From c419aadb190b2eb9c77d3d55dd79dd1a97d6fd08 Mon Sep 17 00:00:00 2001
From: Neil <4138956+nwparker@users.noreply.github.com>
Date: Fri, 24 Jul 2026 20:30:31 -0700
Subject: [PATCH] =?UTF-8?q?oom(01):=20A1-shared-readers=20=E2=80=94=20rein?=
 =?UTF-8?q?troduce=20#10179=20subset=20(#10294)?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Files: 18 applied, 0 deleted (from 6eb70d83703e5c69c2878caca73d536a2abbadab)

Co-authored-by: Orca <help@stably.ai>
---
 src/shared/bounded-secure-json-file.ts        |  10 +
 src/shared/fetch-response-body.ts             | 116 +++++++++
 src/shared/growing-byte-buffer.test.ts        |  54 +++++
 src/shared/growing-byte-buffer.ts             | 100 ++++++++
 src/shared/node-file-content-equality.test.ts |  40 ++++
 src/shared/node-file-content-equality.ts      |  72 ++++++
 src/shared/node-readable-text.test.ts         |  40 ++++
 src/shared/node-readable-text.ts              |  42 ++++
 .../node-source-copy-content-equality.test.ts |  57 +++++
 .../node-source-copy-content-equality.ts      |  64 +++++
 src/shared/nul-delimited-fields.test.ts       |   8 +
 src/shared/nul-delimited-fields.ts            |  12 +
 .../persisted-state-file-bounds.test.ts       | 171 ++++++++++++++
 src/shared/persisted-state-file-bounds.ts     | 222 ++++++++++++++++++
 src/shared/search-subprocess-lines.test.ts    |  55 +++++
 src/shared/search-subprocess-lines.ts         |  75 ++++++
 src/shared/string-chunk-compaction.test.ts    |  17 ++
 src/shared/string-chunk-compaction.ts         |  11 +
 18 files changed, 1166 insertions(+)
 create mode 100644 src/shared/bounded-secure-json-file.ts
 create mode 100644 src/shared/fetch-response-body.ts
 create mode 100644 src/shared/growing-byte-buffer.test.ts
 create mode 100644 src/shared/growing-byte-buffer.ts
 create mode 100644 src/shared/node-file-content-equality.test.ts
 create mode 100644 src/shared/node-file-content-equality.ts
 create mode 100644 src/shared/node-readable-text.test.ts
 create mode 100644 src/shared/node-readable-text.ts
 create mode 100644 src/shared/node-source-copy-content-equality.test.ts
 create mode 100644 src/shared/node-source-copy-content-equality.ts
 create mode 100644 src/shared/nul-delimited-fields.test.ts
 create mode 100644 src/shared/nul-delimited-fields.ts
 create mode 100644 src/shared/persisted-state-file-bounds.test.ts
 create mode 100644 src/shared/persisted-state-file-bounds.ts
 create mode 100644 src/shared/search-subprocess-lines.test.ts
 create mode 100644 src/shared/search-subprocess-lines.ts
 create mode 100644 src/shared/string-chunk-compaction.test.ts
 create mode 100644 src/shared/string-chunk-compaction.ts

diff --git a/src/shared/bounded-secure-json-file.ts b/src/shared/bounded-secure-json-file.ts
new file mode 100644
index 000000000..c9da2b9ce
--- /dev/null
+++ b/src/shared/bounded-secure-json-file.ts
@@ -0,0 +1,10 @@
+import { stringifyJsonWithinByteLimit } from './node-bounded-json-stringify'
+import { writeSecureFile } from './secure-file'
+
+export function writeSecureJsonFileWithinLimit(
+  targetPath: string,
+  value: unknown,
+  maxBytes: number
+): void {
+  writeSecureFile(targetPath, stringifyJsonWithinByteLimit(value, maxBytes).serialized)
+}
diff --git a/src/shared/fetch-response-body.ts b/src/shared/fetch-response-body.ts
new file mode 100644
index 000000000..e9467fd3a
--- /dev/null
+++ b/src/shared/fetch-response-body.ts
@@ -0,0 +1,116 @@
+import {
+  assertJsonTextStructureWithinLimits,
+  type JsonTextStructureLimits
+} from './json-text-structure-limit'
+
+const INITIAL_RESPONSE_CAPACITY_BYTES = 64 * 1024
+
+export const API_RESPONSE_MAX_BYTES = 16 * 1024 * 1024
+export const API_RESPONSE_JSON_LIMITS: JsonTextStructureLimits = {
+  structuralTokens: 1_000_000,
+  nestingDepth: 128
+}
+
+export class FetchResponseBodyTooLargeError extends Error {
+  constructor(
+    readonly observedBytes: number,
+    readonly maxBytes: number
+  ) {
+    super(`Response body exceeds ${maxBytes} byte limit`)
+    this.name = 'FetchResponseBodyTooLargeError'
+  }
+}
+
+function parseContentLength(response: Response): number | null {
+  const raw = response.headers.get('content-length')
+  if (!raw || !/^\d+$/.test(raw)) {
+    return null
+  }
+  const parsed = Number(raw)
+  return Number.isSafeInteger(parsed) ? parsed : null
+}
+
+function isHighLevelOnlyResponse(response: Response): boolean {
+  const partial = response as Partial<Response>
+  // Injected request adapters may expose only the high-level method they implement.
+  return partial.headers === undefined && partial.body === undefined
+}
+
+async function cancelReader(reader: ReadableStreamDefaultReader<Uint8Array>): Promise<void> {
+  try {
+    await reader.cancel()
+  } catch {
+    // An already-errored or closed response needs no further draining.
