app: fold the prober's validated capabilities into core-probe

traceroute.udp4 lands as TracerouteProbe: ICMP time-exceeded read off the
socket error queue via Os.recvmsg(MSG_ERRQUEUE) through the reflection
facade the prober validated on both devices - no root, no raw socket, and
the C-over-JNI shim stays dead. Emits the schema's TracerouteEvidence with
rtt_ns. OsAbi carries the hardcoded sockopt ABI numbers across, including
the measured fact that Os.getsockoptInt exists on neither device, so PMTU
must come from the errqueue, never getsockopt(IP_MTU).

local.mdns_inventory lands as MdnsInventoryProbe with both hardware-bought
lessons intact: the meta-query lies (0 results beside live services on both
devices), and 4s of listening misses what 10s catches.

App version 0.2.2.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/MdnsInventoryProbe.kt

@@ -0,0 +1,107 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import android.net.nsd.NsdManager
+import android.net.nsd.NsdServiceInfo
+import android.net.wifi.WifiManager
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestStatus
+import app.echo_lot.measurement.TestType
+import app.echo_lot.measurement.Tier
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.withContext
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.put
+import kotlinx.serialization.json.putJsonObject
+import java.util.Collections
+
+/**
+ * local.mdns_inventory — what answers mDNS on this network (MulticastLock + NSD discovery).
+ * The service inventory doubles as the VLAN-leakage detector: a chromecast answering on the
+ * guest wifi is a segmentation fault made visible. Folded from the prober, validated on both
+ * known devices (4 services each).
+ *
+ * Two hardware-bought lessons are load-bearing here:
+ *  - The `_services._dns-sd._udp.` meta-query returned 0 on BOTH devices while concrete types
+ *    found live services — NsdManager's meta-query support is unreliable across builds, so the
+ *    concrete types are the measurement and the meta-query result is itself evidence.
+ *  - 4 s of listening missed services that 10 s catches; mDNS answers straggle.
+ */
+class MdnsInventoryProbe : Probe {
+    override val type = TestType.LOCAL_MDNS_INVENTORY
+    override val tier = Tier.APP
+    override val estimatedMs = 10_500L
+
+    /** Meta-query + common concrete types (HTTP covers HA/printers/NAS; googlecast is ubiquitous). */
+    private val queries = listOf(
+        "meta" to "_services._dns-sd._udp.",
+        "http" to "_http._tcp.",
+        "googlecast" to "_googlecast._tcp.",
+    )
+
+    private class Recorder : NsdManager.DiscoveryListener {
+        val names: MutableList<String> = Collections.synchronizedList(mutableListOf())
+        @Volatile var started = false
+        @Volatile var startFailCode: Int? = null
+        override fun onStartDiscoveryFailed(t: String?, code: Int) { startFailCode = code }
+        override fun onStopDiscoveryFailed(t: String?, code: Int) {}
+        override fun onDiscoveryStarted(t: String?) { started = true }
+        override fun onDiscoveryStopped(t: String?) {}
+        override fun onServiceFound(s: NsdServiceInfo?) { s?.serviceName?.let { names.add(it) } }
+        override fun onServiceLost(s: NsdServiceInfo?) {}
+    }
+
+    override suspend fun run(ctx: Context, ids: ProbeIds): Test = withContext(Dispatchers.IO) {
+        val b = TestBuilder(type, tier, ids)
+        val wifi = ctx.getSystemService(WifiManager::class.java)
+        val lock = wifi?.createMulticastLock("echolot")?.apply {
+            setReferenceCounted(false)
+            runCatching { acquire() }
+        }
+        val nsd = ctx.getSystemService(NsdManager::class.java)
+            ?: return@withContext b.build(
+                TestStatus.UNSUPPORTED,
+                evidence = buildJsonObject { put("reason", "NsdManager unavailable") },
+            )
+
+        val recorders = queries.map { (label, type) ->
+            val r = Recorder()
+            runCatching { nsd.discoverServices(type, NsdManager.PROTOCOL_DNS_SD, r) }
+                .onFailure { r.startFailCode = -1 }
+            Triple(label, type, r)
+        }
+        try {
+            delay(10_000)
+            var total = 0
+            var anyStarted = false
+            val evidence = buildJsonObject {
+                put("multicast_lock", lock?.isHeld == true)
+                for ((label, type, r) in recorders) {
+                    runCatching { nsd.stopServiceDiscovery(r) }
+                    anyStarted = anyStarted || r.started
+                    val names = r.names.distinct()
+                    total += names.size
+                    putJsonObject(label) {
+                        put("query", type)
+                        put("started", r.started)
+                        r.startFailCode?.let { put("start_fail_code", it) }
+                        put("found", names.size)
+                        if (names.isNotEmpty()) put("names", names.joinToString(", ").take(300))
+                    }
+                }
+            }
+            val metrics = buildJsonObject { put("services_found", total) }
+            // Zero services on a started discovery is a legitimate result (an empty or properly
+            // isolated network), not a failure — only discovery refusing to start is one.
+            b.build(if (anyStarted) TestStatus.OK else TestStatus.FAILED,
+                evidence = evidence, metrics = metrics)
+        } finally {
+            recorders.forEach { (_, _, r) -> runCatching { nsd.stopServiceDiscovery(r) } }
+            runCatching { lock?.release() }
+        }
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/OsAbi.kt

