docs(prd-0018): resolve TTY open question — keep exec -it

docs/prds/0018-compose-per-instance.md

@@ -310,25 +310,20 @@ existing prefix scan as a fallback for one release.
    `tea pr create` users will already have. Assume v2; if v1 is
    detected, die with a pointer to upgrade.
 
-2. **Foreground vs detached + attach for the agent.** Two viable
-   shapes:
-   - **(a)** `docker compose up -d` everything, then
-     `docker attach claude-bottle-<slug>` for the agent's TTY.
-   - **(b)** `docker compose up -d` sidecars only, then a
-     separate `docker run` for the agent in the foreground using
-     the same project's networks (`--network claude-bottle-net-
-     <slug> --network claude-bottle-egress-<slug>`).
+2. **How does `claude` reach the agent's TTY?** Decided: keep
+   today's `docker exec -it` model. Agent runs `sleep infinity`
+   under compose; `DockerBottle.exec_claude` runs
+   `docker exec -it claude-bottle-<slug> claude ...` exactly like
+   today. Compose owns the lifecycle (so `compose logs` includes
+   the agent's stdout, `compose down` tears it down), but the
+   user-facing exec model is unchanged. Rejected `docker attach`
+   because its default Ctrl-P-Ctrl-Q detach intercept buffers
+   keypresses Claude Code uses; rejected "agent outside compose"
+   because it gives up the unified `compose logs` view that
+   motivated the PRD.
 
-   (a) keeps the agent inside the compose project (so `compose ls`,
-   `compose logs`, `compose down` all see it). (b) avoids the
-   `docker attach` gotcha that `Ctrl-P Ctrl-Q` detaches without
-   tearing down, but loses the unified compose surface.
-   Leaning toward (a); flagging for review.
-
-3. **TTY allocation under compose.** The agent needs `tty: true` +
-   `stdin_open: true` in the service stanza, and `docker attach`
-   has to be invoked with `-it`. Verify this works cleanly on
-   macOS Docker Desktop and Colima before committing.
+3. ~~TTY allocation under compose.~~ Resolved by #2: no `tty:` /
+   `stdin_open:` on the agent service — interactivity is per-exec.
 
 4. **`docker compose logs` ordering.** The dumped log file
    interleaves services by timestamp. Confirm `--timestamps` is