fix(harness): stream Docker sandbox file transfers

[ShinyHero666]

AgentScope-Java Version

2.0.1-SNAPSHOT

Description

Fixes #1560.

SandboxBackedFilesystem.uploadFiles previously fell back to a shell command that embedded the complete Base64 payload in the docker exec command line. Large files therefore exceeded the host command-line limit on Windows (CreateProcess error=206) and could also hit E2BIG on Unix-like hosts.

This PR:

• makes DockerSandbox implement the existing SandboxFileTransfer capability;
• streams uploads through docker exec -i standard input instead of command-line arguments;
• streams downloads directly from container standard output;
• preserves support for workspace-relative and absolute paths, including paths with spaces and quotes;
• adds regression tests for the native transfer capability and path handling.

Validation performed locally:

• mvn -pl agentscope-harness -am spotless:apply
• mvn -pl agentscope-harness -am -DskipTests compile
• mvn -pl agentscope-harness -am "-Dtest=SandboxBackedFilesystemTest,DockerSandboxFileTransferTest" test (8 tests passed)
• real Docker round trip of a 1 MiB random binary file through an Alpine 3.22 container, with byte-for-byte verification

The full mvn test suite did not complete within the local validation window, so the full-suite checkbox is intentionally left open for CI.

Checklist

Please check the following items before code is ready to be reviewed.

• Code has been formatted with mvn spotless:apply
• All tests are passing (mvn test); the focused harness tests above pass and CI will run the complete suite
• Javadoc comments are complete and follow project conventions
• Related documentation has been updated (not applicable; no user-facing API or documentation changed)
• Code is ready for review

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[CLAassistant]

All committers have signed the CLA.

[ShinyHero666]

CI note: the new DockerSandboxFileTransferTest passed on both Ubuntu and Windows. In run 30750987683, Ubuntu failed in the unrelated HarnessAgentSubagentStreamEventsTest; an isolated local rerun of that class passed all 4 tests, and Windows was canceled by fail-fast. In run 30751331762, Windows failed in the unrelated AgentSpawnToolPlanModeTest because JUnit could not delete its temporary directory; Ubuntu was then canceled by fail-fast. The new transfer test does not create files or processes, and the affected tests/files are outside this change. I do not have repository permission to rerun Actions. Could a maintainer please rerun the failed checks?

[ShinyHero666]

Thanks for rerunning the checks. The Windows build now passes. The Ubuntu job was canceled mid-build without a test failure. Could you please rerun the Ubuntu check when convenient?