Preserve SerializableError in CachedError for proper error handling (#77)

* Preserve SerializableError in CachedError for proper error handling

Add serializableError field to CachedError to preserve exception type
information from cached idempotent requests. This enables consumers to
properly handle cached errors based on the original exception type.

Breaking change: CachedError constructor signature now requires
serializableError parameter.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

* Fix IdempotencyHandlerTest to use new CachedError constructor

Update test assertions to construct CachedError with SerializableError
parameter after adding serializableError field to CachedError data class.

---------

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: cjustice

common/src/main/kotlin/xyz/block/bittycity/common/idempotency/SerializableError.kt

@@ -5,7 +5,7 @@ data class SerializableError(
   val type: String
 ) {
 
-  fun asCachedError(): CachedError = CachedError("[$type] $message")
+  fun asCachedError(): CachedError = CachedError("[$type] $message", this)
 
   companion object {
     fun from(t: Throwable): SerializableError = SerializableError(
@@ -15,4 +15,7 @@ data class SerializableError(
   }
 }
 
-data class CachedError(override val message: String?) : Throwable(message)
+data class CachedError(
+  override val message: String?,
+  val serializableError: SerializableError
+) : Throwable(message)

outie/src/test/kotlin/xyz/block/bittycity/outie/controllers/IdempotencyHandlerTest.kt

@@ -3,6 +3,7 @@ package xyz.block.bittycity.outie.controllers
 import app.cash.quiver.extensions.success
 import xyz.block.bittycity.common.idempotency.CachedError
 import xyz.block.bittycity.common.idempotency.IdempotentResumeInputs
+import xyz.block.bittycity.common.idempotency.SerializableError
 import xyz.block.bittycity.outie.models.Inputs
 import xyz.block.bittycity.outie.models.ObservedInMempool
 import xyz.block.bittycity.outie.models.RequirementId
@@ -90,7 +91,11 @@ class IdempotencyHandlerTest : BittyCityTestCase() {
 
     // Second call should return the cached error
     val secondResult = idempotencyHandler.handle(withdrawalToken, backCounter, hurdleResponses)
-    secondResult.shouldBeFailure(CachedError("[java.lang.RuntimeException] Test error"))
+    val expectedError = SerializableError(
+      message = "Test error",
+      type = "java.lang.RuntimeException"
+    )
+    secondResult.shouldBeFailure(CachedError("[java.lang.RuntimeException] Test error", expectedError))
   }
 
   @Test
@@ -515,7 +520,11 @@ class IdempotencyHandlerTest : BittyCityTestCase() {
 
     // Second call should return the cached error
     val secondResult = idempotencyHandler.handleResume(withdrawalToken, resumeResult)
-    secondResult.shouldBeFailure(CachedError("[java.lang.RuntimeException] Test resume error"))
+    val expectedResumeError = SerializableError(
+      message = "Test resume error",
+      type = "java.lang.RuntimeException"
+    )
+    secondResult.shouldBeFailure(CachedError("[java.lang.RuntimeException] Test resume error", expectedResumeError))
   }
 
   @Test