@@ -36,8 +36,7 @@ on:
         description: >
           Test mode: 'standard' (default), 'nightly-pytorch',
           'nightly-numba-cuda', 'nightly-numba-cuda-mlir', or
-          'nightly-cuda-core'. Temporary PR3436 diagnostics use
-          'diagnostic-watermark'.
+          'nightly-cuda-core'.
         type: string
         default: 'standard'
       sha:
@@ -46,12 +45,6 @@ on:
           Defaults to github.sha (current run) when empty.
         type: string
         default: ''
-      source-ref:
-        description: >
-          Optional test-source ref override. Defaults to the artifact SHA,
-          or github.sha when the artifact SHA is empty.
-        type: string
-        default: ''
 
 jobs:
   compute-matrix:
@@ -116,9 +109,9 @@ jobs:
       - name: Checkout ${{ github.event.repository.name }}
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
         with:
-          # Normally sources match the wheels; diagnostics can override only
-          # test sources while retaining the original binary artifacts.
-          ref: ${{ inputs.source-ref || inputs.sha || github.sha }}
+          # Test sources must match the wheels under test (nightly runs
+          # reuse wheels built from an older commit of main).
+          ref: ${{ inputs.sha || github.sha }}
 
       - name: Setup proxy cache
         uses: nv-gha-runners/setup-proxy-cache@main
@@ -364,21 +357,6 @@ jobs:
         shell: bash --noprofile --norc -xeuo pipefail {0}
         run: echo "PYTEST_ADDOPTS=\"--count=${{ inputs.nruns }}\"" >> "$GITHUB_ENV"
 
-      - name: Install cuda.core diagnostic dependencies
-        if: ${{ inputs.test-mode == 'diagnostic-watermark' }}
-        env:
-          CUDA_VER: ${{ matrix.CUDA_VER }}
-          LOCAL_CTK: ${{ matrix.LOCAL_CTK }}
-          PYTEST_ADDOPTS: --collect-only
-          SKIP_CYTHON_TEST: '1'
-        shell: bash --noprofile --norc -xeuo pipefail {0}
-        run: run-tests core
-
-      - name: Diagnose PR3436 watermark teardown
-        if: ${{ inputs.test-mode == 'diagnostic-watermark' }}
-        shell: bash --noprofile --norc -xeuo pipefail {0}
-        run: python ci/tools/diagnose_pr3436_watermark.py
-
       # ── Standard test steps (skipped for nightly modes) ──
       - name: Run cuda.pathfinder tests with see_what_works
         if: ${{ inputs.test-mode == 'standard' && env.TEST_PATHFINDER == 'true' }}
@@ -619,14 +597,3 @@ jobs:
           path: test-results/
           if-no-files-found: ignore
           retention-days: 14
-
-      - name: Upload PR3436 watermark diagnostics
-        if: ${{ !cancelled() && inputs.test-mode == 'diagnostic-watermark' }}
-        uses: actions/upload-artifact@cf430e030ddbb5b0abf93d22962f4752f3646cd9  # v7.0.2
-        with:
-          name: pr3436-watermark-diagnostic-${{ github.run_id }}-${{ github.run_attempt }}
-          path: |
-            watermark-diagnostic/
-            cuda_core/cuda_core_oom_diagnostics.txt
-          if-no-files-found: ignore
-          retention-days: 14