fix: use dbt_<YYMMDD_HHMMSS>_<branch>_<hash> schema naming to prevent CI collisions

.github/workflows/test-warehouse.yml

@@ -55,7 +55,8 @@ jobs:
   test:
     runs-on: ubuntu-latest
     concurrency:
-      # This is what eventually defines the schema name in the data platform.
+      # Serialises runs for the same warehouse × dbt-version × branch.
+      # The schema name is derived from a hash of this group (see "Write dbt profiles").
       group: tests_${{ inputs.warehouse-type }}_dbt_${{ inputs.dbt-version }}_${{ github.head_ref || github.ref_name }}
       cancel-in-progress: true
     steps:
@@ -125,13 +126,35 @@ jobs:
         env:
           CI_WAREHOUSE_SECRETS: ${{ secrets.CI_WAREHOUSE_SECRETS || '' }}
         run: |
-          DBT_VERSION=$(echo "${{ inputs.dbt-version }}" | sed 's/\.//g')
-          UNDERSCORED_REF_NAME=$(echo "${{ inputs.warehouse-type }}_dbt_${DBT_VERSION}_${BRANCH_NAME}" | awk '{print tolower($0)}' | head -c 40 | sed "s/[-\/]/_/g")
+          # Build a short, collision-free schema identifier from the branch
+          # name and an 8-char hash of the full concurrency group.
+          #
+          # Previous approach used `head -c 40` on the full ref string, which
+          # left only 1 character for branch differentiation on long warehouse
+          # names like databricks_catalog, causing cross-branch schema
+          # collisions when CI jobs ran concurrently.
+          #
+          # New approach: <truncated_branch>_<YYMMDD>_<8-char SHA-256 of concurrency group>
+          # The hash guarantees uniqueness across concurrent jobs (different
+          # warehouse types, dbt versions, or branches).  The truncated branch
+          # name keeps schemas human-readable in the data platform.  The date
+          # stamp (YYMMDD) makes it easy to identify and clean up old schemas.
+          #
+          # Schema name budget (PostgreSQL = most restrictive at 63 chars):
+          #   dbt_pkg_  (8)  +  ref (≤40)  +  _elementary (11)  +  _gw7 (4)  = 63
+          # ref = branch (≤24) + _ (1) + date (6) + _ (1) + hash (8) = 40
+          CONCURRENCY_GROUP="tests_${{ inputs.warehouse-type }}_dbt_${{ inputs.dbt-version }}_${BRANCH_NAME}"
+          SHORT_HASH=$(echo -n "$CONCURRENCY_GROUP" | sha256sum | head -c 8)
+          SAFE_BRANCH=$(echo "${BRANCH_NAME}" | awk '{print tolower($0)}' | sed "s/[^a-z0-9]/_/g" | head -c 24)
+          DATE_STAMP=$(date +%y%m%d)
+          SCHEMA_SUFFIX="${SAFE_BRANCH}_${DATE_STAMP}_${SHORT_HASH}"
+
+          echo "Schema suffix: $SCHEMA_SUFFIX (branch='${BRANCH_NAME}', date=${DATE_STAMP}, hash of concurrency group)"
 
           python "${{ github.workspace }}/dbt-data-reliability/integration_tests/profiles/generate_profiles.py" \
             --template "${{ github.workspace }}/dbt-data-reliability/integration_tests/profiles/profiles.yml.j2" \
             --output ~/.dbt/profiles.yml \
-            --schema-name "dbt_pkg_$UNDERSCORED_REF_NAME"
+            --schema-name "dbt_pkg_$SCHEMA_SUFFIX"
 
       - name: Install dependencies
         working-directory: ${{ env.TESTS_DIR }}