Initial commit: rust-craft plugin

Rust-on-NixOS knowledge plugin. Relocates plugin.json into .claude-plugin/
so it loads as a proper plugin, and adds README/LICENSE/.gitignore for
distribution. Skill rust-nix-toolchain (Cranelift vs LLVM codegen, fenix
nightly pins, cargo/clippy gates) with cranelift-limitations reference.

.claude-plugin/plugin.json

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+{
+	"name": "rust-craft",
+	"version": "1.0.0",
+	"description": "Rust development on NixOS — toolchain management (fenix nightly pins), codegen backends (Cranelift vs LLVM), clippy/cargo quality-gate workflows, and common pitfalls.",
+	"author": {
+		"name": "oleks",
+		"email": "plugins@oleks.space"
+	},
+	"repository": "https://claude-plugins.oleks.space/plugins/rust-craft.git",
+	"license": "MIT",
+	"keywords": [
+		"rust",
+		"nixos",
+		"fenix",
+		"cranelift",
+		"llvm",
+		"clippy",
+		"cargo",
+		"toolchain"
+	]
+}

.gitignore

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+.cache/
+.claude/
+*.log

CLAUDE.md

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+# rust-craft Plugin
+
+Rust development knowledge for NixOS environments — toolchain management, codegen backends, and common pitfalls.
+
+## Skills
+
+- **rust-nix-toolchain**: Cranelift vs LLVM codegen backend issues, NixOS fenix toolchain management, cargo quality gate patterns

LICENSE

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+MIT License
+
+Copyright (c) 2026 Oleks Kuksenko
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# claude-plugin-rust-craft
+
+Claude Code plugin — Rust development knowledge for NixOS environments: toolchain management, codegen backends, and common pitfalls.
+
+## Installation
+
+Add to your Claude Code plugin list or install from the [plugin registry](https://claude-plugins.oleks.space):
+
+```
+claude plugin add https://claude-plugins.oleks.space/plugins/rust-craft.git
+```
+
+## Usage
+
+Skills from this plugin are automatically available in Claude Code conversations when installed.
+
+## Skills
+
+- **rust-nix-toolchain** — Cranelift vs LLVM codegen backend issues (`asm!`/`global_asm!` sym operands, wasmtime-fiber failures, "cargo test fails but cargo check works"), NixOS fenix nightly toolchain pins, and cargo/clippy quality-gate patterns. See `skills/rust-nix-toolchain/references/cranelift-limitations.md`.
+
+## License
+
+MIT

