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'.

2 files changed, 56 insertions, 0 deletions

diff --git a/internal/flags/flags.go b/internal/flags/flags.go
index 5d00b74..bbdf4b8 100644
--- a/internal/flags/flags.go
+++ b/internal/flags/flags.go
@@ -42,6 +42,7 @@ type Config struct {
 	CollapsedFields  []string
 	CountField       string
 	GlobalFilter     globalfilter.Filter
+	ResetTimer       time.Duration
 
 	// ShowVersion prints the banner plus version and exits without running.
 	ShowVersion bool
@@ -58,6 +59,12 @@ func init() {
 	current.Store(&defaults)
 }
 
+// DefaultResetTimer is the default cadence for the dashboard's auto-reset
+// timer. It periodically clears aggregate state (live flamegraph trie and
+// stats engine) — the same effect as pressing `r` — to prevent unbounded
+// growth during long traces. A value of 0 disables auto-reset entirely.
+const DefaultResetTimer = 30 * time.Second
+
 // NewFlags returns a configuration instance initialized with project defaults.
 func NewFlags() Config {
 	return Config{
@@ -69,6 +76,7 @@ func NewFlags() Config {
 		TUIExportEnable: true,
 		CollapsedFields: []string{"comm", "tracepoint", "path"},
 		CountField:      "count",
+		ResetTimer:      DefaultResetTimer,
 	}
 }
 
@@ -180,6 +188,8 @@ func parse() error {
 	flag.BoolVar(&cfg.TestLiveFlames, "testliveflames", false, "Run TUI with continuously-updating synthetic flamegraph data for live keyboard-navigation testing")
 	flag.DurationVar(&cfg.LiveInterval, "live-interval", cfg.LiveInterval, "Synthetic live flamegraph refresh interval for --testliveflames")
 	flag.BoolVar(&cfg.TUIExportEnable, "tuiExport", cfg.TUIExportEnable, "Enable TUI CSV snapshot export files (separate from Parquet recording)")
+	flag.DurationVar(&cfg.ResetTimer, "resetTimer", cfg.ResetTimer,
+		"Auto-reset interval for aggregate dashboard state (flamegraph trie + stats engine); set to 0 to disable")
 	flag.BoolVar(&cfg.ShowVersion, "version", false, "Print version banner and exit")
 	fields := flag.String("fields", "",
 		fmt.Sprintf("Comma separated list of fields to collapse, valid are: %v", validFields))
@@ -220,6 +230,12 @@ func parse() error {
 		return fmt.Errorf("invalid count field: %s", cfg.CountField)
 	}
 
+	// A negative reset timer would imply auto-resets in the past, which is
+	// nonsensical. 0 disables, anything positive enables.
+	if cfg.ResetTimer < 0 {
+		return fmt.Errorf("invalid resetTimer: %s (must be >= 0; 0 disables)", cfg.ResetTimer)
+	}
+
 	setCurrent(cfg)
 	return nil
 }
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)
+	}
+}