+  }
+}
+
+export async function readFetchResponseBytesWithinLimit(
+  response: Response,
+  maxBytes = API_RESPONSE_MAX_BYTES
+): Promise<Uint8Array> {
+  if (!Number.isSafeInteger(maxBytes) || maxBytes < 0) {
+    throw new RangeError('Response body limit must be a non-negative safe integer')
+  }
+
+  const contentLength = parseContentLength(response)
+  if (contentLength !== null && contentLength > maxBytes) {
+    await response.body?.cancel().catch(() => undefined)
+    throw new FetchResponseBodyTooLargeError(contentLength, maxBytes)
+  }
+  if (!response.body) {
+    return new Uint8Array()
+  }
+
+  const reader = response.body.getReader()
+  let output = new Uint8Array(Math.min(maxBytes, INITIAL_RESPONSE_CAPACITY_BYTES))
+  let byteLength = 0
+  try {
+    while (true) {
+      const { done, value } = await reader.read()
+      if (done) {
+        return output.subarray(0, byteLength)
+      }
+      const nextLength = byteLength + value.byteLength
+      if (!Number.isSafeInteger(nextLength) || nextLength > maxBytes) {
+        await cancelReader(reader)
+        throw new FetchResponseBodyTooLargeError(nextLength, maxBytes)
+      }
+      if (nextLength > output.byteLength) {
+        const nextCapacity = Math.min(
+          maxBytes,
+          Math.max(INITIAL_RESPONSE_CAPACITY_BYTES, output.byteLength * 2, nextLength)
+        )
+        const expanded = new Uint8Array(nextCapacity)
+        expanded.set(output.subarray(0, byteLength))
+        output = expanded
+      }
+      output.set(value, byteLength)
+      byteLength = nextLength
+    }
+  } finally {
+    reader.releaseLock()
+  }
+}
+
+export async function readFetchResponseTextWithinLimit(
+  response: Response,
+  maxBytes = API_RESPONSE_MAX_BYTES
+): Promise<string> {
+  if (isHighLevelOnlyResponse(response)) {
+    return response.text()
+  }
+  return new TextDecoder().decode(await readFetchResponseBytesWithinLimit(response, maxBytes))
+}
+
+export async function readFetchResponseJsonWithinLimit<T>(
+  response: Response,
+  maxBytes = API_RESPONSE_MAX_BYTES,
+  structureLimits: JsonTextStructureLimits = API_RESPONSE_JSON_LIMITS
+): Promise<T> {
+  if (isHighLevelOnlyResponse(response)) {
+    return response.json() as Promise<T>
+  }
+  const content = await readFetchResponseTextWithinLimit(response, maxBytes)
+  assertJsonTextStructureWithinLimits(content, structureLimits)
+  return JSON.parse(content) as T
+}
diff --git a/src/shared/growing-byte-buffer.test.ts b/src/shared/growing-byte-buffer.test.ts
new file mode 100644
index 000000000..8dc477ae6
--- /dev/null
+++ b/src/shared/growing-byte-buffer.test.ts
@@ -0,0 +1,54 @@
+import { describe, expect, it } from 'vitest'
+import { GrowingByteBuffer } from './growing-byte-buffer'
+
+describe('GrowingByteBuffer', () => {
+  it('retains 100,000 one-byte fragments in one growable allocation', () => {
+    const buffer = new GrowingByteBuffer()
+    const expected = Buffer.alloc(100_000)
+
+    for (let index = 0; index < expected.byteLength; index += 1) {
+      const value = index % 251
+      expected[index] = value
+      buffer.append(Uint8Array.of(value))
+    }
+
+    expect(buffer.byteLength).toBe(expected.byteLength)
+    expect(buffer.takeString('latin1')).toBe(expected.toString('latin1'))
+    expect(buffer.byteLength).toBe(0)
+  })
+
+  it('consumes delimited prefixes and retains a bounded suffix', () => {
+    const buffer = new GrowingByteBuffer()
+    for (const byte of Buffer.from('first\nsecond-tail')) {
+      buffer.append(Uint8Array.of(byte))
+    }
+
+    const newline = buffer.indexOfByte(0x0a)
+    expect(buffer.takePrefixString(newline)).toBe('first')
+    buffer.discardPrefix(1)
+    buffer.retainSuffix(4)
+
+    expect(buffer.toString()).toBe('tail')
+  })
+
+  it('appends only a bounded copy from an oversized source chunk', () => {
+    const buffer = new GrowingByteBuffer()
+    buffer.append(Buffer.from('old'))
+    const source = Buffer.from('discard-prefix-tail')
+
+    buffer.appendRetainedSuffix(source, 4)
+    source.fill(0)
+
+    expect(buffer.byteLength).toBe(4)
+    expect(buffer.toString()).toBe('tail')
+  })
+
+  it('keeps the newest bytes across bounded suffix appends', () => {
+    const buffer = new GrowingByteBuffer()
+
+    buffer.appendRetainedSuffix(Buffer.from('1234'), 6)
+    buffer.appendRetainedSuffix(Buffer.from('5678'), 6)
+
+    expect(buffer.toString()).toBe('345678')
+  })
+})
diff --git a/src/shared/growing-byte-buffer.ts b/src/shared/growing-byte-buffer.ts
new file mode 100644
index 000000000..48c5d90de
--- /dev/null
+++ b/src/shared/growing-byte-buffer.ts
@@ -0,0 +1,100 @@
+export class GrowingByteBuffer {
+  private storage = Buffer.alloc(0)
+  private length = 0
+
+  get byteLength(): number {
+    return this.length
+  }
+
+  append(bytes: Buffer | Uint8Array): void {
+    if (bytes.byteLength === 0) {
+      return
+    }
+    const required = this.length + bytes.byteLength
+    if (required > this.storage.byteLength) {
+      const capacity = Math.max(required, Math.max(256, this.storage.byteLength * 2))
+      const next = Buffer.allocUnsafe(capacity)
+      this.storage.copy(next, 0, 0, this.length)
+      this.storage = next
+    }
+    const source = Buffer.isBuffer(bytes)
+      ? bytes
+      : Buffer.from(bytes.buffer, bytes.byteOffset, bytes.byteLength)
+    source.copy(this.storage, this.length)
+    this.length = required
+  }
+
+  appendRetainedSuffix(bytes: Buffer | Uint8Array, maxBytes: number): void {
+    if (!Number.isSafeInteger(maxBytes) || maxBytes < 0) {
+      throw new RangeError('Retained suffix limit must be a non-negative safe integer')
+    }
+    if (maxBytes === 0) {
+      this.clear()
+      return
+    }
+    const source = Buffer.isBuffer(bytes)
+      ? bytes
+      : Buffer.from(bytes.buffer, bytes.byteOffset, bytes.byteLength)
+    if (source.byteLength >= maxBytes) {
+      this.storage = Buffer.from(source.subarray(source.byteLength - maxBytes))
+      this.length = maxBytes
+      return
+    }
+    const retainedBytes = Math.min(this.length, maxBytes - source.byteLength)
