fix(harness): use stable agent id for session paths

[yuefengw]

AgentScope-Java Version

2.0.1-SNAPSHOT

Description

Fixes #2298.

Use the builder's resolved agent ID consistently for session archive paths in:

• MemoryFlushMiddleware
• CompactionMiddleware
• Context overflow recovery

This prevents session files from being written under the agent display name when name and agentId differ.

Added regression tests covering memory offload and compaction with different name and agentId values. Existing middleware constructors remain backward compatible.

Testing

• mvn -pl agentscope-harness spotless:check
• mvn -pl agentscope-harness -am test

Both passed successfully.

Checklist

• Code has been formatted with mvn spotless:apply
• All tests are passing
• Javadoc comments are complete
• Documentation changes are not required
• Code is ready for review

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

❌ Patch coverage is 84.61538% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...harness/agent/middleware/CompactionMiddleware.java	83.33%	0 Missing and 1 partial ⚠️
...arness/agent/middleware/MemoryFlushMiddleware.java	83.33%	0 Missing and 1 partial ⚠️

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