fix: align cache-ttl pruning with thinking replay sanitization

src/agents/pi-embedded-runner/extensions.ts

@@ -10,6 +10,7 @@ import { setContextPruningRuntime } from "../pi-hooks/context-pruning/runtime.js
 import { computeEffectiveSettings } from "../pi-hooks/context-pruning/settings.js";
 import { makeToolPrunablePredicate } from "../pi-hooks/context-pruning/tools.js";
 import { ensurePiCompactionReserveTokens } from "../pi-settings.js";
+import { resolveTranscriptPolicy } from "../transcript-policy.js";
 import { isCacheTtlEligibleProvider, readLastCacheTtlTimestamp } from "./cache-ttl.js";
 
 function resolveContextWindowTokens(params: {
@@ -46,11 +47,17 @@ function buildContextPruningFactory(params: {
   if (!settings) {
     return undefined;
   }
+  const transcriptPolicy = resolveTranscriptPolicy({
+    modelApi: params.model?.api,
+    provider: params.provider,
+    modelId: params.modelId,
+  });
 
   setContextPruningRuntime(params.sessionManager, {
     settings,
     contextWindowTokens: resolveContextWindowTokens(params),
     isToolPrunable: makeToolPrunablePredicate(settings.tools),
+    dropThinkingBlocks: transcriptPolicy.dropThinkingBlocks,
     lastCacheTouchAt: readLastCacheTtlTimestamp(params.sessionManager),
   });
 

src/agents/pi-hooks/context-pruning/extension.ts

@@ -26,6 +26,7 @@ export default function contextPruningExtension(api: ExtensionAPI): void {
       ctx,
       isToolPrunable: runtime.isToolPrunable,
       contextWindowTokensOverride: runtime.contextWindowTokens ?? undefined,
+      dropThinkingBlocksForEstimate: runtime.dropThinkingBlocks,
     });
 
     if (next === event.messages) {

src/agents/pi-hooks/context-pruning/pruner.test.ts

@@ -194,6 +194,39 @@ describe("pruneContextMessages", () => {
     expect(textBlock.text).toContain("[Tool result trimmed:");
   });
 
+  it("ignores non-latest thinking signatures that will be dropped before send", () => {
+    const messages: AgentMessage[] = [
+      makeUser("first"),
+      makeAssistant([
+        {
+          type: "thinking",
+          thinking: "internal",
+          thinkingSignature: "S".repeat(40_000),
+        } as unknown as AssistantContentBlock,
+        { type: "text", text: "older reply" },
+      ]),
+      makeToolResult([{ type: "text", text: "X".repeat(2_000) }]),
+      makeUser("latest"),
+      makeAssistant([{ type: "text", text: "latest reply" }]),
+    ];
+
+    const result = pruneContextMessages({
+      messages,
+      settings: {
+        ...DEFAULT_CONTEXT_PRUNING_SETTINGS,
+        keepLastAssistants: 1,
+        softTrimRatio: 0.5,
+        softTrim: { maxChars: 200, headChars: 100, tailChars: 50 },
+        hardClear: { ...DEFAULT_CONTEXT_PRUNING_SETTINGS.hardClear, enabled: false },
+      },
+      ctx: { model: { contextWindow: 5_000 } } as unknown as ExtensionContext,
+      isToolPrunable: () => true,
+      dropThinkingBlocksForEstimate: true,
+    });
+
+    expect(result).toBe(messages);
+  });
+
   it("soft-trims image-containing tool results by replacing image blocks with placeholders", () => {
     const messages: AgentMessage[] = [
       makeUser("summarize this"),

src/agents/pi-hooks/context-pruning/pruner.ts

@@ -2,6 +2,7 @@ import type { AgentMessage } from "@mariozechner/pi-agent-core";
 import type { ImageContent, TextContent, ToolResultMessage } from "@mariozechner/pi-ai";
 import type { ExtensionContext } from "@mariozechner/pi-coding-agent";
 import { CHARS_PER_TOKEN_ESTIMATE, estimateStringChars } from "../../../utils/cjk-chars.js";
+import { dropThinkingBlocks } from "../../pi-embedded-runner/thinking.js";
 import type { EffectiveContextPruningSettings } from "./settings.js";
 import { makeToolPrunablePredicate } from "./tools.js";
 
@@ -261,6 +262,7 @@ export function pruneContextMessages(params: {
   ctx: Pick<ExtensionContext, "model">;
   isToolPrunable?: (toolName: string) => boolean;
   contextWindowTokensOverride?: number;
+  dropThinkingBlocksForEstimate?: boolean;
 }): AgentMessage[] {
   const { messages, settings, ctx } = params;
   const contextWindowTokens =
@@ -290,8 +292,11 @@ export function pruneContextMessages(params: {
   const pruneStartIndex = firstUserIndex === null ? messages.length : firstUserIndex;
 
   const isToolPrunable = params.isToolPrunable ?? makeToolPrunablePredicate(settings.tools);
+  const estimatedMessages = params.dropThinkingBlocksForEstimate
+    ? dropThinkingBlocks(messages)
+    : messages;
 
-  const totalCharsBefore = estimateContextChars(messages);
+  const totalCharsBefore = estimateContextChars(estimatedMessages);
   let totalChars = totalCharsBefore;
   let ratio = totalChars / charWindow;
   if (ratio < settings.softTrimRatio) {

src/agents/pi-hooks/context-pruning/runtime.ts

@@ -5,6 +5,7 @@ export type ContextPruningRuntimeValue = {
   settings: EffectiveContextPruningSettings;
   contextWindowTokens?: number | null;
   isToolPrunable: (toolName: string) => boolean;
+  dropThinkingBlocks: boolean;
   lastCacheTouchAt?: number | null;
 };