Apply predictive compact memory optimizations

src/query.ts

@@ -7,6 +7,9 @@ import type { CanUseToolFn } from './hooks/useCanUseTool.js'
 import { FallbackTriggeredError } from './services/api/withRetry.js'
 import {
   calculateTokenWarningState,
+  estimateMaxTurnGrowth,
+  getAutoCompactThreshold,
+  getEffectiveContextWindowSize,
   isAutoCompactEnabled,
   type AutoCompactTrackingState,
 } from './services/compact/autoCompact.js'
@@ -434,7 +437,7 @@ async function* queryLoop(
       queryTracking,
     }
 
-    let messagesForQuery = [...getMessagesAfterCompactBoundary(messages)]
+    let messagesForQuery = getMessagesAfterCompactBoundary(messages)
 
     let tracking = autoCompactTracking
 
@@ -719,6 +722,48 @@ async function* queryLoop(
       }
     }
 
+    // Predictive autocompact: estimate if this turn's growth will push
+    // us past the context window. Uses effectiveContextWindow directly
+    // (without the autocompact buffer) to avoid double-reserving with
+    // getAutoCompactThreshold which already subtracts buffer.
+    if (!compactionResult && isAutoCompactEnabled()) {
+      const model = toolUseContext.options.mainLoopModel
+      const currentTokens =
+        tokenCountWithEstimation(messagesForQuery) - snipTokensFreed
+      const estimatedGrowth = estimateMaxTurnGrowth(model)
+      const predictiveThreshold =
+        getEffectiveContextWindowSize(model) - estimatedGrowth
+      if (currentTokens > predictiveThreshold) {
+        const predictiveResult = await deps.autocompact(
+          messagesForQuery,
+          toolUseContext,
+          {
+            systemPrompt,
+            userContext,
+            systemContext,
+            toolUseContext,
+            forkContextMessages: messagesForQuery,
+          },
+          querySource,
+          tracking,
+          snipTokensFreed,
+        )
+        if (predictiveResult.compactionResult) {
+          messagesForQuery = buildPostCompactMessages(
+            predictiveResult.compactionResult,
+          )
+          snipTokensFreed = 0
+          tracking = tracking
+            ? {
+                ...tracking,
+                compacted: true,
+                consecutiveFailures: predictiveResult.consecutiveFailures ?? 0,
+              }
+            : tracking
+        }
+      }
+    }
+
     let attemptWithFallback = true
 
     queryCheckpoint('query_api_loop_start')
@@ -1075,7 +1120,7 @@ async function* queryLoop(
     // Execute post-sampling hooks after model response is complete
     if (assistantMessages.length > 0) {
       void executePostSamplingHooks(
-        [...messagesForQuery, ...assistantMessages],
+        messagesForQuery.concat(assistantMessages),
         systemPrompt,
         userContext,
         systemContext,
@@ -1768,11 +1813,10 @@ async function* queryLoop(
           userContext,
           systemContext,
           toolUseContext,
-          forkContextMessages: [
-            ...messagesForQuery,
-            ...assistantMessages,
-            ...toolResults,
-          ],
+          forkContextMessages: messagesForQuery.concat(
+            assistantMessages,
+            toolResults,
+          ),
         })
       }
     }
@@ -1789,7 +1833,7 @@ async function* queryLoop(
 
     queryCheckpoint('query_recursive_call')
     const next: State = {
-      messages: [...messagesForQuery, ...assistantMessages, ...toolResults],
+      messages: messagesForQuery.concat(assistantMessages, toolResults),
       toolUseContext: toolUseContextWithQueryTracking,
       autoCompactTracking: tracking,
       turnCount: nextTurnCount,