+    if (retainedBytes < this.length) {
+      this.storage.copy(this.storage, 0, this.length - retainedBytes, this.length)
+      this.length = retainedBytes
+    }
+    this.append(source)
+  }
+
+  indexOfByte(value: number, byteOffset = 0): number {
+    return this.storage.subarray(0, this.length).indexOf(value, byteOffset)
+  }
+
+  takePrefixString(byteLength: number, encoding: BufferEncoding = 'utf8'): string {
+    if (!Number.isSafeInteger(byteLength) || byteLength < 0 || byteLength > this.length) {
+      throw new RangeError('Prefix length exceeds retained bytes')
+    }
+    const value = this.storage.toString(encoding, 0, byteLength)
+    this.discardPrefix(byteLength)
+    return value
+  }
+
+  discardPrefix(byteLength: number): void {
+    if (!Number.isSafeInteger(byteLength) || byteLength < 0 || byteLength > this.length) {
+      throw new RangeError('Prefix length exceeds retained bytes')
+    }
+    if (byteLength === 0) {
+      return
+    }
+    this.storage.copy(this.storage, 0, byteLength, this.length)
+    this.length -= byteLength
+  }
+
+  retainSuffix(maxBytes: number): void {
+    if (!Number.isSafeInteger(maxBytes) || maxBytes < 0) {
+      throw new RangeError('Suffix limit must be a non-negative safe integer')
+    }
+    if (this.length <= maxBytes) {
+      return
+    }
+    this.storage.copy(this.storage, 0, this.length - maxBytes, this.length)
+    this.length = maxBytes
+  }
+
+  toString(encoding: BufferEncoding = 'utf8'): string {
+    return this.storage.toString(encoding, 0, this.length)
+  }
+
+  takeString(encoding: BufferEncoding = 'utf8'): string {
+    const value = this.toString(encoding)
+    this.clear()
+    return value
+  }
+
+  clear(): void {
+    this.storage = Buffer.alloc(0)
+    this.length = 0
+  }
+}
diff --git a/src/shared/node-file-content-equality.test.ts b/src/shared/node-file-content-equality.test.ts
new file mode 100644
index 000000000..af50287b9
--- /dev/null
+++ b/src/shared/node-file-content-equality.test.ts
@@ -0,0 +1,40 @@
+import { mkdtempSync, rmSync, truncateSync, writeFileSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { afterEach, describe, expect, it } from 'vitest'
+import { nodeFileContentsEqual, nodeFileContentsEqualSync } from './node-file-content-equality'
+
+const roots: string[] = []
+
+function createFile(contents: string): string {
+  const root = mkdtempSync(join(tmpdir(), 'orca-file-content-equality-'))
+  roots.push(root)
+  const filePath = join(root, 'owned-launcher')
+  writeFileSync(filePath, contents)
+  return filePath
+}
+
+afterEach(() => {
+  for (const root of roots.splice(0)) {
+    rmSync(root, { recursive: true, force: true })
+  }
+})
+
+describe('Node file content equality', () => {
+  it('compares UTF-8 content without changing its bytes', async () => {
+    const filePath = createFile('launch 🐋\n')
+
+    await expect(nodeFileContentsEqual(filePath, 'launch 🐋\n')).resolves.toBe(true)
+    expect(nodeFileContentsEqualSync(filePath, 'launch 🐋\n')).toBe(true)
+    await expect(nodeFileContentsEqual(filePath, 'different\n')).resolves.toBe(false)
+    expect(nodeFileContentsEqualSync(filePath, 'different\n')).toBe(false)
+  })
+
+  it('rejects a large sparse replacement from metadata without reading its payload', async () => {
+    const filePath = createFile('owned launcher\n')
+    truncateSync(filePath, 256 * 1024 * 1024)
+
+    await expect(nodeFileContentsEqual(filePath, 'owned launcher\n')).resolves.toBe(false)
+    expect(nodeFileContentsEqualSync(filePath, 'owned launcher\n')).toBe(false)
+  })
+})
diff --git a/src/shared/node-file-content-equality.ts b/src/shared/node-file-content-equality.ts
new file mode 100644
index 000000000..5f7ccb729
--- /dev/null
+++ b/src/shared/node-file-content-equality.ts
@@ -0,0 +1,72 @@
+import { closeSync, fstatSync, openSync, readSync } from 'node:fs'
+import { open } from 'node:fs/promises'
+
+export const NODE_FILE_CONTENT_COMPARE_CHUNK_BYTES = 64 * 1024
+
+function expectedBytes(contents: string | Buffer): Buffer {
+  return typeof contents === 'string' ? Buffer.from(contents, 'utf8') : contents
+}
+
+export async function nodeFileContentsEqual(
+  filePath: string,
+  expectedContents: string | Buffer
+): Promise<boolean> {
+  const expected = expectedBytes(expectedContents)
+  const handle = await open(filePath, 'r')
+  try {
+    if ((await handle.stat()).size !== expected.length) {
+      return false
+    }
+    const chunk = Buffer.allocUnsafe(
+      Math.min(NODE_FILE_CONTENT_COMPARE_CHUNK_BYTES, expected.length)
+    )
+    let offset = 0
+    while (offset < expected.length) {
+      const length = Math.min(chunk.length, expected.length - offset)
+      const { bytesRead } = await handle.read(chunk, 0, length, offset)
+      if (
+        bytesRead === 0 ||
+        !chunk.subarray(0, bytesRead).equals(expected.subarray(offset, offset + bytesRead))
+      ) {
+        return false
+      }
+      offset += bytesRead
+    }
+    const probe = Buffer.allocUnsafe(1)
+    return (await handle.read(probe, 0, 1, offset)).bytesRead === 0
+  } finally {
+    await handle.close()
+  }
+}
+
+export function nodeFileContentsEqualSync(
+  filePath: string,
+  expectedContents: string | Buffer
+): boolean {
+  const expected = expectedBytes(expectedContents)
+  const descriptor = openSync(filePath, 'r')
+  try {
+    if (fstatSync(descriptor).size !== expected.length) {
+      return false
+    }
+    const chunk = Buffer.allocUnsafe(
+      Math.min(NODE_FILE_CONTENT_COMPARE_CHUNK_BYTES, expected.length)
+    )
+    let offset = 0
+    while (offset < expected.length) {
+      const length = Math.min(chunk.length, expected.length - offset)
+      const bytesRead = readSync(descriptor, chunk, 0, length, offset)
+      if (
+        bytesRead === 0 ||
+        !chunk.subarray(0, bytesRead).equals(expected.subarray(offset, offset + bytesRead))
+      ) {
+        return false
+      }
+      offset += bytesRead
+    }
+    const probe = Buffer.allocUnsafe(1)
+    return readSync(descriptor, probe, 0, 1, offset) === 0
+  } finally {
+    closeSync(descriptor)
+  }
+}
