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ADR-002: Desktop studio hosted via Wails AssetServer handler ​

  • Status: Accepted
  • Date: 2026-05-05
  • Authors: feature-dev
  • Scope: cmd/iterion-desktop/, pkg/server/, studio/

Context ​

The desktop binary (iterion-desktop) is a thin native shell around the existing CLI studio server (pkg/server). Its value proposition lives in the Wails IPC bindings (window.go.main.App.*): project switcher, secrets/keychain, CLI detection, auto-update — none of which the studio SPA can do on its own.

The original design (Phase 1 of the desktop plan) loaded a tiny embedded "bootstrap stub" in the Wails AssetServer, called GetServerURL / GetSessionToken on window.go.main.App, and navigated the WebView to the embedded loopback HTTP server so the studio SPA loaded from the server directly.

That design has a fatal architectural flaw discovered in iteration 10 of the desktop feature review:

  1. Wails injects /wails/runtime.js and /wails/ipc.js — the scripts that define window.go, window.runtime, window.WailsInvoke — only into HTML responses served by the AssetServer itself (vendor/.../assetserver.go:200-220).
  2. Custom URL schemes (wails://) and the wails.localhost host are the only origins the AssetServer intercepts; everything else, including http://127.0.0.1:<random>, is passed through to the WebView's default network stack (vendor/.../windows/frontend.go:652-658).
  3. BindingsAllowedOrigins was unset, so the message dispatcher (vendor/.../originvalidator/originValidator.go:46-58) would have blocked any binding call from the localhost origin even if the runtime had somehow loaded.
  4. Concretely: after the bootstrap-stub redirected the window to http://127.0.0.1:<port>/, window.go was undefined, isDesktop() returned false, and the SPA quietly fell back to browser mode — every desktop-only view (<Welcome>, <Settings>, <ProjectSwitcher>, <MissingCLIBanner>) was un-mounted, every native-menu emit silently discarded, every desktop.* call rejected with "Not available in browser mode".

Tests missed this because studio/src/__tests__/desktopBridge.test.ts stubs window.go directly, and bindings_project_test.go uses a fake recordingServer plus a stubbed windowReloader. Neither exercises the real cross-origin runtime injection that Wails actually performs at runtime.

Decision ​

The Wails AssetServer hosts the studio SPA through a custom http.Handler (cmd/iterion-desktop/asset_proxy.go). The WebView's main origin stays on the AssetServer URL (wails://wails/ on Mac/Linux, http://wails.localhost/ on Windows) for the lifetime of the app, and:

  • The AssetServer handler serves SPA/static responses — every path outside /api/*, including GET / and hashed chunks under /assets/* — from the GUI binary's own pkg/server.StaticFS embed. Wails detects the handler's text/html response on GET / and injects /wails/runtime.js + /wails/ipc.js, which is what makes window.go.main.App.* reachable to the studio SPA — the exact gap that was the production blocker.
  • Only /api/* HTTP traffic is forwarded to the selected loopback server through httputil.ReverseProxy. The proxy's Rewrite calls SetURL, forces Host to the loopback target, and rewrites any inbound Origin header to http://<targetHost>. That keeps pkg/server's loopback Origin checks and CORS reflection satisfied without teaching HTTP handlers about the wails:// origin scheme. The proxy does not attach or strip desktop auth cookies.
  • Default GUI startup uses per-project headless daemons: it finds or launches iterion-desktop --server-only --project=<dir> and points the /api/* proxy plus direct WS URLs at that daemon. The in-process cmd/iterion-desktop/server_host.go path is the opt-out/fallback used when ITERION_DESKTOP_ATTACH_DAEMON=0 (also false, no, or off) is set or daemon attach/spawn fails; that fallback starts cli.RunStudio with Port=-1, Bind="127.0.0.1", and NoBrowser=true.
  • Both the default headless daemon and the in-process fallback use cli.RunStudio, which builds pkg/server.Config with DisableAuth=true, the same local-editor trust model used by iterion studio; there is no desktop-specific SessionToken field in pkg/server.Config.
  • GetSessionToken remains a Wails binding because the SPA's desktop WS helper calls it together with GetServerURL. In current local desktop builds it returns "", and the SPA omits the token query parameter when the value is empty.
  • WebSocket upgrades (/api/ws, /api/ws/runs/*) cannot flow through the proxy: Wails' AssetServer rejects WS upgrades with 501 by design (vendor/.../assetserver.go:110-114). The studio dials WS endpoints directly at ws://127.0.0.1:<port>/api/ws... using the absolute URL resolved through getDesktopWsBase() in studio/src/lib/desktopBridge.ts. In local desktop mode those dials have no token query parameter; if a future hosted-auth desktop flow supplies a real token, the auth implementation that consumes it should document that conditional behaviour.

