CI: Centralize Rust version management using RUST_STABLE_VERSION

Define RUST_STABLE_VERSION environment variable in CI workflows and use
it consistently instead of hardcoded version numbers. This improves
maintainability by ensuring all workflows reference a single source of
truth for the Rust stable version.

Changes:
- Added RUST_STABLE_VERSION env var to build-reusable.yaml, tests.yaml,
  lint.yaml, and doc-commands.yaml
- Replaced all hardcoded "1.84" references with env variable references
- Added cross-reference comments to track related version definitions
  across rust-toolchain.toml, CI workflows, and documentation

This ensures version consistency and simplifies future Rust version
updates across the entire CI infrastructure.

Author: dannywillems

.github/workflows/build-reusable.yaml

@@ -34,6 +34,15 @@ env:
   MINA_PANIC_ON_BUG: true
   CARGO_INCREMENTAL: 1
   RUSTFLAGS: "-C overflow-checks=off -C debug-assertions=off"
+  # This should be in line with the version in:
+  # - rust-toolchain.toml
+  # - .github/workflows/build-reusable.yaml
+  # - .github/workflows/tests.yaml
+  # - .github/workflows/lint.yaml
+  # - .github/workflows/doc-commands.yaml
+  # - website/scripts/setup/install-rust.sh
+  # - website/docs/developers/getting-started.mdx
+  RUST_STABLE_VERSION: "1.84"
 
 jobs:
   build:
@@ -56,7 +65,7 @@ jobs:
       - name: Setup Rust
         uses: ./.github/actions/setup-rust
         with:
-          toolchain: 1.84
+          toolchain: ${{ env.RUST_STABLE_VERSION }}
           cache-prefix: build-${{ inputs.os }}-${{ inputs.cache-prefix }}v0
 
       - name: Release build
@@ -99,7 +108,7 @@ jobs:
       - name: Setup Rust
         uses: ./.github/actions/setup-rust
         with:
-          toolchain: 1.84
+          toolchain: ${{ env.RUST_STABLE_VERSION }}
           cache-prefix: build-tests-${{ inputs.os }}-${{ inputs.cache-prefix }}v0
 
       - name: Build tests
@@ -125,7 +134,7 @@ jobs:
       - name: Setup Rust
         uses: ./.github/actions/setup-rust
         with:
-          toolchain: 1.84
+          toolchain: ${{ env.RUST_STABLE_VERSION }}
           cache-prefix: build-tests-webrtc-${{ inputs.os }}-${{ inputs.cache-prefix }}v0
 
       - name: Build tests
@@ -152,7 +161,7 @@ jobs:
       - name: Setup Rust
         uses: ./.github/actions/setup-rust
         with:
-          toolchain: 1.84
+          toolchain: ${{ env.RUST_STABLE_VERSION }}
           cache-prefix: build-${{ inputs.os }}-${{ inputs.cache-prefix }}v0
 
       - name: Build benchmarks

.github/workflows/doc-commands.yaml

@@ -14,6 +14,15 @@ on:
 env:
   CARGO_TERM_COLOR: always
   RUST_BACKTRACE: full
+  # This should be in line with the version in:
+  # - rust-toolchain.toml
+  # - .github/workflows/build-reusable.yaml
+  # - .github/workflows/tests.yaml
+  # - .github/workflows/lint.yaml
+  # - .github/workflows/doc-commands.yaml
+  # - website/scripts/setup/install-rust.sh
+  # - website/docs/developers/getting-started.mdx
+  RUST_STABLE_VERSION: "1.84"
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
@@ -36,7 +45,7 @@ jobs:
         uses: ./.github/actions/setup-rust
         with:
           components: rustfmt
-          toolchain: 1.84
+          toolchain: ${{ env.RUST_STABLE_VERSION }}
           cache-prefix: test-doc-commands-v0
 
       - name: Use shared OCaml setting up steps

.github/workflows/lint.yaml

@@ -5,16 +5,26 @@ on:
     branches: [ main, develop ]
   pull_request:
 
+env:
+  # This should be in line with the version in:
+  # - rust-toolchain.toml
+  # - .github/workflows/build-reusable.yaml
+  # - .github/workflows/tests.yaml
+  # - .github/workflows/lint.yaml
+  # - .github/workflows/doc-commands.yaml
+  # - website/scripts/setup/install-rust.sh
+  # - website/docs/developers/getting-started.mdx
+  RUST_STABLE_VERSION: "1.84"
+
 jobs:
   lint:
     timeout-minutes: 10
-    name: Lint - ${{ matrix.os }} - Rust ${{ matrix.toolchain }}
+    name: Lint - ${{ matrix.os }} - Rust ${{ env.RUST_STABLE_VERSION }}
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
         ocaml_version: [4.14.2]
         os: [ubuntu-24.04]
-        toolchain: [1.84]
     steps:
       - uses: actions/checkout@v5
       - name: Setup build dependencies
@@ -26,9 +36,9 @@ jobs:
       - name: Setup Rust
         uses: ./.github/actions/setup-rust
         with:
-          toolchain: ${{ matrix.toolchain }}
+          toolchain: ${{ env.RUST_STABLE_VERSION }}
           components: clippy, rustfmt
-          cache-prefix: lint-${{ matrix.toolchain }}-v0
+          cache-prefix: lint-${{ env.RUST_STABLE_VERSION }}-v0
       - name: Run make check
         run: make check
       - name: Run make lint

.github/workflows/tests.yaml

@@ -17,6 +17,14 @@ env:
   MINA_PANIC_ON_BUG: true
   CARGO_INCREMENTAL: 1
   RUSTFLAGS: "-C overflow-checks=off -C debug-assertions=off"
+  # This should be in line with the version in:
+  # - rust-toolchain.toml
+  # - .github/workflows/build-reusable.yaml
+  # - .github/workflows/tests.yaml
+  # - .github/workflows/lint.yaml
+  # - .github/workflows/doc-commands.yaml
+  # - website/scripts/setup/install-rust.sh
+  # - website/docs/developers/getting-started.mdx
   RUST_STABLE_VERSION: "1.84"
   RUST_NIGHTLY_VERSION: "nightly"
   OCAML_VERSION: "4.14.2"

rust-toolchain.toml

@@ -2,5 +2,9 @@
 channel = "1.84"
 
 # NOTE: When updating the Rust version here, also update:
+# - .github/workflows/build-reusable.yaml (RUST_STABLE_VERSION env var)
+# - .github/workflows/tests.yaml (RUST_STABLE_VERSION env var)
+# - .github/workflows/lint.yaml (RUST_STABLE_VERSION env var)
+# - .github/workflows/doc-commands.yaml (RUST_STABLE_VERSION env var)
 # - website/scripts/setup/install-rust.sh
 # - website/docs/developers/getting-started.mdx (references the install-rust.sh script)