Rust bundled runtime installation retains large native-image buffers on cold and warm startup

从 Rust SDK 入口点 install_bundled_runtime() 开始，然后跟踪 install_hostless_assets 以及 install_runtime_pair 对 runtime.node 的处理。运行 issue 中所述的隔离冷启动和带种子暖启动复现，包括损坏和截断的文件。完成的标准是：有界提取和校验能够保留字节和模式，有效的只读缓存仍可使用，损坏的文件能够以原子方式修复，并且测量覆盖冷启动、暖启动和修复场景。

Description

The Rust SDK's install_bundled_runtime() path allocates complete runtime archive entries and reads installed files into full-size buffers. install_hostless_assets handles runtime.node, then install_runtime_pair extracts and compares it again. On macOS, those allocations can leave substantial physical memory retained by the allocator even after the installer returns, including when every installed file is already valid.

This is an installer-only reproduction, not evidence of a live-object leak or a measurement of a client/model session. No authentication, CLI subprocess or service request is needed.

Reproduction

At SDK revision a675b55531a9dfc647ee015e32d74279568550f3, build a release Rust executable with default bundled-cli features which calls github_copilot_sdk::install_bundled_runtime() once and stays alive for one second afterward. Run the executable with a fresh isolated HOME. For the warm case, first seed that same home's SDK cache using a separate process, then run the measured executable in a new process. Do not reuse the same process, because its OnceLock bypasses installation.

Measure process-lifetime peak RSS/physical footprint with macOS /usr/bin/time -l, and current RSS/physical footprint using proc_pid_rusage(RUSAGE_INFO_V0) after the one-second idle period. Keep allocation-stack logging disabled in these measurements.

Observed SDK-only baseline

Apple M4 Pro, 48 GiB RAM, macOS 26.6.2 (25G83), arm64; rustc 1.94.0; release optimization level 3, debug level 1. Public bundled runtime 1.0.84-8. Five independent processes per cohort; medians (minimum-maximum):

The installed runtime.node is 71,166,736 bytes, SHA-256 839cd681c72cb92f27697d5e3e3ee96d7bb8df4234ffb5f7b442956828ec173a. Filtered embedded runtime archive SHA-256: 6c43b789080fc06b25d406af8fae709daa99f0724c4d290cc8a31160c5a3ad64.

A separate instrumented warm process recorded two page-rounded 71,172,096-byte VM allocations through the SDK runtime installer, one also through std::fs::read; after installation, vmmap reported 165.7 MiB in MALLOC_LARGE (empty) regions. Instrumented values are excluded from the comparison above.

Expected behavior

Runtime extraction and existing-file verification should use bounded buffers, preserve exact output bytes/modes, permit valid read-only warm caches, and repair corrupt files with staged atomic replacement. The full CLI installer is a separate path and outside the memory optimization scope.

A focused fix with runnable reproduction and cold/warm/corrupt/truncated measurements is prepared.