refactor(agent-core-v2): carry the context fold cursor in state and converge fold/projection internals

packages/agent-core-v2/AGENTS.md

@@ -84,7 +84,7 @@ Business code must not `import 'node:fs'`, write SQL, hand-roll append-logs / at
 
 ## Conversation undo
 
-`context.undo` is the only persisted undo fact. `contextMemory/conversationTime.ts` owns the conversation clock (`isUndoAnchor` — the single tick predicate used by `computeUndoCut`, the checkpoint reducers, and the transcript reducer) and the checkpoint protocol. A wire Model whose state must follow conversation undo (todo, plan, task-notification delivery, …) **MUST** be defined with `defineCheckpointedModel` — never hand-roll the push/clear/restore reducers — which also registers it into `CHECKPOINTED_MODELS` for the undo pipeline's pre-cut depth check. World-time state (turn counters, task registries, revision counters) must stay outside checkpointed Models.
+`context.undo` is the only persisted undo fact. `contextMemory/conversationTime.ts` owns the conversation clock (`isUndoAnchor` — the single tick predicate — plus `computeUndoCut` / `computeUndoCutFrom`, the single anchor-walk decision: applied destructively by the `context.undo` Op and non-destructively by the transcript reducer, so a blocked undo reads identically on both sides) and the checkpoint protocol. A wire Model whose state must follow conversation undo (todo, plan, task-notification delivery, …) **MUST** be defined with `defineCheckpointedModel` — never hand-roll the push/clear/restore reducers — which also registers it into `CHECKPOINTED_MODELS` for the undo pipeline's pre-cut depth check. World-time state (turn counters, task registries, revision counters) must stay outside checkpointed Models.
 
 ## Docs
 

packages/agent-core-v2/docs/wire-manifest.d.ts

@@ -339,7 +339,7 @@ interface LlmRequestPayload {
   messageCount: number;
   turnStep?: string;
   attempt?: string;
-  projection?: 'strict' | 'media-degraded' | 'media-stripped';
+  projection?: 'strict' | 'media-degraded' | 'media-stripped' | 'strict-media-degraded' | 'strict-media-stripped';
   droppedCount?: number;
 }
 

packages/agent-core-v2/src/agent/contextMemory/compactionHandoff.ts

@@ -9,6 +9,13 @@
  * wire-replay / reducer paths keep the same heuristics — their estimate
  * fallback only fires when a record lacks `tokensAfter`, so the measured
  * chain is unaffected.
+ *
+ * The result layout is `[kept user messages…, elision?, summary]` (legacy
+ * records: `[summary, …tail]`), so its message COUNT is fully described by
+ * the persisted kept-user counts: `compactionResultMessageCount` is the
+ * read-side mirror for projections that need only the length (the display
+ * transcript's `foldedLength`). Both live in this file so a layout change
+ * lands in one place.
  */
 
 import { estimateTokens, estimateTokensForMessage, estimateTokensForMessages } from '#/kosong/contract/tokens';
@@ -138,6 +145,14 @@ export function buildContextCompactionShape(
   };
 }
 
+export function compactionResultMessageCount(
+  keptUserMessageCount: number | undefined,
+  keptHeadUserMessageCount: number | undefined,
+): number | undefined {
+  if (keptUserMessageCount === undefined) return undefined;
+  return keptUserMessageCount + (keptHeadUserMessageCount === undefined ? 1 : 2);
+}
+
 export function buildCompactionSummaryText(summary: string): string {
   const suffix = summary.trim();
   return `${COMPACTION_SUMMARY_PREFIX}\n${suffix.length > 0 ? suffix : '(no summary available)'}`;

packages/agent-core-v2/src/agent/contextMemory/contextMemory.ts

@@ -1,6 +1,6 @@
 import { createDecorator } from "#/_base/di/instantiation";
 
-import type { UndoCut } from './contextOps';
+import type { UndoCut } from './conversationTime';
 import type { LoopRecordedEvent } from './loopEventFold';
 import type { ContextMessage } from './types';
 

packages/agent-core-v2/src/agent/contextMemory/contextMemoryService.ts

@@ -30,16 +30,18 @@ import {
 } from './contextMemory';
 import { buildContextCompactionShape, type TokenEstimate } from './compactionHandoff';
 import {
-  computeUndoCut,
   ContextModel,
   contextAppendLoopEvent,
   contextAppendMessage,
   contextApplyCompaction,
   contextClear,
   contextUndo,
+} from './contextOps';
+import {
+  computeUndoCut,
   isFullyUndoable,
   type UndoCut,
-} from './contextOps';
+} from './conversationTime';
 import type { LoopRecordedEvent } from './loopEventFold';
 import type { ContextMessage } from './types';
 
@@ -75,7 +77,7 @@ export class AgentContextMemoryService extends Disposable implements IAgentConte
   }
 
   get(): readonly ContextMessage[] {
-    return this.wire.getModel(ContextModel) as readonly ContextMessage[];
+    return this.wire.getModel(ContextModel).messages as readonly ContextMessage[];
   }
 
   append(...messages: readonly ContextMessage[]): void {