Tianyi Cui
c182543dd5
Per a design revision, the per-scenario snapshot fixture becomes EXACTLY the persisted session JSONL (<scenario>/session.jsonl) rather than a hand-authored llm.json. The log already holds all LLM behavior (assistant/chunk carries every StreamChunk) AND all harness behavior (tool/call, tool/result, turn/*, usage), so one artifact drives replay and doubles as a behavioral golden. llm-replay becomes replay-only (the record-tee is removed; recording is now "run the real agent once and harvest the .jsonl", done by the harness in a later commit). deriveReplayScript(events) groups assistant/chunk by (turn,step) in log order — exact because the loop makes one ctx.llm.stream() call per step and tags each chunk with the current (turn,step). The two failure modes the log can't express (a thrown stream — no terminal finish; cancel/hang — timing) use an optional replay.override.json sidecar. Hardens against a Codex review finding: a derived group is only valid if it ends in a `finish` chunk. A group without one is the fingerprint of a thrown stream() and is NOT silently replayed as a clean stop — deriveReplayScript throws, naming the (turn,step), so a missing sidecar override fails loud. Updates the unit tests (parse/derive/load helpers, sidecar override, finish- terminated grouping, HMR), the example README, and the RFC prose to the JSONL format. Two goldens (stdout transcript + re-persisted JSONL) and the harness wiring land in the next commit.
RFCs
One kind of design doc lives here. An RFC records a decision or proposal that shapes this codebase — the why and what we gave up, the parts code and docs can't carry. (Earlier this split into separate "ADR" and "RFC" trees; they were unified, since most ADRs were simply implemented RFCs.)
Layout and naming
Files are grouped by lifecycle into three folders, and an RFC moves between them as its status changes:
proposed/— proposals reviewed before implementation; not yet built (or only partly).implemented/— the decision shipped. The file records what was decided and what was rejected.rejected/— the proposal was considered and declined. Kept for the record so the rejection isn't re-litigated.
Each file is named yyyy-mm-dd-topic-title.md, where the date is when the topic was first proposed (per git history). Cross-references between RFCs use relative markdown links ([topic](../implemented/2026-…-….md)) — never bare prose or numbers — so they are mechanically checkable and survive moves between folders.
When to write one
Write an RFC when a decision is durable (it shapes the codebase beyond a single function or package), contested (there was a real alternative a reasonable engineer might have chosen), and surprising (a future reader would otherwise ask "why on earth is it done this way?"). A proposal for substantial future work starts in proposed/; a decision already made starts in implemented/.
Do NOT write one for a mechanical or local choice (a variable name, a one-file refactor), for anything already enforced and explained by a gate or a convention in AGENTS.md, or for a still-provisional decision tagged TODO(...) in the code — record those as TODOs and promote to an RFC only once they settle. An RFC is never edited into a different decision: supersede it with a new one and cross-link.
Proposed
| Title | First proposed |
|---|---|
| Mutation testing as the coverage counterweight | 2026-06-11 |
| Deterministic tests, the replay invariant fixture, and race stress | 2026-06-11 |
| Architectural conformance — dependency rules and the adapter kit | 2026-06-11 |
| API extractor reports | 2026-06-11 |
| Supply chain checks and vendor drift verification | 2026-06-11 |
| Agent Client Protocol (ACP) support for external editors | 2026-06-14 |
| Multiplex concurrent ACP sessions over one connection | 2026-06-14 |
| Optional Code Mode — model writes TypeScript against an SDK of all tools | 2026-06-15 |
| Runtime schemas for the event vocabulary (Zod vs the merge-extensible-map pattern) | 2026-06-16 |
Implemented
Rejected
| Title | First proposed |
|---|---|
| Deep-readonly public surfaces | 2026-06-11 |