app: core-measurement — the measurement-schema.md document model

Pure Kotlin/JVM, faithful to the schema contract: two-clock (wall RFC3339 +
*_mono_ns), units in field names, observation/interpretation split
(tests[] vs findings[]), columnar train evidence (nulls preserved per
index), the full v1 test-type registry, the anonymization logical types as
field notes, and a finding-requires-evidence invariant.

The one piece with real logic — §7.3 deterministic verdict derivation
(category = worst finding light; >50% failed/unsupported → inconclusive;
overall = worst category, inconclusive only if all are) — is implemented
in Verdicts and fully unit-tested. Document JSON round-trips (snake_case
wire names, null-in-columns), typed builders for train/traceroute/resolver
evidence.

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

echolot-app/core-measurement/build.gradle.kts

@@ -0,0 +1,33 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+plugins {
+    alias(libs.plugins.kotlin.jvm)
+    alias(libs.plugins.kotlin.serialization)
+}
+
+// Pure Kotlin/JVM: the client half of probe-protocol.md. No Android deps, so
+// the Android app modules can depend on it and it stays unit-testable (incl.
+// live integration tests) on any JDK. Crypto, HTTP and UDP come from the JDK
+// (javax.crypto, java.net.http, java.net) — only JSON needs a library.
+dependencies {
+    implementation(libs.kotlinx.serialization.json)
+    testImplementation(kotlin("test"))
+}
+
+kotlin {
+    // Build with the available JDK (Android Studio's JBR is 21) but emit
+    // Java-17 bytecode so the Android app modules can consume this library.
+    jvmToolchain(21)
+    compilerOptions {
+        jvmTarget.set(org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17)
+    }
+}
+java {
+    sourceCompatibility = JavaVersion.VERSION_17
+    targetCompatibility = JavaVersion.VERSION_17
+}
+
+tasks.test {
+    useJUnitPlatform()
+}