ci: enforce FPE masking on GitHub, decommission mirrored GitLab jobs (#5714)

## Summary

Moves the FPE-masking regression gate from the CERN GitLab mirror onto GitHub-hosted CI, and decommissions the now-redundant mirrored GitLab jobs. First concrete step of the GitLab → GitHub CI migration.

### Background
The FPE-masking gate only *enforced* on GitLab: it built `RelWithDebInfo` (DWARF line info present) and left `failOnUnmaskedFpe` at its `true` default, so masks — matched on `source_file():source_line()` — resolve. GitHub built `Release` (no line info) and set `ACTS_SEQUENCER_FAIL_ON_UNMASKED_FPE=0`, so `test_fpe.py`'s masking tests were **silently skipped**.

### Changes
**GitHub (`builds.yml` + `CMakePresets.json`):**
- New `github-ci-fpe` preset: `RelWithDebInfo` + `-g1 -gz` — slim line tables so masks resolve, without full-debug artifact bloat (smaller than GitLab's full `-g`).
- `linux_ubuntu` builds with it; its artifact already feeds the two FPE-aware consumers.
- `linux_examples_test` and `linux_physmon` set `ACTS_SEQUENCER_FAIL_ON_UNMASKED_FPE=1` (enforce). Other jobs (macOS, clang22-extra) stay Release/non-enforcing.

**GitLab (`.gitlab-ci.yml`):**
- Remove `build_linux_ubuntu`, `linux_test_examples`, `linux_physmon` — their only GitLab-unique coverage was this FPE enforcement, now on GitHub.
- GNN/TensorRT (GPU), LCG (CVMFS), clang22, detray, traccc jobs untouched — later migration phases.

### Validation
Proven on this PR's earlier validation runs (see comments below):
- Masking tests **pass at `-g1` post artifact round-trip** ([test_fpe.py run](https://github.com/acts-project/acts/actions/runs/29868661329)).
- physmon runs **FPE-clean under enforcement** on the minimal-debug artifact ([physmon run](https://github.com/acts-project/acts/actions/runs/29895623646)).
- Sizes: build tree ~1.5 GB, artifact ~202 MB — well within limits.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Author: paulgessinger

.github/workflows/builds.yml

@@ -59,7 +59,7 @@ jobs:
           ccache -z &&
           CI/dependencies/run.sh .env
           cmake -B build -S .
-          --preset=github-ci
+          --preset=github-ci-fpe
           -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}"
           -DACTS_BUILD_PLUGIN_ONNX=ON
 
@@ -132,7 +132,10 @@ jobs:
     container: ghcr.io/acts-project/ubuntu2404:87
     needs: [linux_ubuntu]
     env:
-      ACTS_SEQUENCER_FAIL_ON_UNMASKED_FPE: 0
+      # Enforce FPE masking on the RelWithDebInfo (github-ci-fpe) build: source
+      # locations resolve, so the test_fpe.py masking tests run instead of being
+      # skipped. Replaces the FPE coverage previously unique to GitLab.
+      ACTS_SEQUENCER_FAIL_ON_UNMASKED_FPE: 1
 
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
@@ -173,6 +176,11 @@ jobs:
       contents: read
     container: ghcr.io/acts-project/ubuntu2404:87
     needs: [linux_ubuntu]
+    env:
+      # Enforce FPE masking on the RelWithDebInfo (github-ci-fpe) build, matching
+      # what GitLab's linux_physmon did. The full reconstruction must stay
+      # FPE-clean (auto-loaded source masks resolve at -g1).
+      ACTS_SEQUENCER_FAIL_ON_UNMASKED_FPE: 1
 
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0

.gitlab-ci.yml

@@ -198,124 +198,6 @@ build_gnn_tensorrt:
   after_script:
    - !reference [.spack_cleanup, after_script]
 
