feat(server): REST /clarify route for headless clarification answers (#42)

Discovery-stage clarifications could only be answered over WebSocket
(ClientMessage.ClarificationResponse), so the curl-based headless QA
driver parked forever at discovery.

Add POST /sessions/{id}/clarify mirroring approveStageRoute. The server
resolves the live (stageId, requestId) from the session id via
SessionOrchestrator.pendingClarificationFor() — the newest still-live,
unanswered ClarificationRequestedEvent from the event log — so a curl
caller need not know the requestId. Empty answers = free-text skip.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/server/src/main/kotlin/com/correx/apps/server/routes/ClarifyStageRoute.kt

@@ -0,0 +1,38 @@
+package com.correx.apps.server.routes
+
+import com.correx.apps.server.ServerModule
+import com.correx.core.events.events.ClarificationAnswer
+import com.correx.core.events.types.SessionId
+import com.correx.core.utils.TypeId
+import io.ktor.http.HttpStatusCode
+import io.ktor.server.request.receive
+import io.ktor.server.response.respond
+import io.ktor.server.routing.Route
+import io.ktor.server.routing.post
+import kotlinx.serialization.Serializable
+
+// REST parity for stage clarifications (WS already has ClientMessage.ClarificationResponse). Keyed by
+// session — the server resolves the live pending (stageId, requestId) so a headless run (a script,
+// `correx run`) can clear a discovery-stage clarification without a WebSocket. If the caller omits the
+// answer for a question, its value is the empty string (free-text skip). Fixes Vikunja #42.
+@Serializable
+data class ClarifyStageRequest(val answers: List<ClarificationAnswer>)
+
+internal fun Route.clarifyStageRoute(module: ServerModule) {
+    post("/clarify") {
+        val id = call.parameters["id"]
+        if (id == null) {
+            call.respond(HttpStatusCode.BadRequest, "Missing session id")
+            return@post
+        }
+        val sessionId: SessionId = TypeId(id)
+        val pending = module.orchestrator.pendingClarificationFor(sessionId)
+        if (pending == null) {
+            call.respond(HttpStatusCode.NotFound, "No pending clarification for session $id")
+            return@post
+        }
+        val answers = call.receive<ClarifyStageRequest>().answers
+        module.orchestrator.submitClarification(sessionId, pending.stageId, pending.requestId, answers)
+        call.respond(HttpStatusCode.OK)
+    }
+}

apps/server/src/main/kotlin/com/correx/apps/server/routes/SessionRoutes.kt

@@ -100,6 +100,7 @@ fun Route.sessionRoutes(module: ServerModule) {
             getSessionRoute(module)
             cancelSessionRoute(module)
             approveStageRoute(module)
+            clarifyStageRoute(module)
             approveSourcesRoute(module)
             undoSessionRoute(module)
             resumeSessionRoute(module)