fix: address review feedback for sweatbox engine skeleton

Reject NaN/Inf geometry on add; clear Ident on ss; combined runway
name defaults to RwyA; simplify rules switch; test SetMaxAircraft
below current count.

internal/sweatbox/dispatch.go

@@ -2,6 +2,7 @@ package sweatbox
 
 import (
 	"fmt"
+	"math"
 	"strconv"
 	"strings"
 )
@@ -129,6 +130,10 @@ func (e *Engine) cmdXPDRLocked(target, mode string) CommandResult {
 		return CommandResult{OK: false, Message: errMsg}
 	}
 	ac.XPDRMode = mode
+	// Standby and ident are contradictory on the wire; clear flash on ss.
+	if mode == XPDRModeStandby {
+		ac.Ident = false
+	}
 	return CommandResult{OK: true}
 }
 
@@ -177,19 +182,9 @@ func (e *Engine) cmdAddLocked(args []string) CommandResult {
 
 	switch rules {
 	case RulesVFR, RulesIFR, RulesDVFR, RulesSVFR:
-		// ok — also accept lowercase already uppercased
+		// ok (args already upper-cased)
 	default:
-		// accept single-letter v/i/d/s
-		if len(rules) == 1 {
-			switch rules {
-			case "V", "I", "D", "S":
-				// ok
-			default:
-				return CommandResult{OK: false, Message: addUsage}
-			}
-		} else {
-			return CommandResult{OK: false, Message: addUsage}
-		}
+		return CommandResult{OK: false, Message: addUsage}
 	}
 	switch weight {
 	case WeightSmall, WeightSmallP, WeightLarge, WeightHeavy:
@@ -231,14 +226,10 @@ func (e *Engine) cmdAddLocked(args []string) CommandResult {
 		if len(args) < 6 {
 			return CommandResult{OK: false, Message: addUsage}
 		}
-		bearingStr := loc[1:]
-		bearing, err := strconv.ParseFloat(bearingStr, 64)
-		if err != nil {
-			return CommandResult{OK: false, Message: addUsage}
-		}
-		distNM, err1 := strconv.ParseFloat(args[4], 64)
-		alt, err2 := strconv.ParseFloat(args[5], 64)
-		if err1 != nil || err2 != nil || distNM < 0 {
+		bearing, ok1 := parseFiniteFloat(loc[1:])
+		distNM, ok2 := parseFiniteFloat(args[4])
+		alt, ok3 := parseFiniteFloat(args[5])
+		if !ok1 || !ok2 || !ok3 || distNM < 0 {
 			return CommandResult{OK: false, Message: addUsage}
 		}
 		typeTok, errMsg := optionalType(args[6:])
@@ -254,8 +245,8 @@ func (e *Engine) cmdAddLocked(args []string) CommandResult {
 			return CommandResult{OK: false, Message: addUsage}
 		}
 		rwy := strings.ToUpper(loc)
-		distNM, err := strconv.ParseFloat(args[4], 64)
-		if err != nil || distNM < 0 {
+		distNM, ok := parseFiniteFloat(args[4])
+		if !ok || distNM < 0 {
 			return CommandResult{OK: false, Message: addUsage}
 		}
 		typeTok, errMsg := optionalType(args[5:])
@@ -286,6 +277,15 @@ func (e *Engine) cmdAddLocked(args []string) CommandResult {
 	return CommandResult{OK: true, Added: []AircraftSnapshot{ac.snapshot()}}
 }
 
