[9.0.0] Show stack traces in the remote repo contents cache with --verbose_failures

[bazel-io]

Makes it easier to debug issues with this experimental feature and also matches the behavior of remote execution/caching.

Work towards #27965

Closes #27970.

PiperOrigin-RevId: 853238791
Change-Id: Id46ccbb105d93fd17114fab13b086d0b46139fb4

Commit fc5f160

[gemini-code-assist]

Code Review

This pull request adds the ability to show full stack traces for failures in the remote repository contents cache when --verbose_failures is enabled. This improves debuggability. The changes involve plumbing the verboseFailures flag down to RemoteRepoContentsCacheImpl and using it to decide whether to log the full stack trace or just the exception message. My review found one issue where an exception cause was unintentionally dropped, which would hinder debugging.

[gemini-code-assist]

The original ExecutionException e is no longer passed as the cause to the IllegalStateException. This is a regression that loses valuable debugging information, as the original stack trace will be lost. The maybeGetStackTrace(e) method only provides the stack trace as a string in the message when verboseFailures is enabled. It's better to always preserve the original exception as the cause.

Suggested change

	throw new IllegalStateException(
	"waitForBulkTransfer should have thrown: " + maybeGetStackTrace(e));
	throw new IllegalStateException(
	"waitForBulkTransfer should have thrown: " + maybeGetStackTrace(e), e);