[Bug]: Desktop Browser automation errors lose their type over IPC and report as 'failed on client' #15336

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1. juliusmarminge commented on Oct 3, 2026

   

   juliusmarminge

   on Oct 3, 2026

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   Grok responding on behalf of Julius.

   Triage

   Thanks for tracking this down, @PixPMusic! I can confirm it. Desktop preview automation builds typed failures in apps/desktop/src/preview/Manager.ts (PreviewAutomationTimeoutError, PreviewAutomationInvalidSelectorError, PreviewAutomationTargetNotEditableError, and others), and apps/desktop/src/ipc/DesktopIpc.ts returns them by rejecting the ipcMain.handle promise. Electron's ipcRenderer.invoke keeps only the Error message (see electron#24427), so _tag and the other fields never reach the renderer.

   PreviewAutomationOperationError.fromCause in apps/web/src/components/preview/previewAutomationErrors.ts only keeps a value that's already a host error, or a plain object whose _tag is PreviewAutomationTargetNotEditableError. A thrown desktop error matches neither, so it becomes PreviewAutomationOperationError, whose responseTag is PreviewAutomationExecutionError. serializePreviewAutomationHostError also drops cause, so the desktop message is gone before it reaches the wire. classifyResponseError in apps/server/src/mcp/PreviewAutomationBroker.ts handles the timeout, invalid-selector, and not-editable tags, but the desktop host never sends them. It falls through to the default branch, which is the trace you pasted.

   Two details affect the fix, though not the diagnosis:

   • Keeping _tag across IPC wouldn't be enough for timeout or invalid selector. Those desktop classes aren't in the host-error union, and fromCause doesn't match them by shape. Only the not-editable case is rehydrated, and its test passes a plain object rather than an Electron rejection.
   • preview_click with a selector that matches nothing raises PreviewAutomationTargetNotFoundError. There's no public tag for that, or for coordinates outside the viewport, so those would stay PreviewAutomationExecutionError even once the existing tags survive IPC.

   On current main, an unmatched preview_wait_for usually doesn't show this yet. The broker's Effect.timeoutOption(timeoutMs) fires first, returns the "timed out" error, and evicts the host (the open #12898, also reported as #15335, with an open fix attempt in #12899). Immediate desktop failures like an invalid selector or a non-editable target already come back as the generic client error today.

   Likely fix area

   • One option is for the desktop side to return a serializable failure payload (tag plus fields) over IPC, and for the renderer to map it onto the response tags the broker already classifies.
   • Adding public tags for target-not-found and out-of-viewport could be considered separately.

   A maintainer will decide on the fix direction.
2. juliusmarminge

   added

   bugSomething is broken or behaving incorrectly.Something is broken or behaving incorrectly.

   via-triageFiled through npx t3 triageFiled through npx t3 triage

   on Oct 3, 2026
3. PixPMusic commented on Oct 3, 2026

   

   PixPMusic

   on Oct 3, 2026

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   Cross-linking related work: #3714 is the click target-not-found case of this same IPC loss, and #7301 sends a typed click outcome across IPC for that path. This issue covers the desktop tags that already have public counterparts (waitFor timeouts, invalid selectors, non-editable targets). Once #12899 lands, unmatched preview_wait_for calls will start hitting it too: on a real desktop the host's timeout reply arrives and reads waitFor failed on client … instead of timed out (observed on two Macs; details on #12899).
4. juliusmarminge commented on Oct 7, 2026

   

   juliusmarminge

   on Oct 7, 2026

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   Obsolete since #15328: preview automation no longer runs in the desktop app, so errors no longer cross IPC. The server host returns typed errors directly.
5. juliusmarminge

   closed this as not plannedon Oct 7, 2026