I run Claude Code + Codex in parallel and kept losing the thread between them - built a no-server coordination layer that lives in an S3 bucket

Running more than one coding agent at once — a couple of Claude Code instances, sometimes Codex — the coordination was always ad hoc. Two pains drove me nuts: 1. They grab the same work. Both agents decide to refactor api(.)py and you get a mess. No shared "I've got this" between separate processes/machines. 2. They can't talk, and the history is scattered + tool-locked. I was hand-pasting output from one terminal into another, and afterward had no single record of who did what. So I built tracecraft — a CLI that turns any S3-compatible bucket (AWS, R2, MinIO, B2, Wasabi, or HuggingFace Buckets) into a coordination layer. No server, no DB, no daemon; every call is stateless and all state is plain JSON you own. Coordination primitives: \- Atomic task claims — S3 If-None-Match conditional write, so two agents can't both claim the same step. First wins, second backs off. No lock service. \- A mailbox — agents send each other direct messages and broadcasts (each a JSON file). This is the bit that replaced my copy-pasting: one agent does \`tracecraft send developer "contract is in memory key design.contract"\`, the other reads its inbox. \- Shared key-value memory + handoffs with a note for the next agent. The part I'm most happy with is the harness adapter framework — it mirrors each agent's full session transcript into the same bucket, across four harnesses behind one interface: | harness | session storage | adapter | |---|---|---| | Claude Code | \~/.claude/projects/.../<id>.jsonl | byte-offset tail | | Codex | \~/.codex/sessions/.../rollout-\*.jsonl | byte-offset tail | | OpenClaw | <state>/agents/<id>/sessions/\*.jsonl | byte-offset tail | | Hermes | \~/.hermes/state.db (SQLite/WAL) | read-only, rowid cursor, synthesize JSONL | One cursor abstraction makes them all fit: \`read\_new(cursor) -> (bytes, new\_cursor)\` — byte offset for files, rowid for Hermes, the loop doesn't care which. Adding a 5th harness is \~50 lines. Redaction (token shapes for AWS/Anthropic/OpenAI/HF/GitHub/Slack) runs by default. End result: one bucket holds both the coordination events (claims, messages, handoffs) AND each agent's reasoning trace, browsable as plain JSON (including in the HF Hub UI). Straight about what this is: the primitives themselves aren't novel — mcp\_agent\_mail/Beads do mailbox+claims, Anthropic Agent Teams ships in-process claims. What's different is the deployment model — server-less, backend-agnostic, state in a remote bucket — so agents on different machines/clouds coordinate by default. The cross-harness session mirroring into the same place is the part I haven't seen elsewhere. Known gaps: no TTL on claims yet; HF buckets get best-effort claims (no conditional write); replay viewer not built yet. Feedback I'd actually use: \- is the cursor abstraction the right call for the harness layer, or is there a cleaner one? \- which harness should I add next? \- where does "bucket as coordinator" break down at scale?