Expand test coverage across server, agent, and web; fix bugs found during audit.

Adds hundreds of unit/integration/e2e tests, fixes WS bcrypt auth, config merge, fleet analytics, agent schedule/log tail, and documents stale PROBLEMS items. Updates PROBLEMS.md, README, and test scripts; ignores local spread-kits and coverage dirs.

agent/miner/pool_test.go

@@ -0,0 +1,91 @@
+package miner
+
+import (
+	"math/big"
+	"strings"
+	"testing"
+)
+
+func TestUint32ToHexLittleEndian(t *testing.T) {
+	got := uint32ToHex(0x01020304)
+	want := "04030201"
+	if got != want {
+		t.Fatalf("uint32ToHex(0x01020304) = %q, want %q", got, want)
+	}
+}
+
+func TestUint32ToHexZero(t *testing.T) {
+	if got := uint32ToHex(0); got != "00000000" {
+		t.Fatalf("zero nonce hex = %q", got)
+	}
+}
+
+func TestHexEncode(t *testing.T) {
+	if got := hexEncode([]byte{0xde, 0xad, 0xbe, 0xef}); got != "deadbeef" {
+		t.Fatalf("hexEncode = %q", got)
+	}
+}
+
+func TestDifficultyToTargetHexZero(t *testing.T) {
+	if difficultyToTargetHex(0) != "" {
+		t.Fatal("difficulty 0 should yield empty target")
+	}
+	if difficultyToTargetHex(-1) != "" {
+		t.Fatal("negative difficulty should yield empty target")
+	}
+}
+
+func TestDifficultyToTargetHexOne(t *testing.T) {
+	out := difficultyToTargetHex(1)
+	want := strings.Repeat("f", 64)
+	if out != want {
+		t.Fatalf("difficulty 1 target = %q, want %q", out, want)
+	}
+}
+
+func TestDifficultyToTargetHexTwo(t *testing.T) {
+	out := difficultyToTargetHex(2)
+	maxTarget := new(big.Int)
+	maxTarget.SetString("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF", 16)
+	half := new(big.Int).Div(maxTarget, big.NewInt(2))
+	// difficultyToTargetHex reverses byte order before hex encoding
+	bytes := half.Bytes()
+	padded := make([]byte, 32)
+	copy(padded[32-len(bytes):], bytes)
+	for i, j := 0, len(padded)-1; i < j; i, j = i+1, j-1 {
+		padded[i], padded[j] = padded[j], padded[i]
+	}
+	want := strings.ToLower(strings.Repeat("", 0)) // placeholder
+	_ = want
+	const hexdigits = "0123456789abcdef"
+	wantBytes := make([]byte, 64)
+	for i, v := range padded {
+		wantBytes[i*2] = hexdigits[v>>4]
+		wantBytes[i*2+1] = hexdigits[v&0x0f]
+	}
+	want = string(wantBytes)
+	if out != want {
+		t.Fatalf("difficulty 2 target = %q, want %q", out, want)
+	}
+}
+
+func TestDifficultyToTargetHexLength(t *testing.T) {
+	for _, d := range []int64{1, 100, 1000, 1_000_000} {
+		out := difficultyToTargetHex(d)
+		if len(out) != 64 {
+			t.Fatalf("difficulty %d: expected 64 hex chars, got %d (%q)", d, len(out), out)
+		}
+	}
+}
+
+func TestDifficultyToTargetMeetsHash(t *testing.T) {
+	target := difficultyToTargetHex(1000)
+	zeroHash := strings.Repeat("0", 64)
+	if !hashMeetsTarget(zeroHash, target) {
+		t.Fatal("zero hash should meet difficulty-derived target")
+	}
+	highHash := strings.Repeat("f", 64)
+	if hashMeetsTarget(highHash, target) {
+		t.Fatal("max hash should not meet difficulty-derived target")
+	}
+}