76fceae5b3
Establishes the standard way to give a snapshot scenario a non-empty starting
workspace: an optional `<scenario>/workspace/` directory whose contents the
harness copies into the temp cwd before the run (for both record and replay),
so the agent's bash tools see the seeded files. The cwd is normalized in the
goldens, so seeded paths stay stable.
The new `workspace-edit` scenario demonstrates the full read→write→verify cycle
on a seeded file: it ships `workspace/greeting.txt` ("hello"), prompts the agent
to append a WORLD line and cat it back. The recorded log captures the real bash
edits (`echo WORLD >> greeting.txt`, then `cat` showing `hello\nWORLD`), and it
replays deterministically with no key.
Also hardens runScenario teardown (Codex review): workspace seeding and spawn
now run inside the try whose finally removes both temp dirs, so a seeding/spawn
failure can't leak them. Documents the convention in the RFC + example README.
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 |