Checklist

• I've run bundle exec rspec from the root directory to see all new and existing tests pass
• I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• I see several green ci/circleci builds in the "All checks have passed" section of my PR (connect CircleCI to GitHub if not)
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.
• I've added or updated relevant unit tests.

Motivation and Context

Resolves #30037

screengrab checks several possible on-device screenshot directories while cleaning old screenshots and pulling newly captured screenshots. Missing directories are expected during this search, because only one of the candidate paths may exist for a given Android version, storage location, or app configuration.

Those expected misses were still routed through the generic command executor as normal command failures. As a result, every missing candidate path printed both the ls: ... No such file or directory output and Exit status: 1, causing very noisy logs across all locales.

While investigating the report, I also found that the final screenshot summary could say Captured 0 new screenshots! even when screenshots were copied. That happened when screenshots overwrote existing files: the previous implementation calculated the count as the difference between the destination file count before and after pulling.

Description

The investigation traced the noisy output to Screengrab::Runner#if_device_path_exists. That helper intentionally probes candidate screenshot paths using adb shell ls, and already treats missing paths as safe to ignore. The problem was that the command executor printed the failure output before the screengrab helper could ignore it.

This change adds an opt-in suppress_error_output parameter to FastlaneCore::CommandExecutor.execute. The command still returns output and status to the caller, and still raises when no error callback is supplied, but callers that expect a non-zero status can suppress replaying the command output and Exit status line.

screengrab now uses that option only for the expected missing-path probes. Other adb commands continue to use the existing behavior.

This also updates screenshot counting so screengrab counts the PNG files actually copied from the pulled screenshot directories. That makes the final summary accurate even when copied screenshots replace files that already existed in the output directory.

Unit coverage was added for:

• suppressing expected command failure output while preserving status handling
• preserving normal raise behavior when suppressed failures are not handled
• missing screengrab device paths not yielding or printing expected adb failures
• copied screenshot count being returned even when existing files are overwritten
• copied screenshot count from pulled screenshot directories

Testing Steps

I reproduced the issue by following the path from the reported adb shell ls failures back to the screengrab directory probing helper. A missing path produced the same behavior shown in the issue: the missing-file message followed by Exit status: 1.

After the fix, the same missing-path probe still reports the non-zero status to the caller, but no longer prints the expected failure to the user.

I also reproduced the screenshot-count issue by simulating an existing output screenshot and a successful copy of a screenshot with the same destination count. Before the fix, the method reported 0; after the fix, it reports the number of screenshots copied.