diff --git a/src/shared/node-readable-text.test.ts b/src/shared/node-readable-text.test.ts
new file mode 100644
index 000000000..5205b589d
--- /dev/null
+++ b/src/shared/node-readable-text.test.ts
@@ -0,0 +1,40 @@
+import { describe, expect, it } from 'vitest'
+import {
+  NodeReadableTextTooLargeError,
+  readNodeReadableTextWithinLimit
+} from './node-readable-text'
+
+async function* chunks(values: unknown[]): AsyncGenerator<unknown> {
+  yield* values
+}
+
+describe('readNodeReadableTextWithinLimit', () => {
+  it('preserves accepted UTF-8 bytes split across chunks', async () => {
+    const encoded = Buffer.from('hello 🌍')
+
+    await expect(
+      readNodeReadableTextWithinLimit(
+        chunks([encoded.subarray(0, 8), encoded.subarray(8)]),
+        encoded.byteLength
+      )
+    ).resolves.toBe('hello 🌍')
+  })
+
+  it('accepts input exactly at the byte limit', async () => {
+    await expect(
+      readNodeReadableTextWithinLimit(chunks(['ab', Buffer.from('cd')]), 4)
+    ).resolves.toBe('abcd')
+  })
+
+  it('rejects before retaining input beyond the byte limit', async () => {
+    await expect(readNodeReadableTextWithinLimit(chunks(['1234', '5']), 4)).rejects.toEqual(
+      new NodeReadableTextTooLargeError(5, 4)
+    )
+  })
+
+  it('does not let an unlimited sequence of empty chunks grow retained state', async () => {
+    await expect(
+      readNodeReadableTextWithinLimit(chunks(Array.from({ length: 10_000 }, () => '')), 0)
+    ).resolves.toBe('')
+  })
+})
diff --git a/src/shared/node-readable-text.ts b/src/shared/node-readable-text.ts
new file mode 100644
index 000000000..d73370629
--- /dev/null
+++ b/src/shared/node-readable-text.ts
@@ -0,0 +1,42 @@
+const INITIAL_READ_CAPACITY_BYTES = 64 * 1024
+
+export class NodeReadableTextTooLargeError extends Error {
+  constructor(
+    readonly observedBytes: number,
+    readonly maxBytes: number
+  ) {
+    super(`Input exceeds ${maxBytes} byte limit (${observedBytes} bytes received)`)
+    this.name = 'NodeReadableTextTooLargeError'
+  }
+}
+
+export async function readNodeReadableTextWithinLimit(
+  readable: AsyncIterable<unknown>,
+  maxBytes: number
+): Promise<string> {
+  if (!Number.isSafeInteger(maxBytes) || maxBytes < 0) {
+    throw new RangeError('Readable text limit must be a non-negative safe integer')
+  }
+
+  let buffer = Buffer.allocUnsafe(Math.min(INITIAL_READ_CAPACITY_BYTES, maxBytes))
+  let bytes = 0
+  for await (const value of readable) {
+    const chunk = Buffer.isBuffer(value) ? value : Buffer.from(String(value))
+    const observedBytes = bytes + chunk.byteLength
+    if (!Number.isSafeInteger(observedBytes) || observedBytes > maxBytes) {
+      throw new NodeReadableTextTooLargeError(observedBytes, maxBytes)
+    }
+    if (observedBytes > buffer.byteLength) {
+      const nextCapacity = Math.min(
+        maxBytes,
+        Math.max(observedBytes, INITIAL_READ_CAPACITY_BYTES, buffer.byteLength * 2)
+      )
+      const expanded = Buffer.allocUnsafe(nextCapacity)
+      buffer.copy(expanded, 0, 0, bytes)
+      buffer = expanded
+    }
+    chunk.copy(buffer, bytes)
+    bytes = observedBytes
+  }
+  return buffer.subarray(0, bytes).toString('utf8')
+}
diff --git a/src/shared/node-source-copy-content-equality.test.ts b/src/shared/node-source-copy-content-equality.test.ts
new file mode 100644
index 000000000..cebe42e99
--- /dev/null
+++ b/src/shared/node-source-copy-content-equality.test.ts
@@ -0,0 +1,57 @@
+import {
+  closeSync,
+  mkdtempSync,
+  openSync,
+  rmSync,
+  truncateSync,
+  writeFileSync,
+  writeSync
+} from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { afterEach, describe, expect, it } from 'vitest'
+import {
+  NODE_FILE_CONTENT_COMPARE_CHUNK_BYTES,
+  nodeSourceAndCopyContentsEqualSync
+} from './node-source-copy-content-equality'
+
+describe('Node source/copy content equality', () => {
+  const roots: string[] = []
+
+  afterEach(() => {
+    for (const root of roots.splice(0)) {
+      rmSync(root, { recursive: true, force: true })
+    }
+  })
+
+  it('compares multi-megabyte sparse files with fixed-size chunks', () => {
+    const root = mkdtempSync(join(tmpdir(), 'orca-resource-compare-'))
+    roots.push(root)
+    const sourcePath = join(root, 'source.md')
+    const copyPath = join(root, 'copy.md')
+    const sparseBytes = NODE_FILE_CONTENT_COMPARE_CHUNK_BYTES * 128
+    for (const path of [sourcePath, copyPath]) {
+      writeFileSync(path, 'same-prefix')
+      truncateSync(path, sparseBytes)
+    }
+
+    expect(nodeSourceAndCopyContentsEqualSync(sourcePath, copyPath)).toBe(true)
+
+    const descriptor = openSync(copyPath, 'r+')
+    try {
+      writeSync(descriptor, Buffer.from('x'), 0, 1, sparseBytes - 1)
+    } finally {
+      closeSync(descriptor)
+    }
+    expect(nodeSourceAndCopyContentsEqualSync(sourcePath, copyPath)).toBe(false)
+  })
+
+  it('rejects a non-file copy without attempting to consume it', () => {
+    const root = mkdtempSync(join(tmpdir(), 'orca-resource-compare-dir-'))
+    roots.push(root)
+    const sourcePath = join(root, 'source.md')
+    writeFileSync(sourcePath, 'contents')
+
+    expect(nodeSourceAndCopyContentsEqualSync(sourcePath, root)).toBe(false)
+  })
+})
diff --git a/src/shared/node-source-copy-content-equality.ts b/src/shared/node-source-copy-content-equality.ts
new file mode 100644
index 000000000..7c17a1eef
--- /dev/null
+++ b/src/shared/node-source-copy-content-equality.ts
@@ -0,0 +1,64 @@
+import { closeSync, lstatSync, openSync, readSync, statSync } from 'node:fs'
+
+export const NODE_FILE_CONTENT_COMPARE_CHUNK_BYTES = 64 * 1024
+
+function readChunk(descriptor: number, buffer: Buffer): number {
+  let offset = 0
+  while (offset < buffer.length) {
+    const bytesRead = readSync(descriptor, buffer, offset, buffer.length - offset, null)
+    if (bytesRead === 0) {
+      break
+    }
+    offset += bytesRead
+  }
+  return offset
+}
+
+export function nodeSourceAndCopyContentsEqualSync(sourcePath: string, copyPath: string): boolean {
+  try {
+    // Why: source links are intentional, but an owned copy must remain a regular file.
