Unrot the flawd mutation-testing config

Dockerfile

@@ -1,10 +1,30 @@
 # Dockerfile for flawd mutation testing - Rust
 FROM rust:1.77-slim
 
-RUN apt-get update && apt-get install -y git && rm -rf /var/lib/apt/lists/*
+RUN apt-get update && apt-get install -y git curl ca-certificates && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /app
 
+# flawd.toml's [coverage] command runs `cargo llvm-cov`, which shells out to
+# llvm-cov and llvm-profdata. The llvm-tools component supplies both, so the
+# command needs no LLVM_COV/LLVM_PROFDATA overrides. rust-toolchain.toml lands
+# first so the component is added to the toolchain the build actually uses
+# rather than the image's default.
+COPY rust-toolchain.toml ./
+RUN rustup component add llvm-tools-preview
+
+# cargo-llvm-cov ships prebuilt binaries; installing from source here would add
+# several minutes to every image build.
+RUN set -eux; \
+    case "$(uname -m)" in \
+      x86_64)  target=x86_64-unknown-linux-gnu ;; \
+      aarch64) target=aarch64-unknown-linux-gnu ;; \
+      *) echo "no cargo-llvm-cov release for $(uname -m)" >&2; exit 1 ;; \
+    esac; \
+    curl -fsSL "https://github.com/taiki-e/cargo-llvm-cov/releases/latest/download/cargo-llvm-cov-${target}.tar.gz" \
+      | tar xzf - -C "${CARGO_HOME}/bin"; \
+    cargo llvm-cov --version
+
 # Pre-fetch and build dependencies for layer caching (debug/test profile)
 COPY Cargo.toml Cargo.lock ./
 COPY crates/lash-types/Cargo.toml crates/lash-types/Cargo.toml

flawd.toml

@@ -5,7 +5,7 @@ enabled = ["rs"]
 inputs = [
   { format = "lcov", path = "coverage/lcov.info" }
 ]
-command = "LLVM_COV=/opt/homebrew/opt/llvm/bin/llvm-cov LLVM_PROFDATA=/opt/homebrew/opt/llvm/bin/llvm-profdata cargo llvm-cov --lcov --output-path coverage/lcov.info"
+command = "mkdir -p coverage && cargo llvm-cov --workspace --lcov --output-path coverage/lcov.info"
 timeout_seconds = 300
 
 [test]
@@ -24,10 +24,6 @@ dedupe = true
 sampling = "weighted"
 cache = true
 
-[llm]
-mode = "off"
-max_edit_chars = 120
-
 [docker]
 dockerfile = "Dockerfile"
 workdir = "/app"