@@ -0,0 +1,70 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.system.Os
+import java.io.FileDescriptor
+
+/**
+ * Linux socket-option ABI numbers that android.system.OsConstants does NOT reliably expose.
+ * Stable across Android's supported ABIs at the IP/IPv6 protocol levels, which is why they can
+ * be hardcoded: if setsockoptInt with one of these succeeds, the kernel accepted the option; if
+ * it throws ErrnoException, it did not. Either outcome is data. Do not "fix" these to
+ * OsConstants names — they don't exist there (validated in the prober; see its OsAbi.kt).
+ *
+ * Measured fact worth keeping: `Os.getsockoptInt` is absent on both known devices (OnePlus 15
+ * A16, Lenovo TB330FU A15), so path-MTU values must be read from the errqueue (`ee_info`), never
+ * from getsockopt(IP_MTU).
+ */
+object OsAbi {
+    // IP level
+    const val IP_TTL = 2
+    const val IP_MTU_DISCOVER = 10
+    const val IP_MTU = 14
+    const val IP_RECVERR = 11
+    const val IP_PMTUDISC_DO = 2      // set DF, honor PMTU
+    const val IP_PMTUDISC_PROBE = 3   // set DF, ignore PMTU (for probing)
+
+    // IPv6 level
+    const val IPV6_MTU_DISCOVER = 23
+    const val IPV6_MTU = 24
+    const val IPV6_RECVERR = 25
+    const val IPV6_UNICAST_HOPS = 16
+    const val IPV6_PMTUDISC_PROBE = 3
+
+    // recv flags — not in OsConstants on any current API level
+    const val MSG_ERRQUEUE = 0x2000
+    const val MSG_DONTWAIT = 0x40
+
+    // struct sock_extended_err (uapi/linux/errqueue.h), fixed layout on all Android ABIs:
+    // u32 ee_errno; u8 ee_origin; u8 ee_type; u8 ee_code; u8 ee_pad; u32 ee_info; u32 ee_data;
+    // followed directly by the offender sockaddr (SO_EE_OFFENDER).
+    const val SOCK_EE_SIZE = 16
+    const val SO_EE_ORIGIN_ICMP = 2
+    const val ICMP_TIME_EXCEEDED = 11
+    const val ICMP_DEST_UNREACH = 3
+
+    /** Try setsockoptInt; return null on success, or the errno name on failure. */
+    fun trySetIntOpt(fd: FileDescriptor, level: Int, opt: Int, value: Int): String? =
+        try {
+            Os.setsockoptInt(fd, level, opt, value)
+            null
+        } catch (e: Throwable) {
+            e.message ?: e.javaClass.simpleName
+        }
+
+    /**
+     * getsockoptInt is not part of the stable public Os surface on every API level, so it is
+     * reached via reflection; callers must treat failure as "unreadable", not as an error.
+     */
+    fun tryGetIntOpt(fd: FileDescriptor, level: Int, opt: Int): Result<Int> = runCatching {
+        val m = Os::class.java.getMethod(
+            "getsockoptInt",
+            FileDescriptor::class.java,
+            Int::class.javaPrimitiveType,
+            Int::class.javaPrimitiveType,
+        )
+        m.invoke(null, fd, level, opt) as Int
+    }
+}

