install: symlink global AGENTS.md (auto-load pi-extensions skill at session start)

Add pi-global-AGENTS.md, symlinked by install.sh to ~/.pi/agent/AGENTS.md
(pi's global-instructions file, loaded at every startup). Directs the agent
to read the pi-extensions skill at session start and carries a core
fork/recall cheat-sheet, since on-demand skill description-matching was
leaving the extensions under-utilised.

Symlinked (not cp'd) like keybindings.json: pi never rewrites AGENTS.md, and
the entrypoint re-runs install.sh on every container start, so the directive
self-heals across container recreation / volume wipes.

install.sh

@@ -6,6 +6,9 @@
 #                        and AWS_REGION are in every shell that launches pi.
 #   - keybindings.json : mosh/tmux-friendly newline bindings
 #                        (shift+enter, ctrl+j, alt+j).
+#   - pi-global-AGENTS.md : global agent instructions, symlinked to
+#                        ~/.pi/agent/AGENTS.md so pi loads it at every start
+#                        (e.g. "read the pi-extensions skill at session start").
 #   - settings.example.json : template for ~/.pi/agent/settings.json so pi
 #                             starts without --provider/--model. Copy + edit.
 #
@@ -28,6 +31,11 @@ PI_AGENT_DIR="${HOME}/.pi/agent"
 PI_KEYS_SRC="${SCRIPT_DIR}/keybindings.json"
 PI_KEYS_DEST="${HOME}/.pi/agent/keybindings.json"
 
+# global instructions — symlinked (pi doesn't rewrite AGENTS.md at runtime).
+# pi loads ~/.pi/agent/AGENTS.md as global instructions at every startup.
+PI_AGENTS_SRC="${SCRIPT_DIR}/pi-global-AGENTS.md"
+PI_AGENTS_DEST="${HOME}/.pi/agent/AGENTS.md"
+
 # settings template — NOT installed, only referenced (pi rewrites settings.json)
 PI_SETTINGS_EXAMPLE="${SCRIPT_DIR}/settings.example.json"
 PI_SETTINGS_DEST="${HOME}/.pi/agent/settings.json"
@@ -56,6 +64,8 @@ Usage:
 What install does:
   - Requires pi installed (~/.pi/agent/ must exist). Aborts cleanly otherwise.
   - Symlinks keybindings.json into ~/.pi/agent/keybindings.json.
+  - Symlinks pi-global-AGENTS.md into ~/.pi/agent/AGENTS.md (global
+    instructions loaded by pi at every start).
   - If oh-my-zsh is present (~/.oh-my-zsh/custom/), copies pi-env.zsh there
     so every new zsh shell sources ~/.config/pi/.env. Uses cp (not symlink)
     for dotfile-backup portability. Prints source snippet otherwise.
@@ -64,6 +74,7 @@ What install does:
 
 What uninstall does:
   - Removes keybindings.json symlink if it points into this repo.
+  - Removes the AGENTS.md symlink if it points into this repo.
   - Removes pi-env.zsh copy ONLY if its content still matches the repo.
   - Never touches settings.json (it's your file, not managed here).
 
@@ -128,6 +139,25 @@ install_keybindings() {
     ok "Linked keybindings.json → $PI_KEYS_SRC"
 }
 
+install_agents_md() {
+    # Global agent instructions. Symlinked so edits flow through git and the
+    # managed default survives container recreation (entrypoint re-runs this
+    # installer on every start). pi never rewrites AGENTS.md at runtime.
+    note "Linking pi-global-AGENTS.md → $PI_AGENTS_DEST"
+    if [[ -e "$PI_AGENTS_DEST" || -L "$PI_AGENTS_DEST" ]]; then
+        if link_if_into_repo "$PI_AGENTS_DEST"; then
+            ok "pi global AGENTS.md already linked"
+            return 0
+        fi
+        # Back up any existing real file / foreign symlink.
+        local backup="${PI_AGENTS_DEST}.bak.$(date +%Y%m%d-%H%M%S)"
+        mv "$PI_AGENTS_DEST" "$backup"
+        warn "Existing $PI_AGENTS_DEST backed up to $backup"
+    fi
+    ln -s "$PI_AGENTS_SRC" "$PI_AGENTS_DEST"
+    ok "Linked pi-global-AGENTS.md → $PI_AGENTS_SRC"
+}
+
 install_env_loader() {
     # Copy pi-env.zsh into ~/.oh-my-zsh/custom/ (auto-loaded by omz).
     # cp not symlink because that dir is typically part of a dotfiles backup
@@ -217,6 +247,7 @@ do_install() {
     echo
     echo "==> Installation plan:"
     echo "   Symlink keybindings.json → $PI_KEYS_DEST"
+    echo "   Symlink pi-global-AGENTS.md → $PI_AGENTS_DEST"
     if [[ -d "$HOME/.oh-my-zsh/custom" ]]; then
         echo "   Copy pi-env.zsh → $PI_ENV_OMZ_DEST"
     else
@@ -227,6 +258,8 @@ do_install() {
     echo
     install_keybindings
     echo
+    install_agents_md
+    echo
     install_env_loader
     echo
     check_pi_settings
@@ -253,6 +286,15 @@ do_uninstall() {
         ok "No pi keybindings symlink to remove"
     fi
 
+    echo
+    note "Removing pi global AGENTS.md symlink"
+    if link_if_into_repo "$PI_AGENTS_DEST"; then
+        rm "$PI_AGENTS_DEST"
+        ok "Removed pi global AGENTS.md symlink"
+    else
+        ok "No pi global AGENTS.md symlink to remove"
+    fi
+
     echo
     note "Removing pi-env.zsh loader (oh-my-zsh path)"
     # Only remove if content still matches the repo copy — user may have