src/screens/REPL.tsx

@@ -1553,7 +1553,15 @@ export function REPL({
   // Deferred messages for the Messages component — renders at transition
   // priority so the reconciler yields every 5ms, keeping input responsive
   // while the expensive message processing pipeline runs.
-  const deferredMessages = useDeferredValue(messages);
+  // Cap at 500 messages to limit memory double-buffering. The bypass
+  // at display-time uses sync messages during streaming and non-loading,
+  // so this cap only affects reduced-motion scenarios.
+  const DEFERRED_CAP = 500;
+  const cappedMessages = React.useMemo(
+    () => (messages.length > DEFERRED_CAP ? messages.slice(-DEFERRED_CAP) : messages),
+    [messages],
+  );
+  const deferredMessages = useDeferredValue(cappedMessages);
   const deferredBehind = messages.length - deferredMessages.length;
   if (deferredBehind > 0) {
     logForDebugging(

src/services/compact/autoCompact.ts

@@ -64,6 +64,35 @@ export const WARNING_THRESHOLD_BUFFER_TOKENS = 20_000
 export const ERROR_THRESHOLD_BUFFER_TOKENS = 20_000
 export const MANUAL_COMPACT_BUFFER_TOKENS = 3_000
 
+// Conservative estimate for tool result growth per turn.
+// Typical tool results (file reads, grep, bash) average ~5-10K tokens;
+// occasional large reads can spike to 20K+.
+const TOOL_RESULT_GROWTH_ESTIMATE = 15_000
+
+/**
+ * Context-aware autocompact buffer. Larger context windows need more
+ * headroom because a single turn can produce proportionally more tokens
+ * (longer model outputs + larger tool results).
+ */
+export function getAutocompactBufferTokens(model: string): number {
+  const effectiveWindow = getEffectiveContextWindowSize(model)
+  if (effectiveWindow >= 800_000) return 50_000
+  if (effectiveWindow >= 400_000) return 30_000
+  return AUTOCOMPACT_BUFFER_TOKENS
+}
+
+/**
+ * Estimate the maximum token growth a single turn can produce.
+ * Used for predictive autocompact checks before the API call.
+ */
+export function estimateMaxTurnGrowth(model: string): number {
+  const maxOutput = Math.min(
+    getMaxOutputTokensForModel(model),
+    MAX_OUTPUT_TOKENS_FOR_SUMMARY,
+  )
+  return maxOutput + TOOL_RESULT_GROWTH_ESTIMATE
+}
+
 // Stop trying autocompact after this many consecutive failures.
 // BQ 2026-03-10: 1,279 sessions had 50+ consecutive failures (up to 3,272)
 // in a single session, wasting ~250K API calls/day globally.
@@ -73,7 +102,7 @@ export function getAutoCompactThreshold(model: string): number {
   const effectiveContextWindow = getEffectiveContextWindowSize(model)
 
   const autocompactThreshold =
-    effectiveContextWindow - AUTOCOMPACT_BUFFER_TOKENS
+    effectiveContextWindow - getAutocompactBufferTokens(model)
 
   // Override for easier testing of autocompact
   const envPercent = process.env.CLAUDE_AUTOCOMPACT_PCT_OVERRIDE

src/services/compact/compact.ts

@@ -332,13 +332,12 @@ export type RecompactionInfo = {
  * Order: boundaryMarker, summaryMessages, messagesToKeep, attachments, hookResults
  */
 export function buildPostCompactMessages(result: CompactionResult): Message[] {
-  return [
-    result.boundaryMarker,
-    ...result.summaryMessages,
-    ...(result.messagesToKeep ?? []),
-    ...result.attachments,
-    ...result.hookResults,
-  ]
+  return ([result.boundaryMarker] as Message[]).concat(
+    result.summaryMessages,
+    result.messagesToKeep ?? [],
+    result.attachments,
+    result.hookResults,
+  )
 }
 
 /**

src/services/compact/reactiveCompact.ts

@@ -1,22 +1,97 @@
-// Auto-generated stub — replace with real implementation
-export {};
+import { isEnvTruthy } from '../../utils/envUtils.js'
+import {
+  isMediaSizeErrorMessage,
+  isPromptTooLongMessage,
+} from '../api/errors.js'
+import type { AssistantMessage, Message } from '../../types/message.js'
+import { type CompactionResult, compactConversation } from './compact.js'
+import { logError } from '../../utils/log.js'
+import { logForDebugging } from '../../utils/debug.js'
+import type { CacheSafeParams } from '../../utils/forkedAgent.js'
 
