Wipe styx cache when styxcache version changes

styxcache 0.2.0 persists stdout/stderr alongside cache entries, but
legacy 0.1.0 entries predate that and silently replay empty stdout on
hit (see styx-api/styx-runtime-py _replay_stream's missing-file path).
This would re-introduce the ants.print_header.output empty-list bug as
soon as a pre-0.2.0 entry is hit.

Prepare step now reads the installed styxcache version, compares to a
marker file, and wipes the cache dir if they differ.

Author: nx10

.github/workflows/test_full.yaml

@@ -50,6 +50,17 @@ jobs:
         # Purge stale staging dirs from crashed previous runs (safe: atomic-rename commits)
         rm -rf "$STYXCACHE_DIR/.incoming" 2>/dev/null || true
 
+        # Invalidate the whole cache when the styxcache version changes:
+        # legacy entries may lack data (e.g. persisted stdout) that newer
+        # versions expect, and missing-file handling is silent — so we rebuild.
+        version=$(uv run python -c "from importlib.metadata import version; print(version('styxcache'))")
+        marker="$STYXCACHE_DIR/.styxcache_version"
+        if [ ! -f "$marker" ] || [ "$(cat "$marker")" != "$version" ]; then
+          echo "styxcache version changed (now $version); wiping cache"
+          find "$STYXCACHE_DIR" -mindepth 1 -maxdepth 1 -exec rm -rf {} +
+          echo "$version" > "$marker"
+        fi
+
         size_kb=$(du -sk "$STYXCACHE_DIR" 2>/dev/null | awk '{print $1}')
         size_kb=${size_kb:-0}
         cap_kb=$(( STYXCACHE_MAX_GB * 1024 * 1024 ))