microsoft/win-dev-skills is a collection of AI-agent instructions and tools for creating native Windows applications with WinUI 3 and the Windows App SDK. Windows developers use it to guide agents through app development tasks from scaffolding and design to testing, packaging, and release. The catalogue entries are its agents, skills, and plugin components.
Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add microsoft/win-dev-skills --skill windbg-user-mutex-held-across-co-awaitgit clone --depth 1 https://github.com/microsoft/win-dev-skillsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/microsoft/win-dev-skills/windbg-user-mutex-held-across-co-await)<a href="https://agentmods.dev/skills/microsoft/win-dev-skills/windbg-user-mutex-held-across-co-await"><img src="https://agentmods.dev/badge/skills/microsoft/win-dev-skills/windbg-user-mutex-held-across-co-await/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/microsoft/win-dev-skills/windbg-user-mutex-held-across-co-await"><img src="https://agentmods.dev/badge/skills/microsoft/win-dev-skills/windbg-user-mutex-held-across-co-await.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00049 | $0.00879 |
| Opus 5.5 | $0.00020 | $0.00352 |
| Sonnet 5.5 | $0.00010 | $0.00176 |
| Haiku 4.5 | $0.00005 | $0.00088 |
Grade A, and why
windbg-user-mutex-held-across-co-await scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 8d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 87 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Mutex Held Across co_await
Load windbg-diagnostic-method first if it is not already loaded in this
conversation, and apply it throughout for evidence ranking, hypothesis testing,
confidence calibration, independent review, and report validation. This skill
adds the bug-family-specific commands and evidence requirements.
Detection
This pattern can occur in native application, service, or user-mode driver
code, including UMDF components that use C++ coroutines. Look for a lock
acquired before co_await and released after resumption or
coroutine destruction. Mutex ownership belongs to the acquiring thread, not
the coroutine frame. A resumption on another thread can violate that contract.
Even same-thread resumption can create reentrancy or progress problems when
the awaited operation needs a lock the coroutine still holds.
Workflow
- Identify the exact lock primitive and acquisition/release scope in source. Audit every suspension point while the RAII guard or ownership is alive.
- Establish the acquire and resume threads using trace/source evidence. Standard mutexes and SRW locks do not provide a universally queryable owner field; do not fabricate an owning TID from undocumented layouts.
- Verify the awaiter's resumption contract. C++/WinRT can preserve apartment
context for particular awaitables;
resume_backgroundintentionally switches. Do not assume every WinRT awaitable always resumes on a worker or always on the originating thread. - Distinguish wrong-thread release, a dependency cycle, state changed during suspension, lifetime failure, and unrelated memory corruption.
- Move the thread-affine lock into synchronous scopes. Revalidate relevant state after the await rather than treating the pre-await snapshot as current.
If the symptom is general blocking use windbg-user-wait-chain-analysis. For damaged
heap objects use windbg-user-heap-corruption-investigation. If a recording is available,
windbg-user-ttd-reverse-debugging-triage can help establish the ownership timeline.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 8d ago First seen · 87 lines · 49 tokens per session scan A 407528726c53
windbg-user-mutex-held-across-co-await is a skill published in the GitHub repository microsoft/win-dev-skills (472 stars, last pushed 2d ago), licensed MIT. It adds 49 tokens to every session and 879 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-10-08.
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