perf(nav3): Bound navigation argument payload size

Limit the total argument characters sanitized from one back-stack update so large strings and stringified values cannot dominate navigation telemetry payloads or processing time. Preserve the existing entry, depth, and value budgets and verify the new limit with a regression test.\n\nCo-Authored-By: Codex <noreply@openai.com>

Author: 0xadam-brown

sentry-android-navigation3/src/main/kotlin/io/sentry/compose/navigation3/BackStackConverter.kt

@@ -124,6 +124,7 @@ internal class BackStackConverter<T : Any>(
 
     private val activeContainers = IdentityHashMap<Any, Unit>()
     private var remainingValues = MAX_ARGUMENT_COUNT
+    private var remainingCharacters = MAX_ARGUMENT_CHARACTERS
     private var budgetExhausted = false
 
     /**
@@ -158,7 +159,9 @@ internal class BackStackConverter<T : Any>(
       try {
         val sanitized = mutableMapOf<String, Any?>()
         for ((key, childValue) in value) {
-          sanitized[key.toString()] = sanitizeValue(childValue, depth + 1)
+          val keyString = key.toString()
+          consumeCharacters(keyString.length)
+          sanitized[keyString] = sanitizeValue(childValue, depth + 1)
         }
         return sanitized
       } finally {
@@ -185,14 +188,16 @@ internal class BackStackConverter<T : Any>(
       val collection = value?.asSanitizableCollectionOrNull()
 
       return when {
-        value == null || value is String || value is Number || value is Boolean -> value
-        value is CharSequence || value is Char -> value.toString()
-        value is Enum<*> -> value.name
+        value == null || value is Number || value is Boolean -> value
+        value is String -> value.also { consumeCharacters(it.length) }
+        value is CharSequence || value is Char ->
+          value.toString().also { consumeCharacters(it.length) }
+        value is Enum<*> -> value.name.also { consumeCharacters(it.length) }
         value is Map<*, *> -> sanitizeMap(value, depth)
         collection != null -> sanitizeCollection(collection, depth)
         else -> {
           warningState.logUnsupportedValueWarning(value::class.simpleName, logger)
-          value.toString()
+          value.toString().also { consumeCharacters(it.length) }
         }
       }
     }
@@ -225,6 +230,13 @@ internal class BackStackConverter<T : Any>(
       }
     }
 
+    private fun consumeCharacters(count: Int) {
+      if (count > remainingCharacters) {
+        throw DropSubtree(CHARACTER_BUDGET_WARNING, exhaustsBudget = true)
+      }
+      remainingCharacters -= count
+    }
+
     private fun enter(container: Any) {
       if (activeContainers.put(container, Unit) != null) {
         throw DropSubtree(STRUCTURE_WARNING, exhaustsBudget = false)
@@ -281,10 +293,22 @@ internal class BackStackConverter<T : Any>(
        */
       private const val MAX_ARGUMENT_COUNT = 200
 
+      // TODO ADAM: Add visual indicator when we truncate args.
+      /**
+       * Max number of characters visited while sanitizing all entries in a given back stack update.
+       *
+       * Caps payload size in the presence of large individual arguments.
+       */
+      private const val MAX_ARGUMENT_CHARACTERS = 4_096
+
       private const val BUDGET_WARNING =
         "Nav3 arguments exceeded the maximum total value count for one backstack update. Skipping arguments " +
           "for this and older captured entries."
 
+      private const val CHARACTER_BUDGET_WARNING =
+        "Nav3 arguments exceeded the maximum total character count for one backstack update. Skipping " +
+          "arguments for this and older captured entries."
+
       private const val STRUCTURE_WARNING =
         "Nav3 argument sanitization failed (possibly a cyclic or deeply nested structure). Skipping arguments."
     }

sentry-android-navigation3/src/test/kotlin/io/sentry/compose/navigation3/BackStackConverterTest.kt

@@ -503,6 +503,14 @@ class BackStackConverterTest {
     assertThat(sut.convert(HomeScreen()).arguments).isEmpty()
   }
 
+  @Test
+  fun `convert drops arguments when character budget is exceeded`() {
+    val sut =
+      getSut(entryMapper = { entry -> entryInfo(entry, mapOf("value" to "x".repeat(4_097))) })
+
+    assertThat(sut.convert(HomeScreen()).arguments).isEmpty()
+  }
+
   @Test
   fun `arguments do not use caller collection size for allocation`() {
     val values =