Keep build output out of Spotlight (ios#5)

`ci-build` reaches ~700 MB and is rewritten every job, on a machine that
is also the mac-local runner for both app repos, so indexing it lands in
the merge path for everything. `mds_stores` and `mdworker_shared` sit at
the top of CPU while no `xcodebuild` process is near it, which is why
the load looked unexplainable.

Measured, same from-scratch build twice: load peaks at 12.5 with the
output excluded and over a hundred without, and the indexing stops
accumulating rather than trailing the build by minutes.

The marker is written by the job rather than committed, because the
directory it belongs in is created by the build and removed between
runs. The stable caches outside the repo were excluded on the host
itself: DerivedData, the Android SDK, the runner's builds directory and
the Gradle home, 11 GB between them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.gitlab-ci.yml

@@ -76,6 +76,18 @@ unit-tests:
       # Nothing in that says "your CI file is malformed". `ci/lint` does.
       echo "GATE: protocol vectors match flamenet-e2e@$FLAMENET_E2E_PIN"
     - Scripts/generate.sh
+    # Keep the build output out of Spotlight.
+    #
+    # `ci-build` reaches ~700 MB and is rewritten every job. Indexing it drives
+    # this host, which is the mac-local runner and therefore in the merge path
+    # for both app repos, to a load average in the hundreds: `mds_stores` and
+    # `mdworker_shared` sit at the top of CPU while no `xcodebuild` process is
+    # near it. That makes every job slower and the machine unpleasant to use
+    # while CI runs.
+    #
+    # The marker has to be written HERE rather than committed, because the
+    # directory it belongs in is created by the build and removed between runs.
+    - mkdir -p ci-build && touch ci-build/.metadata_never_index
     - |
       # `|| true`, deliberately: the log is the gate, not this pipeline's
       # exit status, and the checks below need to run so they can print the