harness-convert (hc)

Relocate a coding-agent session across harnesses and resume it natively.

The escape hatch: you're 80% through a fix, your harness hits a rate limit / outage mid-task, and you can't even ask it for a handoff. hc reads the session transcript off disk (the dead harness doesn't need to be running or your quota intact), rewrites it into the target harness's format, and you keep going there.

hc --from claude --to codex                 # move the latest Claude session here -> Codex
hc --from codex  --to claude <session-id>   # a specific session
hc --from claude --to codex --dest-cwd DIR  # land it in a different folder
hc list --from codex                        # what's the latest convertible session here

By default it's a dry run; pass --write to create the file, then it prints the exact codex resume / claude --resume command.

How it works

A session is (a) a model-context stream, (b) a UI-render stream, and (c) identity metadata. Conversion maps all three.

• Common interface (hconv/common.py): every harness maps to four records: UserMessage, AssistantMessage, ToolCall, ToolResult. This universal floor guarantees any pair converts and resumes. Private reasoning is dropped (each harness encrypts/owns its own; unrecoverable).
• N² enrichment (hconv/enrich.py): surplus the floor can't hold (session titles, ...) rides a sparse (source, dest) map, layered on top. A pair with no entry is simply common-only. The map never re-encodes the common records.
• Adapters (hconv/adapters/): one per harness, locate / read / dest_path / write. Codex's writer emits BOTH streams (response_item for the model, event_msg for scrollback incl. exec_command_end / patch_apply_end tool cards); Claude's single row set serves both. OpenCode is SQLite, not JSONL: it reads the session/message/part tables read-only, and writes the canonical {info, messages} file that opencode import validates and ingests (safer than poking a live WAL DB), so opencode -s <id> resumes it.
• Ragged-tail close (synthesize_missing_results): the source usually died mid-tool-call, so every orphan ToolCall gets a synthetic result, else the resumed API call rejects the history.

Install

pipx install harness-convert                            # PyPI
npm i -g @theharshitsingh/hc                            # npm (needs python3 on PATH)
brew install harshitsinghbhandari/tap/harness-convert   # Homebrew

Stdlib only, no dependencies. From a checkout, pipx install . or plain python3 hc.py ... also work.

Supported

Codex (~/.codex), Claude Code (~/.claude), and OpenCode (~/.local/share/opencode): any direction between them. Converting into OpenCode writes an import file; resume with opencode import <file> && opencode -s <id> (the command hc prints). Within a harness, sessions are also freely relocatable across working directories (pure metadata rewrite, lossless).

Test

python3 tests/test_hconv.py