Released a Version of Seiro MCP That Supports Codex App
Seiro MCP, which I released at the end of last year to support development for visionOS,
may look like it has not moved much since release, but I actually use it almost every day. Rather than saying I use it, the AI uses it automatically, so when I am developing for visionOS, it is heavily used to check whether the implementation can be built every time, alongside the implementation itself. That Seiro MCP has had about two updates released this month.
The first was a fix for an issue with the validate_sandbox_policy tool.
It seems there were times when Codex could not call it properly depending on its circumstances while using it. This release fixed that. Incidentally, validate_sandbox_policy checks from Seiro MCP whether the project is buildable, and in that part there was a phenomenon where, depending on how it was called, it failed even though the project was actually buildable.
The fixes were as follows.
- Improved
validate_sandbox_policySDK checks to handle Xcode's versioned SDK identifiers (e.g.xros26.2,macosx26.2) by accepting case-insensitive prefix matches (e.g.xrosmatchesxros26.2). #3 - Added stable visionOS SDK aliases (
visionOS/visionOS Simulator, plusxrOSvariants) to the detected SDK list so configuration and tool calls can use human-friendly names. #3
The second fix was personally quite significant: an issue where, for some reason, builds failed when using Codex App, the desktop app version of Codex CLI that was announced a little while ago.
I learned this for the first time, but while Codex CLI and Codex App look like they only differ in UI, they apparently handle paths and related things differently. The build failure happened because the path was wrong, which caused a security sandbox-like error and prevented the build from completing.
I made various fixes below, added tests, and released it.
- Fixed
build_visionos_appfailures caused byRead-only file system (os error 30)when creating artifact directories. - Added robust artifact root writability checks using an actual write probe.
- Added automatic fallback to a writable temporary artifact root (
/tmp/.../seiro-mcp/visionos-builds) when the default root is not writable. - Ensured build output and artifact metadata use the same resolved artifact root.
- Added regression coverage for read-only artifact root scenarios.
So MCP servers that start via standard input and output may be running into similar issues in Codex App elsewhere too.
Seiro MCP only has tiny features, but it is reasonably useful in my own visionOS development, supporting the cycle of checking whether something can build and, when it cannot, having the AI fix it.
By the way, I did not write about this because the focus would spread too much, but Seiro MCP can actually build for macOS too, since it calls xcodebuild, which is obvious in a way. So when building something for visionOS, it can be troublesome to immediately check the logic there, and I sometimes do simultaneous build checks for two versions: a macOS test app and the visionOS target.
- Connection check: macOS
- What I want to build: visionOS
So, as shown above, Seiro MCP is used twice, and each use is quite helpful from a coding perspective.
In any case, while building things for visionOS, I have also been touching AI protocols and learning a lot. As a result, Seiro MCP also became the first OSS product I released in Rust. I may be able to keep going into the next era in roughly this way.