Feat: Add trace_agg_mode to support both transition and trajectory aggregation

[JiahangXu]

Add a trace_agg_mode option to control whether the trace aggregation is performed per transition or per trajectory (by adding response mask for multi-turn). Default remains 'transition' for backward compatibility.

[Copilot]

Pull Request Overview

This PR adds a trace_agg_mode configuration parameter to support both "transition" and "trajectory" level trace aggregation, with "transition" as the default for backward compatibility.

• Introduces a trace_agg_mode parameter that controls aggregation behavior
• Implements trajectory-level aggregation with response masking for multi-turn conversations
• Adds configuration option to the YAML config file

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
agentlightning/verl/trainer.py	Passes trace_agg_mode config to daemon and adds debugging breakpoint
agentlightning/verl/daemon.py	Implements trajectory aggregation logic and response mask generation
agentlightning/verl/config.yaml	Adds trace_agg_mode configuration option with default value

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