Introduce agentscope-harness module

[chickenlj]

This pull request introduces a new agentscope-harness module built with the Harness Engineering practices.

Purpose

agentscope-harness builds on agentscope-core with a higher-level agent runtime for production-style assistants: workspace-first workflows, pluggable execution environments, and richer memory/session tooling.

Entry point

HarnessAgent wraps ReActAgent with opinionated defaults: hooks, toolkit wiring, and configuration for workspace, skills, subagents, and persistence.

Key design ideas

• Workspace-centric context — Loads and injects workspace material (e.g. AGENTS.md, MEMORY.md, knowledge) into the agent’s unified system message via hooks such as WorkspaceContextHook.
• Pluggable filesystem — Abstracts file operations behind a filesystem layer (local, sandbox-backed, remote/composite) so tools and agents share one API regardless of where files actually live.
• Sandbox & isolation — Optional sandbox execution with lifecycle management, state stores, and options for distributed deployments when session/sandbox state must be shared across replicas.
• Session & persistence — WorkspaceSession, session trees, and hooks (e.g. session persistence, traces) tie long-running work to durable session state where configured.
• Memory operations — Memory flush/consolidation, compaction, and eviction policies help keep context bounded; dedicated tools (e.g. memory search/get) support retrieval over workspace memory files.
• Subagents — Declarative subagent specs, spawn/send/list tooling, and background tasks for delegated or async work (SubagentsHook, task repository).
• Relationship to core. Harness does not replace ReActAgent; it composes it with extra hooks, tools, and backends so applications can adopt “harness” behavior incrementally while staying aligned with core APIs (Model, Toolkit, Session, hooks).

This pull request also includes significant enhancements to the ReActAgent class, focusing on improved runtime context handling, per-call system message management, and better integration of hook-supplied tools.

• Runtime Context and System Message Handling
• Hook and Toolkit Integration
• General Refactoring and Minor Improvements

[Copilot]

Copilot wasn't able to review this pull request because it exceeds the maximum number of lines (20,000). Try reducing the number of changed lines and requesting a review from Copilot again.

[codecov]

Codecov Report

❌ Patch coverage is 38.37057% with 2345 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...agent/memory/compaction/ConversationCompactor.java	0.00%	249 Missing ⚠️
...cope/harness/agent/filesystem/LocalFilesystem.java	25.97%	227 Missing and 21 partials ⚠️
...java/io/agentscope/harness/agent/HarnessAgent.java	49.89%	186 Missing and 54 partials ⚠️
...ope/harness/agent/filesystem/RemoteFilesystem.java	40.60%	127 Missing and 31 partials ⚠️
.../harness/agent/filesystem/CompositeFilesystem.java	37.08%	116 Missing and 18 partials ⚠️
...arness/agent/filesystem/BaseSandboxFilesystem.java	17.83%	119 Missing and 10 partials ⚠️
.../agentscope/harness/agent/hook/AgentTraceHook.java	3.41%	112 Missing and 1 partial ⚠️
...cope/harness/agent/memory/session/SessionTree.java	58.36%	76 Missing and 21 partials ⚠️
...ess/agent/filesystem/LocalFilesystemWithShell.java	10.00%	87 Missing and 3 partials ⚠️
...ope/harness/agent/sandbox/AbstractBaseSandbox.java	0.00%	83 Missing ⚠️
... and 37 more

📢 Thoughts on this report? Let us know!