+// parseFiniteFloat parses a float that must be finite (rejects NaN/±Inf).
+func parseFiniteFloat(s string) (float64, bool) {
+	v, err := strconv.ParseFloat(strings.TrimSpace(s), 64)
+	if err != nil || math.IsNaN(v) || math.IsInf(v, 0) {
+		return 0, false
+	}
+	return v, true
+}
+
 func optionalType(args []string) (string, string) {
 	if len(args) == 0 {
 		return "", ""
@@ -367,6 +367,11 @@ func (e *Engine) placeOnApproachLocked(ac *SimAircraft, rwy string, distNM float
 	if !ok {
 		return "Runway/taxiway not found in airport file."
 	}
+	// Record the resolved end designator (combined "33/15" → RwyA).
+	landEnd := rwy
+	if rwy == s.Name || rwy == s.RwyA+"/"+s.RwyB {
+		landEnd = s.RwyA
+	}
 	// Place along final: opposite of landing heading from threshold.
 	finalBearing := normalizeHeading(hdg + 180)
 	lat, lon := destinationPoint(thr.Lat, thr.Lon, finalBearing, distNM*metersPerNM)
@@ -376,7 +381,7 @@ func (e *Engine) placeOnApproachLocked(ac *SimAircraft, rwy string, distNM float
 	ac.Heading = hdg
 	ac.Speed = defaultApproachSpeed(ac.Engine)
 	ac.Status = StatusOnApproach
-	ac.LandingRunway = rwy
-	ac.Instruction = "Approach runway " + rwy
+	ac.LandingRunway = landEnd
+	ac.Instruction = "Approach runway " + landEnd
 	return ""
 }

internal/sweatbox/engine.go

@@ -460,13 +460,18 @@ func initialBearingDeg(lat1, lon1, lat2, lon2 float64) float64 {
 }
 
 // runwayThreshold returns the threshold point and landing heading for a runway
-// end designator (e.g. "19" or "33"). Landing heading is along the runway
-// centerline from the threshold toward the far end.
+// end designator (e.g. "19" or "33"). Combined names ("19/1") default to RwyA.
+// Landing heading is along the runway centerline from the threshold toward the
+// far end.
 func runwayThreshold(s *Surface, end string) (threshold Point, hdg float64, ok bool) {
 	if s == nil || s.Kind != SurfaceRunway || len(s.Points) < 2 {
 		return Point{}, 0, false
 	}
 	end = strings.ToUpper(strings.TrimSpace(end))
+	// Combined "A/B" (or full surface Name) → approach end A by default.
+	if end == s.Name || end == s.RwyA+"/"+s.RwyB {
+		end = s.RwyA
+	}
 	// Points are ordered RwyA → RwyB in .apt files.
 	var thr, far Point
 	var dispFt float64

internal/sweatbox/engine_test.go

@@ -430,6 +430,14 @@ func TestCommand_AddValidation(t *testing.T) {
 		{"add i l j -270 10", false, "Missing parameters"}, // bearing needs alt
 		{"add i l j 33 abc", false, "Missing parameters"},
 		{"add i l j 33 10 EXTRA JUNK", false, "Missing parameters"},
+		// Non-finite geometry args (Issue 1)
+		{"add i l j 33 NaN", false, "Missing parameters"},
+		{"add i l j 33 +Inf", false, "Missing parameters"},
+		{"add i l j 33 -Inf", false, "Missing parameters"},
+		{"add v s p -270 10 NaN", false, "Missing parameters"},
+		{"add v s p -NaN 10 2500", false, "Missing parameters"},
+		{"add v s p -270 Inf 2500", false, "Missing parameters"},
+		{"add v s p -+Inf 10 2500", false, "Missing parameters"},
 	}
 	for _, tc := range cases {
 		r := e.CommandLine(tc.line)
@@ -469,6 +477,90 @@ func TestCommand_AddMaxAircraft(t *testing.T) {
 	}
 }
 
