messages/execution.rs exceeds the audit file-length threshold (819 > 800 LOC)

[nficano]

Category: refactor Severity: major
Location: crates/arcp-core/src/messages/execution.rs:1-8

What

execution.rs is 819 lines and mixes agent parsing, tool payloads, job lifecycle payloads, result chunk assembly, tests, and v0.2 stubs. It is just over the configured threshold and should be split before more execution semantics land.

Evidence

//! Execution messages — tools, jobs, agents, workflows (RFC §10).

use serde::{Deserialize, Serialize};

use crate::error::ErrorCode;
use crate::ids::JobId;

/// Parsed agent identifier per ARCP v1.1 §7.5.

Proposed fix

Extract result chunk assembly/tests and agent reference parsing into separate modules, leaving execution payload DTOs in a smaller file.

Acceptance criteria

• execution.rs is below 800 lines after extraction and all execution/result-chunk tests still pass.