add auto-reset timer for dashboard aggregates

Live flamegraph trie and stats engine grow unboundedly during long
traces. Add a periodic auto-reset (same effect as the 'r' key) so they
stay bounded.

- New CLI flag -resetTimer=30s (default 30s, 0 disables).
- Hotkey I cycles the cadence: off -> 15s -> 30s -> 60s -> 5m -> off.
  Custom intervals (e.g. -resetTimer=47s) advance to the first preset
  greater than the current value, then wrap to off.
- autoResetTickMsg carries a generation counter so changing the cadence
  drops in-flight ticks scheduled under the previous interval.
- Dashboard chrome shows 'auto-reset: 30s' or 'auto-reset: off'.

1 files changed, 40 insertions, 0 deletions

diff --git a/internal/flags/flags_test.go b/internal/flags/flags_test.go
index f5274d8..77c167c 100644
--- a/internal/flags/flags_test.go
+++ b/internal/flags/flags_test.go
@@ -171,3 +171,43 @@ func TestParseInvalidTracepointRegexReturnsError(t *testing.T) {
 		t.Fatalf("unexpected error: %v", err)
 	}
 }
+
+func TestParseResetTimerDefault(t *testing.T) {
+	cfg, err := parseForTest(t)
+	if err != nil {
+		t.Fatalf("parse returned error: %v", err)
+	}
+	if cfg.ResetTimer != DefaultResetTimer {
+		t.Fatalf("default reset timer = %v, want %v", cfg.ResetTimer, DefaultResetTimer)
+	}
+}
+
+func TestParseResetTimerOverride(t *testing.T) {
+	cfg, err := parseForTest(t, "-resetTimer", "45s")
+	if err != nil {
+		t.Fatalf("parse returned error: %v", err)
+	}
+	if cfg.ResetTimer != 45*time.Second {
+		t.Fatalf("reset timer = %v, want 45s", cfg.ResetTimer)
+	}
+}
+
+func TestParseResetTimerZeroDisables(t *testing.T) {
+	cfg, err := parseForTest(t, "-resetTimer", "0")
+	if err != nil {
+		t.Fatalf("parse returned error: %v", err)
+	}
+	if cfg.ResetTimer != 0 {
+		t.Fatalf("reset timer = %v, want 0 (disabled)", cfg.ResetTimer)
+	}
+}
+
+func TestParseResetTimerNegativeReturnsError(t *testing.T) {
+	_, err := parseForTest(t, "-resetTimer", "-5s")
+	if err == nil {
+		t.Fatalf("expected parse error for negative reset timer")
+	}
+	if !strings.Contains(err.Error(), "invalid resetTimer") {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}