diff --git a/packages/opencode/src/auth/index.ts b/packages/opencode/src/auth/index.ts
index 3fd28305368..3f46add2962 100644
--- a/packages/opencode/src/auth/index.ts
+++ b/packages/opencode/src/auth/index.ts
@@ -2,6 +2,7 @@ import path from "path"
 import { Global } from "../global"
 import fs from "fs/promises"
 import z from "zod"
+import { Lock } from "../util/lock"
 
 export const OAUTH_DUMMY_KEY = "opencode-oauth-dummy-key"
 
@@ -43,31 +44,75 @@ export namespace Auth {
   }
 
   export async function all(): Promise<Record<string, Info>> {
-    const file = Bun.file(filepath)
-    const data = await file.json().catch(() => ({}) as Record<string, unknown>)
-    return Object.entries(data).reduce(
-      (acc, [key, value]) => {
-        const parsed = Info.safeParse(value)
-        if (!parsed.success) return acc
-        acc[key] = parsed.data
-        return acc
-      },
-      {} as Record<string, Info>,
-    )
+    const release = await Lock.read("auth")
+    try {
+      const file = Bun.file(filepath)
+      
+      if (!(await file.exists())) return {}
+      
+      const data = await file.json()
+      
+      if (typeof data !== "object" || data === null) {
+        throw new Error("auth.json contains invalid data")
+      }
+      
+      return Object.entries(data).reduce(
+        (acc, [key, value]) => {
+          const parsed = Info.safeParse(value)
+          if (!parsed.success) return acc
+          acc[key] = parsed.data
+          return acc
+        },
+        {} as Record<string, Info>,
+      )
+    } finally {
+      release[Symbol.dispose]()
+    }
   }
 
   export async function set(key: string, info: Info) {
-    const file = Bun.file(filepath)
-    const data = await all()
-    await Bun.write(file, JSON.stringify({ ...data, [key]: info }, null, 2))
-    await fs.chmod(file.name!, 0o600)
+    const release = await Lock.write("auth")
+    try {
+      const file = Bun.file(filepath)
+      const exists = await file.exists()
+      const rawData = exists ? await file.json() : null
+      const data: Record<string, Info> = {}
+
+      if (typeof rawData === "object" && rawData !== null) {
+        Object.entries(rawData).forEach(([k, v]) => {
+          const parsed = Info.safeParse(v)
+          if (parsed.success) data[k] = parsed.data
+        })
+      }
+
+      data[key] = info
+      await Bun.write(file, JSON.stringify(data, null, 2))
+      await fs.chmod(filepath, 0o600)
+    } finally {
+      release[Symbol.dispose]()
+    }
   }
 
   export async function remove(key: string) {
-    const file = Bun.file(filepath)
-    const data = await all()
-    delete data[key]
-    await Bun.write(file, JSON.stringify(data, null, 2))
-    await fs.chmod(file.name!, 0o600)
+    const release = await Lock.write("auth")
+    try {
+      const file = Bun.file(filepath)
+      const exists = await file.exists()
+      const rawData = exists ? await file.json() : null
+      const data: Record<string, Info> = {}
+
+      if (typeof rawData === "object" && rawData !== null) {
+        Object.entries(rawData).forEach(([k, v]) => {
+          const parsed = Info.safeParse(v)
+          if (parsed.success) data[k] = parsed.data
+        })
+      }
+
+      delete data[key]
+      await Bun.write(file, JSON.stringify(data, null, 2))
+      await fs.chmod(filepath, 0o600)
+    } finally {
+      release[Symbol.dispose]()
+    }
   }
 }
diff --git a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
index 8523f61e548..2dab4a42ad0 100644
--- a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
+++ b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
@@ -1794,6 +1794,20 @@ function Task(props: ToolProps<typeof TaskTool>) {
   const local = useLocal()
   const sync = useSync()
 
+  // Ensure child session data is loaded before accessing it
+  createEffect(async () => {
+    const childSessionId = props.metadata.sessionId
+    if (!childSessionId) return
+    const hasMessages = !!sync.data.message[childSessionId]?.length
+    if (!hasMessages) {
+      try {
+        await sync.session.sync(childSessionId)
+      } catch {
+        // Silently ignore sync errors - activity will just not show
+      }
+    }
+  })
+
   const current = createMemo(() =>
     props.metadata.summary?.findLast(
       (x: { id: string; tool: string; state: { status: string; title?: string } }) => x.state.status !== "pending",