[Flaky Test] github.com/elastic/beats/v7/filebeat/input/filestream TestWaitUntilEOF

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## Flaky Test

* **Test Name:** TestWaitUntilEOF
* **Scope:** github.com/elastic/beats/v7/filebeat/input/filestream
* **File:** N/A
* **Location:** N/A
* **Buildkite Link:** https://buildkite.com/organizations/elastic/analytics/suites/beats/tests/5ee83a7f-e80d-8da5-acb4-c168848ae1b2
* **Flaky Instances:** 1
* **Latest Occurrence:** 2026-06-29T04:37:45.779Z

### Details

```json
{
"id": "5ee83a7f-e80d-8da5-acb4-c168848ae1b2",
"web_url": "https://buildkite.com/organizations/elastic/analytics/suites/beats/tests/5ee83a7f-e80d-8da5-acb4-c168848ae1b2",
"scope": "github.com/elastic/beats/v7/filebeat/input/filestream",
"name": "TestWaitUntilEOF",
"location": null,
"file_name": null,
"instances": 1,
"latest_occurrence_at": "2026-06-29T04:37:45.779Z",
"most_recent_instance_at": "2026-06-29T04:37:45.779Z",
"last_resolved_at": null,
"ownership_team_ids": [],
"failure_examples_count": 1
}
```

### Failure Examples

**Example 1:**
**Run:** https://api.buildkite.com/v2/analytics/organizations/elastic/suites/beats/runs/25b6c69f-814c-8cb2-9f05-3ec9f84e679c
**Time:** 2026-06-29T04:07:06.381Z
**Stacktrace:**

```
=== RUN TestWaitUntilEOF
log_generator.go:115: generating 1 log files with 10 lines each...
log_generator.go:135: finished generating 1 log files with 10 lines each
input_wait_until_eof_integration_test.go:68: did not find 'input closing, read_until_eof enabled, waiting EOF or 30s timeout, whichever happens first' in the logs
input_wait_until_eof_integration_test.go:68:
Error Trace: /opt/buildkite-agent/.asdf/installs/golang/1.26.4/packages/pkg/mod/github.com/elastic/elastic-agent-libs@v0.44.0/logp/logptest/logger.go:136
/opt/buildkite-agent/builds/bk-agent-prod-gcp-1782705856976152796/elastic/filebeat/filebeat/input/filestream/environment_test.go:549
/opt/buildkite-agent/builds/bk-agent-prod-gcp-1782705856976152796/elastic/filebeat/filebeat/input/filestream/input_wait_until_eof_integration_test.go:68
Error: Condition never satisfied
Test: TestWaitUntilEOF
Messages: 100ms
logger.go:108: Full logs written to ../../build/integration-tests/testing-logger-540564754.log
--- FAIL: TestWaitUntilEOF (5.11s)

```

Start by running TestWaitUntilEOF in input_wait_until_eof_integration_test.go and inspect the assertion at line 68. Review log generation in log_generator.go and the test logging setup referenced through environment_test.go. Done means the test reliably observes the expected input-closing log without intermittent failures.

Written by the indexing model from the issue text.