+    if (!statSync(sourcePath).isFile() || !lstatSync(copyPath).isFile()) {
+      return false
+    }
+  } catch {
+    return false
+  }
+
+  let sourceDescriptor: number | null = null
+  let copyDescriptor: number | null = null
+  let matches = false
+  let failed = false
+  try {
+    sourceDescriptor = openSync(sourcePath, 'r')
+    copyDescriptor = openSync(copyPath, 'r')
+    const sourceBuffer = Buffer.allocUnsafe(NODE_FILE_CONTENT_COMPARE_CHUNK_BYTES)
+    const copyBuffer = Buffer.allocUnsafe(NODE_FILE_CONTENT_COMPARE_CHUNK_BYTES)
+    while (true) {
+      const sourceBytes = readChunk(sourceDescriptor, sourceBuffer)
+      const copyBytes = readChunk(copyDescriptor, copyBuffer)
+      if (sourceBytes !== copyBytes) {
+        break
+      }
+      if (sourceBytes === 0) {
+        matches = true
+        break
+      }
+      if (!sourceBuffer.subarray(0, sourceBytes).equals(copyBuffer.subarray(0, copyBytes))) {
+        break
+      }
+    }
+  } catch {
+    failed = true
+  }
+  for (const descriptor of [sourceDescriptor, copyDescriptor]) {
+    if (descriptor === null) {
+      continue
+    }
+    try {
+      closeSync(descriptor)
+    } catch {
+      failed = true
+    }
+  }
+  return matches && !failed
+}
diff --git a/src/shared/nul-delimited-fields.test.ts b/src/shared/nul-delimited-fields.test.ts
new file mode 100644
index 000000000..59f8f751b
--- /dev/null
+++ b/src/shared/nul-delimited-fields.test.ts
@@ -0,0 +1,8 @@
+import { describe, expect, it } from 'vitest'
+import { iterateNulDelimitedFields } from './nul-delimited-fields'
+
+describe('iterateNulDelimitedFields', () => {
+  it('preserves empty and trailing fields without materializing a split array', () => {
+    expect([...iterateNulDelimitedFields('one\0\0three\0')]).toEqual(['one', '', 'three', ''])
+  })
+})
diff --git a/src/shared/nul-delimited-fields.ts b/src/shared/nul-delimited-fields.ts
new file mode 100644
index 000000000..64bbf04de
--- /dev/null
+++ b/src/shared/nul-delimited-fields.ts
@@ -0,0 +1,12 @@
+export function* iterateNulDelimitedFields(value: string): Generator<string> {
+  let start = 0
+  while (start <= value.length) {
+    const end = value.indexOf('\0', start)
+    if (end === -1) {
+      yield value.slice(start)
+      return
+    }
+    yield value.slice(start, end)
+    start = end + 1
+  }
+}
diff --git a/src/shared/persisted-state-file-bounds.test.ts b/src/shared/persisted-state-file-bounds.test.ts
new file mode 100644
index 000000000..e6ee2de18
--- /dev/null
+++ b/src/shared/persisted-state-file-bounds.test.ts
@@ -0,0 +1,171 @@
+import { createHash } from 'node:crypto'
+import {
+  mkdtempSync,
+  readFileSync,
+  readdirSync,
+  rmSync,
+  truncateSync,
+  writeFileSync
+} from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { afterEach, beforeEach, describe, expect, it } from 'vitest'
+import { NodeFileReadTooLargeError } from './node-bounded-file-reader'
+import { JsonStringifyByteLimitError } from './node-bounded-json-stringify'
+import {
+  PersistedStateSecretCapacityError,
+  assertPersistedStateSecretWithinLimit,
+  readPersistedStateJsonFileSync,
+  replacePersistedStateJsonWithinLimit,
+  restorePersistedStateBackupSync,
+  stringifyPrettyPersistedStateWithinLimit,
+  stringifyPersistedStateWithinLimit,
+  updatePersistedStateHashWithJsonRange
+} from './persisted-state-file-bounds'
+
+describe('persisted state file bounds', () => {
+  let root = ''
+
+  beforeEach(() => {
+    root = mkdtempSync(join(tmpdir(), 'orca-state-bounds-'))
+  })
+
+  afterEach(() => {
+    rmSync(root, { recursive: true, force: true })
+  })
+
+  it('reads and parses a state file exactly at the byte limit', () => {
+    const path = join(root, 'state.json')
+    const json = `{"value":"${'x'.repeat(20)}"}`
+    writeFileSync(path, json)
+
+    expect(
+      readPersistedStateJsonFileSync<{ value: string }>(path, Buffer.byteLength(json))
+    ).toEqual({
+      byteLength: Buffer.byteLength(json),
+      value: { value: 'x'.repeat(20) }
+    })
+  })
+
+  it('rejects an oversized sparse state file before reading its body', () => {
+    const path = join(root, 'state.json')
+    writeFileSync(path, '')
+    truncateSync(path, 1025)
+
+    expect(() => readPersistedStateJsonFileSync(path, 1024)).toThrow(NodeFileReadTooLargeError)
+  })
+
+  it('rejects structurally amplified state before parsing it', () => {
+    const path = join(root, 'state.json')
+    const json = '{"rows":[{},{}]}'
+    writeFileSync(path, json)
+
+    expect(() =>
+      readPersistedStateJsonFileSync(path, Buffer.byteLength(json), {
+        structuralTokens: 7,
+        nestingDepth: 3
+      })
+    ).toThrow('JSON structure')
+  })
+
+  it('matches native compact JSON exactly at the output boundary', () => {
+    const state = { quote: '"', unicode: '🐋', nested: [1, true, null] }
+    const native = JSON.stringify(state)
+
+    expect(stringifyPersistedStateWithinLimit(state, Buffer.byteLength(native))).toEqual({
+      byteLength: Buffer.byteLength(native),
+      serialized: native
+    })
+    expect(() => stringifyPersistedStateWithinLimit(state, Buffer.byteLength(native) - 1)).toThrow(
+      JsonStringifyByteLimitError
+    )
+  })
+
+  it('matches native pretty JSON and enforces its whitespace-inclusive boundary', () => {
+    const state = { nested: { value: 'x' }, list: [1, 2] }
+    const native = JSON.stringify(state, null, 2)
+
+    expect(stringifyPrettyPersistedStateWithinLimit(state, Buffer.byteLength(native))).toEqual({
+      byteLength: Buffer.byteLength(native),
+      serialized: native
+    })
