test: reproduce #5850 — "No procedure found on path external.openInApp"

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What the bug is

Clicking Open in App (sidebar button or CMD+O) shows a toast:

Failed to open: No procedure found on path "external.openInApp"

instead of opening the worktree in the chosen editor/IDE (IntelliJ IDEA in the report).

Root-cause diagnosis

The desktop has two tRPC backends for a workspace:

1. Electron main (external router with openInApp/openInFinder/openFileInEditor), reached over the local IPC transport (trpc-electron).
2. host-service (@superset/host-service appRouter), reached over HTTP at /trpc/* (served by @hono/trpc-server → fetchRequestHandler). This router has no external namespace at all (see packages/host-service/src/trpc/router/router.ts).

The two transports emit different not-found messages for a missing path:

Transport	Resolver	Message
Electron IPC	callProcedure	No "mutation"-procedure on path "…"
HTTP	resolveResponse	No procedure found on path "…"

The reporter's text is the HTTP variant — proof that the external.openInApp call reached the host-service router (which doesn't implement it) rather than the local Electron router that does.

What the test does / how it proves the bug

packages/host-service/test/integration/external-open-in-app.integration.test.ts drives the real host-service appRouter through fetchRequestHandler (the same adapter the host-service serves with):

• external.openInApp → HTTP 404, code: NOT_FOUND, message exactly No procedure found on path "external.openInApp" — reproducing the reported error at its source.
• Positive control: health.check resolves normally, confirming the router is served correctly and the failure is specific to the missing external namespace.

Both tests pass (bun test in packages/host-service).

Why this is reproduction-only (draft)

The exact error and its source are reproduced deterministically. However, I could not tie it to a live UI code path on main: every current "Open in App" / CMD+O caller routes the mutation to the local Electron client (which implements external.openInApp), and remote/host workspaces are guarded (V2WorkspaceOpenInButton renders only for local workspaces, useOpenInExternalEditor and the command-palette openIn provider both short-circuit non-local hosts). So the reporter's build/state most likely routed the call to the host-service in a way current source no longer does.

This test therefore (a) reproduces and localizes the exact error, and (b) acts as a regression guard documenting that open-in must never be routed to the host-service HTTP router.

Maintainers: please confirm the installed build and whether the affected workspace was local or hosted on another machine, so the fix can target the correct routing guard.

Refs #5850

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Summary by cubic

Added an integration test in packages/host-service/test/integration/external-open-in-app.integration.test.ts that reproduces #5850 by calling external.openInApp against the host-service HTTP tRPC endpoint (fetchRequestHandler), returning the exact error: No procedure found on path "external.openInApp". This confirms the failure originates from the host-service router (not the Electron external router) and documents the expected 404, serving as a regression guard.

^{Written for commit 7029301. Summary will update on new commits.}