perf(runtime): bound Read line-index memory to the page

packages/runtime/src/__tests__/read-page.test.ts

@@ -18,6 +18,8 @@
  */
 
 import assert from 'node:assert/strict';
+import { execFile } from 'node:child_process';
+import { promisify } from 'node:util';
 import { test } from 'node:test';
 import {
   readPage,
@@ -175,3 +177,47 @@ test('archive Read preserves fields beside structured text across pages', () =>
     assert.deepEqual(JSON.parse(recovered), value);
   }
 });
+
+test('small line ranges do not need a whole-file line index', async () => {
+  // 固定堆预算验证实际资源边界，不依赖耗时阈值或具体索引实现。
+  const { stdout } = await promisify(execFile)(
+    process.execPath,
+    [
+      '--max-old-space-size=64',
+      '--input-type=module',
+      '--eval',
+      `
+        import assert from 'node:assert/strict';
+        import { readPage } from ${JSON.stringify(new URL('../read-page.js', import.meta.url).href)};
+        const content = 'x\\n'.repeat(8_000_000);
+        const page = readPage(content, { path: 'log.txt', offset: 2_000_000, limit: 20 });
+        assert.equal(page.totalLines, 8_000_001);
+        assert.equal(page.offset, 2_000_000);
+        assert.equal(page.returnedLines, 20);
+        assert.equal(page.content, 'x\\n'.repeat(19) + 'x');
+        assert.equal(page.next, null);
+        console.log('bounded read passed');
+      `,
+    ],
+    { timeout: 30_000 },
+  );
+  assert.equal(stdout.trim(), 'bounded read passed');
+});
+
+test('line ranges preserve empty lines, trailing newlines and offsets beyond EOF', () => {
+  for (const content of ['', '\n', '\n\n', 'a\nb', 'a\nb\n', 'a\r\n😀\n\nlast']) {
+    const lines = content.split('\n');
+    for (let offset = 0; offset <= lines.length + 1; offset++) {
+      for (const limit of [undefined, 1, 2, 100]) {
+        const selected = lines.slice(offset, limit === undefined ? undefined : offset + limit);
+        assert.deepEqual(readPage(content, { path: 'file.txt', offset, limit }), {
+          content: selected.join('\n'),
+          offset,
+          returnedLines: selected.length,
+          totalLines: lines.length,
+          next: null,
+        });
+      }
+    }
+  }
+});

packages/runtime/src/read-page.ts

@@ -119,10 +119,34 @@ export function readPage(
       'Invalid Read continuation position. Copy the complete next object from the preceding result.',
     );
   }
-  const starts = [0];
-  for (let at = content.indexOf('\n'); at >= 0; at = content.indexOf('\n', at + 1))
+  // 总行数仍需扫描全文，但只为本页可能返回的字符保留行索引，避免短行日志
+  // 为一个小响应分配与整个文件行数成正比的临时数组。
+  let totalLines = 1;
+  let offset = resolved.position === undefined ? (input.offset ?? 0) : 0;
+  let start = resolved.position ?? (offset === 0 ? 0 : content.length);
+  let lineStart = 0;
+  let end = content.length;
+  for (let at = content.indexOf('\n'); at >= 0; at = content.indexOf('\n', at + 1)) {
+    const line = totalLines++;
+    if (resolved.position !== undefined && at < resolved.position) {
+      offset = line;
+      lineStart = at + 1;
+    } else if (resolved.position === undefined && line === offset) {
+      start = at + 1;
+      lineStart = start;
+    }
+    if (input.limit !== undefined && line === offset + input.limit && at >= start) end = at;
+  }
+  const lastLine = Math.min(totalLines, offset + (input.limit ?? totalLines));
+  const starts = [lineStart];
+  const indexEnd = Math.min(end, start + maxChars);
+  for (
+    let at = content.indexOf('\n', start);
+    at >= 0 && at < indexEnd;
+    at = content.indexOf('\n', at + 1)
+  ) {
     starts.push(at + 1);
-  const totalLines = starts.length;
+  }
   const lineAt = (position: number): number => {
     let low = 0;
     let high = starts.length - 1;
@@ -131,17 +155,13 @@ export function readPage(
       if (starts[middle]! <= position) low = middle;
       else high = middle - 1;
     }
-    return low;
+    return offset + low;
   };
-  const offset = resolved.position === undefined ? (input.offset ?? 0) : lineAt(resolved.position);
-  const start = resolved.position ?? starts[Math.min(offset, totalLines)] ?? content.length;
-  const lastLine = Math.min(totalLines, offset + (input.limit ?? totalLines));
-  const end = lastLine < totalLines ? starts[lastLine]! - 1 : content.length;
   let digest = resolved.digest;
   const makePage = (stop: number): ReadPage => {
     const complete = stop >= end;
     const nextLine = Math.max(offset, lineAt(stop));
-    const boundary = stop === (starts[nextLine + 1] ?? content.length + 1) - 1;
+    const boundary = content[stop] === '\n';
     const partialLine = !complete && !boundary;
     const returnedLines =
       offset >= totalLines
@@ -163,7 +183,7 @@ export function readPage(
       offset,
       returnedLines,
       totalLines,
-      ...(partialLine || (offset < totalLines && start > starts[offset]!)
+      ...(partialLine || (offset < totalLines && start > lineStart)
         ? { partialLine: true as const }
         : {}),
       next,