feat: name each preview artifact for its pull request and head

The app attributes an artifact to a pull request per run, and every preview
shares the setup PR's run, so the name carries the pull request and the head
it reviewed, as the legacy codeboarding-pr-<pr>-<head> names did.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: ivanmilevtues

action.yml

@@ -725,7 +725,7 @@ runs:
     # where a new user's open pull requests get their first review: the ones the app listed
     # in the setup PR's description, each applied to the commit this run just analysed and
     # analysed incrementally from it (see review-preview-pr.sh). Nothing is posted on them.
-    # The app finds each as codeboarding-preview-<run>-<attempt>-pr<number> plus its metadata.
+    # The app finds each as codeboarding-preview-<run>-<attempt>-pr<number>-<head sha>.
     # Not codeboarding-review-<run>-...: the app takes the newest artifact with that prefix as
     # the setup PR's own review, so a preview named that way would replace the setup PR's map.
     # All best effort: the setup PR's map is already uploaded and must not fail because of them.
@@ -774,7 +774,7 @@ runs:
       continue-on-error: true
       uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
       with:
-        name: codeboarding-preview-${{ github.run_id }}-${{ github.run_attempt }}-pr${{ steps.preview_1.outputs.pr_number }}
+        name: codeboarding-preview-${{ github.run_id }}-${{ github.run_attempt }}-pr${{ steps.preview_1.outputs.pr_number }}-${{ steps.preview_1.outputs.head_sha }}
         path: ${{ steps.preview_1.outputs.artifact_dir }}
         if-no-files-found: error
         retention-days: 14
@@ -829,7 +829,7 @@ runs:
       continue-on-error: true
       uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
       with:
-        name: codeboarding-preview-${{ github.run_id }}-${{ github.run_attempt }}-pr${{ steps.preview_2.outputs.pr_number }}
+        name: codeboarding-preview-${{ github.run_id }}-${{ github.run_attempt }}-pr${{ steps.preview_2.outputs.pr_number }}-${{ steps.preview_2.outputs.head_sha }}
         path: ${{ steps.preview_2.outputs.artifact_dir }}
         if-no-files-found: error
         retention-days: 14
@@ -863,7 +863,7 @@ runs:
       continue-on-error: true
       uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
       with:
-        name: codeboarding-preview-${{ github.run_id }}-${{ github.run_attempt }}-pr${{ steps.preview_3.outputs.pr_number }}
+        name: codeboarding-preview-${{ github.run_id }}-${{ github.run_attempt }}-pr${{ steps.preview_3.outputs.pr_number }}-${{ steps.preview_3.outputs.head_sha }}
         path: ${{ steps.preview_3.outputs.artifact_dir }}
         if-no-files-found: error
         retention-days: 14

scripts/action/review-preview-pr.sh

@@ -9,7 +9,7 @@
 # reported as its changes. A pull request that does not apply cleanly there is skipped.
 #
 # Usage: review-preview-pr.sh <n>. Outputs pr_number=, title= and artifact_dir= when a
-# preview was built; nothing when there is no n-th entry or it was skipped.
+# preview was built, plus head_sha=; nothing when there is no n-th entry or it was skipped.
 set -euo pipefail
 # shellcheck source=scripts/action/analysis-state.sh
 source "$(dirname "$0")/analysis-state.sh"
@@ -58,4 +58,4 @@ BASE_ARTIFACT_NAME="$(jq -r '.base_artifact // ""' "$review_meta")" \
   PR_NUMBER="$pr" SEED_SOURCE=base CHAIN_DEPTH=1 ANALYSED_FILES_CHANGED="$analysed" \
   BASIS=preview SETUP_PR="$SETUP_PR" \
   "$ACTION_PATH/scripts/action/build-review-artifact.sh"
-printf 'pr_number=%s\ntitle=%s\n' "$pr" "${title//$'\n'/ }" >> "$GITHUB_OUTPUT"
+printf 'pr_number=%s\nhead_sha=%s\ntitle=%s\n' "$pr" "$head_sha" "${title//$'\n'/ }" >> "$GITHUB_OUTPUT"

tests/test_setup_previews.py

@@ -186,6 +186,7 @@ def _run(self, pr_head: str | None = None) -> dict[str, str]:
     def test_the_pull_request_is_applied_to_the_analysed_commit(self) -> None:
         out = self._run()
         self.assertEqual(out["pr_number"], "412")
+        self.assertEqual(out["head_sha"], self.pr_head, "the artifact name carries it, so the app needs no download")
         seen = (self.preview_dir / "state-1" / "seen-files").read_text().split()
         # Z's file is there because the base is Z; the PR's file because it was applied; nothing else.
         self.assertIn("ledger.txt", seen)