diff --git a/scripts/defines.ts b/scripts/defines.ts
index 3249e6809..fa7a7b8d8 100644
--- a/scripts/defines.ts
+++ b/scripts/defines.ts
@@ -59,7 +59,7 @@ export const DEFAULT_BUILD_FEATURES = [
   'DAEMON', // 守护进程模式，长驻 supervisor 管理后台 worker（非 GB 级主因）
   'ACP', // ACP 代理协议，支持外部 agent 接入
   'WORKFLOW_SCRIPTS', // 工作流脚本（.claude/workflows/ 中的 YAML/MD）
-  // 'HISTORY_SNIP', // 历史消息裁剪，压缩上下文窗口
+  'HISTORY_SNIP', // 历史消息裁剪，压缩上下文窗口
   // 'CONTEXT_COLLAPSE', // 已禁用：实现是空壳 stub，启用后会抑制 auto compact 导致上下文管理完全失效
   'MONITOR_TOOL', // Monitor 工具，流式监控后台进程输出
   // 'FORK_SUBAGENT',            // 已禁用：显式 `fork: true` 参数触发 fork 路径（继承父级上下文和模型），不影响 forceAsync 和探索任务模型选择
diff --git a/src/QueryEngine.ts b/src/QueryEngine.ts
index 8ffa5e9d0..8e48ed757 100644
--- a/src/QueryEngine.ts
+++ b/src/QueryEngine.ts
@@ -1003,15 +1003,6 @@ export class QueryEngine {
               uuid: msg.uuid,
             }
           }
-          // Proactive truncation: prevent unbounded growth when API doesn't
-          // return compact_boundary (e.g. third-party compat layers).
-          if (feature('HISTORY_SNIP') && snipModule) {
-            const truncated = snipModule.proactiveTruncate(this.mutableMessages)
-            if (truncated !== this.mutableMessages) {
-              this.mutableMessages.length = 0
-              this.mutableMessages.push(...truncated)
-            }
-          }
           // Don't yield other system messages in headless mode
           break
         }
diff --git a/src/services/compact/snipCompact.ts b/src/services/compact/snipCompact.ts
index 3be2ef624..4e4a0d9fc 100644
--- a/src/services/compact/snipCompact.ts
+++ b/src/services/compact/snipCompact.ts
@@ -163,77 +163,3 @@ export function isSnipRuntimeEnabled(): boolean {
 export function shouldNudgeForSnips(messages: Message[]): boolean {
   return messages.length >= SNIP_NUDGE_THRESHOLD
 }
-
-/**
- * Maximum total character length of message content before proactive
- * truncation kicks in. ~150 MB of string data corresponds to roughly
- * 1.5x the default 200k-token context window at 4 chars/token — well
- * beyond what any model can actually use in a single request.
- */
-const PROACTIVE_TRUNCATE_CHARS = 150_000_000
-
-/**
- * Minimum number of messages to keep when falling back to tail-only
- * retention (i.e. when no compact_boundary exists in the array).
- */
-const PROACTIVE_TRUNCATE_MIN_TAIL = 50
-
-/**
- * Proactively truncate old messages when the in-memory store grows too
- * large. Unlike `snipCompactIfNeeded` (which waits for a snip_boundary
- * from the API), this runs client-side after every push — ensuring
- * unbounded growth cannot happen even when the API never returns a
- * compact_boundary (e.g. third-party compat layers).
- *
- * Strategy:
- * 1. If a `compact_boundary` exists, keep it and everything after it.
- * 2. Otherwise, keep only the last `PROACTIVE_TRUNCATE_MIN_TAIL` messages.
- *
- * Returns the same array reference when no truncation is needed.
- */
-export function proactiveTruncate(messages: Message[]): Message[] {
-  if (messages.length < PROACTIVE_TRUNCATE_MIN_TAIL) return messages
-
-  let totalChars = 0
-  for (const msg of messages) {
-    const content = msg.message?.content
-    if (typeof content === 'string') {
-      totalChars += content.length
-    } else if (Array.isArray(content)) {
-      for (const block of content) {
-        if (typeof block === 'string') {
-          totalChars += (block as string).length
-        } else if (block && typeof block === 'object') {
-          const obj = block as unknown as Record<string, unknown>
-          const text = obj.text ?? obj.content
-          if (typeof text === 'string') {
-            totalChars += text.length
-          }
-        }
-      }
-    }
-  }
-
-  if (totalChars < PROACTIVE_TRUNCATE_CHARS) return messages
-
-  // Find last compact_boundary — the standard anchor point
-  let boundaryIdx = -1
-  for (let i = messages.length - 1; i >= 0; i--) {
-    const msg = messages[i]!
-    if (
-      msg.type === 'system' &&
-      (msg as Record<string, unknown>).subtype === 'compact_boundary'
-    ) {
-      boundaryIdx = i
-      break
-    }
-  }
-
-  const keepFrom =
-    boundaryIdx >= 0
-      ? boundaryIdx
-      : Math.max(0, messages.length - PROACTIVE_TRUNCATE_MIN_TAIL)
-  if (keepFrom === 0) return messages
-
-  return messages.slice(keepFrom)
-}
diff --git a/src/utils/telemetry/instrumentation.ts b/src/utils/telemetry/instrumentation.ts
index d5bcf7ffb..fffe84def 100644
--- a/src/utils/telemetry/instrumentation.ts
+++ b/src/utils/telemetry/instrumentation.ts
@@ -206,49 +206,10 @@ async function getOtlpReaders() {
 
   return exporters.map(exporter => {
     if ('export' in exporter) {
-      const reader = new PeriodicExportingMetricReader({
+      return new PeriodicExportingMetricReader({
         exporter,
         exportIntervalMillis: exportInterval,
       })
-      // Wrap the export callback to auto-shutdown the reader on auth
-      // failures (401/403). Without this the PeriodicExportingMetricReader's
-      // internal setInterval keeps retrying forever, leaking handles.
-      const originalExport = (
-        exporter as unknown as {
-          export: (
-            metrics: unknown,
-            callback: (result: { error?: Error }) => void,
-          ) => unknown
-        }
-      ).export.bind(exporter)
-      ;(
-        exporter as unknown as {
-          export: (
-            metrics: unknown,
-            callback: (result: { error?: Error }) => void,
-          ) => unknown
-        }
-      ).export = (metrics, callback) => {
-        return originalExport(metrics, result => {
-          if (result.error) {
-            const msg = result.error.message || ''
-            if (
-              msg.includes('401') ||
-              msg.includes('403') ||
-              msg.includes('Unauthorized') ||
-              msg.includes('authentication')
-            ) {
-              logForDebugging(
-                `[3P telemetry] Auth error detected, shutting down metric reader`,
-                { level: 'error' },
-              )
-              void reader.shutdown()
-            }
-          }
-          callback(result)
-        })
-      }
-      return reader
     }
     return exporter
   })