+    expect(() =>
+      stringifyPrettyPersistedStateWithinLimit(state, Buffer.byteLength(native) - 1)
+    ).toThrow(JsonStringifyByteLimitError)
+  })
+
+  it('bounds secret plaintext before encryption can expand it', () => {
+    assertPersistedStateSecretWithinLimit('🐋', 4)
+
+    expect(() => assertPersistedStateSecretWithinLimit('🐋x', 4)).toThrow(
+      PersistedStateSecretCapacityError
+    )
+  })
+
+  it('checks replacement growth before constructing the next payload', () => {
+    const serialized = '{"value":"slot"}'
+    const exactBytes =
+      Buffer.byteLength(serialized) - Buffer.byteLength('slot') + Buffer.byteLength('expanded')
+
+    expect(
+      replacePersistedStateJsonWithinLimit({
+        serialized,
+        currentBytes: Buffer.byteLength(serialized),
+        search: 'slot',
+        replacement: 'expanded',
+        maxBytes: exactBytes
+      })
+    ).toEqual({ byteLength: exactBytes, serialized: '{"value":"expanded"}' })
+    expect(() =>
+      replacePersistedStateJsonWithinLimit({
+        serialized,
+        currentBytes: Buffer.byteLength(serialized),
+        search: 'slot',
+        replacement: 'expanded',
+        maxBytes: exactBytes - 1
+      })
+    ).toThrow(JsonStringifyByteLimitError)
+  })
+
+  it('hashes bounded string ranges without splitting UTF-16 surrogate pairs', () => {
+    const value = `prefix-${'x'.repeat(8)}🐋-${'y'.repeat(8)}-suffix`
+    const expected = createHash('sha1').update(value).digest('hex')
+    const actual = createHash('sha1')
+
+    updatePersistedStateHashWithJsonRange(actual, value, 0, value.length, 2)
+
+    expect(actual.digest('hex')).toBe(expected)
+  })
+
+  it('atomically restores only a valid in-limit backup', () => {
+    const backupPath = join(root, 'backup.json')
+    const targetPath = join(root, 'profile', 'orca-data.json')
+    writeFileSync(backupPath, '{"repos":[{"id":"recovered"}]}')
+
+    restorePersistedStateBackupSync(backupPath, targetPath, 1024)
+
+    expect(JSON.parse(readFileSync(targetPath, 'utf8'))).toEqual({
+      repos: [{ id: 'recovered' }]
+    })
+    const originalTarget = readFileSync(targetPath)
+    writeFileSync(backupPath, '{{invalid')
+    expect(() => restorePersistedStateBackupSync(backupPath, targetPath, 1024)).toThrow()
+    expect(readFileSync(targetPath)).toEqual(originalTarget)
+    expect(
+      readdirSync(join(root, 'profile')).filter((name) => name.endsWith('.recovery.tmp'))
+    ).toEqual([])
+  })
+
+  it('leaves the target untouched when a backup exceeds the cap', () => {
+    const backupPath = join(root, 'backup.json')
+    const targetPath = join(root, 'orca-data.json')
+    writeFileSync(targetPath, '{"original":true}')
+    writeFileSync(backupPath, '')
+    truncateSync(backupPath, 1025)
+
+    expect(() => restorePersistedStateBackupSync(backupPath, targetPath, 1024)).toThrow(
+      NodeFileReadTooLargeError
+    )
+    expect(readFileSync(targetPath, 'utf8')).toBe('{"original":true}')
+  })
+})
diff --git a/src/shared/persisted-state-file-bounds.ts b/src/shared/persisted-state-file-bounds.ts
new file mode 100644
index 000000000..4fe8a977b
--- /dev/null
+++ b/src/shared/persisted-state-file-bounds.ts
@@ -0,0 +1,222 @@
+import { randomUUID, type Hash } from 'node:crypto'
+import { mkdirSync, renameSync, rmSync, writeFileSync } from 'node:fs'
+import { dirname } from 'node:path'
+import {
+  NodeFileReadTooLargeError,
+  readNodeFileSyncWithinLimit,
+  type BoundedNodeFileRead
+} from './node-bounded-file-reader'
+import {
+  JsonStringifyByteLimitError,
+  stringifyJsonWithinByteLimit
+} from './node-bounded-json-stringify'
+import {
+  assertJsonTextStructureWithinLimits,
+  type JsonTextStructureLimits
+} from './json-text-structure-limit'
+
+export const ORCA_PERSISTED_STATE_MAX_BYTES = 64 * 1024 * 1024
+export const ORCA_PERSISTED_STATE_SECRET_MAX_BYTES = 4 * 1024 * 1024
+export const ORCA_PERSISTED_STATE_HASH_CHUNK_CODE_UNITS = 64 * 1024
+export const ORCA_PERSISTED_STATE_JSON_LIMITS: JsonTextStructureLimits = {
+  structuralTokens: 4_000_000,
+  nestingDepth: 256
+}
+
+export type PersistedStateJsonRead<T> = {
+  byteLength: number
+  value: T
+}
+
+export class PersistedStateSecretCapacityError extends Error {
+  constructor(
+    readonly observedBytes: number,
+    readonly maxBytes = ORCA_PERSISTED_STATE_SECRET_MAX_BYTES
+  ) {
+    super(`Persisted state secret exceeds ${maxBytes} bytes`)
+    this.name = 'PersistedStateSecretCapacityError'
+  }
+}
+
+export function isPersistedStateFileCapacityError(
+  error: unknown
+): error is NodeFileReadTooLargeError {
+  return error instanceof NodeFileReadTooLargeError
+}
+
+export function readPersistedStateJsonFileSync<T>(
+  filePath: string,
+  maxBytes = ORCA_PERSISTED_STATE_MAX_BYTES,
+  structureLimits: JsonTextStructureLimits = ORCA_PERSISTED_STATE_JSON_LIMITS
+): PersistedStateJsonRead<T> {
+  const { buffer } = readPersistedStateFileBytesSync(filePath, maxBytes)
+  return {
+    byteLength: buffer.byteLength,
+    value: parsePersistedStateJsonBuffer<T>(buffer, structureLimits)
+  }
+}
+
+export function readPersistedStateFileBytesSync(
+  filePath: string,
+  maxBytes = ORCA_PERSISTED_STATE_MAX_BYTES
+): BoundedNodeFileRead {
+  return readNodeFileSyncWithinLimit(filePath, maxBytes)
+}
+
+export function parsePersistedStateJsonBuffer<T>(
+  buffer: Buffer,
+  structureLimits: JsonTextStructureLimits = ORCA_PERSISTED_STATE_JSON_LIMITS
+): T {
+  const serialized = buffer.toString('utf8')
+  assertJsonTextStructureWithinLimits(serialized, structureLimits)
+  return JSON.parse(serialized) as T
+}
+