The bootstrap-stub directory (cmd/iterion-desktop/frontend-stub/) and the embed.go that wired it up are deleted — they're obsolete with the proxy approach.

Alternatives considered ​

1. Inject Wails runtime + IPC scripts via the local server ​

Embed runtime_prod_desktop.js and ipc.js from vendor/.../runtime/ into the desktop binary, serve them at /wails/runtime.js + /wails/ipc.js from pkg/server, and add <script> tags to studio/index.html.

Rejected: the runtime needs the window.wailsbindings JSON to populate window.go.<package>.<class>.<method>. That JSON is generated by Wails internals during reflection on the Bind list; it's not exposed through any public API. Without it, window.go would be {} even with the runtime loaded. Reverse-engineering the bindings emitter into the desktop binary would re-implement substantial Wails machinery and have to track every Wails bump.

2. Move all desktop functionality to same-origin /api/* endpoints ​

Refactor every Wails binding (ListProjects, SetSecret, DetectExternalCLIs, CheckForUpdate, …) into HTTP handlers on pkg/server, drop Bind: []interface{}{app}, and remove the dependency on Wails IPC entirely.

Rejected (for v1): large blast radius — every binding, every desktop test, every frontend caller would change. This is a viable v2 if Wails IPC ever proves limiting (single-fenced WebView, reflection startup cost), but the proxy approach lets v1 keep the existing binding surface intact.

3. Allow-list the localhost origin via BindingsAllowedOrigins, keep ​

the redirect

Set BindingsAllowedOrigins: "http://127.0.0.1:*" and have the studio's index.html fetch + execute /wails/runtime.js + /wails/ipc.js cross-origin from the AssetServer.

Rejected: the wails:// scheme on Mac/Linux is custom and WebKit disallows cross-scheme <script> loads from http://. Even on Windows (http://wails.localhost), the runtime.js served by the AssetServer includes the dynamically-generated window.wailsbindings = '...' prefix with the bindings JSON; embedding the static vendor/ JS file alone wouldn't include that prefix, so window.go would still be empty.

Consequences ​

Positive ​

  • window.go.main.App.* is reachable on the studio SPA in desktop mode. Welcome, Settings, ProjectSwitcher, MissingCLIBanner, and the native-menu event subscriptions all work as designed.
  • The HTTP proxy is deliberately small: it only forwards /api/* to the current loopback server, forces the target Host, and rewrites Origin to match the loopback target. It does not own authentication state.
  • iterion studio, the default desktop headless daemon, and the in-process fallback use the same cli.RunStudio / DisableAuth=true local trust model; desktop only changes how the SPA is hosted and how WS URLs are resolved.
  • The reviewer's blocker is resolved without restructuring the binding surface or vendoring more Wails internals.

Negative ​

  • Adds proxy code (asset_proxy.go + tests).
  • Desktop REST calls have TWO HTTP servers in the request path: the Wails AssetServer (intercepting wails:// / wails.localhost) and the selected loopback pkg/server daemon/fallback. Latency overhead is one extra in-process hop (negligible) but every observability story has to account for both layers. SPA/static responses are served directly from the GUI embed; only /api/* uses the proxy hop. We mitigate by keeping the proxy minimal (no caching, no body-rewriting, only rewrite-time URL/Host/Origin tweaks).
  • WebSockets are the exception to the single AssetServer origin: they dial the loopback server directly because Wails rejects WS upgrades. Origin allow-listing in pkg/server must continue to include the Wails origins for this desktop path.
  • GetSessionToken is still part of the desktop binding contract even though local desktop returns an empty string. This keeps the SPA helper stable today, but a future hosted-auth token flow must wire both the producer and the server-side consumer before documenting tokenized WS dials as active behaviour.

Operational ​

  • docs/desktop-architecture.md updated to reflect the AssetServer handler's GUI-embedded SPA/static path, /api/* proxy, default daemon mode, and WS carve-out.
  • docs/desktop-qa.md first checkbox now exercises the actual production path (bindings reachable on studio), so a regression of the original blocker would surface immediately on the next QA pass.