fix(core): atomic metadata writes, restoredAt persistence, and session count/sorting bugs

- BUG-28: Use atomic write-then-rename for metadata files to prevent
  race condition data loss between concurrent TS and bash writers
- BUG-29: Read and write restoredAt field in metadata so it persists
  across server restarts
- BUG-12: Count all non-exited sessions (idle, ready, active) as
  "working" instead of only active ones
- BUG-13: Check status-based error conditions (errored, needs_input,
  stuck) before activity-based checks in getAttentionLevel() so errored
  sessions immediately appear in the Respond Kanban zone

Closes #238

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/core/src/metadata.ts

@@ -22,6 +22,7 @@
 import {
   readFileSync,
   writeFileSync,
+  renameSync,
   existsSync,
   mkdirSync,
   unlinkSync,
@@ -63,6 +64,16 @@ function serializeMetadata(data: Record<string, string>): string {
   );
 }
 
+/**
+ * Atomically write a file by writing to a temp file then renaming.
+ * rename() is atomic on POSIX, so concurrent writers never produce torn data.
+ */
+function atomicWriteFileSync(filePath: string, content: string): void {
+  const tmpPath = `${filePath}.tmp.${process.pid}.${Date.now()}`;
+  writeFileSync(tmpPath, content, "utf-8");
+  renameSync(tmpPath, filePath);
+}
+
 /** Validate sessionId to prevent path traversal. */
 const VALID_SESSION_ID = /^[a-zA-Z0-9_-]+$/;
 
@@ -100,6 +111,7 @@ export function readMetadata(dataDir: string, sessionId: SessionId): SessionMeta
     agent: raw["agent"],
     createdAt: raw["createdAt"],
     runtimeHandle: raw["runtimeHandle"],
+    restoredAt: raw["restoredAt"],
     role: raw["role"],
     dashboardPort: raw["dashboardPort"] ? Number(raw["dashboardPort"]) : undefined,
     terminalWsPort: raw["terminalWsPort"] ? Number(raw["terminalWsPort"]) : undefined,
@@ -144,6 +156,7 @@ export function writeMetadata(
   if (metadata.agent) data["agent"] = metadata.agent;
   if (metadata.createdAt) data["createdAt"] = metadata.createdAt;
   if (metadata.runtimeHandle) data["runtimeHandle"] = metadata.runtimeHandle;
+  if (metadata.restoredAt) data["restoredAt"] = metadata.restoredAt;
   if (metadata.role) data["role"] = metadata.role;
   if (metadata.dashboardPort !== undefined)
     data["dashboardPort"] = String(metadata.dashboardPort);
@@ -152,7 +165,7 @@ export function writeMetadata(
   if (metadata.directTerminalWsPort !== undefined)
     data["directTerminalWsPort"] = String(metadata.directTerminalWsPort);
 
-  writeFileSync(path, serializeMetadata(data), "utf-8");
+  atomicWriteFileSync(path, serializeMetadata(data));
 }
 
 /**
@@ -183,7 +196,7 @@ export function updateMetadata(
   }
 
   mkdirSync(dirname(path), { recursive: true });
-  writeFileSync(path, serializeMetadata(existing), "utf-8");
+  atomicWriteFileSync(path, serializeMetadata(existing));
 }
 
 /**

packages/web/src/lib/serialize.ts

@@ -380,7 +380,7 @@ export async function enrichSessionsMetadata(
 export function computeStats(sessions: DashboardSession[]): DashboardStats {
   return {
     totalSessions: sessions.length,
-    workingSessions: sessions.filter((s) => s.activity === "active").length,
+    workingSessions: sessions.filter((s) => s.activity !== null && s.activity !== "exited").length,
     openPRs: sessions.filter((s) => s.pr?.state === "open").length,
     needsReview: sessions.filter((s) => s.pr && !s.pr.isDraft && s.pr.reviewDecision === "pending")
       .length,

packages/web/src/lib/types.ts

@@ -187,16 +187,18 @@ export function getAttentionLevel(session: DashboardSession): AttentionLevel {
   }
 
   // ── Respond: agent is waiting for human input ─────────────────────
+  // Check status-based error conditions first — these are authoritative
+  // and should not be masked by a stale activity value.
   if (
-    session.activity === ACTIVITY_STATE.WAITING_INPUT ||
-    session.activity === ACTIVITY_STATE.BLOCKED
+    session.status === SESSION_STATUS.ERRORED ||
+    session.status === SESSION_STATUS.NEEDS_INPUT ||
+    session.status === SESSION_STATUS.STUCK
   ) {
     return "respond";
   }
   if (
-    session.status === SESSION_STATUS.NEEDS_INPUT ||
-    session.status === SESSION_STATUS.STUCK ||
-    session.status === SESSION_STATUS.ERRORED
+    session.activity === ACTIVITY_STATE.WAITING_INPUT ||
+    session.activity === ACTIVITY_STATE.BLOCKED
   ) {
     return "respond";
   }