-import type { Message } from 'src/types/message';
-import type { CompactionResult } from './compact.js';
+export const isReactiveOnlyMode: () => boolean = () => false
 
-export const isReactiveOnlyMode: () => boolean = () => false;
 export const reactiveCompactOnPromptTooLong: (
   messages: Message[],
   cacheSafeParams: Record<string, unknown>,
   options: { customInstructions?: string; trigger?: string },
-) => Promise<{ ok: boolean; reason?: string; result?: CompactionResult }> = async () => ({ ok: false });
-export const isReactiveCompactEnabled: () => boolean = () => false;
-export const isWithheldPromptTooLong: (message: Message) => boolean = () => false;
-export const isWithheldMediaSizeError: (message: Message) => boolean = () => false;
+) => Promise<{ ok: boolean; reason?: string; result?: CompactionResult }> =
+  async (messages, cacheSafeParams, options) => {
+    const params = cacheSafeParams as unknown as CacheSafeParams
+    try {
+      const result = await compactConversation(
+        messages,
+        params.toolUseContext,
+        params,
+        true,
+        options.customInstructions,
+        true,
+        {
+          isRecompactionInChain: false,
+          turnsSincePreviousCompact: 0,
+          autoCompactThreshold: 0,
+          querySource: 'compact',
+        },
+      )
+      return { ok: true, result }
+    } catch (error) {
+      logError(error)
+      return { ok: false, reason: String(error) }
+    }
+  }
+
+export const isReactiveCompactEnabled: () => boolean = () => {
+  if (isEnvTruthy(process.env.DISABLE_COMPACT)) return false
+  return true
+}
+
+export const isWithheldPromptTooLong: (message: Message) => boolean =
+  message => {
+    if (message.type !== 'assistant' || !message.isApiErrorMessage) return false
+    return isPromptTooLongMessage(message as AssistantMessage)
+  }
+
+export const isWithheldMediaSizeError: (message: Message) => boolean =
+  message => {
+    if (message.type !== 'assistant' || !message.isApiErrorMessage) return false
+    return isMediaSizeErrorMessage(message as AssistantMessage)
+  }
+
 export const tryReactiveCompact: (params: {
-  hasAttempted: boolean;
-  querySource: string;
-  aborted: boolean;
-  messages: Message[];
-  cacheSafeParams: Record<string, unknown>;
-}) => Promise<CompactionResult | null> = async () => null;
+  hasAttempted: boolean
+  querySource: string
+  aborted: boolean
+  messages: Message[]
+  cacheSafeParams: Record<string, unknown>
+}) => Promise<CompactionResult | null> = async ({
+  hasAttempted,
+  aborted,
+  messages,
+  cacheSafeParams,
+}) => {
+  if (hasAttempted || aborted) return null
+  const params = cacheSafeParams as unknown as CacheSafeParams
+  try {
+    const result = await compactConversation(
+      messages,
+      params.toolUseContext,
+      params,
+      true,
+      undefined,
+      true,
+      {
+        isRecompactionInChain: false,
+        turnsSincePreviousCompact: 0,
+        autoCompactThreshold: 0,
+      },
+    )
+    return result
+  } catch (error) {
+    logForDebugging(
+      `reactiveCompact: emergency compaction failed — ${String(error)}`,
+      { level: 'warn' },
+    )
+    logError(error)
+    return null
+  }
+}

src/utils/readFileInRange.ts

@@ -101,6 +101,20 @@ export async function readFileInRange(
       throw new FileTooLargeError(stats.size, maxBytes)
     }
 
+    // For targeted reads of moderately large files, prefer streaming to
+    // avoid loading the full file into memory when only a slice is needed.
+    const isTargetedRead = offset > 0 || maxLines !== undefined
+    if (isTargetedRead && stats.size > FAST_PATH_MAX_SIZE / 4) {
+      return readFileInRangeStreaming(
+        filePath,
+        offset,
+        maxLines,
+        maxBytes,
+        truncateOnByteLimit,
+        signal,
+      )
+    }
+
     const text = await readFile(filePath, { encoding: 'utf8', signal })
     return readFileInRangeFast(
       text,