[wan9chi]

Motivation

A task that creates a symbolic link doesn't have it among its outputs unless an output glob matches it. Nitro's dependency tracer, for example, links .output/server/node_modules/tslib into .nf3. fspy records nothing for symlink, so a hit leaves the link out. When the task checks the path first, as nf3 does, the link is a plain input and a clean checkout misses.

Changes

fspy records the path of a new link as a write, before the call:

• Unix preload: symlink and symlinkat.
• Linux seccomp supervisor: the same calls for static binaries.
• Windows: NtFsControlFile with FSCTL_SET_REPARSE_POINT(_EX), which covers CreateSymbolicLinkW and junctions.

vt needs no change: a written symlink counts as a file, and the archive stores links as links (#885).

E2E cases: symlink_in_output (synthetic, vtt symlink) and nitro_auto_outputs_restore_links (the nitro_build_cache Nitro build with automatic tracking only). Both run only on Unix in the first commit, because Windows already behaves differently there, and on every platform after.

Part of a stack that lets automatic tracking cache tasks which read their own outputs and list the folders holding them, so they also hit on a clean checkout.

🤖 Generated with Claude Code

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Note

Medium Risk
Changes syscall/NT detour behavior for symlink creation across all tracked task runs; incorrect recording could affect cache fingerprints and restored outputs, but the pattern matches existing hard-link and rename tracking.

Overview
Symbolic links a task creates are now tracked as outputs and restored on cache hit, even when no output glob covers them—fixing cases like Nitro’s dependency links under .output/server/node_modules and clean-checkout misses when the task stat’d the link path first.

fspy records the link path as a write before the syscall returns (failed creates still count): symlink / symlinkat on Unix preload and Linux seccomp; on Windows, NtFsControlFile when FSCTL_SET_REPARSE_POINT(_EX) runs (covers CreateSymbolicLinkW and junctions). The symlink target string is not accessed for tracking.

Vite Task logic is unchanged—written symlinks already archive and replay as links (#885); rebuildable docs note Windows junctions count as written symlinks, not folders. vtt symlink works on Windows for e2e. New snapshot tests: symlink_in_output and nitro_auto_outputs_restore_links (auto tracking only).

^{Reviewed by Cursor Bugbot for commit f7f77b5. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

fspy benchmark

linux

dynamic/launch             change  -0.55%  [ -5.12% ..  +3.81%]  overhead   +60.84%
dynamic/access             change  +0.42%  [ -3.47% ..  +7.41%]  overhead   +27.85%
dynamic/access-relative    change  +1.78%  [ -1.78% ..  +5.03%]  overhead   +79.65%
dynamic/access-contended   change  +0.32%  [ -5.64% ..  +5.43%]  overhead   +53.92%
static/launch              change  +0.34%  [ -3.92% ..  +3.83%]  overhead  +197.70%
static/access              change  -0.16%  [ -1.99% ..  +1.32%]  overhead +1561.95%
static/access-relative     change  -0.02%  [ -1.23% ..  +1.42%]  overhead +2055.79%
static/access-contended    change  +0.26%  [ -0.41% ..  +0.70%]  overhead +2099.90%

macos

dynamic/launch             change  +0.02%  [ -4.93% ..  +5.94%]  overhead  +241.34%
dynamic/access             change  +0.65%  [ -5.25% ..  +9.49%]  overhead    +4.38%
dynamic/access-relative    change  -3.16%  [-10.93% ..  +3.49%]  overhead  +224.93%
dynamic/access-contended   change  +2.06%  [-13.13% .. +20.40%]  overhead    +2.45%

windows

dynamic/launch             change  +0.41%  [ -2.90% ..  +2.46%]  overhead   +25.51%
dynamic/access             change  +0.39%  [ -0.20% ..  +1.19%]  overhead    +1.18%
dynamic/access-relative    change  +0.00%  [ -0.75% ..  +0.78%]  overhead    +1.17%
dynamic/access-contended   change  +0.19%  [ -0.92% ..  +1.28%]  overhead    +1.31%