ci: GHA fallback centos task runs out of space

[maflcko]

https://github.com/bitcoin-core/gui/actions/runs/17433074590/job/49495964258?pr=884#step:8:3785

...
+ eval 'TEST_RUNNER_EXTRA=()'
++ TEST_RUNNER_EXTRA=()
+ LD_LIBRARY_PATH=/home/runner/work/_temp/depends/x86_64-pc-linux-gnu/lib
+ /home/runner/work/_temp/build/test/functional/test_runner.py --ci -j4 --tmpdirprefix /home/runner/work/_temp/ci/scratch/test_runner/ --ansi --combinedlogslen=99999999 --timeout-factor=40 --quiet --failfast
WARNING! There may be insufficient free space in /home/runner/work/_temp/ci/scratch/test_runner//test_runner_₿_🏃_20250903_092842 to run the Bitcoin functional test suite. Running the test suite with fewer than 1426.0 MB of free space might cause tests to fail.
...................................................................................................
                                                                                                   
1/272 - feature_block.py failed, Duration: 50 s
...


 node0 stderr Error: A fatal internal error occurred, see debug.log for details: Disk space is too low!
Error: A fatal internal error occurred, see debug.log for details: Disk space is too low!
Error: A fatal internal error occurred, see debug.log for details: Disk space is too low! 

[maflcko]

It may be possible to free up some space with something like https://github.com/google/oss-fuzz/blob/14cab84abbc736e24fede3f0267a8e220fb4974e/.github/workflows/project_tests.yml#L65-L74

[willcl-ark]

Free disk space:
+ [[ ci_native_centos == \c\i\_\n\a\t\i\v\e\_\a\s\a\n ]]
++ /home/runner/work/_temp/depends/config.guess
Filesystem      Size  Used Avail Use% Mounted on
overlay          72G   48G   25G  67% /
tmpfs            64M     0   64M   0% /dev
shm              64M     0   64M   0% /dev/shm
/dev/root        72G   48G   25G  67% /etc/hosts
tmpfs           7.9G     0  7.9G   0% /proc/acpi
tmpfs           7.9G     0  7.9G   0% /proc/scsi
tmpfs           7.9G     0  7.9G   0% /sys/firmware

This job is using more than 25GB?

It may be possible to free up some space with something like google/oss-fuzz@14cab84/.github/workflows/project_tests.yml#L65-L74

Yes we can try to free up space. I'll take a look where the space is being used and see what we can free.

[willcl-ark]

Seems we are probably already swapping before we start the functional tests:

https://github.com/willcl-ark/bitcoin/actions/runs/17442003339/job/49527090325#step:8:3768

I tested cleaning scratch dir and object files in this run which got it to pass. They seem the obvious choices to me to remove (probably right after building), any other ideas here?

[maflcko]

Yeah, I guess we could nuke the build dir object files, but it seems tedious and could make debugging later harder?

I'd say the underlying issue is with GitHub Actions. Conceptually they looked at the npm hell and implemented it for CI. The GHA runners are optimized so that you can test your "sort" module out of the box without installing any dependencies. The runners ship with npm, android, chromium, powershell, graalvm, dotnet, all popular docker images ... (at least the last time I looked in google/oss-fuzz@b7f04d7).

So I think the correct fix is to remove stuff on the GHA vm, not inside our CI docker container.

[fanquake]

Yes we can try to free up space. I'll take a look where the space is being used and see what we can free.

#33304 should free up ~1.5GB of disk usage, an take some pressure off caching generally.