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/Probe.kt

@@ -55,9 +55,10 @@ class TestBuilder(
         evidence: JsonObject? = null,
         metrics: JsonObject? = null,
         error: TestError? = null,
+        params: JsonObject? = null,
     ): Test = Test(
         id = id, type = type, networkRef = networkRef, sessionRef = sessionRef, tier = tier,
         startedMonoNs = startedMonoNs, endedMonoNs = ids.monoNs(),
-        status = status, error = error, evidence = evidence, metrics = metrics,
+        status = status, error = error, params = params, evidence = evidence, metrics = metrics,
     )
 }

echolot-app/core-probe/src/main/kotlin/app/echo_lot/probe/TracerouteProbe.kt

@@ -0,0 +1,255 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.probe
+
+import android.content.Context
+import android.system.Os
+import android.system.OsConstants
+import app.echo_lot.measurement.Flow
+import app.echo_lot.measurement.Hop
+import app.echo_lot.measurement.HopProbe
+import app.echo_lot.measurement.Test
+import app.echo_lot.measurement.TestError
+import app.echo_lot.measurement.TestStatus
+import app.echo_lot.measurement.TestType
+import app.echo_lot.measurement.Tier
+import app.echo_lot.measurement.TracerouteEvidence
+import app.echo_lot.measurement.toEvidence
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.withContext
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.put
+import java.io.FileDescriptor
+import java.net.InetAddress
+import java.net.InetSocketAddress
+import java.nio.ByteBuffer
+import java.nio.ByteOrder
+
+/**
+ * traceroute.udp4 — UDP traceroute reading ICMP time-exceeded off the socket error queue via
+ * Os.recvmsg(MSG_ERRQUEUE): no root, no raw socket, no native code. Folded from the prober,
+ * which validated real hop addresses on both known devices (6 hops on the OnePlus 15, 5 on the
+ * Lenovo) and thereby retired the planned C-over-JNI errqueue shim.
+ *
+ * StructMsghdr/StructCmsghdr/recvmsg are reached via reflection (repo convention for uncertain
+ * OS paths): present since roughly API 34, absent before, and the probe must run — and report —
+ * on both. An absent API is UNSUPPORTED with the reason, never a crash.
+ */
+class TracerouteProbe(
+    private val targetHost: String = "1.1.1.1",
+    private val maxHops: Int = 6,
+) : Probe {
+    override val type = TestType.TRACEROUTE_UDP4
+    override val tier = Tier.APP
+    // Validated wall clock is ~250 ms on a healthy path; the ceiling is maxHops silent hops at
+    // 900 ms each, which only a blackholing path produces.
+    override val estimatedMs = 1_500L
+
+    private companion object {
+        const val BASE_PORT = 33434
+        /** ICMP errors take one RTT to surface on the errqueue; poll briefly, never block. */
+        const val HOP_DEADLINE_NS = 900_000_000L
+        const val POLL_INTERVAL_MS = 40L
+    }
+
+    override suspend fun run(ctx: Context, ids: ProbeIds): Test = withContext(Dispatchers.IO) {
+        val b = TestBuilder(type, tier, ids)
+        val params = buildJsonObject {
+            put("target", targetHost); put("max_hops", maxHops); put("base_port", BASE_PORT)
+        }
+
+        val api = ErrqueueApi.resolve()
+            ?: return@withContext b.build(
+                TestStatus.UNSUPPORTED,
+                params = params,
+                error = TestError(
+                    "no_recvmsg",
+                    "StructMsghdr/Os.recvmsg not on this API level — errqueue unreadable",
+                ),
+            )
+
+        var fd: FileDescriptor? = null
+        try {
+            fd = Os.socket(OsConstants.AF_INET, OsConstants.SOCK_DGRAM, OsConstants.IPPROTO_UDP)
+            OsAbi.trySetIntOpt(fd, OsConstants.IPPROTO_IP, OsAbi.IP_RECVERR, 1)?.let {
+                return@withContext b.build(
+                    TestStatus.UNSUPPORTED,
+                    params = params,
+                    error = TestError("ip_recverr_rejected", it),
+                )
+            }
+            val target = InetAddress.getByName(targetHost)
+
+            val hops = ArrayList<Hop>(maxHops)
