add changelog

AGENTS.md

@@ -62,3 +62,11 @@ with `curl` when fields change; never hand-edit `testdata/` payloads.
   - `alt_baro` may be the string `"ground"` instead of a number → `readsb.AltBaro`.
   - readsb timestamps are fractional-second Unix floats → `readsb.UnixTime`.
   - `outline.json` points are `[lat, lon, altFeet]` tuples → `readsb.RangePoint`.
+
+## Changelog
+
+`CHANGELOG.md` follows [Keep a Changelog](https://keepachangelog.com/) and
+SemVer. Record every user-facing change under `## [Unreleased]` as part of the
+change itself — don't defer it to release time. When tagging a release, rename
+`[Unreleased]` to the new version with the date and add a fresh empty
+`[Unreleased]` section plus its compare link at the bottom.

CHANGELOG.md

@@ -0,0 +1,45 @@
+# Changelog
+
+All notable changes to this project are documented here.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+## [0.2.1] - 2026-06-23
+
+### Added
+
+- `MinSpeed`/`MaxSpeed` aircraft filters in `pkg/types/readsb`, selectable
+  between ground speed and true airspeed via the `SpeedSource` type. `MaxSpeed`
+  drops aircraft with no speed reading.
+
+## [0.2.0] - 2026-06-23
+
+### Added
+
+- Client retry configuration with exponential backoff (`RetryConfig`,
+  `WithRetry`). Retries transport errors and 5xx responses; never retries 4xx or
+  context cancellation.
+- String-typed enums for readsb message type and emitter category.
+
+## [0.1.1] - 2026-06-22
+
+### Added
+
+- License.
+
+## [0.1.0] - 2026-06-22
+
+### Added
+
+- Initial release: `pkg/types/readsb` and `pkg/types/wingbits` decode types,
+  the `pkg/client` HTTP client with one-shot queries and channel/iterator
+  polling for every endpoint, the `cmd/wingbits` CLI, and a README.
+
+[Unreleased]: https://gitea.libretechconsulting.com/rmcguire/wingbits/compare/v0.2.1...HEAD
+[0.2.1]: https://gitea.libretechconsulting.com/rmcguire/wingbits/compare/v0.2.0...v0.2.1
+[0.2.0]: https://gitea.libretechconsulting.com/rmcguire/wingbits/compare/v0.1.1...v0.2.0
+[0.1.1]: https://gitea.libretechconsulting.com/rmcguire/wingbits/compare/v0.1.0...v0.1.1
+[0.1.0]: https://gitea.libretechconsulting.com/rmcguire/wingbits/releases/tag/v0.1.0

pkg/types/readsb/filter.go

@@ -104,6 +104,38 @@ func OnGround() AircraftFilter {
 	return func(a *Aircraft) bool { return a.AltBaro.OnGround }
 }
 
+// SpeedSource selects which speed reading a speed filter compares against. Its
+// zero value is GroundSpeed.
+type SpeedSource int
+
+const (
+	// GroundSpeed measures against GS (ground speed, knots).
+	GroundSpeed SpeedSource = iota
+	// TrueAirspeed measures against TAS (true airspeed, knots).
+	TrueAirspeed
+)
+
+func (s SpeedSource) of(a *Aircraft) float64 {
+	if s == TrueAirspeed {
+		return float64(a.TAS)
+	}
+	return a.GS
+}
+
+// MinSpeed keeps aircraft at or above knots, measured by src.
+func MinSpeed(knots float64, src SpeedSource) AircraftFilter {
+	return func(a *Aircraft) bool { return src.of(a) >= knots }
+}
+
+// MaxSpeed keeps aircraft with a positive reading at or below knots, measured by
+// src; aircraft with no reading are dropped.
+func MaxSpeed(knots float64, src SpeedSource) AircraftFilter {
+	return func(a *Aircraft) bool {
+		v := src.of(a)
+		return v > 0 && v <= knots
+	}
+}
+
 // WithinNM keeps aircraft within the given range (nautical miles) of the receiver.
 func WithinNM(nm float64) AircraftFilter {
 	return func(a *Aircraft) bool { return a.RDst > 0 && a.RDst <= nm }

pkg/types/readsb/readsb_test.go

@@ -68,6 +68,19 @@ func TestAircraftFilters(t *testing.T) {
 			t.Errorf("WithinNM kept %s at %.1f nm", a.Hex, a.RDst)
 		}
 	}
+	fast := r.Filter(MinSpeed(250, GroundSpeed))
+	for _, a := range fast {
+		if a.GS < 250 {
+			t.Errorf("MinSpeed kept %s at %.0f kt", a.Hex, a.GS)
+		}
+	}
+	// MaxSpeed drops aircraft with no reading, so every kept aircraft is positive.
+	slow := r.Filter(MaxSpeed(250, GroundSpeed))
+	for _, a := range slow {
+		if a.GS <= 0 || a.GS > 250 {
+			t.Errorf("MaxSpeed kept %s at %.0f kt", a.Hex, a.GS)
+		}
+	}
 	// Composition is AND: position AND high altitude is a subset of each.
 	both := r.Filter(WithPosition(), MinAltitude(30000))
 	if len(both) > len(pos) || len(both) > len(high) {