fix(atlas): restrict idle-event session append to boulder-owned subagent sessions only

src/hooks/atlas/boulder-session-lineage.ts

@@ -0,0 +1,44 @@
+import type { PluginInput } from "@opencode-ai/plugin"
+import { log } from "../../shared/logger"
+import { HOOK_NAME } from "./hook-name"
+
+export async function isSessionInBoulderLineage(input: {
+  client: PluginInput["client"]
+  sessionID: string
+  boulderSessionIDs: string[]
+}): Promise<boolean> {
+  const visitedSessionIDs = new Set<string>()
+  let currentSessionID = input.sessionID
+
+  while (!visitedSessionIDs.has(currentSessionID)) {
+    visitedSessionIDs.add(currentSessionID)
+
+    const sessionResult = await input.client.session
+      .get({ path: { id: currentSessionID } })
+      .catch((error: unknown) => {
+        log(`[${HOOK_NAME}] Failed to resolve session lineage`, {
+          sessionID: input.sessionID,
+          currentSessionID,
+          error,
+        })
+        return null
+      })
+
+    if (!sessionResult || sessionResult.error) {
+      return false
+    }
+
+    const parentSessionID = sessionResult.data?.parentID
+    if (!parentSessionID) {
+      return false
+    }
+
+    if (input.boulderSessionIDs.includes(parentSessionID)) {
+      return true
+    }
+
+    currentSessionID = parentSessionID
+  }
+
+  return false
+}