diff --git a/build.ts b/build.ts
index 4854fd51c..6cb8e73ec 100644
--- a/build.ts
+++ b/build.ts
@@ -21,7 +21,13 @@ const result = await Bun.build({
   outdir,
   target: 'bun',
   splitting: true,
-  define: getMacroDefines(),
+  define: {
+    ...getMacroDefines(),
+    // React production mode — eliminates _debugStack Error objects
+    // (6,889 objects × ~1.7KB = 12MB in development builds) and removes
+    // prop-type / key warnings not useful in a production CLI tool.
+    'process.env.NODE_ENV': JSON.stringify('production'),
+  },
   features,
 })
 
diff --git a/scripts/dev.ts b/scripts/dev.ts
index 452cf7ea2..72919caa8 100644
--- a/scripts/dev.ts
+++ b/scripts/dev.ts
@@ -14,7 +14,12 @@ const __dirname = dirname(__filename)
 const projectRoot = join(__dirname, '..')
 const cliPath = join(projectRoot, 'src/entrypoints/cli.tsx')
 
-const defines = getMacroDefines()
+const defines = {
+  ...getMacroDefines(),
+  // React production mode — prevents 6,889+ _debugStack Error objects
+  // (12MB) from accumulating during long-running sessions.
+  'process.env.NODE_ENV': JSON.stringify('production'),
+}
 
 const defineArgs = Object.entries(defines).flatMap(([k, v]) => [
   '-d',
diff --git a/src/entrypoints/cli.tsx b/src/entrypoints/cli.tsx
index 7e4da4ed0..efe7e5272 100644
--- a/src/entrypoints/cli.tsx
+++ b/src/entrypoints/cli.tsx
@@ -1,4 +1,8 @@
 #!/usr/bin/env bun
+// Performance shim MUST be the first import — it replaces globalThis.performance
+// with a JS-backed implementation before React/OTel capture the native reference.
+// Without this, JSC's C++ Vector grows without bound in long-running sessions.
+import '../utils/performanceShim.js';
 import { feature } from 'bun:bundle';
 import { isEnvTruthy } from '../utils/envUtils.js';
 
diff --git a/src/query.ts b/src/query.ts
index 767ba998f..cb9c0e1a5 100644
--- a/src/query.ts
+++ b/src/query.ts
@@ -124,6 +124,7 @@ import { count } from './utils/array.js'
 import {
   createTrace,
   endTrace,
+  flushLangfuse,
   isLangfuseEnabled,
 } from './services/langfuse/index.js'
 import { getAPIProvider } from './utils/model/providers.js'
@@ -339,6 +340,11 @@ export async function* query(
         terminal?.reason === 'aborted_streaming' ||
         terminal?.reason === 'aborted_tools'
       endTrace(langfuseTrace, undefined, isAborted ? 'interrupted' : undefined)
+      // Flush the processor to release span data (including serialized
+      // conversation history stored as langfuse.observation.input). Without
+      // this, SpanImpl objects retain hundreds of KB of JSON until the
+      // processor's batch timer fires (default 10s).
+      await flushLangfuse()
     }
 
     // Break the closure chain: toolUseContext captures langfuseTrace which
@@ -349,6 +355,21 @@ export async function* query(
       paramsWithTrace.toolUseContext.langfuseRootTrace = null
       paramsWithTrace.toolUseContext.langfuseBatchSpan = null
     }
+
+    // Clear JSC's native Performance buffers. OTel (otperformance) references
+    // globalThis.performance which stores marks/measures/resource timings in a
+    // C++ Vector that never shrinks. Long-running sessions accumulate hundreds
+    // of MB of dead capacity even after spans are flushed and nullified.
+    const gPerf = globalThis.performance
+    if (gPerf && typeof gPerf.clearMarks === 'function') {
+      try {
+        gPerf.clearMarks()
+        gPerf.clearMeasures?.()
+        gPerf.clearResourceTimings?.()
+      } catch {
+        // Non-critical — some environments may not support all methods
+      }
+    }
   }
 
   // Only reached if queryLoop returned normally. Skipped on throw (error
diff --git a/src/services/langfuse/client.ts b/src/services/langfuse/client.ts
index 256cd8af8..7fd50f2ed 100644
--- a/src/services/langfuse/client.ts
+++ b/src/services/langfuse/client.ts
@@ -61,6 +61,16 @@ export function initLangfuse(): boolean {
   }
 }
 
