docker: split python dep install into cached layer above COPY . .

Before this change, `uv pip install -e ".[all]"` ran AFTER `COPY . .`,
so every commit that changed any .py file busted the layer cache and
re-did the entire Python dep resolve + wheel download + native extension
compile (~4-5 min on cold Docker Hub cache).

Split it into two steps:

1. Before `COPY . .`: copy only pyproject.toml + uv.lock + README.md,
   then `uv sync --frozen --no-install-project --all-extras`.  This
   layer is cached unless any of those three files change, so .py-only
   commits skip the heavy work entirely.
2. After `COPY . .` (and its downstream chmod/chown step): run
   `uv pip install --no-cache-dir --no-deps -e .` to create the
   editable link.  With --no-deps this is a ~1s op — no resolution, no
   downloads, no compilation.

Combined with the per-arch runner split in the previous commit, this
should drop cache-hit build times to the sub-5-min range.

Dockerfile

@@ -55,6 +55,29 @@ RUN npm install --prefer-offline --no-audit && \
     (cd ui-tui && npm install --prefer-offline --no-audit) && \
     npm cache clean --force
 
+# ---------- Layer-cached Python dependency install ----------
+# Copy only pyproject.toml + uv.lock so the Python dep resolve + wheel
+# download + native-extension compile layer is cached unless those inputs
+# change.  Before this split the Python install sat after `COPY . .`, so
+# every source-only commit re-did ~4-5 min of dep work on cold builds.
+#
+# README.md is referenced by pyproject.toml's `readme =` field, but it's
+# excluded from the build context by .dockerignore's `*.md`.  uv's build
+# frontend stats the readme path during dep resolution, so we `touch` an
+# empty placeholder — the real README is restored by `COPY . .` below.
+#
+# `uv sync --frozen --no-install-project --extra all` installs only the
+# deps reachable through the composite `[all]` extra (handpicked set
+# intended for the production image).  We do NOT use `--all-extras`:
+# that would pull in `[rl]` (atroposlib + tinker + torch + wandb from
+# git), `[yc-bench]` (another git dep), and `[termux-all]` (Android
+# redundancy), none of which belong in the published container.
+#
+# The editable link is created after the source copy below.
+COPY pyproject.toml uv.lock ./
+RUN touch ./README.md
+RUN uv sync --frozen --no-install-project --extra all
+
 # ---------- Source code ----------
 # .dockerignore excludes node_modules, so the installs above survive.
 COPY --chown=hermes:hermes . .
@@ -77,9 +100,10 @@ RUN chmod -R a+rX /opt/hermes && \
 # Start as root so the entrypoint can usermod/groupmod + gosu.
 # If HERMES_UID is unset, the entrypoint drops to the default hermes user (10000).
 
-# ---------- Python virtualenv ----------
+# ---------- Link hermes-agent itself (editable) ----------
-RUN uv venv && \
+# Deps are already installed in the cached layer above; `--no-deps` makes
-    uv pip install --no-cache-dir -e ".[all]"
+# this a fast (~1s) egg-link creation with no resolution or downloads.
+RUN uv pip install --no-cache-dir --no-deps -e "."
 
 # ---------- Runtime ----------
 ENV HERMES_WEB_DIST=/opt/hermes/hermes_cli/web_dist