ci: check for an already-published version before authenticating

.github/workflows/publish.yml

@@ -56,23 +56,37 @@ jobs:
           fi
           echo "publishing dtg-credentials ${crate}"
 
-      - name: Authenticate to crates.io
-        uses: rust-lang/crates-io-auth-action@v1
-        id: auth
-
-      - name: Publish
-        env:
-          CARGO_REGISTRY_TOKEN: ${{ steps.auth.outputs.token }}
+      # Before authenticating, not after. The skip is what makes a re-pushed tag
+      # recoverable, and it cannot do that job from behind the auth step: the
+      # v0.6.0 tag push found 0.6.0 already on crates.io (published by hand
+      # minutes earlier) and still failed, because it never got past
+      # "No Trusted Publishing config found" to reach the check that would have
+      # said there was nothing to do. A step that decides whether to act should
+      # not sit downstream of acquiring the means to act.
+      - name: Skip if this version is already published
+        id: check
         run: |
           set -euo pipefail
           version=$(cargo metadata --no-deps --format-version 1 | jq -r '.packages[0].version')
+          echo "version=${version}" >> "$GITHUB_OUTPUT"
 
           # The sparse index is newline-delimited JSON, one object per version.
           # A 404 (name never published) is a clean "not there".
           if curl -sSf "https://index.crates.io/dt/g-/dtg-credentials" 2>/dev/null \
               | jq -se --arg v "$version" 'any(.[]; .vers == $v)' >/dev/null; then
             echo "::notice::dtg-credentials ${version} is already on crates.io — nothing to do"
-            exit 0
+            echo "published=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "published=false" >> "$GITHUB_OUTPUT"
           fi
 
-          cargo publish --locked
+      - name: Authenticate to crates.io
+        if: steps.check.outputs.published == 'false'
+        uses: rust-lang/crates-io-auth-action@v1
+        id: auth
+
+      - name: Publish
+        if: steps.check.outputs.published == 'false'
+        env:
+          CARGO_REGISTRY_TOKEN: ${{ steps.auth.outputs.token }}
+        run: cargo publish --locked