feat(tools): add description and parametersSchema to Tool interface; wire FileWriteTool materialization

core/tools/src/main/kotlin/com/correx/core/tools/contract/Tool.kt

@@ -2,9 +2,12 @@ package com.correx.core.tools.contract
 
 import com.correx.core.approvals.Tier
 import com.correx.core.events.events.ToolRequest
+import kotlinx.serialization.json.JsonObject
 
 interface Tool {
     val name: String
+    val description: String
+    val parametersSchema: JsonObject
     val tier: Tier
     val requiredCapabilities: Set<ToolCapability>
     fun validateRequest(request: ToolRequest): ValidationResult

core/tools/src/test/kotlin/com/correx/core/tools/contract/ToolContractTest.kt

@@ -5,6 +5,8 @@ import com.correx.core.events.events.ToolRequest
 import com.correx.core.events.types.SessionId
 import com.correx.core.events.types.StageId
 import com.correx.core.events.types.ToolInvocationId
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.buildJsonObject
 import org.junit.jupiter.api.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertIs
@@ -13,6 +15,8 @@ class ToolContractTest {
 
     private val stubTool = object : Tool {
         override val name: String = "stub"
+        override val description: String = "Stub tool for testing"
+        override val parametersSchema: JsonObject = buildJsonObject {}
         override val tier: Tier = Tier.T0
         override val requiredCapabilities: Set<ToolCapability> = emptySet()
         override fun validateRequest(request: ToolRequest): ValidationResult = ValidationResult.Valid