ci+hub: durable reviewer hub via in-repo HTML + perf-CI matrix on Linux

Two additions that close out the reviewer-prep work cleanly:

1. doc/reviewer/hub.html  +  publish-workflow integration
   ──────────────────────────────────────────────────────
   Move the hand-curated reviewer hub from the codeberg `pages`
   branch (where it lived as an opaque snapshot) into the repo as
   `doc/reviewer/hub.html`.  `.gitea/workflows/doxygen-pages.yml`
   gains a conditional `if [ -f doc/reviewer/hub.html ]; then …`
   step that installs it as the publish `index.html` and demotes
   the auto-generated Doxygen index to `/doxygen.html`.

   Effect: merging any of the open PRs into main will trigger the
   workflow, which republishes BOTH the Doxygen + the reviewer hub
   together.  The reviewer URL stays live across merges with zero
   manual intervention.

   Source-controlled benefits:
     * hub edits go through normal PRs, not orphan-branch
       force-pushes
     * old hub versions live in git history
     * the in-repo links now target `branch/main/…` instead of the
       transient `preview/reviewer-snapshot-vN/…` paths

2. .gitea/workflows/perf-compile-time.yml — Linux CI bench
   ────────────────────────────────────────────────────────
   New workflow runs on every push to main that touches the build
   system or public headers.  Five-step matrix measures and reports:
     Run 1   cold baseline (no PCH, no Unity, no ccache)
     Run 2   + PCH only
     Run 3   + PCH + Unity (current default)
     Run 4   + FAST_TEST_BUILD=ON  (-O0 -g — Linux's expected ~40 % win)
     Run 5   + ccache warm rerun   (expected ≥ 90 % cache hit)

   Validates the Apple-M1 predictions in doc/architecture/compile-time.md
   against the Linux + g++ runner where Backend dominates more and
   the Apple-clang+PCH friction that defeats ccache locally does not
   apply.  Job is data-collection only; never blocks a merge.

doc updates:
  * doc/architecture/compile-time.md — new "Cross-platform perf bench"
    section linking to the workflow + the table of macOS-vs-Linux
    expected deltas.
  * doc/reviewer/README.md — new "Hub-Page durability" subsection
    explaining how the hub survives merges.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/workflows/doxygen-pages.yml

@@ -75,16 +75,31 @@ jobs:
         run: |
           set -eu
           # Build the publish payload in a clean scratch dir so the
-          # orphan branch contains only the Doxygen output (and a
-          # marker README), never any build/source artefacts.
+          # orphan branch contains only the reviewer hub + Doxygen
+          # output (and a marker README), never any build/source
+          # artefacts.
           publish_dir=$(mktemp -d)
           cp -r doc/doxygen/html/. "$publish_dir/"
 
+          # ── Reviewer hub override ─────────────────────────────────
+          # If doc/reviewer/hub.html is present, install it as the
+          # publish landing page and demote the auto-generated Doxygen
+          # index to /doxygen.html.  The hub is hand-curated and lives
+          # under source control; this step keeps it visible after
+          # every push to main, surviving the auto-publish cycle.
+          if [ -f doc/reviewer/hub.html ]; then
+              mv "$publish_dir/index.html" "$publish_dir/doxygen.html"
+              cp doc/reviewer/hub.html "$publish_dir/index.html"
+              echo "DOC ▸ reviewer hub installed; Doxygen index now at /doxygen.html"
+          fi
+
           cat > "$publish_dir/README.txt" <<EOF
-          conformallab++ — Doxygen HTML API documentation.
+          conformallab++ — Doxygen HTML API documentation + reviewer hub.
           Auto-generated by .gitea/workflows/doxygen-pages.yml from
           commit ${GITHUB_SHA:-$(git rev-parse HEAD)} on $(date -Iseconds).
           Source: https://codeberg.org/TMoussa/ConformalLabpp
+          Reviewer hub: doc/reviewer/hub.html (in-repo)
+          Doxygen index: /doxygen.html
           EOF
 
           cd "$publish_dir"

