feat(daemon): make hostReserve env-configurable for dev capacity squeeze

Adds SPINIFEX_RESERVED_VCPU and SPINIFEX_RESERVED_MEM_GB env-var overrides
read at daemon startup. Invalid values are logged and ignored so a typo
doesn't silently widen the reserve. Unblocks the LB E2E on capacity-tight
dev hosts (8 vCPU box: default 2-vCPU reserve + 3x t3.nano test load
leaves 0 free for the sys.micro LB VM). Lays groundwork for the planned
operator-tunable [capacity] config.

bead: mulga-siv-78

spinifex/daemon/daemon.go

@@ -408,11 +408,12 @@ func NewResourceManager(gpuModels []instancetypes.GPUModel, gpuMgr *gpu.Manager)
 		return nil, fmt.Errorf("detect system memory: %w", err)
 	}
 
-	reservedVCPU, reservedMem, err := applyHostReserve(defaultHostReserve, numCPU, totalMemGB)
+	reserve := resolveHostReserve(os.Getenv)
+	reservedVCPU, reservedMem, err := applyHostReserve(reserve, numCPU, totalMemGB)
 	if err != nil {
 		slog.Error("host below minimum reserve — daemon refuses to start",
 			"err", err, "hostVCPU", numCPU, "hostMemGB", totalMemGB,
-			"reserveVCPU", defaultHostReserve.vCPU, "reserveMemGB", defaultHostReserve.memGB)
+			"reserveVCPU", reserve.vCPU, "reserveMemGB", reserve.memGB)
 		return nil, fmt.Errorf("validate host reserve: %w", err)
 	}
 

spinifex/daemon/resource.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"log/slog"
+	"strconv"
 
 	"github.com/aws/aws-sdk-go/service/ec2"
 	"github.com/mulgadc/spinifex/spinifex/types"
@@ -27,6 +28,30 @@ type hostReserve struct {
 // the daemon itself needs little.
 var defaultHostReserve = hostReserve{vCPU: 2, memGB: 2.0}
 
+// resolveHostReserve returns defaultHostReserve, with vCPU/memGB overridden
+// when SPINIFEX_RESERVED_VCPU / SPINIFEX_RESERVED_MEM_GB are set to valid
+// non-negative values. Invalid values are logged and ignored — keeps a
+// typo'd env from silently widening the reserve. Intended as a stop-gap
+// until the planned operator-tunable [capacity] config lands.
+func resolveHostReserve(getenv func(string) string) hostReserve {
+	r := defaultHostReserve
+	if v := getenv("SPINIFEX_RESERVED_VCPU"); v != "" {
+		if n, err := strconv.Atoi(v); err == nil && n >= 0 {
+			r.vCPU = n
+		} else {
+			slog.Warn("ignoring SPINIFEX_RESERVED_VCPU", "value", v, "err", err)
+		}
+	}
+	if v := getenv("SPINIFEX_RESERVED_MEM_GB"); v != "" {
+		if f, err := strconv.ParseFloat(v, 64); err == nil && f >= 0 {
+			r.memGB = f
+		} else {
+			slog.Warn("ignoring SPINIFEX_RESERVED_MEM_GB", "value", v, "err", err)
+		}
+	}
+	return r
+}
+
 // minHostMemHeadroomGB is the minimum schedulable memory we require above
 // the reserve, so a host that just meets the reserve still has a small
 // amount left to launch the smallest guest type.

spinifex/daemon/resource_test.go

@@ -373,3 +373,72 @@ func TestAllocateForLaunch(t *testing.T) {
 		})
 	}
 }
+
+func TestResolveHostReserve(t *testing.T) {
+	tests := []struct {
+		name     string
+		env      map[string]string
+		wantVCPU int
+		wantMem  float64
+	}{
+		{
+			name:     "no env returns default",
+			env:      map[string]string{},
+			wantVCPU: defaultHostReserve.vCPU,
+			wantMem:  defaultHostReserve.memGB,
+		},
+		{
+			name:     "vCPU override",
+			env:      map[string]string{"SPINIFEX_RESERVED_VCPU": "1"},
+			wantVCPU: 1,
+			wantMem:  defaultHostReserve.memGB,
+		},
+		{
+			name:     "memory override",
+			env:      map[string]string{"SPINIFEX_RESERVED_MEM_GB": "0.5"},
+			wantVCPU: defaultHostReserve.vCPU,
+			wantMem:  0.5,
+		},
+		{
+			name: "both overrides",
+			env: map[string]string{
+				"SPINIFEX_RESERVED_VCPU":   "0",
+				"SPINIFEX_RESERVED_MEM_GB": "1.5",
+			},
+			wantVCPU: 0,
+			wantMem:  1.5,
+		},
+		{
+			name:     "invalid vCPU falls back to default",
+			env:      map[string]string{"SPINIFEX_RESERVED_VCPU": "garbage"},
+			wantVCPU: defaultHostReserve.vCPU,
+			wantMem:  defaultHostReserve.memGB,
+		},
+		{
+			name:     "negative vCPU falls back to default",
+			env:      map[string]string{"SPINIFEX_RESERVED_VCPU": "-1"},
+			wantVCPU: defaultHostReserve.vCPU,
+			wantMem:  defaultHostReserve.memGB,
+		},
+		{
+			name:     "invalid memory falls back to default",
+			env:      map[string]string{"SPINIFEX_RESERVED_MEM_GB": "not-a-number"},
+			wantVCPU: defaultHostReserve.vCPU,
+			wantMem:  defaultHostReserve.memGB,
+		},
+		{
+			name:     "negative memory falls back to default",
+			env:      map[string]string{"SPINIFEX_RESERVED_MEM_GB": "-0.5"},
+			wantVCPU: defaultHostReserve.vCPU,
+			wantMem:  defaultHostReserve.memGB,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got := resolveHostReserve(func(k string) string { return tc.env[k] })
+			assert.Equal(t, tc.wantVCPU, got.vCPU)
+			assert.InDelta(t, tc.wantMem, got.memGB, 0.001)
+		})
+	}
+}