fix(quic): PTO timer + IDN/IPv6 hostname + Huffman lookup table + amortized compaction

Closes the remaining items from the round-2 audit.

Driver send-loop PTO timer:
  Loop suspends on `withTimeoutOrNull(ptoMillis) { sendWakeup.receive() }`
  instead of unconditional receive. PTO doubles on each consecutive timeout
  up to 60s; resets to 1s on any wakeup.
  Without this, a single lost ClientHello with no inbound traffic to drive
  wakeups left the connection wedged forever. The PTO wake now gives the
  writer a chance to re-emit on retransmission.

JdkCertificateValidator hostname matching:
  - IDN.toASCII normalization on both the cert SAN and the input host so
    a SAN of `xn--bcher-kva.de` matches an input of `bücher.de`.
  - IPv6 literals compared via InetAddress.getByName().hostAddress so
    `::1` and `0:0:0:0:0:0:0:1` compare equal.
  - Wildcard public-suffix-label rejection: requires the suffix to contain
    at least 2 dots, so `*.com` is rejected even if a misbehaving CA
    issued such a cert.

QpackHuffman.decode O(N×256) → O(N×L) where L is the number of distinct
code lengths (≤ 26):
  Previously the inner loop scanned all 256 symbols per output byte. Now
  it walks length buckets in ascending order and does a HashMap lookup at
  each. For ASCII text the hot path matches at length 5-8.

Http3FrameReader.push + CapsuleReader.push amortized compaction:
  Was O(N) memcpy on every push → O(N²) over the lifetime of a long-lived
  stream. Now compacts only when consumed prefix is at least half the
  buffer, giving amortized O(1) per byte.

All :quic:jvmTest + :nestsClient:jvmTest pass.

End of round-2 audit fixes. The branch now passes:
  - Every RFC 9001 Appendix A test vector bit-for-bit
  - The full in-memory client+server pipe handshake
  - Hostile-input fuzzing of decodeFrames
  - Coalesced-packets ACK regression
  - Multi-cipher-suite (AES-GCM + ChaCha20-Poly1305) handshake
  - Negative-path TLS rejection (session_id_echo, version, group, missing
    extensions)

https://claude.ai/code/session_01EC1tfXfap8k8GyKvrxkxZx

quic/src/commonMain/kotlin/com/vitorpamplona/quic/connection/QuicConnectionDriver.kt

@@ -29,6 +29,7 @@ import kotlinx.coroutines.cancel
 import kotlinx.coroutines.channels.Channel
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.sync.withLock
+import kotlinx.coroutines.withTimeoutOrNull
 
 /**
  * Owns the UDP socket and runs the read + send loops for a [QuicConnection].
@@ -86,6 +87,12 @@ class QuicConnectionDriver(
     }
 
     private suspend fun sendLoop() {
+        // PTO budget: how long the loop will sleep before waking itself to
+        // check for retransmission opportunities. RFC 9002 §6.2 — initial
+        // PTO is roughly 3 × (smoothed RTT + max_ack_delay). We don't track
+        // RTT yet, so use a conservative fixed value that doubles on each
+        // consecutive timeout (Exponential backoff caps after ~6 timeouts).
+        var ptoMillis = 1_000L
         while (connection.status != QuicConnection.Status.CLOSED) {
             connection.lock.withLock {
                 while (true) {
@@ -93,8 +100,22 @@ class QuicConnectionDriver(
                     socket.send(out)
                 }
             }
-            // Suspend until the next wakeup — no busy polling.
-            sendWakeup.receive()
+            // Suspend until either: a wakeup arrives, or the PTO timer expires.
+            // The PTO wake ensures a single lost ClientHello doesn't wedge
+            // the connection forever — eventually the loop wakes, the writer
+            // re-emits Initial CRYPTO that's still in the send buffer (since
+            // we don't free it until ACK), and the handshake retries.
+            val woke =
+                withTimeoutOrNull(ptoMillis) {
+                    sendWakeup.receive()
+                    Unit
+                }
+            ptoMillis =
+                if (woke == null) {
+                    (ptoMillis * 2).coerceAtMost(60_000L)
+                } else {
+                    1_000L
+                }
         }
     }
 

quic/src/commonMain/kotlin/com/vitorpamplona/quic/http3/Http3FrameReader.kt

@@ -43,8 +43,10 @@ class Http3FrameReader {
 
     fun push(bytes: ByteArray) {
         if (bytes.isEmpty()) return
-        // Compact + grow.
-        if (pos > 0) {
+        // Amortized compaction: only shift bytes down when the consumed
+        // prefix is at least half the buffer. Otherwise we'd do O(N) memcpy
+        // on every chunk → O(N²) total over a long stream.
+        if (pos * 2 > buf.size) {
             buf = buf.copyOfRange(pos, buf.size)
             pos = 0
         }

quic/src/commonMain/kotlin/com/vitorpamplona/quic/qpack/QpackHuffman.kt

@@ -292,26 +292,49 @@ object QpackHuffman {
             intArrayOf(0x3fffffff, 30),
         )
 
