diff --git a/core/artifacts/build.gradle b/core/artifacts/build.gradle
index 29c06aaa..2c9f9705 100644
--- a/core/artifacts/build.gradle
+++ b/core/artifacts/build.gradle
@@ -6,4 +6,5 @@ plugins {
 
 dependencies {
     implementation(project(":core:events"))
+    testImplementation "org.jetbrains.kotlin:kotlin-test:$kotlin_version"
 }
diff --git a/core/artifacts/src/main/kotlin/com/correx/core/artifacts/MaterializingArtifactWriter.kt b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/MaterializingArtifactWriter.kt
new file mode 100644
index 00000000..abc47e20
--- /dev/null
+++ b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/MaterializingArtifactWriter.kt
@@ -0,0 +1,14 @@
+package com.correx.core.artifacts
+
+import com.correx.core.artifacts.kind.FileWrittenArtifact
+import com.correx.core.artifacts.kind.FileWrittenPayload
+import java.nio.file.Path
+
+interface MaterializingArtifactWriter {
+    suspend fun materialize(payload: FileWrittenPayload, sandboxRoot: Path): MaterializationResult
+}
+
+sealed interface MaterializationResult {
+    data class Success(val artifact: FileWrittenArtifact, val resolvedPath: Path) : MaterializationResult
+    data class Failure(val reason: String) : MaterializationResult
+}
diff --git a/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/ArtifactKind.kt b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/ArtifactKind.kt
new file mode 100644
index 00000000..06a5b049
--- /dev/null
+++ b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/ArtifactKind.kt
@@ -0,0 +1,10 @@
+package com.correx.core.artifacts.kind
+
+import kotlinx.serialization.KSerializer
+
+interface ArtifactKind {
+    val id: String
+    val payloadSerializer: KSerializer<*>
+    fun deriveJsonSchema(): JsonSchema
+    val llmEmitted: Boolean
+}
diff --git a/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/ArtifactKindRegistry.kt b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/ArtifactKindRegistry.kt
new file mode 100644
index 00000000..bf07cc20
--- /dev/null
+++ b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/ArtifactKindRegistry.kt
@@ -0,0 +1,21 @@
+package com.correx.core.artifacts.kind
+
+interface ArtifactKindRegistry {
+    fun register(kind: ArtifactKind)
+    fun get(id: String): ArtifactKind?
+}
+
+class DefaultArtifactKindRegistry : ArtifactKindRegistry {
+    private val kinds: MutableMap<String, ArtifactKind> = mutableMapOf()
+
+    init {
+        register(FileWrittenKind)
+        register(ProcessResultKind)
+    }
+
+    override fun register(kind: ArtifactKind) {
+        kinds[kind.id] = kind
+    }
+
+    override fun get(id: String): ArtifactKind? = kinds[id]
+}
diff --git a/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/FileWrittenKind.kt b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/FileWrittenKind.kt
new file mode 100644
index 00000000..451c57cf
--- /dev/null
+++ b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/FileWrittenKind.kt
@@ -0,0 +1,20 @@
+package com.correx.core.artifacts.kind
+
+import kotlinx.serialization.KSerializer
+
+object FileWrittenKind : ArtifactKind {
+    override val id: String = "file_written"
+    override val payloadSerializer: KSerializer<*> = FileWrittenPayload.serializer()
+    override val llmEmitted: Boolean = false
+
+    override fun deriveJsonSchema(): JsonSchema = JsonSchema(
+        type = "object",
+        properties = mapOf(
+            "path" to JsonSchemaProperty(type = "string", description = "Relative file path, no .. components"),
+            "content" to JsonSchemaProperty(type = "string", description = "File content"),
+            "mode" to JsonSchemaProperty(type = "string", description = "Unix file mode", default = "0644"),
+        ),
+        required = listOf("path", "content"),
+        additionalProperties = false,
+    )
+}
diff --git a/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/FileWrittenPayload.kt b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/FileWrittenPayload.kt
new file mode 100644
index 00000000..d0e4e3de
--- /dev/null
+++ b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/FileWrittenPayload.kt
@@ -0,0 +1,18 @@
+package com.correx.core.artifacts.kind
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class FileWrittenPayload(
+    val path: String,
+    val content: String,
+    val mode: String = "0644",
+)
+
+@Serializable
+data class FileWrittenArtifact(
+    val path: String,
+    val contentHash: String,
+    val size: Long,
+    val mode: String,