+export async function flushLangfuse(): Promise<void> {
+  try {
+    if (processor) {
+      await processor.forceFlush()
+    }
+  } catch (e) {
+    logForDebugging(`[langfuse] Flush error: ${e}`, { level: 'error' })
+  }
+}
+
 export async function shutdownLangfuse(): Promise<void> {
   try {
     if (processor) {
diff --git a/src/services/langfuse/index.ts b/src/services/langfuse/index.ts
index b533bec69..d52088a26 100644
--- a/src/services/langfuse/index.ts
+++ b/src/services/langfuse/index.ts
@@ -1,6 +1,7 @@
 export {
   initLangfuse,
   shutdownLangfuse,
+  flushLangfuse,
   isLangfuseEnabled,
   getLangfuseProcessor,
 } from './client.js'
diff --git a/src/utils/performanceShim.ts b/src/utils/performanceShim.ts
new file mode 100644
index 000000000..174518bb6
--- /dev/null
+++ b/src/utils/performanceShim.ts
@@ -0,0 +1,165 @@
+/**
+ * Performance shim — replaces globalThis.performance to prevent JSC's C++ Vector
+ * from growing without bound.
+ *
+ * In Bun, globalThis.performance is JSC's native Performance object. It stores
+ * marks, measures, and resource timings in a C++ Vector that never shrinks even
+ * after clearMarks(). Long-running sessions (daemon, /loop) accumulate hundreds
+ * of MB of dead capacity.
+ *
+ * This shim keeps performance.now() on the native object (fast, no memory cost)
+ * but redirects mark/measure/getEntries operations to a plain JS Map that the GC
+ * can reclaim. Third-party code (React reconciler, OTel/Langfuse) uses
+ * performance.now() for timing — that stays native. The accumulating operations
+ * go to GC-able JS memory instead.
+ *
+ * MUST be installed before React/OTel import — see cli.tsx first import.
+ */
+
+const original = globalThis.performance
+
+// JS-backed storage — fully GC-able
+const marks = new Map<string, number>()
+const measures = new Map<
+  string,
+  { name: string; startTime: number; duration: number }
+>()
+
+function now(): number {
+  return original.now()
+}
+
+function mark(name: string): PerformanceMark {
+  marks.set(name, now())
+  // Return a minimal PerformanceMark-like object to satisfy the interface.
+  // React/OTel only use mark() for side effects, not the return value.
+  return {
+    name,
+    entryType: 'mark',
+    startTime: marks.get(name)!,
+    duration: 0,
+  } as PerformanceMark
+}
+
+function measure(
+  name: string,
+  startMarkOrOptions?: string | MeasureOptions,
+  endMark?: string,
+): void {
+  let startTime: number
+  let duration: number
+
+  if (typeof startMarkOrOptions === 'string') {
+    const start = marks.get(startMarkOrOptions)
+    const end = endMark ? marks.get(endMark) : now()
+    startTime = start ?? now()
+    duration = (end ?? now()) - startTime
+  } else if (startMarkOrOptions && typeof startMarkOrOptions === 'object') {
+    startTime = startMarkOrOptions.start ?? 0
+    duration = (startMarkOrOptions.end ?? now()) - startTime
+  } else {
+    startTime = 0
+    duration = now()
+  }
+
+  measures.set(name, { name, startTime, duration })
+}
+
+interface MeasureOptions {
+  start?: number
+  end?: number
+  detail?: unknown
+}
+
+interface PerformanceEntryLike {
+  readonly name: string
+  readonly entryType: string
+  readonly startTime: number
+  readonly duration: number
+}
+
+function getEntriesByType(type: string): PerformanceEntryLike[] {
+  if (type === 'mark') {
+    return [...marks.entries()].map(([name, startTime]) => ({
+      name,
+      entryType: 'mark',
+      startTime,
+      duration: 0,
+    }))
+  }
+  if (type === 'measure') {
+    return [...measures.values()].map(m => ({
+      name: m.name,
+      entryType: 'measure',
+      startTime: m.startTime,
+      duration: m.duration,
+    }))
+  }
+  return []
+}
+
+function getEntriesByName(name: string, type?: string): PerformanceEntryLike[] {
+  const entries = getEntriesByType(type ?? 'mark').concat(
+    type === undefined ? getEntriesByType('measure') : [],
+  )
+  return entries.filter(e => e.name === name)
+}
+
+function clearMarks(name?: string): void {
+  if (name !== undefined) {
+    marks.delete(name)
+  } else {
+    marks.clear()
+  }
+}
+
+function clearMeasures(name?: string): void {
+  if (name !== undefined) {
+    measures.delete(name)
+  } else {
+    measures.clear()
+  }
+}
+
+// Plain object shim — must NOT inherit from Performance.prototype because
+// native getters (onresourcetimingbufferfull, timeOrigin, toJSON) check
+// that `this` is an actual JSC Performance instance and throw otherwise.
+const shim = {
+  now,
+  mark,
+  measure: measure as typeof performance.measure,
+  getEntriesByType: getEntriesByType as typeof performance.getEntriesByType,
+  getEntriesByName: getEntriesByName as typeof performance.getEntriesByName,
+  clearMarks: clearMarks as typeof performance.clearMarks,
+  clearMeasures: clearMeasures as typeof performance.clearMeasures,
+  clearResourceTimings: (() => {}) as typeof performance.clearResourceTimings,
+  setResourceTimingBufferSize:
+    (() => {}) as typeof performance.setResourceTimingBufferSize,
+  // Delegate read-only properties to the original
+  get timeOrigin() {
+    return original.timeOrigin
+  },
+  get onresourcetimingbufferfull() {
+    return (original as any).onresourcetimingbufferfull
+  },
+  set onresourcetimingbufferfull(_v: any) {
+    // no-op — prevent accumulation
+  },
+  toJSON() {
+    return original.toJSON()
+  },
+} as typeof performance
+
+/**
+ * Install the shim onto globalThis.performance. Safe to call multiple times.
+ * Must run before React and OTel import to prevent them from capturing the
+ * native Performance reference.
+ */
+export function installPerformanceShim(): void {
+  if ((globalThis as any).__performanceShimInstalled) return
+  ;(globalThis as any).__performanceShimInstalled = true
+  globalThis.performance = shim
+}
+
+// Auto-install on import
+installPerformanceShim()
diff --git a/vite.config.ts b/vite.config.ts
index 7a3a1d350..8f52dc0a2 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -116,6 +116,9 @@ export default defineConfig({
   // Compile-time constant replacement (MACRO.* defines)
   define: {
     ...getMacroDefines(),
+    // React production mode — eliminates _debugStack Error objects
+    // (6,889 objects × ~1.7KB = 12MB in development builds)
+    'process.env.NODE_ENV': JSON.stringify('production'),
   },
 
   resolve: {