+    /**
+     * Lookup tables grouped by code length. `byLength[L]` is a HashMap from
+     * `code` (an Int up to 30 bits) to `symbol` (0..255) for all symbols
+     * whose Huffman code is exactly L bits long. Lengths used in the table
+     * range from 5 to 30. We omit the EOS (length 30, code 0x3FFFFFFF) since
+     * it must never appear in valid input.
+     */
+    private val byLength: Array<HashMap<Int, Int>> = buildLookupByLength()
+
+    /** Sorted ascending list of distinct code lengths actually used by the table. */
+    private val lengths: IntArray = byLength.indices.filter { byLength[it].isNotEmpty() }.toIntArray()
+
+    private fun buildLookupByLength(): Array<HashMap<Int, Int>> {
+        val out = Array(31) { HashMap<Int, Int>() }
+        for (sym in 0..255) {
+            val code = table[sym][0]
+            val len = table[sym][1]
+            out[len][code] = sym
+        }
+        return out
+    }
+
     /** Decode a Huffman-encoded byte sequence into a UTF-8 string. */
     fun decode(encoded: ByteArray): ByteArray {
-        val result = ArrayList<Byte>()
+        val result = ArrayList<Byte>(encoded.size * 2) // rough upper bound
         var bitBuf = 0L
         var bitsAvailable = 0
         var i = 0
         while (i < encoded.size || bitsAvailable >= 5) {
-            // Pull more bits
+            // Pull more bits.
             while (bitsAvailable < 32 && i < encoded.size) {
                 bitBuf = (bitBuf shl 8) or (encoded[i].toLong() and 0xFF)
                 bitsAvailable += 8
                 i++
             }
-            // Try matching the longest code we can
+            // Try matching at each used code length, ascending. The first
+            // match wins (Huffman is a prefix code, so this is unambiguous).
             var matched = false
-            for (sym in 0..255) {
-                val (code, len) = Pair(table[sym][0], table[sym][1])
-                if (len > bitsAvailable) continue
-                val candidate = (bitBuf ushr (bitsAvailable - len)) and ((1L shl len) - 1)
-                if (candidate.toInt() == code) {
+            for (len in lengths) {
+                if (len > bitsAvailable) break
+                val candidate = ((bitBuf ushr (bitsAvailable - len)) and ((1L shl len) - 1)).toInt()
+                val sym = byLength[len][candidate]
+                if (sym != null) {
                     result.add(sym.toByte())
                     bitsAvailable -= len
                     bitBuf = bitBuf and ((1L shl bitsAvailable) - 1)

quic/src/commonMain/kotlin/com/vitorpamplona/quic/webtransport/WtCapsule.kt

@@ -71,7 +71,8 @@ class CapsuleReader {
 
     fun push(bytes: ByteArray) {
         if (bytes.isEmpty()) return
-        if (pos > 0) {
+        // Amortized compaction (same pattern as Http3FrameReader).
+        if (pos * 2 > buf.size) {
             buf = buf.copyOfRange(pos, buf.size)
             pos = 0
         }

quic/src/jvmAndroid/kotlin/com/vitorpamplona/quic/tls/JdkCertificateValidator.kt

@@ -22,6 +22,8 @@ package com.vitorpamplona.quic.tls
 
 import com.vitorpamplona.quic.QuicCodecException
 import java.io.ByteArrayInputStream
+import java.net.IDN
+import java.net.InetAddress
 import java.security.KeyStore
 import java.security.Signature
 import java.security.cert.CertificateFactory
@@ -133,18 +135,41 @@ class JdkCertificateValidator(
         cert: X509Certificate,
         host: String,
     ): Boolean {
-        // SAN check — RFC 6125. Walk subject alt names and accept any DNS or IP match.
         val sans = cert.subjectAlternativeNames ?: return false
+        // Normalize host once: IDN → ASCII for DNS comparison, parsed-and-
+        // re-stringified for IP literals so v6 forms compare equal.
+        val normalizedHost = idnAscii(host)
+        val hostAsIp =
+            try {
+                InetAddress.getByName(host).hostAddress
+            } catch (_: Throwable) {
+                null
+            }
         for (entry in sans) {
             val type = entry[0] as Int
             val value = entry[1].toString()
             // GeneralName type 2 = dNSName, type 7 = iPAddress.
-            if (type == 2 && dnsMatches(value, host)) return true
-            if (type == 7 && value.equals(host, ignoreCase = true)) return true
+            if (type == 2 && dnsMatches(idnAscii(value), normalizedHost)) return true
+            if (type == 7 && hostAsIp != null) {
+                val sanIp =
+                    try {
+                        InetAddress.getByName(value).hostAddress
+                    } catch (_: Throwable) {
+                        null
+                    }
+                if (sanIp != null && sanIp.equals(hostAsIp, ignoreCase = true)) return true
+            }
         }
         return false
     }
 
+    private fun idnAscii(name: String): String =
+        try {
+            IDN.toASCII(name).lowercase()
+        } catch (_: Throwable) {
+            name.lowercase()
+        }
+
     private fun dnsMatches(
         pattern: String,
         host: String,
@@ -156,7 +181,13 @@ class JdkCertificateValidator(
         val lhost = host.lowercase()
         if (!lhost.endsWith(suffix)) return false
         val prefix = lhost.substring(0, lhost.length - suffix.length)
-        return prefix.isNotEmpty() && '.' !in prefix
+        if (prefix.isEmpty() || '.' in prefix) return false
+        // RFC 6125 §6.4.3 — disallow wildcards in the public-suffix label.
+        // Heuristic: require ≥ 2 dots in the suffix (e.g. *.example.com is OK,
+        // *.com is not). Conservative; doesn't consult the actual PSL but
+        // matches what most browsers do for non-PSL-aware certs.
+        val suffixDots = suffix.count { it == '.' }
+        return suffixDots >= 2
     }
 
     companion object {