fix: CI toolchain tests actually use correct toolchain + assertions

Review findings addressed:

1. Linux musl/LLVM steps were NOT actually using those toolchains
   (mcpp.toml [toolchain].default overrides global default).
   Fix:
   - musl: use `mcpp build --target x86_64-linux-musl`
   - LLVM: sed-override mcpp.toml before build
   - All steps: grep assertion on "Resolved <toolchain>" output

2. Windows: remove `|| true` on critical config/default commands
   that silently swallowed failures.

3. Windows: add explicit `mcpp new hello → mcpp run` smoke test
   (covers first-run user path that E2E skips due to missing
   fresh-sandbox capability).

4. All toolchain build steps: assert via grep that the expected
   toolchain was actually resolved.

Author: Sunrisepeak

.github/workflows/ci-windows.yml

@@ -96,10 +96,20 @@ jobs:
           export MCPP="$MCPP_SELF"
           export MCPP_VENDORED_XLINGS="$XLINGS_BIN"
           export MCPP_E2E_TOOLCHAIN_MIRROR=GLOBAL
-          "$MCPP_SELF" self config --mirror GLOBAL 2>/dev/null || true
-          "$MCPP_SELF" toolchain default llvm@20.1.7 2>/dev/null || true
+          "$MCPP_SELF" self config --mirror GLOBAL
+          "$MCPP_SELF" toolchain default llvm@20.1.7
           bash tests/e2e/run_all.sh
 
+      - name: "Toolchain: LLVM — mcpp new → run"
+        shell: bash
+        run: |
+          export MCPP_VENDORED_XLINGS="$XLINGS_BIN"
+          TMP=$(mktemp -d)
+          cd "$TMP"
+          "$MCPP_SELF" new hello_win
+          cd hello_win
+          "$MCPP_SELF" run
+
       - name: "Toolchain: LLVM — build mcpp (self-host)"
         shell: bash
         run: |
@@ -108,8 +118,7 @@ jobs:
           MCPP=/tmp/mcpp-fresh.exe
           "$MCPP" toolchain default llvm@20.1.7
           "$MCPP" clean --bmi-cache
-          "$MCPP" build
-          "$MCPP" --version
+          "$MCPP" build 2>&1 | tee /dev/stderr | grep -q "Resolved llvm@20.1.7"
 
       - name: Package Windows release zip
         id: package

.github/workflows/ci.yml

@@ -136,21 +136,21 @@ jobs:
 
       - name: "Toolchain: GCC — build mcpp + test"
         run: |
-          "$MCPP" toolchain default gcc@16.1.0
           "$MCPP" clean
-          "$MCPP" build
+          "$MCPP" build 2>&1 | tee /dev/stderr | grep -q "Resolved gcc@16.1.0"
           "$MCPP" test
 
-      - name: "Toolchain: musl-gcc — build mcpp"
+      - name: "Toolchain: musl-gcc — build mcpp (--target)"
         run: |
-          "$MCPP" toolchain install gcc 15.1.0-musl
-          "$MCPP" toolchain default gcc@15.1.0-musl
           "$MCPP" clean
-          "$MCPP" build
+          "$MCPP" build --target x86_64-linux-musl 2>&1 | tee /dev/stderr | grep -q "musl"
 
       - name: "Toolchain: LLVM — build mcpp"
         run: |
           "$MCPP" toolchain install llvm 20.1.7
-          "$MCPP" toolchain default llvm@20.1.7
+          # Override project toolchain to use LLVM for this build
+          sed -i 's/^default = "gcc@16.1.0"/default = "llvm@20.1.7"/' mcpp.toml
           "$MCPP" clean
-          "$MCPP" build
+          "$MCPP" build 2>&1 | tee /dev/stderr | grep -q "Resolved llvm@20.1.7"
+          # Restore
+          sed -i 's/^default = "llvm@20.1.7"/default = "gcc@16.1.0"/' mcpp.toml