diff --git a/tmux/.tmux.conf b/tmux/.tmux.conf
index 60ebfb1..a9db29b 100644
--- a/tmux/.tmux.conf
+++ b/tmux/.tmux.conf
@@ -27,8 +27,19 @@ bind -T off F12 \
 setw -g mode-keys vi
 set-option -g status-keys vi
 
-bind | split-window -h -c '#{pane_current_path}'
-bind - split-window -v -c '#{pane_current_path}'
+# Splits keep the source pane's cwd AND its active Python venv. #{@venv} is set
+# per-pane by the shell (see .virtual_env_config.zsh); we go through run-shell
+# because tmux expands FORMATS in a run-shell command but NOT in split-window's
+# own -e value. The new pane inherits VIRTUAL_ENV and .zshrc re-activates it;
+# when the source pane has no venv we omit -e so no empty var leaks in. New
+# *windows* deliberately don't inherit it.
+bind | run-shell 'v="#{@venv}"; d="#{pane_current_path}"; if [ -n "$v" ]; then tmux split-window -h -c "$d" -e VIRTUAL_ENV="$v"; else tmux split-window -h -c "$d"; fi'
+bind - run-shell 'v="#{@venv}"; d="#{pane_current_path}"; if [ -n "$v" ]; then tmux split-window -v -c "$d" -e VIRTUAL_ENV="$v"; else tmux split-window -v -c "$d"; fi'
+
+# New windows always start in the base environment: -e clears any inherited
+# VIRTUAL_ENV (e.g. if the tmux server was first started from inside a venv, so
+# its global env carries one), regardless of what the source pane had.
+bind c new-window -e VIRTUAL_ENV=
 
 # Switch windows
 bind-key -n M-Left select-window -t -1
diff --git a/zsh/.mac_config.zsh_mac.example b/zsh/.mac_config.zsh_mac.example
index 8880c93..74ca4ac 100644
--- a/zsh/.mac_config.zsh_mac.example
+++ b/zsh/.mac_config.zsh_mac.example
@@ -30,3 +30,5 @@ fi
 export DYLD_FALLBACK_LIBRARY_PATH="$HOMEBREW_PREFIX/lib:${DYLD_FALLBACK_LIBRARY_PATH}"
 export GI_TYPELIB_PATH="$HOMEBREW_PREFIX/lib/girepository-1.0:${GI_TYPELIB_PATH}"
 export PKG_CONFIG_PATH="$HOMEBREW_PREFIX/lib/pkgconfig:$HOMEBREW_PREFIX/share/pkgconfig:${PKG_CONFIG_PATH}"
+alias code="workon claude; claude"
+alias python="python3"
diff --git a/zsh/.virtual_env_config.zsh_mac.example b/zsh/.virtual_env_config.zsh_mac.example
index 93987e0..c542367 100644
--- a/zsh/.virtual_env_config.zsh_mac.example
+++ b/zsh/.virtual_env_config.zsh_mac.example
@@ -10,6 +10,20 @@ export VIRTUALENVWRAPPER_VIRTUALENV=$PREFIX/bin/virtualenv
 mkdir -p $WORKON_HOME
 source $PREFIX/bin/virtualenvwrapper.sh
 
-if [ -n "$VIRTUAL_ENV" ] && [[ -f "$VIRTUAL_ENV/bin/activate" ]]; then
-      source $VIRTUAL_ENV/bin/activate;
-fi
+# NOTE: an inherited VIRTUAL_ENV is *not* re-activated here — that happens at the
+# very end of .zshrc so activate captures the fully-built PATH (see the comment
+# there). Sourcing virtualenvwrapper.sh above only defines workon/deactivate/etc.
+
+# Mirror the current venv into a per-pane tmux option so that splitting a pane
+# can carry it into the new pane (.tmux.conf reads #{@venv} with `-e`). Per-pane
+# (not session) state is what lets two panes hold different venvs and lets new
+# *windows* start clean. Only fork tmux when the value actually changes.
+_venv_track_precmd() {
+    [[ -n $TMUX ]] || return
+    if [[ "${VIRTUAL_ENV:-}" != "${_LAST_TRACKED_VENV-unset}" ]]; then
+        tmux set -p @venv "${VIRTUAL_ENV:-}" 2>/dev/null
+        _LAST_TRACKED_VENV="${VIRTUAL_ENV:-}"
+    fi
+}
+autoload -Uz add-zsh-hook
+add-zsh-hook precmd _venv_track_precmd
diff --git a/zsh/.zshrc b/zsh/.zshrc
index e561c88..7528bea 100644
--- a/zsh/.zshrc
+++ b/zsh/.zshrc
@@ -176,3 +176,26 @@ zstyle :bracketed-paste-magic paste-finish pastefinish
 ZSH_AUTOSUGGEST_CLEAR_WIDGETS+=(bracketed-paste)
 export PATH=$PATH:/Users/ising/.runai/bin
 source <(/Users/ising/.runai/bin/runai --quiet completion zsh)
+
+# Re-activate an inherited virtualenv — MUST be the last PATH-affecting line.
+#
+# When VIRTUAL_ENV is present in the environment (a tmux pane split carries it
+# in via `-e VIRTUAL_ENV=...`, see .tmux.conf) we source the venv's activate
+# script here rather than in .virtual_env_config.zsh. activate snapshots the
+# current PATH into _OLD_VIRTUAL_PATH and restores it on `deactivate`; if we
+# activated earlier (before .mac_config.zsh, go, runai below all prepend to
+# PATH) that snapshot would be incomplete and `deactivate` would strip
+# ~/.local/bin & friends — dropping claude and co. off PATH. Keeping this last
+# guarantees the snapshot is the fully-built PATH.
+#
+# ANY new PATH mutation must go ABOVE this block.
+#
+# A new tmux window clears the var to empty (`bind c ... -e VIRTUAL_ENV=`) to
+# force the base environment; drop that empty value so nothing sees a bogus venv.
+[ -z "${VIRTUAL_ENV:-}" ] && unset VIRTUAL_ENV
+if [ -n "$VIRTUAL_ENV" ] && [ -f "$VIRTUAL_ENV/bin/activate" ]; then
+    # Guard against double-activation on a manual `source ~/.zshrc`.
+    if [[ ":$PATH:" != *":$VIRTUAL_ENV/bin:"* ]]; then
+        source "$VIRTUAL_ENV/bin/activate"
+    fi
+fi