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fix: freeze memory metadata timestamps in system prompt head #20

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fix: freeze memory metadata timestamps in system prompt head #20

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23 changes: 14 additions & 9 deletions src/prompt.test.ts
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Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
import { describe, expect, test } from "bun:test";

import type { MemoryBlock } from "./memory";

import { renderMemoryBlocks } from "./prompt";

describe("renderMemoryBlocks", () => {
Expand Down Expand Up @@ -47,9 +49,8 @@ describe("renderMemoryBlocks", () => {
expect(xml).toContain("</memory_instructions>");
});

test("includes memory metadata block with timestamps", () => {
const testDate = new Date("2025-01-15T10:30:00Z");
const xml = renderMemoryBlocks([
test("memory metadata is stable across calls (cache-friendly head)", () => {
const blocks: MemoryBlock[] = [
{
scope: "global",
label: "human",
Expand All @@ -58,14 +59,18 @@ describe("renderMemoryBlocks", () => {
readOnly: false,
value: "hi",
filePath: "/tmp/human.md",
lastModified: testDate,
lastModified: new Date("2025-01-15T10:30:00Z"),
},
]);
];

const first = renderMemoryBlocks(blocks);
// small delay simulates two distinct requests
const second = renderMemoryBlocks(blocks);

expect(xml).toContain("<memory_metadata>");
expect(xml).toContain("The current system date is:");
expect(xml).toContain("Memory blocks were last modified:");
expect(xml).toContain("</memory_metadata>");
expect(first).toContain("<memory_metadata>");
expect(first).not.toContain("The current system date is:");
expect(first).not.toContain("Memory blocks were last modified:");
expect(second).toBe(first);
});

test("handles empty value gracefully", () => {
Expand Down
10 changes: 1 addition & 9 deletions src/prompt.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -5,16 +5,8 @@ const LINE_NUMBER_WARNING =
"# NOTE: Line numbers shown below (with arrows like '1→') are to help during editing. Do NOT include line number prefixes in your memory edit tool calls.";

function renderMemoryMetadata(blocks: MemoryBlock[]): string {
const now = new Date();

const lastModified = blocks.reduce(
(latest, block) => (block.lastModified > latest ? block.lastModified : latest),
new Date(0)
);

return `<memory_metadata>
- The current system date is: ${now.toISOString()}
- Memory blocks were last modified: ${lastModified.toISOString()}
- Memory blocks are editable via memory_set / memory_replace.
- Use memory tools to manage your memory blocks
</memory_metadata>`;
}
Expand Down