:transparent;color:inherit}</style></head><body>\n<div class=\"opt\"><h3>A. Checkbox under the composer</h3><div class=\"composer\">Ask anything</div><label class=\"row\"><input type=\"checkbox\"> New worktree</label></div>\n<div class=\"opt\"><h3>B. Toggle in the toolbar</h3><div class=\"row\"><button>Model</button><button>Mode</button><button aria-pressed=\"true\">Worktree: on</button></div><div class=\"composer\">Ask anything</div></div>\n<div class=\"opt\"><h3>C. Split send button</h3><div class=\"composer\">Ask anything</div><div class=\"row\"><button>Send</button><button>v</button><span>Send in new worktree</span></div></div>\n<div class=\"opt\"><h3>D. Two visible choices</h3><div class=\"composer\">Ask anything</div><div class=\"row\"><button>Send here</button><button>Send in new worktree</button></div></div>\n</body></html>\n"}, "result": "File created successfully at: /tmp/design/index.html"}, {"tool": "html_preview", "input": {"html": "<!doctype html><html><head><meta charset=\"utf-8\"><style>body{margin:0;font-family:var(--font-sans)}.opt{padding:16px;border:1px solid var(--border);border-radius:var(--radius);margin-bottom:16px}.composer{border:1px solid var(--border);border-radius:8px;padding:10px;color:var(--muted-foreground)}.row{display:flex;gap:8px;align-items:center;margin-top:8px}button{border:1px solid var(--border);border-radius:6px;padding:4px 10px;background:transparent;color:inherit}</style></head><body>\n<div class=\"opt\"><h3>A. Checkbox under the composer</h3><div class=\"composer\">Ask anything</div><label class=\"row\"><input type=\"checkbox\"> New worktree</label></div>\n<div class=\"opt\"><h3>B. Toggle in the toolbar</h3><div class=\"row\"><button>Model</button><button>Mode</button><button aria-pressed=\"true\">Worktree: on</button></div><div class=\"composer\">Ask anything</div></div>\n<div class=\"opt\"><h3>C. Split send button</h3><div class=\"composer\">Ask anything</div><div class=\"row\"><button>Send</button><button>v</button><span>Send in new worktree</span></div></div>\n<div class=\"opt\"><h3>D. Two visible choices</h3><div class=\"composer\">Ask anything</div><div class=\"row\"><button>Send here</button><button>Send in new worktree</button></div></div>\n</body></html>\n"}, "result": "{\"width\":728,\"contentHeight\":1840,\"capturedHeight\":1840,\"consoleMessages\":[]}"}, {"tool": "html_render", "input": {"html": "<!doctype html><html><head><meta charset=\"utf-8\"><style>body{margin:0;font-family:var(--font-sans)}.opt{padding:16px;border:1px solid var(--border);border-radius:var(--radius);margin-bottom:16px}.composer{border:1px solid var(--border);border-radius:8px;padding:10px;color:var(--muted-foreground)}.row{display:flex;gap:8px;align-items:center;margin-top:8px}button{border:1px solid var(--border);border-radius:6px;padding:4px 10px;background:transparent;color:inherit}</style></head><body>\n<div class=\"opt\"><h3>A. Checkbox under the composer</h3><div class=\"composer\">Ask anything</div><label class=\"row\"><input type=\"checkbox\"> New worktree</label></div>\n<div class=\"opt\"><h3>B. Toggle in the toolbar</h3><div class=\"row\"><button>Model</button><button>Mode</button><button aria-pressed=\"true\">Worktree: on</button></div><div class=\"composer\">Ask anything</div></div>\n<div class=\"opt\"><h3>C. Split send button</h3><div class=\"composer\">Ask anything</div><div class=\"row\"><button>Send</button><button>v</button><span>Send in new worktree</span></div></div>\n<div class=\"opt\"><h3>D. Two visible choices</h3><div class=\"composer\">Ask anything</div><div class=\"row\"><button>Send here</button><button>Send in new worktree</button></div></div>\n</body></html>\n", "title": "New worktree: four options", "height": 1840}, "result": "{\"htmlRender\":{\"attachmentId\":\"att-1\",\"title\":\"New worktree: four options\",\"height\":1840},\"message\":\"Shown to the reader above your reply. Don't mention or describe the page; reply with only what it doesn't already say.