-build_linux_ubuntu:
-  stage: build
-  image: registry.cern.ch/ghcr.io/acts-project/ubuntu2404:87
-
-  cache:
-   - !reference [.ccache_base, cache]
-   - !reference [.spack_cache, cache]
-
-  artifacts:
-    paths:
-      - build/
-    exclude:
-      - build/bin/ActsUnitTest*
-      - build/bin/ActsIntegrationTest*
-      - build/**/*.o
-    expire_in: 1 day
-
-  script:
-    - git clone $CLONE_URL src
-
-    - cd src
-    - git checkout $HEAD_SHA
-
-    - CI/dependencies/setup.sh -c g++ -e .env
-    - source .env
-
-    - cd ..
-
-    - mkdir build
-    - >
-      cmake -B build -S src
-      --preset=gitlab-ci
-      -DACTS_BUILD_PLUGIN_ONNX=ON
-
-    - ccache -z
-    - cmake --build build -- -j8
-    - ccache -s
-
-    - ctest --test-dir build -j$(nproc)
-    - cmake --build build --target integrationtests
-
-    # Install main project
-    - cmake --install build
-
-    # Downstream configure
-    - >
-      cmake -B build-downstream -S src/Tests/DownstreamProject
-      -GNinja
-      -DCMAKE_BUILD_TYPE=Release
-      -DCMAKE_CXX_FLAGS=-Werror
-      -DCMAKE_PREFIX_PATH="${INSTALL_DIR}"
-
-    # Downstream build
-    - cmake --build build-downstream
-
-    # Downstream tests
-    - ctest --test-dir build-downstream --output-on-failure
-
-  after_script:
-   - !reference [.spack_cleanup, after_script]
-
-linux_test_examples:
-  stage: test
-  image: registry.cern.ch/ghcr.io/acts-project/ubuntu2404:87
-  needs: [build_linux_ubuntu]
-
-  cache:
-   - !reference [.spack_cache, cache]
-
-  script:
-    - apt-get update && apt-get install -y git-lfs
-
-    - git clone $CLONE_URL src
-    - cd src
-    - git checkout $HEAD_SHA
-    - CI/dependencies/setup.sh -c g++ -e .env -f
-    - source .env
-    - cd ..
-
-    - source build/this_acts_withdeps.sh
-    - cd src
-    - pytest -rsfExw --durations=10 -k "not gnn" -v
-
-  after_script:
-   - !reference [.spack_cleanup, after_script]
-
-linux_physmon:
-  stage: test
-  needs: [build_linux_ubuntu]
-  image: registry.cern.ch/ghcr.io/acts-project/ubuntu2404:87
-
-  artifacts:
-    when: always
-    paths:
-      - src/physmon
-    expire_in: 1 week
-
-  cache:
-   - !reference [.spack_cache, cache]
-
-  script:
-    - apt-get update && apt-get install -y git-lfs time
-
-    - git clone $CLONE_URL src
-    - cd src
-    - git checkout $HEAD_SHA
-    - CI/dependencies/setup.sh -c g++ -e .env -f
-    - source .env
-    - cd ..
-
-    - git config --global safe.directory "$GITHUB_WORKSPACE"
-    - source build/this_acts_withdeps.sh
-    - cd src
-    - CI/physmon/phys_perf_mon.sh all physmon $(nproc)
-
-  after_script:
-   - !reference [.spack_cleanup, after_script]
-
 ###############################
 ### UBUNTU EXTRA JOB MATRIX ###
 ###############################

CMakePresets.json

@@ -105,6 +105,16 @@
                 "CMAKE_BUILD_TYPE": "Release"
             }
         },
+        {
+            "name": "github-ci-fpe",
+            "displayName": "GitHub-CI FPE (minimal-debug RelWithDebInfo)",
+            "inherits": "github-ci",
+            "cacheVariables": {
+                "CMAKE_BUILD_TYPE": "RelWithDebInfo",
+                "CMAKE_CXX_FLAGS_RELWITHDEBINFO": "-O2 -DNDEBUG -g1 -gz",
+                "CMAKE_C_FLAGS_RELWITHDEBINFO": "-O2 -DNDEBUG -g1 -gz"
+            }
+        },
         {
             "name": "github-ci-coverage",
             "displayName": "GitHub-CI Coverage",