feat(compact): move pairing helpers (PR1 round 1)

packages/compact/compact-basic/README.md

@@ -9,7 +9,7 @@ This is the implementation tier of the compaction capability — see the [interf
 This backend owns the compaction policy:
 
 - **Estimation** — a configurable characters-per-token heuristic counts the current session prefix supplied to pre-step, derived history, and system prompt, matching the next request rather than stale logged prefix state.
-- **Retention** — compact the oldest whole surface units while preserving a recent tail and balanced tool-call/result cuts. Turn boundaries do not protect old steps inside a runaway turn. An open indivisible tail declines until it closes; a single unit larger than the budget remains out of scope.
+- **Retention** — compact the oldest whole surface units while preserving a recent tail and balanced tool-call/result cuts through the [`dsh-compact` boundary helpers](../compact/README.md#tool-pairing-boundaries). Turn boundaries do not protect old steps inside a runaway turn. An open indivisible tail declines until it closes; a single unit larger than the budget remains out of scope.
 - **Convergence** — retry head-checkpoint compaction up to `compactionRetries`; reject a summary that does not shrink its source, and throw if retries cannot return below threshold.
 - **Summarization** — a direct `llm/stream` call uses the configured model and cap without running the loop-only `agent/request` seam. The input transcript preserves non-text blocks as tagged placeholders; only returned text enters the checkpoint, excluding reasoning and tool calls that would leak private reasoning or create an orphaned call.
 - **Framing** — the replacement user message marks established checkpoint context with `<compacted-summary>` tags. The raw summary remains on the provenance event, and later automatic cycles merge the prior checkpoint.

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

@@ -7,12 +7,11 @@
  */
 
 import { Context } from 'cordis'
-import { CompactService, renderTranscript } from '@deepseek-ai/dsh-compact'
+import { CompactService, renderTranscript, toolPairingBalancedAfter, toolPairingBalancedBefore } from '@deepseek-ai/dsh-compact'
 import type { CompactionResult } from '@deepseek-ai/dsh-compact'
 import { BlockAssembler } from '@deepseek-ai/dsh-llm'
 import type { ContentBlock, FinishReason, GenerateOptions, Message } from '@deepseek-ai/dsh-llm'
 import type { Session, SessionEvent } from '@deepseek-ai/dsh-session'
-import { isToolPairingBalanced } from '@deepseek-ai/dsh-session'
 import type { Agent } from '@deepseek-ai/dsh-agent'
 import type { BasicCompactConfig, ResolvedConfig } from './types.ts'
 import { resolveConfig } from './types.ts'
@@ -348,15 +347,14 @@ export class BasicCompactService extends CompactService {
     }
 
     // Both range edges must preserve assistant tool-call/result pairing.
-    const events = session.events
-    if (!isToolPairingBalanced(nodes, events, start)) {
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const startNode = nodes[startIdx]!
+    if (!toolPairingBalancedBefore(session, startNode)) {
       throw new Error(`compactRegion: start seq ${start} is not a balanced boundary (would split a step's tool-call/result pair)`)
     }
-    // The cut after `end` is named by `end`'s surface successor, or `null` when
-    // `end` is the tail.
     // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-    const afterEnd: number | null = nodes[endIdx]!.next
-    if (!isToolPairingBalanced(nodes, events, afterEnd)) {
+    const endNode = nodes[endIdx]!
+    if (!toolPairingBalancedAfter(session, endNode)) {
       throw new Error(`compactRegion: end seq ${end} is not a balanced boundary (would split a step, or the step is still open)`)
     }
 
@@ -511,7 +509,7 @@ export class BasicCompactService extends CompactService {
     // splitting an assistant↔result pair.
     while (keepFromIdx > 0) {
       // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-      if (isToolPairingBalanced(nodes, events, nodes[keepFromIdx]!.seq)) break
+      if (toolPairingBalancedBefore(session, nodes[keepFromIdx]!)) break
       keepFromIdx -= 1
     }
     if (keepFromIdx === 0) return null

packages/compact/compact-basic/tests/compact-loop-repro.spec.ts

@@ -1,10 +1,10 @@
 import { describe, expect, it } from 'vitest'
 import { Context } from 'cordis'
+import { toolPairingBalancedAfter, toolPairingBalancedBefore } from '@deepseek-ai/dsh-compact'
 import LlmService from '@deepseek-ai/dsh-llm'
 import type { ContentBlock, GenerateOptions, StreamChunk } from '@deepseek-ai/dsh-llm'
 import { CallId, LlmAdapter } from '@deepseek-ai/dsh-llm'
 import SessionStore from '@deepseek-ai/dsh-session'
-import { isToolPairingBalanced } from '@deepseek-ai/dsh-session'
 import SystemPrompt from '@deepseek-ai/dsh-system-prompt'
 import ToolRegistry, { defineTool } from '@deepseek-ai/dsh-tools'
 import AgentRegistry, { AgentId } from '@deepseek-ai/dsh-agent'
@@ -124,9 +124,9 @@ describe('CBR-001: a real-loop checkpoint is a valid boundary on both sides', ()
       for (const cp of checkpoints) {
         const node = nodes.find(n => n.seq === cp.seq)
         if (!node) continue // shadowed by a later checkpoint — no longer an edge.
-        expect(isToolPairingBalanced(nodes, events, node.seq),
+        expect(toolPairingBalancedBefore(agent.session, node),
           `checkpoint seq ${node.seq} must be a balanced region START`).toBe(true)
-        expect(isToolPairingBalanced(nodes, events, node.next),
+        expect(toolPairingBalancedAfter(agent.session, node),
           `checkpoint seq ${node.seq} must be a balanced region END`).toBe(true)
       }
     } finally {