Description

Unit tests in cmd/middleware (and occasionally adjacent packages) intermittently report FAIL (unknown) even though the test itself passes. The tool first-run middleware creates its spinners via uxlib.NewSpinner without a Writer, which defaults to os.Stdout. On start/stop the spinner emits cursor escape codes (\033[?25l / \033[?25h) directly to stdout. Under go test -json, those raw bytes corrupt the event stream, so the runner misattributes a passing test as a failure - sometimes onto an unrelated test that ran concurrently.

Symptom

=== FAIL: cmd/middleware TestToolFirstRunMiddleware_OfferInstall_PromptError (unknown)
25h--- PASS: TestToolFirstRunMiddleware_OfferInstall_PromptError (0.00s)

The 25h prefix is the tail of the show-cursor escape \033[?25h.

Root cause

• SpinnerOptions.Writer defaults to os.Stdout (cli/azd/pkg/ux/spinner.go).
• The detect/install spinners in cli/azd/cmd/middleware/tool_first_run.go do not set Writer.
• forbidigo only guards os.Stdout writes in *_test.go, so it does not catch this production-code path.

Expected

Spinners exercised by tests should write to the console handle (io.Discard under MockConsole), keeping the go test -json stream clean. Related to #8385.