.gitea/workflows/perf-compile-time.yml

@@ -0,0 +1,175 @@
+name: Compile-time perf bench
+
+# Cross-platform compile-time benchmark.  Validates the predictions
+# made in doc/architecture/compile-time.md against the eulernest CI
+# runner (Linux + g++ on ARM64).
+#
+# Specifically tests whether:
+#   1. FAST_TEST_BUILD=ON delivers the ~40 % wall-time reduction on
+#      Linux + g++ that was predicted from `-ftime-trace` profiling
+#      (recall: on Apple clang + Apple M1 it was net-neutral).
+#   2. ccache hit rate is in the predicted 80%+ range on a warm
+#      rerun (where the macOS-local hit rate was 0 % due to
+#      Apple-clang + PCH friction).
+#
+# When run:
+#   * push to main (after PR #19 lands)
+#   * workflow_dispatch (manual trigger for ad-hoc verification)
+#
+# NOT run on every PR — this is a perf data-collection job, not a
+# correctness gate.  Pollutes the summary with timings but does not
+# block merges.
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - "code/CMakeLists.txt"
+      - "code/tests/**/CMakeLists.txt"
+      - "code/include/**"
+      - ".gitea/workflows/perf-compile-time.yml"
+  workflow_dispatch: {}
+
+jobs:
+  compile-time-matrix:
+    runs-on: eulernest
+    container:
+      image: git.eulernest.eu/conformallab/ci-cpp:latest
+      options: "--memory=2400m --memory-swap=2400m"
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install ccache (idempotent)
+        run: |
+          which ccache >/dev/null 2>&1 || apt-get install -y --no-install-recommends ccache
+
+      # ─── Run 1: baseline (PCH OFF, Unity OFF, ccache cleared) ──────
+      - name: "Run 1: cold baseline (no PCH, no Unity, no ccache)"
+        run: |
+          ccache -C >/dev/null 2>&1 || true
+          rm -rf build-baseline
+          cmake -S code -B build-baseline -G Ninja \
+              -DWITH_CGAL_TESTS=ON \
+              -DCONFORMALLAB_USE_PCH=OFF \
+              -DCMAKE_UNITY_BUILD=OFF \
+              -DCONFORMALLAB_USE_CCACHE=OFF
+          start=$(date +%s)
+          nice -n 19 cmake --build build-baseline --target conformallab_cgal_tests -j1
+          end=$(date +%s)
+          echo "PERF baseline_wall=$((end - start)) s"
+          echo "PERF_BASELINE_WALL=$((end - start))" >> $GITHUB_ENV
+
+      # ─── Run 2: PCH only ──────────────────────────────────────────
+      - name: "Run 2: PCH only (Unity off, ccache off)"
+        run: |
+          ccache -C >/dev/null 2>&1 || true
+          rm -rf build-pch
+          cmake -S code -B build-pch -G Ninja \
+              -DWITH_CGAL_TESTS=ON \
+              -DCONFORMALLAB_USE_PCH=ON \
+              -DCMAKE_UNITY_BUILD=OFF \
+              -DCONFORMALLAB_USE_CCACHE=OFF
+          start=$(date +%s)
+          nice -n 19 cmake --build build-pch --target conformallab_cgal_tests -j1
+          end=$(date +%s)
+          echo "PERF pch_only_wall=$((end - start)) s"
+          echo "PERF_PCH_WALL=$((end - start))" >> $GITHUB_ENV
+
+      # ─── Run 3: default (PCH + Unity Build + #6 Dense→Core) ───────
+      - name: "Run 3: default config (PCH + Unity + Dense→Core)"
+        run: |
+          ccache -C >/dev/null 2>&1 || true
+          rm -rf build-default
+          cmake -S code -B build-default -G Ninja \
+              -DWITH_CGAL_TESTS=ON \
+              -DCONFORMALLAB_USE_CCACHE=OFF
+          start=$(date +%s)
+          nice -n 19 cmake --build build-default --target conformallab_cgal_tests -j1
+          end=$(date +%s)
+          echo "PERF default_wall=$((end - start)) s"
+          echo "PERF_DEFAULT_WALL=$((end - start))" >> $GITHUB_ENV
+
+      # ─── Run 4: + FAST_TEST_BUILD (-O0 -g) ────────────────────────
+      - name: "Run 4: default + FAST_TEST_BUILD=ON (-O0 -g for tests)"
+        run: |
+          ccache -C >/dev/null 2>&1 || true
+          rm -rf build-fast
+          cmake -S code -B build-fast -G Ninja \
+              -DWITH_CGAL_TESTS=ON \
+              -DCONFORMALLAB_FAST_TEST_BUILD=ON \
+              -DCONFORMALLAB_USE_CCACHE=OFF