+            var hopsSeen = 0
+            var reachedTarget = false
+            var srcPort = 0
+            for (ttl in 1..maxHops) {
+                OsAbi.trySetIntOpt(fd, OsConstants.IPPROTO_IP, OsAbi.IP_TTL, ttl)
+                val t0 = System.nanoTime()
+                val sent = runCatching {
+                    Os.sendto(fd, ByteArray(32), 0, 32, 0, target, BASE_PORT + ttl)
+                }
+                if (sent.isFailure) {
+                    hops.add(Hop(ttl, listOf(HopProbe(icmp = "sendto failed: " +
+                        (sent.exceptionOrNull()?.message ?: "?")))))
+                    continue
+                }
+                if (srcPort == 0) {
+                    // Only readable after the implicit bind the first send performs.
+                    srcPort = runCatching {
+                        (Os.getsockname(fd) as? InetSocketAddress)?.port ?: 0
+                    }.getOrDefault(0)
+                }
+
+                var hop: ErrqueueApi.ErrEvent? = null
+                val deadline = System.nanoTime() + HOP_DEADLINE_NS
+                while (hop == null && System.nanoTime() < deadline) {
+                    hop = api.pollErrqueue(fd)
+                    if (hop == null) delay(POLL_INTERVAL_MS)
+                }
+                val rttNs = System.nanoTime() - t0
+                when {
+                    hop == null -> hops.add(Hop(ttl, listOf(HopProbe()))) // silent hop: all null
+                    hop.parseError != null ->
+                        hops.add(Hop(ttl, listOf(HopProbe(icmp = "unparsed: ${hop.parseError}"))))
+                    else -> {
+                        hopsSeen++
+                        hops.add(Hop(ttl, listOf(HopProbe(
+                            replyFrom = hop.offender,
+                            rttNs = rttNs,
+                            icmp = when (hop.icmpType) {
+                                OsAbi.ICMP_TIME_EXCEEDED -> "time_exceeded"
+                                OsAbi.ICMP_DEST_UNREACH -> "dest_unreachable"
+                                else -> "type_${hop.icmpType}"
+                            },
+                        ))))
+                        if (hop.icmpType == OsAbi.ICMP_DEST_UNREACH) reachedTarget = true
+                    }
+                }
+                if (reachedTarget) break
+            }
+
+            // dst_port varies per TTL (classic traceroute, and what was validated on hardware),
+            // so this flow is explicitly NOT fixed-tuple; base_port is in params.
+            val evidence = TracerouteEvidence(
+                flow = Flow(srcPort = srcPort, dstPort = BASE_PORT, fixedTuple = false),
+                hops = hops,
+            ).toEvidence()
+            val metrics = buildJsonObject {
+                put("hops_seen", hopsSeen)
+                put("reached_target", reachedTarget)
+            }
+            val status = when {
+                hopsSeen > 0 -> TestStatus.OK
+                // API present, sends succeeded, nothing surfaced: a fact about this path or
+                // kernel, not proof the mechanism is missing.
+                else -> TestStatus.PARTIAL
+            }
+            b.build(status, params = params, evidence = evidence, metrics = metrics)
+        } catch (e: Throwable) {
+            b.build(
+                TestStatus.FAILED,
+                params = params,
+                error = TestError("uncaught", e.message ?: e.javaClass.simpleName),
+            )
+        } finally {
+            fd?.let { runCatching { Os.close(it) } }
+        }
+    }
+}
+
+/**
+ * Reflection facade over android.system.{StructMsghdr, StructCmsghdr, Os.recvmsg}.
+ * Resolved once; null if any piece is missing on this API level.
+ */
+internal class ErrqueueApi private constructor(
+    private val msghdrCtor: java.lang.reflect.Constructor<*>,
+    private val recvmsg: java.lang.reflect.Method,
+    private val cmsgLevel: java.lang.reflect.Field,
+    private val cmsgType: java.lang.reflect.Field,
+    private val cmsgData: java.lang.reflect.Field,
