Fix the release verify picking a musl binary on glibc runners

With --baseline the build also emits musl variants, and the verify step used
`find dist -type f -name utmstack | head -1`, which took whichever directory
sorted first. On the x64 runners that was opencode-linux-x64-baseline-musl —
a musl-linked binary, which cannot execute on a glibc runner. The kernel
reports the missing ELF interpreter as "No such file or directory" and the
step died with 127, having built perfectly good binaries.

Verify now addresses dist/opencode-<matrix.target>/bin directly, so each job
tests the artifact it is actually responsible for.

Packaging now skips musl variants entirely. They come out of the build for
free, but they are untested and unadvertised, and the installer refuses musl
with an explicit message — shipping them would promise support we have not
verified.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Rick Valdes

.github/workflows/utmstack-release.yml

@@ -80,8 +80,14 @@ jobs:
         working-directory: packages/opencode
         run: |
           set -eu
-          BIN=$(find dist -type f \( -name utmstack -o -name utmstack.exe \) | head -1)
-          [ -n "$BIN" ] || { echo "no utmstack binary produced"; exit 1; }
+          # Address the exact matrix target. `find | head -1` picked whichever
+          # directory sorted first, which on x64 runs was the musl variant —
+          # a musl-linked binary cannot execute on a glibc runner (missing ELF
+          # interpreter, which surfaces as "No such file or directory" / 127).
+          DIST="dist/opencode-${{ matrix.target }}"
+          BIN="$DIST/bin/utmstack"
+          [ -f "$BIN" ] || BIN="$DIST/bin/utmstack.exe"
+          [ -f "$BIN" ] || { echo "no binary at $DIST/bin"; ls -R dist | head -40; exit 1; }
           echo "binary: $BIN"
 
           got=$("$BIN" --version | tr -d '\r')
@@ -117,6 +123,10 @@ jobs:
           for dir in dist/*/; do
             name=$(basename "$dir")
             [ -d "$dir/bin" ] || continue
+            # The build emits musl variants for free, but they are untested and
+            # unadvertised, and the installer refuses musl outright. Publishing
+            # them would promise support we have not verified.
+            case "$name" in *-musl*) echo "skipping $name (musl, not published)"; continue ;; esac
             asset=$(echo "$name" | sed 's/^opencode-/utmstack-/')
             if [ "${{ matrix.ext }}" = "tar.gz" ]; then
               tar -czf "$OUT/${asset}.tar.gz" -C "$dir/bin" .