Desktop sidecar crash: STATUS_STACK_BUFFER_OVERRUN (0xC0000409 / exit 3221226505) from @parcel/watcher std::regex_match on long paths (upstream parcel-bundler/watcher#250) #32443

Summary

On Windows, the OpenCode Desktop sidecar process crashes with exit code 3221226505 (0xC0000409, STATUS_STACK_BUFFER_OVERRUN), taking the local server offline and making the conversation unresponsive. Forensic analysis of the Windows minidump points the crash at the bundled native file-watcher module @parcel/watcher-win32-x64\watcher.node. The crash is triggered when the watcher's glob/regex engine processes very long filesystem paths, matching the known upstream bug parcel-bundler/watcher#250.

This looks like the same crash class as #29033 (open) and #28413 (closed) — both report the identical exit code on Windows, but neither pinpointed the underlying module. This report adds the minidump-confirmed root cause and the upstream link.

Environment

• OpenCode version: Desktop v1.17.7 (Windows x64)
• Operating System: Windows 11 (10.0.26100)
• Terminal: desktop
• The crash is not model-specific — it was observed across multiple models. The trigger is the filesystem path, not the AI model.

Symptoms

Root cause (minidump evidence)

A Windows crash dump is generated under:

%APPDATA%\ai.opencode.desktop\Crashpad\reports\

Key facts from the dump:

The stack overflow originates in the watcher's native code — not in the Node application logic or in user scripts. It matches the known upstream issue:

Stack overflow crash (STATUS_STACK_BUFFER_OVERRUN / 0xC0000409) in std::regex_match on long paths when using a glob ignore option — parcel-bundler/watcher#250

@parcel/watcher applies std::regex_match to filesystem paths; with sufficiently long input strings the regex engine consumes enough stack space to trip the compiler /GS buffer-security check. The crash is therefore path-length dependent.

Steps to reproduce

Warning: this will disconnect the OpenCode session. Run only in a disposable workspace.

Create a file with a very long basename inside a directory that OpenCode is watching:

$dir  = "C:\some\watched\workspace"
$long = "VERY_LONG_BASENAME_" + ("x" * 200) + "_20260101T000000Z.txt"
Set-Content -Path (Join-Path $dir $long) -Value "test"

A deep directory hierarchy combined with a very long basename (total path well beyond 260 characters) reliably trips the watcher's regex engine and crashes the sidecar within seconds.

Why it can look model-dependent

Sessions that happen to create long paths crash; sessions that don't, never see it. This creates a false correlation between the crash and a specific model. The real variable is path length, not the model.

Recommendations

1. Upgrade or replace @parcel/watcher to a release that resolves parcel-bundler/watcher#250.
2. Bound/normalize path length before passing paths to the watcher's glob-ignore matching, if upgrading isn't immediately possible.
3. Add a config toggle to disable file watching for users running file-intensive tasks.
4. Graceful degradation: when the sidecar crashes, preserve conversation state and allow reconnection without losing context.
5. Long-path testing: exercise the bundled native watcher with paths > 260 characters on Windows.

Workaround (user-side)

• Keep workspace file/directory basenames short.
• Do file-intensive/intermediate work outside the watched workspace, then copy only short-named final artifacts into it.
• Avoid printing long recursive path listings that the watcher may then process.

Related

• Sidecar crashes with STATUS_STACK_BUFFER_OVERRUN (0xC0000409) on Windows with CJK paths #29033 (open) — same exit code / STATUS_STACK_BUFFER_OVERRUN on Windows, root cause not identified
• [Bug] Sidecar crashes with exit code 3221226505 (0xC0000409) on Windows - causes local server to go offline #28413 (closed, not planned) — same exit code 3221226505