Bump MSRV to 1.85 and read it from Cargo.toml in CI (#7)

A transitive dependency (getrandom 0.4.1 via tempfile/prost-build)
now requires Rust 1.85+ (edition2024). Since this is a library crate,
Cargo.lock is not committed, so CI resolves the latest compatible
versions which broke the 1.83 build.

Bump rust-version in Cargo.toml to 1.85 and update the CI test matrix
to read the MSRV from Cargo.toml rather than hardcoding it, preventing
future drift.

Author: peteski22

.github/workflows/test.yaml

@@ -17,12 +17,21 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
-        rust: [stable, 1.83.0]
+        rust: [stable, msrv]
     steps:
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+      - name: Determine Rust version
+        id: rust-version
+        run: |
+          if [ "${{ matrix.rust }}" = "msrv" ]; then
+            MSRV=$(grep '^rust-version' Cargo.toml | sed 's/.*"\(.*\)"/\1/')
+            echo "toolchain=${MSRV}" >> "$GITHUB_OUTPUT"
+          else
+            echo "toolchain=${{ matrix.rust }}" >> "$GITHUB_OUTPUT"
+          fi
       - uses: dtolnay/rust-toolchain@stable # Action's stable branch. No SHA pinning - repo doesn't publish releases.
         with:
-          toolchain: ${{ matrix.rust }}
+          toolchain: ${{ steps.rust-version.outputs.toolchain }}
       - name: Install protoc (Ubuntu)
         if: runner.os == 'Linux'
         run: sudo apt-get update && sudo apt-get install -y protobuf-compiler

Cargo.toml

@@ -2,7 +2,7 @@
 name = "mcpd-plugins-sdk"
 version = "0.0.1"
 edition = "2021"
-rust-version = "1.83"
+rust-version = "1.85"
 authors = ["Mozilla AI"]
 license = "Apache-2.0"
 description = "Rust SDK for building mcpd plugins"