+)
diff --git a/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/JsonSchema.kt b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/JsonSchema.kt
new file mode 100644
index 00000000..e55bbb58
--- /dev/null
+++ b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/JsonSchema.kt
@@ -0,0 +1,18 @@
+package com.correx.core.artifacts.kind
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class JsonSchema(
+    val type: String,
+    val properties: Map<String, JsonSchemaProperty> = emptyMap(),
+    val required: List<String> = emptyList(),
+    val additionalProperties: Boolean = false,
+)
+
+@Serializable
+data class JsonSchemaProperty(
+    val type: String,
+    val description: String = "",
+    val default: String? = null,
+)
diff --git a/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/ProcessResultArtifact.kt b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/ProcessResultArtifact.kt
new file mode 100644
index 00000000..6239be6c
--- /dev/null
+++ b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/ProcessResultArtifact.kt
@@ -0,0 +1,12 @@
+package com.correx.core.artifacts.kind
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class ProcessResultArtifact(
+    val command: String,
+    val exitCode: Int,
+    val stdout: String,
+    val stderr: String,
+    val durationMs: Long,
+)
diff --git a/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/ProcessResultKind.kt b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/ProcessResultKind.kt
new file mode 100644
index 00000000..1b31a109
--- /dev/null
+++ b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/ProcessResultKind.kt
@@ -0,0 +1,22 @@
+package com.correx.core.artifacts.kind
+
+import kotlinx.serialization.KSerializer
+
+object ProcessResultKind : ArtifactKind {
+    override val id: String = "process_result"
+    override val payloadSerializer: KSerializer<*> = ProcessResultArtifact.serializer()
+    override val llmEmitted: Boolean = false
+
+    override fun deriveJsonSchema(): JsonSchema = JsonSchema(
+        type = "object",
+        properties = mapOf(
+            "command" to JsonSchemaProperty(type = "string"),
+            "exitCode" to JsonSchemaProperty(type = "integer"),
+            "stdout" to JsonSchemaProperty(type = "string"),
+            "stderr" to JsonSchemaProperty(type = "string"),
+            "durationMs" to JsonSchemaProperty(type = "integer"),
+        ),
+        required = listOf("command", "exitCode", "stdout", "stderr", "durationMs"),
+        additionalProperties = false,
+    )
+}
diff --git a/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/TypedArtifactSlot.kt b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/TypedArtifactSlot.kt
new file mode 100644
index 00000000..49e051b7
--- /dev/null
+++ b/core/artifacts/src/main/kotlin/com/correx/core/artifacts/kind/TypedArtifactSlot.kt
@@ -0,0 +1,8 @@
+package com.correx.core.artifacts.kind
+
+import com.correx.core.events.types.ArtifactId
+
+data class TypedArtifactSlot(
+    val name: ArtifactId,
+    val kind: ArtifactKind,
+)
diff --git a/core/artifacts/src/test/kotlin/com/correx/core/artifacts/kind/ArtifactKindRegistryTest.kt b/core/artifacts/src/test/kotlin/com/correx/core/artifacts/kind/ArtifactKindRegistryTest.kt
new file mode 100644
index 00000000..2e57745c
--- /dev/null
+++ b/core/artifacts/src/test/kotlin/com/correx/core/artifacts/kind/ArtifactKindRegistryTest.kt
@@ -0,0 +1,39 @@
+package com.correx.core.artifacts.kind
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNotNull
+import kotlin.test.assertNull
+
+class ArtifactKindRegistryTest {
+    private val registry = DefaultArtifactKindRegistry()
+
+    @Test
+    fun `built-in kinds are registered`() {
+        assertNotNull(registry.get("file_written"))
+        assertNotNull(registry.get("process_result"))
+    }
+
+    @Test
+    fun `get returns null for unknown kind`() {
+        assertNull(registry.get("nonexistent"))
+    }
+
+    @Test
+    fun `FileWrittenKind is not llmEmitted`() {
+        assertEquals(false, registry.get("file_written")!!.llmEmitted)
+    }
+
+    @Test
+    fun `ProcessResultKind is not llmEmitted`() {
+        assertEquals(false, registry.get("process_result")!!.llmEmitted)
+    }
+
+    @Test
+    fun `FileWrittenKind schema has required fields`() {
+        val schema = FileWrittenKind.deriveJsonSchema()
+        assertEquals("object", schema.type)
+        assert("path" in schema.required)
+        assert("content" in schema.required)
+    }
+}