+          start=$(date +%s)
+          nice -n 19 cmake --build build-fast --target conformallab_cgal_tests -j1
+          end=$(date +%s)
+          echo "PERF fast_test_wall=$((end - start)) s"
+          echo "PERF_FAST_WALL=$((end - start))" >> $GITHUB_ENV
+
+      # ─── Run 5: ccache hit-rate validation ─────────────────────────
+      - name: "Run 5: ccache hit-rate (rebuild build-default)"
+        run: |
+          ccache -C >/dev/null 2>&1 || true
+          ccache --zero-stats >/dev/null
+          # First rebuild: populate ccache.
+          rm -rf build-cc
+          cmake -S code -B build-cc -G Ninja \
+              -DWITH_CGAL_TESTS=ON \
+              -DCONFORMALLAB_USE_CCACHE=ON
+          nice -n 19 cmake --build build-cc --target conformallab_cgal_tests -j1 >/dev/null
+          ccache_first=$(ccache -s 2>&1 | grep -E "^\s*Hits" | head -1 | awk '{print $2}')
+          # Second rebuild: expect cache hits.
+          rm -rf build-cc-warm
+          cmake -S code -B build-cc-warm -G Ninja \
+              -DWITH_CGAL_TESTS=ON \
+              -DCONFORMALLAB_USE_CCACHE=ON
+          start=$(date +%s)
+          nice -n 19 cmake --build build-cc-warm --target conformallab_cgal_tests -j1
+          end=$(date +%s)
+          warm_wall=$((end - start))
+          ccache_stats=$(ccache -s 2>&1 | grep -E "Hits|Misses" | head -4)
+          echo "── ccache stats after warm rebuild ──"
+          echo "$ccache_stats"
+          echo "PERF ccache_warm_wall=${warm_wall} s"
+          echo "PERF_CCACHE_WARM_WALL=$warm_wall" >> $GITHUB_ENV
+
+      # ─── Test correctness (last gate; perf data already collected) ─
+      - name: Verify all configs produced working binaries
+        if: always()
+        run: |
+          for build in build-baseline build-pch build-default build-fast; do
+              if [ -d "$build" ]; then
+                  ctest --test-dir "$build" -R "^cgal\." --output-on-failure --timeout 120 \
+                      | tail -3
+              fi
+          done
+
+      # ─── Final summary ─────────────────────────────────────────────
+      - name: Compile-time perf summary
+        if: always()
+        run: |
+          echo "══════════════════════════════════════════════════════"
+          echo "  COMPILE-TIME PERF BENCH — Linux ARM64 / g++ / -j1"
+          echo "══════════════════════════════════════════════════════"
+          printf "  %-30s  %4s s\n" "Run 1: cold baseline"          "${PERF_BASELINE_WALL:-?}"
+          printf "  %-30s  %4s s\n" "Run 2: + PCH"                  "${PERF_PCH_WALL:-?}"
+          printf "  %-30s  %4s s\n" "Run 3: + PCH + Unity (default)" "${PERF_DEFAULT_WALL:-?}"
+          printf "  %-30s  %4s s\n" "Run 4: + FAST_TEST_BUILD"      "${PERF_FAST_WALL:-?}"
+          printf "  %-30s  %4s s\n" "Run 5: + ccache warm rerun"    "${PERF_CCACHE_WARM_WALL:-?}"
+          echo "──────────────────────────────────────────────────────"
+          echo "Predictions to validate vs Apple-M1 baseline:"
+          echo "  ┃ FAST_TEST_BUILD: expected ~40 % faster than default"
+          echo "  ┃ ccache warm:     expected ≤ 10 s (vs Apple's 55 s)"
+          echo "──────────────────────────────────────────────────────"
+          # Compute relative deltas
+          if [ -n "${PERF_DEFAULT_WALL:-}" ] && [ -n "${PERF_FAST_WALL:-}" ]; then
+              pct=$(awk -v d="${PERF_DEFAULT_WALL}" -v f="${PERF_FAST_WALL}" \
+                  'BEGIN { printf "%.0f", 100.0 * (d - f) / d }')
+              echo "  Δ FAST_TEST_BUILD vs default: ${pct} % wall reduction"
+          fi
+          if [ -n "${PERF_DEFAULT_WALL:-}" ] && [ -n "${PERF_CCACHE_WARM_WALL:-}" ]; then
+              pct=$(awk -v d="${PERF_DEFAULT_WALL}" -v c="${PERF_CCACHE_WARM_WALL}" \
+                  'BEGIN { printf "%.0f", 100.0 * (d - c) / d }')
+              echo "  Δ ccache warm vs default:     ${pct} % wall reduction"
+          fi
+          echo "══════════════════════════════════════════════════════"