feat: wire L3 write path via Embedder into router

Introduces Embedder contract in core:inference with a NoopEmbedder
default (zero vector) and wires both Embedder and L3MemoryStore into
DefaultRouterFacade. Each ChatTurnEvent emission now embeds the turn
content and writes a corresponding L3MemoryEntry, so cross-session
memory is captured at the source of truth (the event emission point).

InfrastructureModule defaults to NoopEmbedder + InMemoryL3MemoryStore
so the system runs without an external embedding model or vector store
wired. The TurboVec adapter stays unwired for now; switching to it is
a configuration concern (Epic 12 config layer).

Also gitignores apps/tui/logs/ (Kotlin TUI runtime logs, pre-Go rewrite).

core/inference/src/main/kotlin/com/correx/core/inference/Embedder.kt

@@ -0,0 +1,20 @@
+package com.correx.core.inference
+
+/**
+ * Interface for computing vector embeddings of text.
+ * Implementations provide pre-computed vectors for similarity search and retrieval.
+ */
+interface Embedder {
+    /**
+     * Dimensionality of the returned embeddings.
+     */
+    val dimension: Int
+
+    /**
+     * Compute a vector embedding for the given text.
+     *
+     * @param text The text to embed.
+     * @return A vector of [dimension] floats.
+     */
+    suspend fun embed(text: String): FloatArray
+}

core/inference/src/main/kotlin/com/correx/core/inference/NoopEmbedder.kt

@@ -0,0 +1,8 @@
+package com.correx.core.inference
+
+/**
+ * Returns a zero vector. Lets the L3 write path run without an embedding model wired.
+ */
+class NoopEmbedder(override val dimension: Int = 1536) : Embedder {
+    override suspend fun embed(text: String): FloatArray = FloatArray(dimension)
+}

core/router/src/main/kotlin/com/correx/core/router/RouterFacade.kt

@@ -10,10 +10,13 @@ import com.correx.core.events.types.EventId
 import com.correx.core.events.types.InferenceRequestId
 import com.correx.core.events.types.SessionId
 import com.correx.core.events.types.StageId
+import com.correx.core.inference.Embedder
 import com.correx.core.inference.InferenceRequest
 import com.correx.core.inference.InferenceRouter
 import com.correx.core.inference.ModelCapability
 import com.correx.core.inference.ResponseFormat
+import com.correx.core.router.l3.L3MemoryEntry
+import com.correx.core.router.l3.L3MemoryStore
 import com.correx.core.router.model.RouterConfig
 import com.correx.core.router.model.RouterResponse
 import kotlinx.datetime.Clock
@@ -34,6 +37,8 @@ class DefaultRouterFacade(
     private val eventStore: EventStore,
     private val config: RouterConfig,
     private val validateSteering: (suspend (String) -> String?)? = null,
+    private val embedder: Embedder,
+    private val l3MemoryStore: L3MemoryStore,
 ) : RouterFacade {
 
     override suspend fun onUserInput(
@@ -96,6 +101,18 @@ class DefaultRouterFacade(
                 ),
             ),
         )
+
+        val vector = embedder.embed(content)
+        l3MemoryStore.store(
+            L3MemoryEntry(
+                id = turnId,
+                sessionId = sessionId,
+                turnId = turnId,
+                text = content,
+                vector = vector,
+                timestampMs = nowMs,
+            )
+        )
     }
 
     private suspend fun emitSteeringNote(sessionId: SessionId, content: String, effectiveStageId: StageId) {