fix(harness): target active session in HarnessAgent interrupt API

[StevenZhang2002]

Background

Issue #2610: HarnessAgent.interrupt() / interrupt(Msg) unconditionally resolved the default
session id (the agent name), so streams started via streamEvents(List, RuntimeContext) with a
custom sessionId could never be cancelled — the interrupt signal was always sent to the wrong
session slot.

Purpose

Make the interrupt API target the session that is actually running:

1. The context-free overloads now prefer the active call's RuntimeContext (obtained from the
   delegate's current runtime context) when one exists, while keeping the legacy default-session
   fallback when no call is in flight.
2. New interrupt(RuntimeContext) / interrupt(RuntimeContext, Msg) overloads let callers target
   an explicit (userId, sessionId) slot. Because each caller supplies the session it wants to
   cancel, this is safe under concurrency (multiple sessions running in parallel).

Changes

• agentscope-harness/src/main/java/io/agentscope/harness/agent/HarnessAgent.java:
  • interrupt() and interrupt(Msg) now prefer the active call's runtime context when present,
    and fall back to the default session otherwise.
  • Added interrupt(RuntimeContext ctx) and interrupt(RuntimeContext ctx, Msg msg) overloads
    that delegate directly to the target session (with Javadoc documenting the issue context).
• agentscope-harness/src/test/java/io/agentscope/harness/agent/HarnessAgentInterruptTest.java
  (new): a blocking model is used to keep a stream in flight while an interrupt is fired. Covers:
  • interrupt(ctx, msg) cancels a stream running under a custom sessionId → GenerateReason.INTERRUPTED
  • interrupt(ctx) cancels a custom-session stream without a message
  • context-free interrupt(msg) prefers the active call's custom session
  • context-free interrupt(msg) still works for streams under the default session (backward compat)
  • context-free interrupt() / interrupt(msg) with no active call fall back to the default
    session without throwing (backward compat)

How to Test

All five test cases in HarnessAgentInterruptTest should pass; no existing tests are affected.

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)
• Javadoc comments are complete and follow project conventions
• Related documentation has been updated (e.g. links, examples, etc.)
• Code is ready for review

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All committers have signed the CLA.

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✅ All modified and coverable lines are covered by tests.

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