Why a harness?

When developers use AI assistants directly in a terminal, they quickly face four structural failures:

1. Runaway edits across multiple files: the agent tries to solve a narrow problem and changes unrelated modules, creating huge, noisy diffs.
2. Broken builds: the agent declares victory without checking compilation or dependency integrity.
3. Test hallucination: the model reports that "tests passed" without running the test command.
4. Context loss between sessions: decisions, prior solutions, and blockers disappear when the terminal closes or restarts.

The PREVC contract turns AI assistance into a deterministic engineering flow, governed by rules on disk, executable checks, and auditable transitions.

Structural comparison

Unassisted AI chat	Engineering with a harness
Runaway edits: changes spread across unrelated files.	Bounded scope: each lane declares file ownership.
Broken build: success is declared without verification.	Required verification: completion waits for objective checks.
Test hallucination: results are asserted without a command.	Real evidence: terminal output and evidence rungs are required.
Context loss: each session starts from zero.	Durable continuity: state, blockers, and handoff survive on disk.

PREVC contract: the seven stages prepare → plan → execute → validate → judge → refine → confirm are grouped into four phases: Prepare, Execute, Validate, and Confirm. Each transition requires evidence from the prior stage.

What the harness answers

Before any significant change, the harness answers:

1. Where am I and what rules does this repository have?
2. What has already been done and what is blocked?
3. What is the single active unit of work?
4. How will I prove that the change worked?
5. Who decides whether the result can be accepted?
6. What does a next session need to read in order to continue?

The OpenCode identity

The OpenCode Harness is a methodological reference. It organizes the PREVC cycle, durable state, evidence, and handoffs so teams can resume work across sessions without relying on chat memory. Use this documentation to define the process and criteria before choosing how to execute each lane.

How this is implemented in OpenCode

• Shared contract: PREVC defines phases, WIP=1, evidence, and human confirmation for OpenCode and Oh My Pi.
• Methodological adapter: OpenCode provides durable state, multi-session continuity, plugins, and skills that implement the contract in this tree.
• Auditable evidence rungs: executable evidence (Rungs 1 through 5) is required before advancing phases or allowing handoff.

What the harness does NOT do

• It does not make the agent autonomous.
• It does not replace human review.
• It does not provide an operating-system sandbox.
• It does not make code quality automatic — it requires traceable evidence.

Core principle

The repository is the system of record. State that lives only in chat is not trustworthy state.