+// Issue 5: SetMaxAircraft reduced below current count keeps existing AC
+// and rejects further adds until under the new cap.
+func TestSetMaxAircraft_BelowCurrentCount(t *testing.T) {
+	e := loadKBTVEngine(t)
+	var css []string
+	for i := 0; i < 3; i++ {
+		r := e.CommandLine("add v s p @GA1")
+		if !r.OK {
+			t.Fatalf("add %d: %s", i, r.Message)
+		}
+		css = append(css, r.Added[0].Callsign)
+	}
+	if e.Count() != 3 {
+		t.Fatalf("count = %d", e.Count())
+	}
+	e.SetMaxAircraft(1)
+	if e.Settings().MaxAircraft != 1 {
+		t.Fatalf("max = %d", e.Settings().MaxAircraft)
+	}
+	if e.Count() != 3 {
+		t.Fatalf("existing aircraft must be kept: count=%d", e.Count())
+	}
+	r := e.CommandLine("add v s p @GA2")
+	if r.OK || !contains(r.Message, "Maximum") {
+		t.Fatalf("add while over cap: %+v", r)
+	}
+	// Free slots until under cap, then add succeeds.
+	if !e.Delete(css[0]) || !e.Delete(css[1]) {
+		t.Fatal("delete")
+	}
+	if e.Count() != 1 {
+		t.Fatalf("count after del = %d", e.Count())
+	}
+	r = e.CommandLine("add v s p @GA2")
+	if r.OK {
+		t.Fatal("still at cap (1); further add should fail")
+	}
+	e.Delete(css[2])
+	r = e.CommandLine("add v s p @GA2")
+	if !r.OK {
+		t.Fatalf("add under cap: %s", r.Message)
+	}
+	if e.Count() != 1 {
+		t.Fatalf("count = %d", e.Count())
+	}
+}
+
+func (e *Engine) mustGet(t *testing.T, cs string) AircraftSnapshot {
+	t.Helper()
+	ac, ok := e.Get(cs)
+	if !ok {
+		t.Fatalf("missing %s", cs)
+	}
+	return ac
+}
+
+func TestCommand_AddCombinedRunwayName(t *testing.T) {
+	// Issue 3: combined designator "33/15" should place on RwyA approach.
+	e := loadKBTVEngine(t)
+	r := e.CommandLine("add i l j 33/15 8")
+	if !r.OK {
+		t.Fatalf("add combined: %s", r.Message)
+	}
+	ac := r.Added[0]
+	if ac.Status != StatusOnApproach {
+		t.Errorf("status = %s", ac.Status)
+	}
+	if ac.LandingRunway != "33" {
+		t.Errorf("LandingRunway = %s, want 33 (RwyA)", ac.LandingRunway)
+	}
+	// Same geometry as end designator "33".
+	r2 := e.CommandLine("add i l j 33 8")
+	if !r2.OK {
+		t.Fatal(r2.Message)
+	}
+	ac2 := r2.Added[0]
+	if math.Abs(ac.Lat-ac2.Lat) > 1e-6 || math.Abs(ac.Lon-ac2.Lon) > 1e-6 {
+		t.Errorf("combined vs end mismatch: (%v,%v) vs (%v,%v)", ac.Lat, ac.Lon, ac2.Lat, ac2.Lon)
+	}
+	if math.Abs(ac.Heading-ac2.Heading) > 1e-6 {
+		t.Errorf("hdg %v vs %v", ac.Heading, ac2.Heading)
+	}
+}
+
 func TestCommand_DelPosSqId(t *testing.T) {
 	e := loadKBTVEngine(t)
 	r := e.CommandLine("add v s p @GA1")
@@ -511,6 +603,7 @@ func TestCommand_DelPosSqId(t *testing.T) {
 		t.Errorf("sqi: %+v", ac)
 	}
 
+	// ss must clear Ident after id/sqi (Issue 2).
 	r = e.Command(cs, "ss")
 	if !r.OK {
 		t.Fatal(r.Message)
@@ -519,6 +612,9 @@ func TestCommand_DelPosSqId(t *testing.T) {
 	if ac.XPDRMode != XPDRModeStandby {
 		t.Errorf("mode = %s", ac.XPDRMode)
 	}
+	if ac.Ident {
+		t.Error("ss should clear Ident")
+	}
 	r = e.Command(cs, "sn")
 	if !r.OK {
 		t.Fatal(r.Message)
@@ -528,10 +624,6 @@ func TestCommand_DelPosSqId(t *testing.T) {
 		t.Errorf("mode = %s", ac.XPDRMode)
 	}
 
-	// Clear ident then set via id.
-	e.mu.Lock()
-	e.aircraft[cs].Ident = false
-	e.mu.Unlock()
 	r = e.Command(cs, "id")
 	if !r.OK {
 		t.Fatal(r.Message)
@@ -540,6 +632,11 @@ func TestCommand_DelPosSqId(t *testing.T) {
 	if !ac.Ident {
 		t.Error("ident not set")
 	}
+	// ss after id clears ident again
+	r = e.Command(cs, "ss")
+	if !r.OK || e.mustGet(t, cs).Ident {
+		t.Fatalf("ss after id: ok=%v ident=%v", r.OK, e.mustGet(t, cs).Ident)
+	}
 
 	// Bad squawk.
 	r = e.Command(cs, "sq abcd")