hpatch

A Codex Responses router that lets agents edit with compact selectors and replacement text instead of emitting full patches.

hpatch-router sits between Codex and the Responses API. It replaces the Code Mode apply_patch surface with constrained functions.hpatch, resolves successful scripts against the declared workspace, and hands Codex a real apply_patch carrier so sandbox checks and the normal diff UI remain intact. The repository also includes the standalone hpatch CLI and reusable Go engine used by the router.

TL;DR:

Why hpatch?

A direct Code Mode edit makes the model repeat patch framing, old context, replacement text, and the JavaScript carrier. The router moves patch reconstruction out of model output:

flowchart LR
    subgraph output["Alternative model-output payloads"]
        H["hpatch pathfunctions.hpatch + selectors + replacement"]
        A["apply_patch baselinefunctions.exec + JavaScript carrier+ old context + replacement + patch framing"]
    end

    subgraph router["Router and Codex after model output"]
        B["Router reads the immutableworkspace baseline"]
        C["Router generates theapply_patch envelope"]
        D["Codex applies the patchsandbox checks + normal diff"]
    end

    H --> B --> C --> D
    A --> D

The patch is not eliminated: the router generates it after inference. Savings are the difference between the two model-output payload estimates shown above. State reports, rejection diagnostics, and the net cost of installing the hpatch tool definition while removing the Code Mode apply_patch section are tracked separately as input overhead. These are reproducible GPT-5 token estimates, not provider billing totals.

For an 11-line function replacement, hpatch asks the model for this:

functions.hpatch
in parser.go
rsel 50:60
type