feat(compact): recover context overflow (PR3 phase 2)

packages/compact/compact-basic/src/automatic.ts

@@ -1,12 +1,12 @@
 /**
- * Automatic pre-step pressure listener for compact-basic.
+ * Automatic post-step pressure and context-overflow recovery listeners.
  *
  * @module @deepseek-ai/dsh-compact-basic/automatic
  */
 
 import type { Context } from 'cordis'
-import type { CompactionResult } from '@deepseek-ai/dsh-compact'
-import type { Message } from '@deepseek-ai/dsh-llm'
+import type { CompactionResult, CompactionTrigger } from '@deepseek-ai/dsh-compact'
+import { CONTEXT_WINDOW_EXCEEDED_CODE } from '@deepseek-ai/dsh-llm'
 import {
   TOKEN_METER_MODEL_UNCONFIGURED,
   TokenMeterError,
@@ -14,10 +14,10 @@ import {
 import type { Agent } from '@deepseek-ai/dsh-agent'
 
 interface AutomaticCompactor {
+  readonly config: { readonly maxOverflowRetries: number }
   compactIfNeeded(
     agent: Agent,
-    fullSystemPrompt: string,
-    sessionPrefix: readonly Message[],
+    trigger: CompactionTrigger,
     signal: AbortSignal,
   ): Promise<CompactionResult | null>
 }
@@ -31,30 +31,54 @@ export function registerAutomaticCompaction(
   ctx: Context,
   service: AutomaticCompactor,
 ): void {
-  ctx.on('agent/pre-step', async (
+  const logResult = (result: CompactionResult, trigger: string): void => {
+    ctx.logger.info(
+      `compaction (${trigger}): shadowed ${result.shadowedSeqs.length} surface nodes `
+      + `(seqs ${result.shadowedRange.start}-${result.shadowedRange.end}, `
+      + `~${result.shadowedTokenCount} tokens)`,
+    )
+  }
+
+  ctx.on('agent/post-step', async (
     agent: Agent,
     _turn: number,
     _step: number,
-    fullSystemPrompt: string,
-    sessionPrefix: readonly Message[],
     signal: AbortSignal,
   ) => {
     try {
-      const result = await service.compactIfNeeded(agent, fullSystemPrompt, sessionPrefix, signal)
-      if (result !== null) {
-        ctx.logger.info(
-          `compaction: shadowed ${result.shadowedSeqs.length} surface nodes `
-          + `(seqs ${result.shadowedRange.start}-${result.shadowedRange.end}, `
-          + `~${result.shadowedTokenCount} tokens)`,
-        )
-      }
+      const result = await service.compactIfNeeded(agent, 'pressure', signal)
+      if (result !== null) logResult(result, 'post-step pressure')
     } catch (error: unknown) {
       // A named routed model without a meter profile is configuration failure,
       // not an optional operational compaction miss.
       if (error instanceof TokenMeterError
         && error.code === TOKEN_METER_MODEL_UNCONFIGURED) throw error
       const message = error instanceof Error ? error.message : String(error)
-      ctx.logger.warn(`compaction failed: ${message}; proceeding with full history`)
+      ctx.logger.warn(`post-step compaction failed: ${message}; continuing the turn`)
     }
   })
+
+  ctx.on('agent/request-error', async (agent, _turn, _step, error, retryAttempt, signal, next) => {
+    if (error.code !== CONTEXT_WINDOW_EXCEEDED_CODE
+      || retryAttempt >= service.config.maxOverflowRetries
+      || signal.aborted) return next()
+
+    let generation: number
+    let result: CompactionResult | null
+    try {
+      generation = agent.session.surface.replaceGeneration
+      result = await service.compactIfNeeded(agent, 'context-overflow', signal)
+    } catch (recoveryError: unknown) {
+      const message = recoveryError instanceof Error ? recoveryError.message : String(recoveryError)
+      ctx.logger.warn(
+        `context-overflow compaction failed: ${message}; preserving the original request error`,
+      )
+      return next()
+    }
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition -- signal can abort while compaction is awaited.
+    if (signal.aborted || result === null
+      || agent.session.surface.replaceGeneration <= generation) return next()
+    logResult(result, 'context overflow recovery')
+    return { action: 'retry' }
+  })
 }