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fix(read): report maxLinesReached in tail mode #778

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fix(read): report maxLinesReached in tail mode #778

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2 changes: 1 addition & 1 deletion packages/agent-core/src/tools/builtin/file/read.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -412,7 +412,7 @@ export class ReadTool implements BuiltinTool<ReadInput> {
return this.finishReadResult({
renderedLines,
truncatedLineNumbers,
maxLinesReached: false,
maxLinesReached: effectiveLimit >= MAX_LINES && entries.length >= effectiveLimit,

@chatgpt-codex-connector chatgpt-codex-connector Bot Jun 15, 2026

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P2 Badge Avoid reporting the line cap for exact-size tail reads

When line_offset is -MAX_LINES and the file contains exactly MAX_LINES lines, entries.length equals effectiveLimit even though no content was omitted by the internal cap, so the result now reports Max 1000 lines reached. for a complete read. Forward reads only set this flag after seeing an extra eligible line; tail mode needs the same distinction, e.g. requiring more total lines than the retained tail window/effective limit.

Useful? React with 👍 / 👎.

maxBytesReached,
lineEndingStyle,
startLine: renderedCandidates[0]?.entry.lineNo ?? 0,
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16 changes: 16 additions & 0 deletions packages/agent-core/test/tools/read.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -622,6 +622,22 @@ describe('ReadTool', () => {
expect(result.output).not.toContain(`${String(MAX_LINES + 1)}\tline ${String(MAX_LINES + 1)}`);
});

it('caps tail reads at MAX_LINES', async () => {
const content = Array.from({ length: MAX_LINES + 5 }, (_, i) => `line ${String(i + 1)}`).join(
'\n',
);
const tool = toolWithContent(content);

const result = await executeTool(
tool,
context({ path: '/tmp/tail-big.txt', line_offset: -MAX_LINES }),
);

expect(result.output).toContain(`Max ${String(MAX_LINES)} lines reached.`);
expect(result.output).toContain(`${String(MAX_LINES + 5)}\tline ${String(MAX_LINES + 5)}`);
expect(result.output).toMatch(/^6\tline 6/);
});

it('tail byte truncation keeps the newest lines closest to EOF', async () => {
const numLines = Math.floor(MAX_BYTES / 1001) + 20;
const content = Array.from({ length: numLines }, (_, i) => {
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