+export function stringifyPersistedStateWithinLimit(
+  value: unknown,
+  maxBytes = ORCA_PERSISTED_STATE_MAX_BYTES
+): { byteLength: number; serialized: string } {
+  return stringifyJsonWithinByteLimit(value, maxBytes)
+}
+
+export function stringifyPrettyPersistedStateWithinLimit(
+  value: unknown,
+  maxBytes = ORCA_PERSISTED_STATE_MAX_BYTES
+): { byteLength: number; serialized: string } {
+  return stringifyJsonWithinByteLimit(value, maxBytes, 2)
+}
+
+export function encodePersistedStateJsonStringContent(
+  value: string,
+  maxBytes = ORCA_PERSISTED_STATE_MAX_BYTES
+): string {
+  const { serialized } = stringifyJsonWithinByteLimit(value, maxBytes)
+  return serialized.slice(1, -1)
+}
+
+export function assertPersistedStateSecretWithinLimit(
+  value: string,
+  maxBytes = ORCA_PERSISTED_STATE_SECRET_MAX_BYTES
+): void {
+  const observedBytes = Buffer.byteLength(value, 'utf8')
+  if (observedBytes > maxBytes) {
+    throw new PersistedStateSecretCapacityError(observedBytes, maxBytes)
+  }
+}
+
+export function replacedPersistedStateJsonByteLength(options: {
+  currentBytes: number
+  maxBytes?: number
+  replacement: string
+  search: string
+}): number {
+  const maxBytes = options.maxBytes ?? ORCA_PERSISTED_STATE_MAX_BYTES
+  if (!Number.isSafeInteger(maxBytes) || maxBytes < 0) {
+    throw new RangeError('Persisted state JSON byte limit must be a non-negative safe integer')
+  }
+  if (!Number.isSafeInteger(options.currentBytes) || options.currentBytes < 0) {
+    throw new RangeError('Persisted state JSON byte count must be a non-negative safe integer')
+  }
+  if (options.currentBytes > maxBytes) {
+    throw new JsonStringifyByteLimitError(options.currentBytes, maxBytes)
+  }
+  const nextBytes =
+    options.currentBytes -
+    Buffer.byteLength(options.search, 'utf8') +
+    Buffer.byteLength(options.replacement, 'utf8')
+  if (!Number.isSafeInteger(nextBytes) || nextBytes < 0 || nextBytes > maxBytes) {
+    throw new JsonStringifyByteLimitError(nextBytes, maxBytes)
+  }
+  return nextBytes
+}
+
+export function replacePersistedStateJsonWithinLimit(options: {
+  currentBytes: number
+  maxBytes?: number
+  replacement: string
+  search: string
+  serialized: string
+}): { byteLength: number; serialized: string } {
+  const byteLength = replacedPersistedStateJsonByteLength(options)
+  const searchIndex = options.serialized.indexOf(options.search)
+  if (searchIndex === -1) {
+    throw new Error('Persisted state JSON replacement slot is missing')
+  }
+  if (options.serialized.includes(options.search, searchIndex + options.search.length)) {
+    throw new Error('Persisted state JSON replacement slot is ambiguous')
+  }
+  return {
+    byteLength,
+    serialized: options.serialized.replace(options.search, () => options.replacement)
+  }
+}
+
+export function updatePersistedStateHashWithJsonRange(
+  hash: Pick<Hash, 'update'>,
+  value: string,
+  start = 0,
+  end = value.length,
+  chunkCodeUnits = ORCA_PERSISTED_STATE_HASH_CHUNK_CODE_UNITS
+): void {
+  if (
+    !Number.isSafeInteger(start) ||
+    !Number.isSafeInteger(end) ||
+    start < 0 ||
+    end < start ||
+    end > value.length
+  ) {
+    throw new RangeError('Persisted state hash range is invalid')
+  }
+  if (!Number.isSafeInteger(chunkCodeUnits) || chunkCodeUnits <= 0) {
+    throw new RangeError('Persisted state hash chunk size must be a positive safe integer')
+  }
+
+  let offset = start
+  while (offset < end) {
+    let nextOffset = Math.min(end, offset + chunkCodeUnits)
+    if (
+      nextOffset < end &&
+      isHighSurrogate(value.charCodeAt(nextOffset - 1)) &&
+      isLowSurrogate(value.charCodeAt(nextOffset))
+    ) {
+      nextOffset += 1
+    }
+    hash.update(value.slice(offset, nextOffset), 'utf8')
+    offset = nextOffset
+  }
+}
+
+export function restorePersistedStateBackupSync(
+  sourcePath: string,
+  targetPath: string,
+  maxBytes = ORCA_PERSISTED_STATE_MAX_BYTES
+): number {
+  const read = readValidatedPersistedStateBytesSync(sourcePath, maxBytes)
+  mkdirSync(dirname(targetPath), { recursive: true })
+  const temporaryPath = `${targetPath}.${process.pid}.${randomUUID()}.recovery.tmp`
+  try {
+    writeFileSync(temporaryPath, read.buffer)
+    renameSync(temporaryPath, targetPath)
+  } catch (error) {
+    rmSync(temporaryPath, { force: true })
+    throw error
+  }
+  return read.buffer.byteLength
+}
+
+function readValidatedPersistedStateBytesSync(
+  filePath: string,
+  maxBytes: number
+): BoundedNodeFileRead {
+  const read = readPersistedStateFileBytesSync(filePath, maxBytes)
+  parsePersistedStateJsonBuffer(read.buffer)
+  return read
+}
+
+function isHighSurrogate(code: number): boolean {
+  return code >= 0xd800 && code <= 0xdbff
+}
+
+function isLowSurrogate(code: number): boolean {
+  return code >= 0xdc00 && code <= 0xdfff
+}
diff --git a/src/shared/search-subprocess-lines.test.ts b/src/shared/search-subprocess-lines.test.ts
new file mode 100644
index 000000000..334477607
--- /dev/null
+++ b/src/shared/search-subprocess-lines.test.ts
@@ -0,0 +1,55 @@
+import { describe, expect, it } from 'vitest'
+import { SearchSubprocessLineAccumulator } from './search-subprocess-lines'
+
+describe('SearchSubprocessLineAccumulator', () => {
+  it('preserves UTF-8 records split across raw byte chunks', () => {
+    const parser = new SearchSubprocessLineAccumulator(32)
+    const bytes = Buffer.from('first🐋\nsecond')
+    const lines: string[] = []
+
+    expect(parser.push(bytes.subarray(0, 7), (line) => lines.push(line))).toBe(true)
+    expect(parser.push(bytes.subarray(7), (line) => lines.push(line))).toBe(true)
