Summary

mongodb-runner (used by `run-mongodb.sh` in drivers-evergreen-tools) only captures mongod/mongos
server logs while its own CLI process is alive, and that process exits as soon as the deployment
is up. Every log line written after startup is silently lost.
We need to update the runner so servers log to disk for their whole lifetime.

As part of JAVA-6108 we are adding a workaround on the drivers-evergreen-tools end to capture
the logs on POSIX systems.

Motivation

Who is the affected end user?

Driver teams running CI using drivers-evergreen-tools (e.g. JAVA-6108).

How does this affect the end user?

Not blocked, but debugging test failures is severely degraded: no server-side logs in the
uploaded artifacts to explain failures or crashes that show up only in driver test runs.

How likely is it that this problem or use case will occur?

Main path — every CI run that uses the mongodb-runner path loses all post-startup server logs.

If the problem does occur, what are the consequences and how severe are they?

Slow, guesswork triage of driver test failures (e.g. recent mongo-java-driver patch runs with 45
failing tasks had no server logs to work from).

Is this issue urgent?

Timed to the JAVA-6108 migration, which is in progress.

Is this ticket required by a downstream team?

Yes, all drivers; owned by the devtools-shared (mongodb-runner) team upstream.

Is this ticket only for tests?

No — it changes how server processes are launched and where their logs are written.

Acceptance Criteria

• Servers write logs to the `logDir` file for their whole lifetime, including post-startup, on
  all platforms (Linux, macOS, Windows)
• Fix landed upstream in mongodb-js/devtools-shared and released
• Pin bumped in drivers-evergreen-tools; the POSIX tee wrapper from JAVA-6108 is removed.
• Unit tests for the new log-tail behavior; drivers-evergreen-tools CI asserts logs keep flowing
  after startup