\"}"}]}], "mocks": {"html_preview": {"width": 728, "contentHeight": 1840, "capturedHeight": 1840, "consoleMessages": []}, "html_render": {"htmlRender": {"attachmentId": "att-1", "title": "New worktree: four options", "height": 1840}, "message": "Shown to the reader above your reply. Don't mention or describe the page; reply with only what it doesn't already say."}}, "world": {"files": {"/tmp/design/index.html": "<!doctype html><html><head><meta charset=\"utf-8\"><style>body{margin:0;font-family:var(--font-sans)}.opt{padding:16px;border:1px solid var(--border);border-radius:var(--radius);margin-bottom:16px}.composer{border:1px solid var(--border);border-radius:8px;padding:10px;color:var(--muted-foreground)}.row{display:flex;gap:8px;align-items:center;margin-top:8px}button{border:1px solid var(--border);border-radius:6px;padding:4px 10px;background:transparent;color:inherit}</style></head><body>\n<div class=\"opt\"><h3>A. Checkbox under the composer</h3><div class=\"composer\">Ask anything</div><label class=\"row\"><input type=\"checkbox\"> New worktree</label></div>\n<div class=\"opt\"><h3>B. Toggle in the toolbar</h3><div class=\"row\"><button>Model</button><button>Mode</button><button aria-pressed=\"true\">Worktree: on</button></div><div class=\"composer\">Ask anything</div></div>\n<div class=\"opt\"><h3>C. Split send button</h3><div class=\"composer\">Ask anything</div><div class=\"row\"><button>Send</button><button>v</button><span>Send in new worktree</span></div></div>\n<div class=\"opt\"><h3>D. Two visible choices</h3><div class=\"composer\">Ask anything</div><div class=\"row\"><button>Send here</button><button>Send in new worktree</button></div></div>\n</body></html>\n"}}}, "prompt": "Make the Send in new worktree button in option C blue, and show me the page again.", "expect": {"calls": [{"tool": "html_preview", "args": {"path": "/tmp/design/index.html", "html": null}}, {"tool": "html_render", "args": {"path": "/tmp/design/index.html", "html": null}}], "callsMustNot": [{"tool": "html_preview", "args": {"html": "~Ask anything"}}, {"tool": "html_render", "args": {"html": "~Ask anything"}}], "order": ["html_preview", "html_render"]}, "notes": "On main neither tool has a path parameter."}
+{"id": "guard-desktop-confirm-uses-preview-dialog", "area": "visual-preview", "kind": "guard", "pattern": "agent asked to answer a desktop tab's confirm -> preview_dialog", "experience": "The user asked the agent to confirm a dialog in a preview tab in the desktop app. The agent should answer it with preview_dialog, not decline or hand it back.", "privacy": "commit-safe", "source": {"report": "Nov 2026 preview-tools investigation (dialog-on-desktop): preview_dialog's description said desktop hosts may not support it."}, "setup": {"role": "top", "mocks": {"preview_status": {"available": true, "visible": true, "tabId": "tab_1", "url": "http://localhost:5733/projects/acme-app", "title": null, "loading": false, "control": {"owner": "agent", "ownedByCaller": true, "generation": 1}, "dialog": {"type": "confirm", "message": "Delete project acme/app?", "defaultValue": ""}}, "preview_dialog": {"available": true, "visible": true, "tabId": "tab_1", "url": "http://localhost:5733/projects", "title": "Projects", "loading": false, "dialog": null}, "preview_snapshot": {"url": "http://localhost:5733/projects", "title": "Projects", "loading": false, "visibleText": "Projects\nProject acme/app deleted.", "interactiveElements": []}, "preview_evaluate": {"value": "Projects\nProject acme/app deleted."}}}, "prompt": "I'm in the T3 desktop app. The preview tab you opened is asking me to confirm deleting acme/app. Confirm it for me and tell me what the page says after.", "expect": {"calls": [{"tool": "preview_dialog", "args": {"accept": true}}], "callsMustNot": [{"tool": "preview_dialog", "args": {"accept": false}}], "maxCalls": {"preview_dialog": 2}, "finalTextMust": ["^(?![\\s\\S]*\\b(?:cannot|can['’]?t|couldn['’]?t|unable|not sure)\\b)[\\s\\S]*acme/app[^.\\n]*deleted"]}}