fix: ensure mcp-client crate builds on its own

.github/workflows/rust-ci.yml

@@ -83,6 +83,15 @@ jobs:
       - name: cargo clippy
         run: cargo clippy --target ${{ matrix.target }} --all-features -- -D warnings || echo "FAILED=${FAILED:+$FAILED, }cargo clippy" >> $GITHUB_ENV
 
+      # Running `cargo build` from the workspace root builds the workspace using
+      # the union of all features from third-party deps. This can mask errors
+      # where individual crates have underspecified features. To avoid this, we
+      # run `cargo build` from each crate individually, though because this is
+      # slower, we only do this for the x86_64-unknown-linux-gnu target.
+      - name: cargo build individual crates
+        if: ${{ matrix.target == 'x86_64-unknown-linux-gnu' }}
+        run: find . -name Cargo.toml -mindepth 2 -maxdepth 2 -execdir cargo build \; || echo "FAILED=${FAILED:+$FAILED, }cargo build individual crates" >> $GITHUB_ENV
+
       - name: cargo test
         run: cargo test --target ${{ matrix.target }} || echo "FAILED=${FAILED:+$FAILED, }cargo test" >> $GITHUB_ENV
 

codex-rs/mcp-client/Cargo.toml

@@ -11,11 +11,11 @@ serde_json = "1"
 tracing = { version = "0.1.41", features = ["log"] }
 tracing-subscriber = { version = "0.3", features = ["fmt", "env-filter"] }
 tokio = { version = "1", features = [
-    "io-std",
+    "io-util",
     "macros",
     "process",
     "rt-multi-thread",
-    "signal",
+    "sync",
 ] }
 
 [dev-dependencies]