test+refactor: real sidecar test, deterministic test sleeps, slog step line (#22)

* test(sidecar): replace assertTrue(true) placeholder with real server test

MainTest.mainExists() always passed and inflated the green-check count.
DriverServiceTest covers RPCs, but SidecarServer start/stop had no
coverage. Drop the placeholder and add SidecarServerTest that binds to
port 0, asserts a real ephemeral port, and stops cleanly.

* test(agent): drop 50ms sleep before cancel in TestServer_AcceptCancelsOnContext

Accept's closeListenerOnCancel watcher closes the listener as soon as
ctx fires, regardless of whether the outer Accept has reached
listener.Accept() yet. The sleep was a CI-flake surface (50ms is not
enough on a slow runner), and dropping it still exercises the same
outcome — Accept returns with ctx.Err() after cancellation.

Stable across 50x -count runs.

* test(agent): replace 2s sleep with done-chan in TestConn_SnapshotTimesOutIfSDKSilent

The silent-SDK fake held the connection open via time.Sleep(2s), which
coupled the test's wall clock to the server's 200ms snapshot-timeout
assertion. Swap for a done channel closed by t.Cleanup — the goroutine
exits when the test ends, independent of timing.

* test(maestro): make WaitForHealth_PollsUntilReady deterministic

Replace the 50ms wall-clock sleep that flipped healthReady with a
healthReadyAfterCall counter in the fake server. The handler returns
ready=true once healthCalls reaches the threshold, so the test's
"at least 2 polls before ready" assertion is satisfied by call
count rather than a race between the flip goroutine and the 25ms
poll loop.

* refactor(runner): route per-step progress through slog instead of fmt.Printf

The runner already carries a *slog.Logger for warnings (logger.Warn on
decode failures, predicate errors). The per-step status line was the
outlier — a bare fmt.Printf that wrote to os.Stdout unconditionally,
bypassing both the injected logger and any caller-configured writer.

Switch it to logger.Info("step", "index", ..., "screen", ..., "nodes", ...).
The caller (cmd/uatu) is responsible for wiring a logger whose handler
renders to the right stream; the next commit adds that wiring.

* feat(cli): render runner progress via a thin slog handler on stdout

progressHandler writes Info records as "msg key=value ..." and prefixes
warnings/errors with their level, matching the prose style of the
surrounding CLI status prints. Wired into the runner via
runner.Options.Logger so the per-step status line still lands on stdout
without slog's default time= / level= framing.

cmd/uatu/progress_logger.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"log/slog"
+	"strings"
+)
+
+// newProgressLogger wires a slog.Logger that prints user-facing progress
+// lines to the CLI's stdout stream. Info messages render as
+// "msg key=value ..." to match the prose style of other CLI prints;
+// warnings and errors get a "warn:" / "error:" prefix so they stand
+// out in the same stream.
+func newProgressLogger(writer io.Writer) *slog.Logger {
+	return slog.New(&progressHandler{writer: writer, level: slog.LevelInfo})
+}
+
+type progressHandler struct {
+	writer io.Writer
+	level  slog.Level
+}
+
+func (h *progressHandler) Enabled(_ context.Context, level slog.Level) bool {
+	return level >= h.level
+}
+
+func (h *progressHandler) Handle(_ context.Context, record slog.Record) error {
+	var builder strings.Builder
+	if record.Level >= slog.LevelWarn {
+		fmt.Fprintf(&builder, "%s: ", strings.ToLower(record.Level.String()))
+	}
+	builder.WriteString(record.Message)
+	record.Attrs(func(attr slog.Attr) bool {
+		fmt.Fprintf(&builder, " %s=%s", attr.Key, formatAttrValue(attr.Value))
+		return true
+	})
+	builder.WriteByte('\n')
+	_, err := io.WriteString(h.writer, builder.String())
+	return err
+}
+
+func (h *progressHandler) WithAttrs(_ []slog.Attr) slog.Handler { return h }
+func (h *progressHandler) WithGroup(_ string) slog.Handler      { return h }
+
+func formatAttrValue(value slog.Value) string {
+	if value.Kind() == slog.KindString {
+		return fmt.Sprintf("%q", value.String())
+	}
+	return value.String()
+}

cmd/uatu/test_run.go

@@ -181,6 +181,7 @@ func runTestPipeline(ctx context.Context, options testOptions, stdout io.Writer)
 		Driver:          driverClient,
 		Verifier:        verifierInstance,
 		TraceWriter:     traceWriter,
+		Logger:          newProgressLogger(stdout),
 	})
 
 	terminateCtx, terminateCancel := context.WithTimeout(context.Background(), 5*time.Second)