feat(shared): add opt-in diagnostics client with compile-time kill switch

Ship client-side telemetry, crash capture, and bug-report assembly behind a
user opt-in, with NoOp transport until Cloudflare is wired. Builds can set
vnidrop.diagnostics.included=false to omit the Share-diagnostics UI and
disable the telemetry/crash auto-upload stack while keeping bug reports.

shared/src/iosMain/kotlin/com/vnidrop/app/diagnostics/PendingCrashStore.ios.kt

@@ -0,0 +1,67 @@
+package com.vnidrop.app.diagnostics
+
+import kotlinx.cinterop.ExperimentalForeignApi
+import kotlinx.cinterop.addressOf
+import kotlinx.cinterop.convert
+import kotlinx.cinterop.usePinned
+import platform.Foundation.NSData
+import platform.Foundation.NSFileManager
+import platform.Foundation.NSString
+import platform.Foundation.NSUTF8StringEncoding
+import platform.Foundation.create
+import platform.Foundation.dataUsingEncoding
+import platform.Foundation.dataWithContentsOfFile
+import platform.Foundation.writeToFile
+import platform.posix.memcpy
+
+actual fun createPendingCrashStore(appDataDir: String): PendingCrashStore =
+	IosPendingCrashStore(appDataDir)
+
+@OptIn(ExperimentalForeignApi::class)
+private class IosPendingCrashStore(
+	appDataDir: String,
+) : PendingCrashStore {
+	private val fileManager = NSFileManager.defaultManager
+	private val directory = appDataDir.trimEnd('/') + "/diagnostics/crashes"
+
+	override fun write(report: CrashReport) {
+		ensureDirectory()
+		val path = "$directory/${report.id}.crash"
+		val payload = CrashReportCodec.encode(report)
+		val data = (payload as NSString).dataUsingEncoding(NSUTF8StringEncoding) ?: return
+		data.writeToFile(path, atomically = true)
+	}
+
+	override fun list(): List<CrashReport> {
+		ensureDirectory()
+		val names = fileManager.contentsOfDirectoryAtPath(directory, null).orEmpty()
+			.filterIsInstance<String>()
+			.filter { it.endsWith(".crash") }
+		return names.mapNotNull { name ->
+			val path = "$directory/$name"
+			val data = NSData.dataWithContentsOfFile(path) ?: return@mapNotNull null
+			val text = data.toUtf8String()
+			CrashReportCodec.decode(text)
+		}.sortedByDescending { it.timestampMillis }
+	}
+
+	override fun delete(id: String) {
+		fileManager.removeItemAtPath("$directory/$id.crash", null)
+	}
+
+	private fun ensureDirectory() {
+		fileManager.createDirectoryAtPath(directory, withIntermediateDirectories = true, attributes = null, error = null)
+	}
+}
+
+@OptIn(ExperimentalForeignApi::class)
+private fun NSData.toUtf8String(): String {
+	val size = length.toInt()
+	if (size == 0) return ""
+	val result = ByteArray(size)
+	val source = bytes ?: return ""
+	result.usePinned { pinned ->
+		memcpy(pinned.addressOf(0), source, size.convert())
+	}
+	return result.decodeToString()
+}

shared/src/iosMain/kotlin/com/vnidrop/app/diagnostics/PlatformCrashHook.ios.kt

@@ -0,0 +1,16 @@
+package com.vnidrop.app.diagnostics
+
+import kotlin.experimental.ExperimentalNativeApi
+
+@OptIn(ExperimentalNativeApi::class)
+actual fun installPlatformCrashHook(onCrash: (Throwable) -> Unit) {
+	val previous = setUnhandledExceptionHook { throwable ->
+		runCatching { onCrash(throwable) }
+		// Terminate like the default hook after capture.
+		terminateWithUnhandledException(throwable)
+	}
+	// Keep a reference so the previous hook is not GC'd unused; we intentionally
+	// replace the default with capture-then-terminate.
+	@Suppress("UNUSED_VARIABLE")
+	val ignored = previous
+}

shared/src/iosMain/kotlin/com/vnidrop/app/logging/PlatformLogStore.ios.kt

@@ -1,19 +1,21 @@
 package com.vnidrop.app.logging
 
-import platform.Foundation.NSData
 import kotlinx.cinterop.ExperimentalForeignApi
 import kotlinx.cinterop.addressOf
 import kotlinx.cinterop.convert
 import kotlinx.cinterop.usePinned
+import platform.Foundation.NSData
 import platform.Foundation.NSDate
 import platform.Foundation.NSFileManager
 import platform.Foundation.NSFileModificationDate
 import platform.Foundation.NSFileSize
 import platform.Foundation.NSNumber
+import platform.Foundation.dataWithContentsOfFile
 import platform.Foundation.timeIntervalSince1970
 import platform.posix.fclose
 import platform.posix.fopen
 import platform.posix.fwrite
+import platform.posix.memcpy
 
 actual fun createPlatformLogStore(appDataDir: String, policy: LogRotationPolicy): PlatformLogStore =
 	IosPlatformLogStore(appDataDir, policy)
@@ -61,6 +63,31 @@ private class IosPlatformLogStore(
 			.sortedByDescending { it.modifiedAtMillis }
 	}
 
+	override fun readLatest(maxBytes: Long): String {
+		if (maxBytes <= 0) return ""
+		ensureDirectory()
+		val paths = listOf(activePath) +
+			(1..policy.maxFiles).map { "$directory/app.$it.log" }
+		val chunks = ArrayList<ByteArray>()
+		var remaining = maxBytes
+		for (path in paths) {
+			if (remaining <= 0 || !fileManager.fileExistsAtPath(path)) continue
+			val slice = readTail(path, remaining)
+			if (slice.isEmpty()) continue
+			chunks.add(0, slice)
+			remaining -= slice.size.toLong()
+		}
+		if (chunks.isEmpty()) return ""
+		val total = chunks.sumOf { it.size }
+		val out = ByteArray(total)
+		var offset = 0
+		for (chunk in chunks) {
+			chunk.copyInto(out, offset)
+			offset += chunk.size
+		}
+		return out.decodeToString()
+	}
+
 	private fun rotate() {
 		if (policy.maxFiles == 0) {
 			fileManager.removeItemAtPath(activePath, null)
@@ -92,4 +119,31 @@ private class IosPlatformLogStore(
 		val date = attributes[NSFileModificationDate] as? NSDate ?: return 0L
 		return (date.timeIntervalSince1970 * 1000.0).toLong()
 	}
+
+	private fun readTail(path: String, maxBytes: Long): ByteArray {
+		val data = NSData.dataWithContentsOfFile(path) ?: return ByteArray(0)
+		val all = data.toByteArray()
+		if (all.isEmpty() || maxBytes <= 0) return ByteArray(0)
+		if (all.size.toLong() <= maxBytes) return all
+		val start = all.size - maxBytes.toInt()
+		val slice = all.copyOfRange(start, all.size)
+		val newline = slice.indexOf('\n'.code.toByte())
+		return if (newline in 0 until slice.lastIndex) {
+			slice.copyOfRange(newline + 1, slice.size)
+		} else {
+			slice
+		}
+	}
+}
+
+@OptIn(ExperimentalForeignApi::class)
+private fun NSData.toByteArray(): ByteArray {
+	val size = length.toInt()
+	if (size == 0) return ByteArray(0)
+	val result = ByteArray(size)
+	val source = bytes ?: return ByteArray(0)
+	result.usePinned { pinned ->
+		memcpy(pinned.addressOf(0), source, size.convert())
+	}
+	return result
 }