Some research

tests/docker/Dockerfile

@@ -7,12 +7,15 @@
 # Claude Code.
 FROM python:3.11-slim
 
-# bash: the thing being wrapped. tmux: TmuxPlexerController's real backend.
-# procps: `ps`, used by tests/plexer.py and tests/bashrc.py to prove a
-# process is actually gone, not just assumed gone. git: sysinfo/create_skill
-# paths touch it; harmless to have for a "simulate everything" image.
+# bash/zsh/fish: the shells being wrapped (tests/bashrc.py drives all three
+# for real -- a real `<shell> -i` against a real installed hook, not just the
+# deterministic file-level checks that run outside the container too).
+# tmux: TmuxPlexerController's real backend. procps: `ps`, used by
+# tests/plexer.py and tests/bashrc.py to prove a process is actually gone,
+# not just assumed gone. git: sysinfo/create_skill paths touch it; harmless
+# to have for a "simulate everything" image.
 RUN apt-get update \
-    && apt-get install -y --no-install-recommends bash tmux procps git ca-certificates \
+    && apt-get install -y --no-install-recommends bash zsh fish tmux procps git ca-certificates \
     && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /app