### Motivation
This PR evolves the harness from a pure execution runtime into an
**observable, replayable agent evaluation platform**. The current
`harness/graph` checkpoint mechanism is insufficient for true
event-sourced introspection—we need append-only event logs capturing
every tool call, state transition, memory write, and approval decision,
enabling deterministic replay, fork/diff, postmortem analysis, and
time-travel debugging.
### Key Design Goals
1. **Event-Sourced Execution Model**
Replace coarse checkpoints with granular, append-only event logs. Every
operation becomes a durable event: tool invocation, state mutation,
memory update, human approval. This unlocks deterministic replay,
branching execution histories, and regression datasets derived directly
from production failures.
2. **First-Class Replay & Evaluation Loop**
Replay is not an afterthought—it is a core primitive. A single live run
seeds an offline corpus that supports: repeated playback, model
substitution, tool result mocking, and strategy comparison. The harness
graduates from "executor" to "continuous evaluation platform" where
failed production traces convert directly into offline regression
suites.
3. **Operational Observability**
Beyond raw traces, expose metrics that prove stability over time:
- Tool success / failure rates
- Approval latency distributions
- Retry frequencies
- Checkpoint restore reliability
- Memory retrieval quality
- Cost per completed task
- Fork replay pass rates
The underlying thesis: the bottleneck for most agent systems is not
execution capability, but the inability to **demonstrate continuous,
measurable improvement**.
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
### Summary
Adopt sync.WaitGroup.Go (Go 1.25) to simplify tracked goroutine
spawning. This replaces the error-prone trio of wg.Add(1), go func(),
and defer wg.Done() with a single, self-contained call.
More info: https://github.com/golang/go/issues/63796
Signed-off-by: grandpig <grandpig@outlook.com>
### What problem does this PR solve?
- OpenTelemetry integration
- Checkpoint conformance tests
- State inspector API
- Callbacks
- A series of fault injection tests
- Pregel integration tests
### Type of change
- [x] Refactoring
### What problem does this PR solve?
- Tools management
- Pregel engine wrapper for better usage
- UT race
- Coding style
### Type of change
- [x] Refactoring
Refactor the Go agent port's logging so every log line — gin access,
agent canvas events, harness warnings, fatal boot errors — flows through
a single common.Logger (zap) backed by a rotated file, with structured
fields, level filtering, and configurable rotation.
---------
Co-authored-by: Claude <noreply@anthropic.com>
### What problem does this PR solve?
go-version of Pregel-based BSP engine
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
