diff --git a/.gitea/workflows/repro.yaml b/.gitea/workflows/repro.yaml
index a960b52..9299cab 100644
--- a/.gitea/workflows/repro.yaml
+++ b/.gitea/workflows/repro.yaml
@@ -28,17 +28,37 @@ jobs:
             extra-substituters = https://nix-cache.nul.ie
             extra-trusted-public-keys = nix-cache.nul.ie-1:BzH5yMfF4HbzY1C977XzOxoPhEc9Zbu39ftPkUbH+m4=
 
-      - name: Build devshell with full logs
+      - name: Nix build-dir / store settings
         run: |
-          set -eo pipefail
-          # -L prints full build logs inline (including the gtest assertion that
-          # fails); --keep-going surfaces the failure without aborting early.
-          # determinate-nix isn't in the cache yet (the failing master run never
-          # pushed it), so this rebuilds it and reruns the unit tests.
-          nix build -L --keep-going --no-link .#ci.x86_64-linux.shell 2>&1 | tee repro.log
+          echo "===== nix config (build-dir / store / sandbox) ====="
+          nix config show 2>/dev/null | grep -iE 'build-dir|store|sandbox|temp' || true
+          echo "===== TMPDIR/env ====="
+          echo "TMPDIR=$TMPDIR RUNNER_TEMP=$RUNNER_TEMP GITHUB_WORKSPACE=$GITHUB_WORKSPACE HOME=$HOME"
 
-      - name: Show failing assertion
-        if: failure()
+      - name: Mount table
         run: |
-          echo "===== readLinkAt / gtest failure detail ====="
-          grep -nE 'FAILED|readLinkAt|Failure|Expected|Actual|Value of|which is|error:' repro.log || true
+          echo "===== df -T ====="
+          df -T || df -h
+          echo "===== mount ====="
+          mount 2>/dev/null | grep -iE 'overlay|tmpfs|/nix|ext4|xfs|btrfs|9p|fuse' || mount
+
+      - name: Symlink-length probe
+        run: |
+          # Determine, per candidate dir, the longest symlink target that can be
+          # created (the test needs PATH_MAX/2 = 2048 and PATH_MAX-1 = 4095).
+          probe() {
+            local d="$1"
+            [ -d "$d" ] || { echo "  $d: (absent)"; return; }
+            local fstype; fstype=$(stat -f -c %T "$d" 2>/dev/null || echo '?')
+            local res=""
+            for n in 256 1000 2048 3000 4095; do
+              local tgt; tgt=$(head -c "$n" < /dev/zero | tr '\0' 'y')
+              if ln -sf "$tgt" "$d/.symtest.$n" 2>/dev/null; then res="$res $n"; else res="$res !$n"; fi
+              rm -f "$d/.symtest.$n" 2>/dev/null || true
+            done
+            echo "  $d [$fstype]:$res"
+          }
+          echo "===== max symlink target length per dir (n = ok, !n = ENAMETOOLONG) ====="
+          for d in /tmp /var/tmp /dev/shm /nix /nix/var "$HOME" "$RUNNER_TEMP" "$GITHUB_WORKSPACE" /root /build; do
+            probe "$d"
+          done