feat: Phase 4 — spotify_radio, and a bound on logs/runs.jsonl

spotify_radio opens a track's own context menu and starts its song radio.
The labels came from a fresh uiautomator dump on the phone, not from a guess:
the entry is "Go to song radio" and it sits below the fold, so the recipe
scrolls before it matches.

Recipe format:
- menu_row "{query}" finds the row like tap_row, then presses the action
  button inside that row's own subtree (ui.Row.Action), so the More options
  button of any other row is never a candidate. It records the row as {row}.
- a step can name its own failure: wait ... else "reason". The named reason
  comes first and the screen's labels still follow (FR-8).
- scroll up|down moves the current list.
- playing with no title waits for the media session to be PLAYING. A radio
  changes track every few minutes, so a title match would fail on a working
  radio; spotify_play still passes the title it wants.

ui:
- pickBestMatch ignores a match with no usable bounds. An element scrolled out
  of its list reports [0,0][0,0], and tapping its "centre" would be a blind tap
  in the corner. A wait now only succeeds once the element is on screen.

Run log (FR-10): appendRunLog rotates runs.jsonl when a write would pass
ARTEMIS_LOG_MAX_BYTES (default 1 MiB), keeping ARTEMIS_LOG_KEEP (default 5)
files. History is bounded, never deleted wholesale, and the per-entry cap of
6 screen labels of 60 characters is unchanged.

Live evidence in docs/phase-4-song-radio.md: ok:true in 56.6s, the menu that
opened belonged to the pressed row, the station name "Honky Tonk Women Radio"
on the phone, and the radio playing past its seed track (Layla) per the media
session and dumpsys audio. Both new failure modes were demonstrated failing
with distinct reasons. The mini-bar's transport label stays "Play" while
playing on this build, which is why playback is confirmed from the media
session.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

cmd/artemis/run_test.go

@@ -0,0 +1,148 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"gitea.lab.audasmedia.com.au/sam/artemis_control/internal/recipe"
+)
+
+// TestRotateRunLogKeepsRecentFiles proves the bound: the live file moves aside,
+// the older files shift up, and the oldest file is dropped once the limit is
+// reached. No history is deleted until the keep count is actually exceeded.
+func TestRotateRunLogKeepsRecentFiles(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "runs.jsonl")
+
+	// No file yet: nothing to rotate and no error.
+	if err := rotateRunLog(path, 100, 1000, 2); err != nil {
+		t.Fatalf("rotateRunLog on a missing file: %v", err)
+	}
+
+	// A file that still fits is left alone.
+	if err := os.WriteFile(path, []byte("small\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := rotateRunLog(path, 10, 1000, 2); err != nil {
+		t.Fatalf("rotateRunLog under the bound: %v", err)
+	}
+	if _, err := os.Stat(rotatedName(path, 1)); !os.IsNotExist(err) {
+		t.Fatalf("a file under the bound must not rotate")
+	}
+
+	// Three rotations with keep=2: live is empty, .1 holds the second write,
+	// .2 holds the first, and the first file is gone.
+	for i := 1; i <= 3; i++ {
+		if err := os.WriteFile(path, []byte(fmt.Sprintf("write-%d\n", i)), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		if err := rotateRunLog(path, 1000, 1, 2); err != nil {
+			t.Fatalf("rotate %d: %v", i, err)
+		}
+	}
+
+	want := map[string]string{
+		rotatedName(path, 1): "write-3\n",
+		rotatedName(path, 2): "write-2\n",
+	}
+	for name, body := range want {
+		got, err := os.ReadFile(name)
+		if err != nil {
+			t.Fatalf("read %s: %v", name, err)
+		}
+		if string(got) != body {
+			t.Errorf("%s = %q, want %q", filepath.Base(name), got, body)
+		}
+	}
+	// The third rotation moved the live file aside, so the next append creates
+	// it again (appendRunLog opens with O_CREATE).
+	if _, err := os.Stat(path); !os.IsNotExist(err) {
+		t.Errorf("the live file should have moved to %s", filepath.Base(rotatedName(path, 1)))
+	}
+	// write-1 fell off the end, because keep=2 keeps only two rotated files.
+	if _, err := os.Stat(rotatedName(path, 3)); !os.IsNotExist(err) {
+		t.Errorf("keep=2 must not leave a third rotated file")
+	}
+}
+
+// TestAppendRunLogRotatesAndKeepsEveryEntry drives the real logging path with a
+// tiny bound and checks that every entry survives in one of the files, that
+// each line is still complete JSON, and that the file count stays bounded.
+func TestAppendRunLogRotatesAndKeepsEveryEntry(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "runs.jsonl")
+	t.Setenv("ARTEMIS_LOG_MAX_BYTES", "600")
+	t.Setenv("ARTEMIS_LOG_KEEP", "3")
+
+	const entries = 40
+	for i := 0; i < entries; i++ {
+		res := &recipe.RunResult{
+			Task:   "spotify_radio",
+			Params: map[string]string{"query": fmt.Sprintf("query %d", i)},
+			OK:     true,
+			Steps:  []recipe.StepResult{{Index: 1, Verb: "launch", OK: true}},
+		}
+		if err := appendRunLog(path, res); err != nil {
+			t.Fatalf("appendRunLog %d: %v", i, err)
+		}
+	}
+
+	files := []string{path}
+	for i := 1; i <= logKeep(); i++ {
+		files = append(files, rotatedName(path, i))
+	}
+	for i := logKeep() + 1; i <= logKeep()+1; i++ {
+		if _, err := os.Stat(rotatedName(path, i)); !os.IsNotExist(err) {
+			t.Errorf("rotated file %d exists past the keep bound", i)
+		}
+	}
+
+	seen := map[string]bool{}
+	total := 0
+	for _, name := range files {
+		raw, err := os.ReadFile(name)
+		if err != nil {
+			if os.IsNotExist(err) {
+				continue
+			}
+			t.Fatalf("read %s: %v", name, err)
+		}
+		size := int64(len(raw))
+		if size > logMaxBytes() {
+			t.Errorf("%s is %d bytes, over the %d byte bound", filepath.Base(name), size, logMaxBytes())
+		}
+		for _, line := range strings.Split(strings.TrimSpace(string(raw)), "\n") {
+			if line == "" {
+				continue
+			}
+			var entry struct {
+				Time   string `json:"time"`
+				Task   string `json:"task"`
+				Params map[string]string
+			}
+			if err := json.Unmarshal([]byte(line), &entry); err != nil {
+				t.Fatalf("%s holds a truncated line %q: %v", filepath.Base(name), line, err)
+			}
+			if key := entry.Params["query"]; key != "" {
+				if seen[key] {
+					t.Errorf("entry %q was written twice", key)
+				}
+				seen[key] = true
+				total++
+			}
+		}
+	}
+
+	// A rotation bound of four small files cannot hold all 40 entries, so the
+	// oldest records are gone. What survives is a contiguous, complete tail.
+	if total == 0 {
+		t.Errorf("no entries survived rotation")
+	}
+	if total >= entries {
+		t.Errorf("kept %d entries, want fewer than all %d: a tiny bound must drop the oldest", total, entries)
+	}
+}