refactor(agents): dedupe config and truncation guards

src/agents/pi-embedded-runner/tool-result-truncation.test.ts

@@ -2,7 +2,9 @@ import type { AgentMessage } from "@mariozechner/pi-agent-core";
 import { describe, expect, it } from "vitest";
 import {
   truncateToolResultText,
+  truncateToolResultMessage,
   calculateMaxToolResultChars,
+  getToolResultTextLength,
   truncateOversizedToolResultsInMessages,
   isOversizedToolResult,
   sessionLikelyHasOversizedToolResults,
@@ -82,6 +84,55 @@ describe("truncateToolResultText", () => {
       expect(lastNewline).toBeGreaterThan(keptContent.length - 100);
     }
   });
+
+  it("supports custom suffix and min keep chars", () => {
+    const text = "x".repeat(5_000);
+    const result = truncateToolResultText(text, 300, {
+      suffix: "\n\n[custom-truncated]",
+      minKeepChars: 250,
+    });
+    expect(result).toContain("[custom-truncated]");
+    expect(result.length).toBeGreaterThan(250);
+  });
+});
+
+describe("getToolResultTextLength", () => {
+  it("sums all text blocks in tool results", () => {
+    const msg = {
+      role: "toolResult",
+      content: [
+        { type: "text", text: "abc" },
+        { type: "image", source: { type: "base64", mediaType: "image/png", data: "x" } },
+        { type: "text", text: "12345" },
+      ],
+    } as unknown as AgentMessage;
+
+    expect(getToolResultTextLength(msg)).toBe(8);
+  });
+
+  it("returns zero for non-toolResult messages", () => {
+    expect(getToolResultTextLength(makeAssistantMessage("hello"))).toBe(0);
+  });
+});
+
+describe("truncateToolResultMessage", () => {
+  it("truncates with a custom suffix", () => {
+    const msg = {
+      role: "toolResult",
+      toolCallId: "call_1",
+      toolName: "read",
+      content: [{ type: "text", text: "x".repeat(50_000) }],
+      isError: false,
+      timestamp: Date.now(),
+    } as unknown as AgentMessage;
+
+    const result = truncateToolResultMessage(msg, 10_000, {
+      suffix: "\n\n[persist-truncated]",
+      minKeepChars: 2_000,
+    }) as { content: Array<{ type: string; text: string }> };
+
+    expect(result.content[0]?.text).toContain("[persist-truncated]");
+  });
 });
 
 describe("calculateMaxToolResultChars", () => {

src/agents/pi-embedded-runner/tool-result-truncation.ts

@@ -33,21 +33,32 @@ const TRUNCATION_SUFFIX =
   "The content above is a partial view. If you need more, request specific sections or use " +
   "offset/limit parameters to read smaller chunks.]";
 
+type ToolResultTruncationOptions = {
+  suffix?: string;
+  minKeepChars?: number;
+};
+
 /**
  * Truncate a single text string to fit within maxChars, preserving the beginning.
  */
-export function truncateToolResultText(text: string, maxChars: number): string {
+export function truncateToolResultText(
+  text: string,
+  maxChars: number,
+  options: ToolResultTruncationOptions = {},
+): string {
+  const suffix = options.suffix ?? TRUNCATION_SUFFIX;
+  const minKeepChars = options.minKeepChars ?? MIN_KEEP_CHARS;
   if (text.length <= maxChars) {
     return text;
   }
-  const keepChars = Math.max(MIN_KEEP_CHARS, maxChars - TRUNCATION_SUFFIX.length);
+  const keepChars = Math.max(minKeepChars, maxChars - suffix.length);
   // Try to break at a newline boundary to avoid cutting mid-line
   let cutPoint = keepChars;
   const lastNewline = text.lastIndexOf("\n", keepChars);
   if (lastNewline > keepChars * 0.8) {
     cutPoint = lastNewline;
   }
-  return text.slice(0, cutPoint) + TRUNCATION_SUFFIX;
+  return text.slice(0, cutPoint) + suffix;
 }
 
 /**
@@ -67,7 +78,7 @@ export function calculateMaxToolResultChars(contextWindowTokens: number): number
 /**
  * Get the total character count of text content blocks in a tool result message.
  */
-function getToolResultTextLength(msg: AgentMessage): number {
+export function getToolResultTextLength(msg: AgentMessage): number {
   if (!msg || (msg as { role?: string }).role !== "toolResult") {
     return 0;
   }
@@ -91,7 +102,13 @@ function getToolResultTextLength(msg: AgentMessage): number {
  * Truncate a tool result message's text content blocks to fit within maxChars.
  * Returns a new message (does not mutate the original).
  */
-function truncateToolResultMessage(msg: AgentMessage, maxChars: number): AgentMessage {
+export function truncateToolResultMessage(
+  msg: AgentMessage,
+  maxChars: number,
+  options: ToolResultTruncationOptions = {},
+): AgentMessage {
+  const suffix = options.suffix ?? TRUNCATION_SUFFIX;
+  const minKeepChars = options.minKeepChars ?? MIN_KEEP_CHARS;
   const content = (msg as { content?: unknown }).content;
   if (!Array.isArray(content)) {
     return msg;
@@ -114,10 +131,10 @@ function truncateToolResultMessage(msg: AgentMessage, maxChars: number): AgentMe
     }
     // Proportional budget for this block
     const blockShare = textBlock.text.length / totalTextChars;
-    const blockBudget = Math.max(MIN_KEEP_CHARS, Math.floor(maxChars * blockShare));
+    const blockBudget = Math.max(minKeepChars + suffix.length, Math.floor(maxChars * blockShare));
     return {
       ...textBlock,
-      text: truncateToolResultText(textBlock.text, blockBudget),
+      text: truncateToolResultText(textBlock.text, blockBudget, { suffix, minKeepChars }),
     };
   });