skills/rust-nix-toolchain/SKILL.md

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+---
+name: rust-nix-toolchain
+description: >-
+  This skill should be used when the user encounters
+  "asm! and global_asm! sym operands are not yet supported",
+  "wasmtime-fiber" compilation failures,
+  "cargo test fails but cargo check works",
+  "cranelift codegen backend" issues,
+  "update Rust nightly on NixOS",
+  "fenix toolchain pin",
+  or mentions Rust codegen backend problems on NixOS.
+  Covers the Cranelift vs LLVM codegen backend split,
+  NixOS fenix toolchain management, and common
+  Rust nightly pitfalls.
+---
+
+# Rust Nightly Toolchain on NixOS
+
+## Cranelift vs LLVM Codegen Backend
+
+NixOS dev setups commonly use `codegen-backend = "cranelift"` in `~/.cargo/config.toml` for faster dev builds. **Cranelift does NOT support `global_asm! { sym }` operands.** This causes `wasmtime-fiber` and other crates using `global_asm!` with `sym` to fail.
+
+### Symptom
+
+```
+error: asm! and global_asm! sym operands are not yet supported
+  --> wasmtime-fiber-28.0.1/src/stackswitch/x86_64.rs
+```
+
+### Why `cargo check` works but `cargo test` fails
+
+- `cargo check` / `cargo clippy` only verify types and borrow checking — **no codegen**
+- `cargo test` / `cargo build` invoke the codegen backend, hitting the Cranelift limitation
+- This makes the error appear only at test/build time, not during linting
+
+### Fix: Override codegen backend for tests
+
+```bash
+# One-shot: force LLVM for this test run
+CARGO_PROFILE_DEV_CODEGEN_BACKEND=llvm cargo test --lib
+
+# Or permanently in the project's .cargo/config.toml:
+# [profile.dev]
+# codegen-backend = "llvm"
+```
+
+### Where the Cranelift backend is configured
+
+Check `~/.cargo/config.toml`:
+
+```toml
+[profile.dev]
+codegen-backend = "cranelift"  # faster codegen for dev builds
+
+[unstable]
+codegen-backend = true
+```
+
+This is a **user-level** config that affects all projects. Project-level `.cargo/config.toml` can override it.
+
+## NixOS Fenix Toolchain Management
+
+### How the Rust nightly is pinned
+
+On NixOS with fenix, the Rust nightly version is determined by:
+
+1. **`flake.nix`** declares fenix input: `fenix.url = "github:nix-community/fenix"`
+2. **`flake.lock`** pins a specific fenix commit, which bundles nightly manifests
+3. **NixOS module** (e.g. `nixos/rust-dev.nix`) selects components:
+
+```nix
+rust-nightly = fenix.packages.${pkgs.stdenv.hostPlatform.system}.complete.withComponents [
+  "cargo" "clippy" "rustc" "rustfmt"
+  "rust-src" "rust-analyzer"
+  "rustc-codegen-cranelift-preview"
+];
+```
+
+### Updating the nightly
+
+```bash
+cd ~/projects/servers/<hostname>
+nix flake update fenix
+sudo nixos-rebuild switch --flake '.#<hostname>'
+```
+
+This pulls the latest fenix commit which includes the most recent nightly.
+
+### Pinning a specific nightly date
+
+Replace `complete.withComponents` with `toolchainOf`:
+
+```nix
+rust-nightly = fenix.packages.${system}.toolchainOf {
+  channel = "nightly";
+  date = "2026-03-15";
+  sha256 = "<manifest-hash>";  # required for pure evaluation
+}.withComponents [ "cargo" "clippy" "rustc" "rustfmt" "rust-src" ];
+```
+
+## Cargo Quality Gate
+
+Standard Rust quality gate sequence:
+
+```bash
+# 1. Format
+cargo fmt
+
+# 2. Lint (zero warnings required)
+cargo clippy --all --benches --tests --examples --all-features
+
+# 3. Test (use LLVM if Cranelift is default)
+CARGO_PROFILE_DEV_CODEGEN_BACKEND=llvm cargo test --lib
+```
+
+### Common clippy patterns
+
+| Warning | Fix |
+|---------|-----|
+| `collapsible_match` / `collapsible_if` | Merge nested `if` into match guard: `Variant if condition => { ... }` |
+| `new_without_default` | Add `impl Default for T { fn default() -> Self { Self::new() } }` |
+| `let_unit_value` | Remove `let _ =` from expressions returning `()` |
+| `unnecessary_sort_by` | Use `sort_by_key(|x| Reverse(x.field))` instead of `sort_by(|a, b| b.field.cmp(&a.field))` |
+| `derivable_impls` | Replace manual `impl Default` with `#[derive(Default)]` |
+| `manual_map` | Replace `if let Some(x) = opt { Some(f(x)) } else { None }` with `opt.map(f)` |
+| `useless_conversion` | Remove redundant `.into_iter()` on values already implementing `IntoIterator` |
+
+### Feature-gated fields in tests
+
+When a struct has `#[cfg(feature = "...")]` fields, tests compiled with `--all-features` must include those fields:
+
+```rust
+let cfg = MyConfig {
+    normal_field: value,
+    #[cfg(feature = "discord")]
+    discord: None,  // must be present when feature is active
+};
+```

skills/rust-nix-toolchain/references/cranelift-limitations.md

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+# Cranelift Codegen Backend Limitations
+
+## Background
+
+The Cranelift codegen backend (`rustc-codegen-cranelift-preview`) is an alternative to LLVM for Rust compilation. It's significantly faster for debug builds but has feature gaps.
+
+## Known Unsupported Features
+
+### `global_asm!` with `sym` operands
+
+**Status**: Not supported as of March 2026
+
+The error originates in `compiler/rustc_codegen_cranelift/src/global_asm.rs` in the rust-lang/rust repo. When Cranelift encounters a `GlobalAsmOperandRef::SymFn` operand, it emits:
+
+```
+error: asm! and global_asm! sym operands are not yet supported
+```
+
+**Affected crates** (non-exhaustive):
+- `wasmtime-fiber` (all versions, including v42+) — uses `global_asm!` with `sym` for fiber context switching
+- Any crate using `global_asm!` with function symbol references
+
+**Source**: [rust-lang/rust global_asm.rs](https://github.com/rust-lang/rust/blob/main/compiler/rustc_codegen_cranelift/src/global_asm.rs)
+
+### Diagnostic confusion
+
+The error message says "not yet supported" which looks like a Rust nightly regression. It's NOT — it's a Cranelift limitation that has existed since the backend was introduced. The confusion arises because:
+
+1. `cargo check` and `cargo clippy` don't invoke codegen → no error
+2. `cargo build` / `cargo test` invoke codegen → Cranelift fails
+3. The error message doesn't mention Cranelift, so it looks like a rustc bug
+
+## Workarounds
+
+### Per-invocation override
+
+```bash
+CARGO_PROFILE_DEV_CODEGEN_BACKEND=llvm cargo test
+CARGO_PROFILE_DEV_CODEGEN_BACKEND=llvm cargo build
+```
+
+### Per-project override
+
+Create `.cargo/config.toml` in the project:
+
+```toml
+[profile.dev]
+codegen-backend = "llvm"
+```
+
+### Selective override (keep Cranelift for most builds)
+
+Use LLVM only for test profile:
+
+```toml
+[profile.test]
+codegen-backend = "llvm"
+```
+
+## Detection
+
+If `cargo check` passes but `cargo test` fails with `global_asm!` errors, check:
+
+```bash
+grep -r "codegen-backend" ~/.cargo/config.toml .cargo/config.toml 2>/dev/null
+```