Add Nix flake for mciasctl and mciasgrpcctl

Vendor dependencies and expose control program binaries via
nix build. Uses nixpkgs-unstable for Go 1.26 support.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/google.golang.org/grpc/CONTRIBUTING.md

@@ -0,0 +1,102 @@
+# How to contribute
+
+We welcome your patches and contributions to gRPC! Please read the gRPC
+organization's [governance
+rules](https://github.com/grpc/grpc-community/blob/master/governance.md) before
+proceeding.
+
+If you are new to GitHub, please start by reading [Pull Request howto](https://help.github.com/articles/about-pull-requests/)
+
+## Legal requirements
+
+In order to protect both you and ourselves, you will need to sign the
+[Contributor License
+Agreement](https://identity.linuxfoundation.org/projects/cncf). When you create
+your first PR, a link will be added as a comment that contains the steps needed
+to complete this process.
+
+## Getting Started
+
+A great way to start is by searching through our open issues. [Unassigned issues
+labeled as "help
+wanted"](https://github.com/grpc/grpc-go/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20label%3A%22Status%3A%20Help%20Wanted%22%20no%3Aassignee)
+are especially nice for first-time contributors, as they should be well-defined
+problems that already have agreed-upon solutions.
+
+## Code Style
+
+We follow [Google's published Go style
+guide](https://google.github.io/styleguide/go/). Note that there are three
+primary documents that make up this style guide; please follow them as closely
+as possible. If a reviewer recommends something that contradicts those
+guidelines, there may be valid reasons to do so, but it should be rare.
+
+## Guidelines for Pull Requests
+
+How to get your contributions merged smoothly and quickly:
+
+- Create **small PRs** that are narrowly focused on **addressing a single
+  concern**. We often receive PRs that attempt to fix several things at the same
+  time, and if one part of the PR has a problem, that will hold up the entire
+  PR.
+
+- For **speculative changes**, consider opening an issue and discussing it
+  first. If you are suggesting a behavioral or API change, consider starting
+  with a [gRFC proposal](https://github.com/grpc/proposal). Many new features
+  that are not bug fixes will require cross-language agreement.
+
+- If you want to fix **formatting or style**, consider whether your changes are
+  an obvious improvement or might be considered a personal preference. If a
+  style change is based on preference, it likely will not be accepted. If it
+  corrects widely agreed-upon anti-patterns, then please do create a PR and
+  explain the benefits of the change.
+
+- For correcting **misspellings**, please be aware that we use some terms that
+  are sometimes flagged by spell checkers. As an example, "if an only if" is
+  often written as "iff". Please do not make spelling correction changes unless
+  you are certain they are misspellings.
+
+- Provide a good **PR description** as a record of **what** change is being made
+  and **why** it was made. Link to a GitHub issue if it exists.
+
+- Maintain a **clean commit history** and use **meaningful commit messages**.
+  PRs with messy commit histories are difficult to review and won't be merged.
+  Before sending your PR, ensure your changes are based on top of the latest
+  `upstream/master` commits, and avoid rebasing in the middle of a code review.
+  You should **never use `git push -f`** unless absolutely necessary during a
+  review, as it can interfere with GitHub's tracking of comments.
+
+- **All tests need to be passing** before your change can be merged. We
+  recommend you run tests locally before creating your PR to catch breakages
+  early on:
+
+  - `./scripts/vet.sh` to catch vet errors.
+  - `go test -cpu 1,4 -timeout 7m ./...` to run the tests.
+  - `go test -race -cpu 1,4 -timeout 7m ./...` to run tests in race mode.
+
+  Note that we have a multi-module repo, so `go test` commands may need to be
+  run from the root of each module in order to cause all tests to run.
+
+  *Alternatively*, you may find it easier to push your changes to your fork on
+  GitHub, which will trigger a GitHub Actions run that you can use to verify
+  everything is passing.
+
+- If you are adding a new file, make sure it has the **copyright message**
+  template at the top as a comment. You can copy the message from an existing
+  file and update the year.
+
+- The grpc package should only depend on standard Go packages and a small number
+  of exceptions. **If your contribution introduces new dependencies**, you will
+  need a discussion with gRPC-Go maintainers. A GitHub action check will run on
+  every PR, and will flag any transitive dependency changes from any public
+  package.
+
+- Unless your PR is trivial, you should **expect reviewer comments** that you
+  will need to address before merging. We'll label the PR as `Status: Requires
+  Reporter Clarification` if we expect you to respond to these comments in a
+  timely manner. If the PR remains inactive for 6 days, it will be marked as
+  `stale`, and we will automatically close it after 7 days if we don't hear back
+  from you. Please feel free to ping issues or bugs if you do not get a response
+  within a week.
+
+- Exceptions to the rules can be made if there's a compelling reason to do so.