fix(grok): install grok CLI to ~/.grok/bin (its real default), not ~/.local/bin

The image build failed at `chown ... /home/agent/.local: No such file or
directory`. The grok installer's default is $HOME/.grok/bin — the binary lands at
~/.grok/bin/grok; ~/.local/bin/grok is only a convenience SYMLINK the installer
creates on macOS but not in the Linux container. So the Dockerfile referenced a
directory that never existed:
  - PATH pointed at ~/.local/bin -> `grok` would not be found at runtime even if
    the build had passed;
  - chown targeted ~/.local -> the build aborted.

Point PATH + chown at ~/.grok/bin / ~/.grok. Also harden the install: download the
script to a file (a `curl | bash` pipe swallows a curl failure as a silent no-op)
and verify the binary installed and runs (`test -x` + `grok --version`), so a
broken install fails the build loudly instead of producing a grok-less image.

docker/agent-grok.Dockerfile

@@ -14,26 +14,32 @@ FROM roboco-agent-base
 
 USER root
 
-# Install the official grok CLI (Grok Build) for the agent user: the binary lands
+# Install the official grok CLI (Grok Build) for the agent user. The installer's
-# at ~/.local/bin/grok and its runtime (bin / bundled / skills) at ~/.grok, both
+# default is $HOME/.grok/bin, so the binary lands at ~/.grok/bin/grok alongside
-# agent-owned. Pinned — untrusted model output runs under it, so bump the version
+# its runtime (downloads / bundled / skills) under ~/.grok, all agent-owned.
-# deliberately, never float. (curl + bash are provided by roboco-agent-base.)
+# Pinned — untrusted model output runs under it, so bump the version deliberately,
+# never float. Download the installer to a file first (a `curl | bash` pipe hides
+# a curl failure as a silent no-op) and verify the binary installed AND runs, so
+# a broken install fails the build here, not at spawn. (curl/bash from the base.)
 ARG GROK_CLI_VERSION=0.2.56
-RUN su agent -s /bin/bash -c "export HOME=/home/agent; \
+RUN su agent -s /bin/bash -c "set -euo pipefail; export HOME=/home/agent; \
-      curl -fsSL https://x.ai/cli/install.sh | bash -s ${GROK_CLI_VERSION}" \
+      curl -fsSL https://x.ai/cli/install.sh -o /tmp/grok-install.sh; \
+      bash /tmp/grok-install.sh ${GROK_CLI_VERSION}; \
+      test -x /home/agent/.grok/bin/grok; \
+      /home/agent/.grok/bin/grok --version" \
     && rm -rf /tmp/*
 
 # Entrypoint: render ~/.grok/config.toml + the per-role flags, then run grok
 # headless (overrides the base image's `claude` entrypoint).
 COPY docker/scripts/grok-cli-agent-entrypoint.sh /app/scripts/grok-cli-agent-entrypoint.sh
 RUN chmod 0755 /app/scripts/grok-cli-agent-entrypoint.sh \
-    && chown -R agent:agent /home/agent/.grok /home/agent/.local
+    && chown -R agent:agent /home/agent/.grok
 
 USER agent
 
-# grok installs to ~/.local/bin; put it ahead of the venv on PATH so the
+# grok installs to ~/.grok/bin; put it ahead of the venv on PATH so the
 # entrypoint finds `grok` (and still resolves `python` to /app/.venv/bin).
-ENV PATH="/home/agent/.local/bin:/app/.venv/bin:$PATH"
+ENV PATH="/home/agent/.grok/bin:/app/.venv/bin:$PATH"
 
 LABEL role="grok-cli-runtime"
 LABEL description="Grok (xAI) agent runtime — Grok Build via the official grok CLI"