fix: improve agent request error handling with structured details

[zeroklaw]

Summary

Closes #225

The error message reported in issue #225 was:

20:10:55 ERROR yoke::dispatcher: Workflow execution failed workflow=implement_issue.toml repo=mintybasil/yoke event_id=issue-216 error=Execution failed: Step 'Plan' failed: Harness error: HTTP request failed: error sending request for url (http://10.200.0.3:8500/v1/responses)

This error message is lacking details — there is no indication of why the request failed (timeout, connection refused, DNS error, etc.) and no status code.

Root cause

HarnessError::Http used #[from] reqwest::Error, which delegates to reqwest::Error's default Display impl. That impl only produces error sending request for url (...) and does not include the underlying cause (timeout, connection refused, DNS failure) or a status code if one was received.

Additionally, when response.text().await? failed on the body read, the already-captured HTTP status code was silently lost.

Changes

src/harness.rs

1. Replaced HarnessError::Http(#[from] reqwest::Error) with a structured variant:

   Http {
       message: String,
   }

2. Added HarnessError::from_reqwest_error(err, url) — a helper that builds a descriptive Http error by:

   • Surfacing timeout status (is_timeout()) as timeout reached
   • Surfacing connect-failure status (is_connect()) as connection failed
   • Including the HTTP status code if one was received (err.status())
   • Walking the full std::error::Error::source() cause chain to get the real root cause (e.g. dns error: failed to lookup address information, Connection refused (os error 111))

3. Updated execute_step_with_error_path to use .map_err(|e| HarnessError::from_reqwest_error(e, &url))? instead of the bare ? operator on both the request send and the body read, so both failure paths produce a structured, descriptive error.

Before (issue #225):

HTTP request failed: error sending request for url (http://10.200.0.3:8500/v1/responses)

After (timeout example):

HTTP request failed: error sending request for url (http://10.200.0.3:8500/v1/responses): timeout reached: operation timed out

After (connection refused example):

HTTP request failed: error sending request for url (http://localhost:8500/v1/responses): connection failed: Connection refused (os error 111)

After (DNS failure example):

HTTP request failed: error sending request for url (http://nonexistent.invalid:8500/v1/responses): connection failed: dns error: failed to lookup address information: nonexistent.invalid

Test plan

• cargo build — compiles cleanly
• cargo test — all 120+ tests pass (lib + integration)
• cargo clippy --lib -- -W clippy::all — no warnings
• New unit tests for the structured HarnessError::Http variant:
  • test_harness_error_http_includes_url — verifies URL, timeout indicator, and cause chain appear in the display
  • test_harness_error_http_connection_refused — verifies connection-failure indicator and cause
  • test_harness_error_http_minimal — verifies the message is still meaningful with no extra details
• New integration test test_harness_http_error_includes_details (regression test for issue Improve agent request error handling #225)