feat: workflow exit codes & kill mechanism

- Add exit_code to workflow_runs (0=success, 1=role error, 2=maxRounds, 137=killed, 255=crash)
- Expand status enum: started/completed/failed/killed
- Add kill-thread IPC message for graceful workflow termination
- Add 'nerve workflow kill <runId>' CLI command
- Show exit_code in 'nerve workflow list' output

Fixes #121

packages/core/src/daemon-ipc-protocol.ts

@@ -27,11 +27,18 @@ export type DaemonIpcListSensesRequest = {
   type: "list-senses";
 };
 
+/** Client → daemon: kill a running or queued workflow thread by runId. */
+export type DaemonIpcKillWorkflowRequest = {
+  type: "kill-workflow";
+  runId: string;
+};
+
 /** Union of all JSON requests the daemon IPC server accepts. */
 export type DaemonIpcRequest =
   | DaemonIpcTriggerWorkflowRequest
   | DaemonIpcTriggerSenseRequest
-  | DaemonIpcListSensesRequest;
+  | DaemonIpcListSensesRequest
+  | DaemonIpcKillWorkflowRequest;
 
 /** Successful trigger / trigger-sense reply (no body). */
 export type DaemonIpcTriggerOkResponse = { ok: true };
@@ -87,6 +94,10 @@ export function parseDaemonIpcRequest(line: string): DaemonIpcRequest | null {
     if (req.type === "list-senses") {
       return { type: "list-senses" };
     }
+    if (req.type === "kill-workflow") {
+      if (typeof req.runId !== "string" || req.runId.length === 0) return null;
+      return { type: "kill-workflow", runId: req.runId };
+    }
     return null;
   } catch {
     return null;

packages/core/src/index.ts

@@ -38,6 +38,7 @@ export type {
   DaemonIpcTriggerWorkflowRequest,
   DaemonIpcTriggerSenseRequest,
   DaemonIpcListSensesRequest,
+  DaemonIpcKillWorkflowRequest,
   DaemonIpcRequest,
   DaemonIpcTriggerOkResponse,
   DaemonIpcErrorResponse,