+
+    expect(lines).toEqual(['first🐋'])
+    expect(parser.finish()).toBe('second')
+  })
+
+  it('accepts an exact byte limit and rejects the next byte without decoding it', () => {
+    const parser = new SearchSubprocessLineAccumulator(4)
+    const lines: string[] = []
+
+    expect(parser.push(Buffer.from('four\n'), (line) => lines.push(line))).toBe(true)
+    expect(parser.push(Buffer.from('fives'), (line) => lines.push(line))).toBe(false)
+
+    expect(lines).toEqual(['four'])
+    expect(parser.finish()).toBeNull()
+  })
+
+  it('preserves empty lines and line order within one chunk', () => {
+    const parser = new SearchSubprocessLineAccumulator(8)
+    const lines: string[] = []
+
+    expect(parser.push(Buffer.from('\na\n\n'), (line) => lines.push(line))).toBe(true)
+
+    expect(lines).toEqual(['', 'a', ''])
+  })
+
+  it('retains one growable buffer for adversarial one-byte fragments', () => {
+    const parser = new SearchSubprocessLineAccumulator(256 * 1024)
+    const byte = Buffer.from('x')
+    let accepted = true
+
+    for (let index = 0; index < 200_000; index += 1) {
+      accepted = parser.push(byte, () => {}) && accepted
+    }
+
+    expect(accepted).toBe(true)
+    expect(Reflect.get(parser, 'buffer')).toBeInstanceOf(Buffer)
+    expect(parser.finish()).toBe('x'.repeat(200_000))
+    expect(Reflect.get(parser, 'buffer')).toBeNull()
+  })
+
+  it('rejects invalid byte limits', () => {
+    expect(() => new SearchSubprocessLineAccumulator(-1)).toThrow(RangeError)
+  })
+})
diff --git a/src/shared/search-subprocess-lines.ts b/src/shared/search-subprocess-lines.ts
new file mode 100644
index 000000000..5c04d9e82
--- /dev/null
+++ b/src/shared/search-subprocess-lines.ts
@@ -0,0 +1,75 @@
+export const SEARCH_SUBPROCESS_MAX_LINE_BYTES = 64 * 1024 * 1024
+const SEARCH_SUBPROCESS_INITIAL_LINE_BUFFER_BYTES = 4 * 1024
+
+export class SearchSubprocessLineAccumulator {
+  private buffer: Buffer | null = null
+  private bytes = 0
+
+  constructor(private readonly maxLineBytes = SEARCH_SUBPROCESS_MAX_LINE_BYTES) {
+    if (!Number.isSafeInteger(maxLineBytes) || maxLineBytes < 0) {
+      throw new RangeError('Search line limit must be a non-negative safe integer')
+    }
+  }
+
+  push(rawChunk: Buffer | string, onLine: (line: string) => void): boolean {
+    const chunk = Buffer.isBuffer(rawChunk) ? rawChunk : Buffer.from(rawChunk, 'utf8')
+    let cursor = 0
+    while (cursor < chunk.length) {
+      const newline = chunk.indexOf(0x0a, cursor)
+      const end = newline === -1 ? chunk.length : newline
+      const segmentBytes = end - cursor
+      if (this.bytes + segmentBytes > this.maxLineBytes) {
+        this.clear()
+        return false
+      }
+
+      if (newline !== -1 && this.bytes === 0) {
+        onLine(chunk.toString('utf8', cursor, end))
+      } else if (segmentBytes > 0) {
+        this.append(chunk.subarray(cursor, end))
+        if (newline !== -1) {
+          onLine(this.takeLine())
+        }
+      } else if (newline !== -1) {
+        onLine(this.takeLine())
+      }
+
+      if (newline === -1) {
+        return true
+      }
+      cursor = newline + 1
+    }
+    return true
+  }
+
+  finish(): string | null {
+    return this.bytes > 0 ? this.takeLine() : null
+  }
+
+  clear(): void {
+    this.buffer = null
+    this.bytes = 0
+  }
+
+  private append(segment: Buffer): void {
+    const requiredBytes = this.bytes + segment.length
+    if (!this.buffer || this.buffer.length < requiredBytes) {
+      const doubledCapacity = this.buffer?.length ? this.buffer.length * 2 : 0
+      const nextCapacity = Math.min(
+        this.maxLineBytes,
+        Math.max(SEARCH_SUBPROCESS_INITIAL_LINE_BUFFER_BYTES, doubledCapacity, requiredBytes)
+      )
+      const next = Buffer.allocUnsafe(nextCapacity)
+      this.buffer?.copy(next, 0, 0, this.bytes)
+      this.buffer = next
+    }
+    segment.copy(this.buffer, this.bytes)
+    this.bytes = requiredBytes
+  }
+
+  private takeLine(): string {
+    const line = this.buffer?.toString('utf8', 0, this.bytes) ?? ''
+    this.clear()
+    return line
+  }
+}
diff --git a/src/shared/string-chunk-compaction.test.ts b/src/shared/string-chunk-compaction.test.ts
new file mode 100644
index 000000000..dad53ba1d
--- /dev/null
+++ b/src/shared/string-chunk-compaction.test.ts
@@ -0,0 +1,17 @@
+import { describe, expect, it } from 'vitest'
+import { appendCompactedStringChunk, RETAINED_STRING_CHUNK_LIMIT } from './string-chunk-compaction'
+
+describe('appendCompactedStringChunk', () => {
+  it('preserves 100,000 fragments within the retained chunk limit', () => {
+    const chunks: string[] = []
+    let maxRetainedChunks = 0
+
+    for (let index = 0; index < 100_000; index += 1) {
+      appendCompactedStringChunk(chunks, String.fromCharCode(97 + (index % 26)))
+      maxRetainedChunks = Math.max(maxRetainedChunks, chunks.length)
+    }
+
+    expect(maxRetainedChunks).toBeLessThanOrEqual(RETAINED_STRING_CHUNK_LIMIT)
+    expect(chunks.join('')).toHaveLength(100_000)
+  })
+})
diff --git a/src/shared/string-chunk-compaction.ts b/src/shared/string-chunk-compaction.ts
new file mode 100644
index 000000000..1acb98ead
--- /dev/null
+++ b/src/shared/string-chunk-compaction.ts
@@ -0,0 +1,11 @@
+export const RETAINED_STRING_CHUNK_LIMIT = 1_024
+
+export function appendCompactedStringChunk(chunks: string[], value: string): void {
+  chunks.push(value)
+  if (chunks.length <= RETAINED_STRING_CHUNK_LIMIT) {
+    return
+  }
+  const compacted = chunks.join('')
+  chunks.length = 0
+  chunks.push(compacted)
+}