test: pin the translation layer with an offline suite

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: '22'
-      # There is no test suite yet. Importing the module would start the proxy,
-      # so the gate is a parse-and-strip check: it catches broken syntax and
-      # type-stripping errors without binding a port.
-      - run: node --experimental-strip-types --check codex-proxy.ts
+      # `npm test` runs node:test over the translation layer. There is nothing
+      # to install -- the bridge has no dependencies and no build step, and the
+      # suite never opens a socket or calls the upstream API.
+      - run: npm test

README.md

@@ -7,7 +7,7 @@ Responses API** — run Claude Code (or any Anthropic-API client) on
 `gpt-5.6-*` models while keeping the client's own tools, skills and MCP
 servers.
 
-461 lines, zero dependencies, Node ≥ 22, no build step:
+One file, zero dependencies, Node ≥ 22, no build step:
 
 ```sh
 OPENAI_API_KEY=sk-... PORT=4001 ./codex-proxy.ts
@@ -58,6 +58,19 @@ upstream. Disable with `CODEX_CARRY_REASONING=0`.
 Model aliases: `codex-luna` → `gpt-5.6-luna`, `codex-sol` → `gpt-5.6-sol`,
 `codex-terra` → `gpt-5.6-terra`; any `gpt-*` name passes through unchanged.
 
+## Tests
+
+```sh
+npm test
+```
+
+The translation layer is exported from `codex-proxy.ts`, and the server only
+starts when the file is the process entry point — so `node --test` can pin
+every conversion without opening a socket or calling the upstream API. The
+streaming tests replay a recorded Responses SSE stream from
+`test/fixtures/`, re-fed at several chunk sizes to prove events that span a
+socket boundary are reassembled.
+
 ## Non-goals
 
 Auth beyond a bearer key, retries, rate limiting, multi-tenant use. It is a