Fix: deliver backend events to the chat on desktop (spinner never stops, #462) - #488

Problem

On the desktop app, after sending a prompt the chat shows a loading spinner forever and no response appears, although Claude runs and answers. The answer only shows up after closing and reopening the chat, because history is then read from the session file. Cancel does nothing, because the session id from the init message never arrives. Dragging an image into the prompt does nothing either.

Two defects combined:

1. Wrong environment check. The listener was chosen at module load with if (window.__TAURI__). In Tauri v2, window.__TAURI__ only exists when app.withGlobalTauri is enabled, which it is not in tauri.conf.json, so on desktop the check is false. It is also inverted: web mode's initializeWebMode() installs a fake window.__TAURI__, so the check is true in the browser.
2. require() in an ESM bundle. Inside the check the code called require("@tauri-apps/api/event"). require does not exist in Vite's ESM output, so even with withGlobalTauri enabled it throws, and the catch hides it ("Tauri APIs not available, using web mode").

Either way, the desktop app listened for DOM events on window while the backend emits through Tauri IPC (claude-output, claude-error, claude-complete), so nothing arrived. FloatingPromptInput.tsx used the same pattern for getCurrentWebviewWindow (drag-and-drop got a stub without onDragDropEvent), and useClaudeMessages.ts had the same require().

Approach

• Shared listener (src/lib/tauriEvents.ts): statically imports Tauri's listen and decides at call time whether to use it, with the detection the API adapter already uses for commands (detectEnvironment, which checks __TAURI_INTERNALS__; exported as isTauriRuntime). Commands and events can therefore never disagree about the environment. Web mode keeps the DOM CustomEvent fallback with the same { payload } shape.
• Testable core (src/lib/tauriEventsCore.ts): the selection logic (createListen) has no runtime imports, so it can be checked without a Tauri runtime.
• Chat (ClaudeCodeSession.tsx): the require() block and inline fallback are replaced by the shared listen; listener call sites are unchanged.
• Drag-and-drop (FloatingPromptInput.tsx): static getCurrentWebviewWindow import; the native listener is registered only in the Tauri runtime.
• useClaudeMessages.ts: static import instead of require(), behaviour otherwise unchanged (currently only used by ClaudeCodeSession.refactored.tsx).
• Two follow-ups for code that now runs on desktop for the first time:
  • One tab per drop. Drag-drop events are window-wide and inactive chat tabs stay mounted (hidden), so a dropped image would be added to every open chat. Only the tab whose prompt is on screen reacts now (src/lib/domVisibility.ts).
  • No double handling during the listener switch. The backend emits each line on the session-scoped channel, then on the generic one, and the chat swaps generic for scoped listeners after init. Lines arriving during the swap were handled twice. Once a scoped listener receives an event on a channel, the generic listener for that channel ignores it. Flags are per channel, so a completion event is never skipped.
• Not changed: withGlobalTauri stays off (it would not fix the require() layer and would expose the whole Tauri API on window). No Rust changes, no new dependencies.

Testing

Reproduce-then-fix check. The original code from main (TypeScript types stripped with Node's stripTypeScriptTypes, logic untouched) and this branch were run in the same simulated environments. Desktop means __TAURI_INTERNALS__ present, no window.__TAURI__ and no require, as in the real app. Web mode means after initializeWebMode(). A fake IPC emitter stands in for the backend's app.emit().

With withGlobalTauri forced on, the original code still falls back to DOM events, logging "Tauri APIs not available, using web mode". That confirms the require() layer.

Listener switch. A model of the chat's generic-to-scoped switch, with the backend's emit order (scoped, then generic), slow listener registration, and 0–20 lines arriving mid-switch:

Unit checks

• Listener: Tauri or web is chosen per call, DOM events are ignored in Tauri mode, unlisten removes the handler, and a failing Tauri listen rejects instead of silently falling back.
• Drag-drop visibility: with two mounted tabs, unguarded both react, guarded only the visible one; expanded mode and unmounted refs are handled.

Build and static checks

• npx tsc --noEmit: no new errors. The only error is the existing one in src/lib/analytics/index.ts.
• vite build and tauri build --debug --bundles app succeed.
• cargo test: 9/9 pass (no Rust changes).
• No require() of Tauri APIs remains in src/.

Manual (macOS desktop build)

Documentation

New exports have JSDoc comments. No README or configuration change; no new dependencies.

Fixes #462