+    private val msgControl: java.lang.reflect.Field,
+) {
+    class ErrEvent(
+        val offender: String?,
+        val icmpType: Int,
+        val origin: Int,
+        val parseError: String? = null,
+    )
+
+    /** One non-blocking MSG_ERRQUEUE read; null when the queue is empty. */
+    fun pollErrqueue(fd: FileDescriptor): ErrEvent? {
+        return try {
+            val iov = arrayOf(ByteBuffer.allocate(512))
+            // (SocketAddress msg_name, ByteBuffer[] msg_iov, StructCmsghdr[] msg_control, flags)
+            val msghdr = msghdrCtor.newInstance(
+                InetSocketAddress(0), iov, null, 0,
+            )
+            recvmsg.invoke(null, fd, msghdr, OsAbi.MSG_ERRQUEUE or OsAbi.MSG_DONTWAIT)
+            val control = msgControl.get(msghdr) as? Array<*>
+                ?: return ErrEvent(null, -1, -1, "msg_control empty after recvmsg")
+            for (cmsg in control.filterNotNull()) {
+                val level = cmsgLevel.getInt(cmsg)
+                val type = cmsgType.getInt(cmsg)
+                if (level == OsConstants.IPPROTO_IP && type == OsAbi.IP_RECVERR) {
+                    return parseSockExtendedErr(cmsgData.get(cmsg))
+                }
+            }
+            ErrEvent(null, -1, -1, "no IP_RECVERR cmsg among ${control.size}")
+        } catch (e: Throwable) {
+            // The single most load-bearing line: reflection wraps errno in
+            // InvocationTargetException, and EAGAIN there means "queue empty", not failure.
+            val cause = (e as? java.lang.reflect.InvocationTargetException)?.cause ?: e
+            val msg = cause.message ?: cause.javaClass.simpleName
+            if ("EAGAIN" in msg || "EWOULDBLOCK" in msg) null
+            else ErrEvent(null, -1, -1, msg)
+        }
+    }
+
+    /** cmsg_data = struct sock_extended_err + offender sockaddr_in (see OsAbi). */
+    private fun parseSockExtendedErr(data: Any?): ErrEvent {
+        val bytes: ByteArray = when (data) {
+            is ByteArray -> data
+            is ByteBuffer -> ByteArray(data.remaining()).also { data.duplicate().get(it) }
+            else -> return ErrEvent(null, -1, -1, "cmsg_data is ${data?.javaClass?.name}")
+        }
+        if (bytes.size < OsAbi.SOCK_EE_SIZE) {
+            return ErrEvent(null, -1, -1, "cmsg_data too short: ${bytes.size}")
+        }
+        val origin = bytes[4].toInt() and 0xFF
+        val icmpType = bytes[5].toInt() and 0xFF
+        // SO_EE_OFFENDER: sockaddr_in directly after the fixed struct; family is in native
+        // byte order, sin_addr at offset +4 within the sockaddr.
+        val offender = if (bytes.size >= OsAbi.SOCK_EE_SIZE + 8) {
+            val family = ByteBuffer.wrap(bytes, OsAbi.SOCK_EE_SIZE, 2)
+                .order(ByteOrder.nativeOrder()).short.toInt()
+            if (family == OsConstants.AF_INET) {
+                val a = bytes.copyOfRange(OsAbi.SOCK_EE_SIZE + 4, OsAbi.SOCK_EE_SIZE + 8)
+                InetAddress.getByAddress(a).hostAddress
+            } else null
+        } else null
+        return ErrEvent(offender, icmpType, origin)
+    }
+
+    companion object {
+        fun resolve(): ErrqueueApi? = runCatching {
+            val msghdrCls = Class.forName("android.system.StructMsghdr")
+            val cmsghdrCls = Class.forName("android.system.StructCmsghdr")
+            ErrqueueApi(
+                // Picked by shape, not by position: the 4-arg form is
+                // (SocketAddress, ByteBuffer[], StructCmsghdr[], int) on every level that has it.
+                msghdrCtor = msghdrCls.constructors.first { it.parameterCount == 4 },
+                recvmsg = Os::class.java.getMethod(
+                    "recvmsg", FileDescriptor::class.java, msghdrCls, Int::class.javaPrimitiveType,
+                ),
+                cmsgLevel = cmsghdrCls.getField("cmsg_level"),
+                cmsgType = cmsghdrCls.getField("cmsg_type"),
+                cmsgData = cmsghdrCls.getField("cmsg_data"),
+                msgControl = msghdrCls.getField("msg_control"),
+            )
+        }.getOrNull()
+    }
+}