several bugfixes, add internal.IntLen, round up http-linux example with new router API

internal/strconv.go

@@ -0,0 +1,19 @@
+package internal
+
+// IntLen returns the number of bytes [strconv.AppendInt] emits for value in the
+// given base, including a leading minus sign for negatives. Lets callers size a
+// buffer, or test whether a value fits an existing slot, before writing a byte.
+// base must be in the range 2..36, as accepted by [strconv.AppendInt].
+func IntLen(value int64, base int) int {
+	n := 1
+	u := uint64(value)
+	if value < 0 {
+		n++    // Leading minus sign.
+		u = -u // Two's-complement magnitude; correct even for math.MinInt64.
+	}
+	for u >= uint64(base) {
+		u /= uint64(base)
+		n++
+	}
+	return n
+}