Flag silent skill runs in PR body + dispatch summary

Companion to the tracking comments: when the skill concludes
successfully but produces zero commits, the PR body previously
read as if content was added. Reviewers had no way to distinguish
"skill ran silently" from "skill produced stuff".

Adds:
  - A new step that rev-counts commits between pre_skill SHA and
    HEAD. Output exposed as steps.skill_commits.outputs.count.
  - A [!NOTE] block in the PR body when SKILL_COMMIT_COUNT=0 and
    no NO_CHANGES.md was written. Lists the three likely causes
    (docs already ahead of pin; no doc-relevant release; skill's
    verification matched existing prose).
  - A row in the workflow_dispatch summary comment showing the
    commit count.

Surfaced by the e2e test on PR #777: the skill ran to success but
produced nothing because main was already ahead of the pinned
scratch branch. PR body looked like a normal augmented PR.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: rdimitrov

.github/workflows/upstream-release-docs.yml

@@ -690,6 +690,26 @@ jobs:
             if they exist -- they're signal files handed off to the
             next workflow step, not part of the docs.
 
+      # Count the commits the skill itself added between pre_skill
+      # and now. Zero commits means skill_gen and skill_review both
+      # concluded there was nothing to change -- e.g. because main
+      # already has the content for this release (a re-run or test
+      # after the same content was merged via a different PR), or
+      # because the release genuinely had no doc-relevant impact
+      # but the skill didn't produce NO_CHANGES.md. Either way the
+      # resulting PR is silent and reviewers can't tell that from
+      # a successful run with content -- we emit a visible note in
+      # the PR body when this is the case.
+      - name: Count skill commits
+        id: skill_commits
+        if: always() && steps.skill_gen.conclusion == 'success'
+        env:
+          BASELINE_SHA: ${{ steps.pre_skill.outputs.sha }}
+        run: |
+          COUNT=$(git rev-list "$BASELINE_SHA..HEAD" --count)
+          echo "count=$COUNT" >> "$GITHUB_OUTPUT"
+          echo "Skill produced $COUNT commit(s) between pre_skill and now."
+
       # Auto-apply the same formatters the project's pre-commit hook
       # runs, scoped to the files the skill touched. The skill's
       # sandbox doesn't include npm run prettier/eslint, so without
@@ -857,6 +877,7 @@ jobs:
           COMPARE_OK: ${{ steps.reviewers.outputs.compare_ok }}
           MENTION_BLOCK: ${{ steps.reviewers.outputs.mention_block }}
           ASSIGN_LIST: ${{ steps.reviewers.outputs.list }}
+          SKILL_COMMIT_COUNT: ${{ steps.skill_commits.outputs.count }}
         run: |
           START='<!-- upstream-release-docs:start -->'
           END='<!-- upstream-release-docs:end -->'
@@ -878,6 +899,30 @@ jobs:
               echo "$NOTE_BLOCK"
               echo ""
             fi
+            # When the skill ran to success but produced zero commits,
+            # we have no NOTE_BLOCK (no NO_CHANGES.md), no content for
+            # reviewers to look at, and a PR body that otherwise reads
+            # as if content was added. Surface the silence explicitly.
+            if [ "$SKILL_COMMIT_COUNT" = "0" ] && [ -z "$NOTE_BLOCK" ]; then
+              echo "> [!NOTE]"
+              echo "> The \`upstream-release-docs\` skill ran to success but"
+              echo "> produced no content commits on this PR. Likely causes:"
+              echo ">"
+              echo "> - The docs already cover this release (e.g. this PR"
+              echo ">   was dispatched after an earlier PR for the same"
+              echo ">   tag had merged, or \`main\` is already ahead of the"
+              echo ">   pinned base)."
+              echo "> - The release genuinely had no doc-relevant changes"
+              echo ">   but the skill did not write \`NO_CHANGES.md\` (which"
+              echo ">   would have triggered the standard 'no changes'"
+              echo ">   note above)."
+              echo "> - The skill's source verification concluded the"
+              echo ">   existing prose already matches upstream behavior."
+              echo ">"
+              echo "> Only the version bump and any refreshed reference"
+              echo "> assets are included in this PR."
+              echo ""
+            fi
             if [ -n "$AUTOGEN_NOTE" ]; then
               echo "$AUTOGEN_NOTE"
               echo ""
@@ -945,6 +990,7 @@ jobs:
           GEN_CONCLUSION: ${{ steps.skill_gen.conclusion }}
           REVIEW_CONCLUSION: ${{ steps.skill_review.conclusion }}
           AUTOFIX_CONCLUSION: ${{ steps.autofix.conclusion }}
+          SKILL_COMMIT_COUNT: ${{ steps.skill_commits.outputs.count }}
         run: |
           gh pr comment "$PR_NUMBER" --body "## Upstream-release-docs run summary
 
@@ -955,6 +1001,7 @@ jobs:
           | Generation (\`skill_gen\`) | \`${GEN_CONCLUSION:-(not run)}\` |
           | Editorial review (\`skill_review\`) | \`${REVIEW_CONCLUSION:-(not run)}\` |
           | Autofix (prettier/eslint) | \`${AUTOFIX_CONCLUSION:-(not run)}\` |
+          | Skill commits produced | \`${SKILL_COMMIT_COUNT:-?}\` |
 
           Full report and Claude's step-by-step log: $RUN_URL" || true