pi: extensions as a directory of links, so a machine can have its own

~/.pi/agent/extensions was a link to the repo's directory, so anything that
installs a pi extension wrote into this checkout -- herdr's pi integration did,
on one machine. It is now a real directory with the repo's tracked extensions
linked in one by one, and a file a machine adds there stays that machine's.
pi follows the links, and skips a dangling one silently, so an extension
deleted from the repo leaves a harmless stale link.

The old directory link is removed first: linking into it would write through
to the repo and turn its files into links to themselves. Only tracked files are
linked, so a machine's leftovers in the repo's directory are not linked back.

The filed version put this loop in link.sh; it lives in link/pi.sh, since
link.sh holds one-line links only and a part also obeys ~/.config/dot/skip.

From change request 3f6b05.

3 files changed, 34 insertions, 3 deletions

diff --git a/AGENTS.md b/AGENTS.md
index bfdce1a..4cbdd1d 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -57,6 +57,7 @@ what it needs through these, each of them optional and absent by default:
 | `~/.claude/rules/*.md` | extra Claude Code user memory, loaded next to `config/claude/CLAUDE.md` |
 | `~/.config/pi/settings.d/*.json` | pi settings merged into the generated `~/.pi/agent/settings.json` by `link/pi.sh` |
 | `~/.config/pi/models.d/*.json` | pi providers merged into the generated `~/.pi/agent/models.json` by `link/pi.sh` |
+| `~/.pi/agent/extensions/*`, real files | pi extensions only this machine has -- herdr's pi integration installs `herdr-agent-state.ts` here | pi itself, beside the repo's extensions, which `link/pi.sh` links in one by one |
 
 A credential in a pi provider -- `apiKey`, or anything under `headers` -- is a
 **reference**, not a name: `"$SILICONFLOW_API_KEY"`, not `"SILICONFLOW_API_KEY"`.
diff --git a/link.sh b/link.sh
index a1f61b2..8ca0932 100755
--- a/link.sh
+++ b/link.sh
@@ -35,9 +35,8 @@ link_all "$config_dir/nvim" "$xdg_config_dir/nvim"
 link_all "$config_dir/bat" "$xdg_config_dir/bat"
 
 link "$config_dir/aider.conf.yml" "$HOME/.aider.conf.yml"
-link "$config_dir/pi/extensions" "$HOME/.pi/agent/extensions"
 link "$config_dir/pi/compact-tools.json" "$HOME/.pi/agent/compact-tools.json"
-# settings.json and models.json are both generated by link/pi.sh; AGENTS.md and
+# extensions/, settings.json and models.json are all link/pi.sh's; AGENTS.md and
 # mcp.json, if any, come from another layer.
 
 # Utils
diff --git a/link/pi.sh b/link/pi.sh
index 0fde248..5aec48f 100755
--- a/link/pi.sh
+++ b/link/pi.sh
@@ -1,6 +1,7 @@
 #!/bin/bash
 
-# pi's settings.json, generated. Dry run by default; pass `yes` to apply.
+# pi's extensions directory, and its settings.json and models.json, generated.
+# Dry run by default; pass `yes` to apply.
 
 set -euo pipefail
 
@@ -40,6 +41,36 @@ then
   exit 0
 fi
 
+# pi's extensions: a real directory, with this repo's tracked extensions linked
+# in one by one, so an extension only one machine has -- herdr's pi integration
+# writes herdr-agent-state.ts here -- sits beside them instead of landing in this
+# checkout. pi loads every *.ts and *.js there and follows links, and it skips a
+# dangling one silently (resource-loader.js, pi 1.0.0), so the link left behind
+# by an extension deleted from the repo does no harm.
+#
+# Machines used to link the whole directory to the repo. That link goes first:
+# linking into it would write through to the repo and turn its files into links
+# to themselves. Tracked files only, so nothing a machine left in the repo's
+# directory is linked back in.
+pi_extensions="$pi_dir/extensions"
+if [[ -L "$pi_extensions" ]]
+then
+  if [[ -n "${is_dry_run}" ]]
+  then
+    yellow "$pi_extensions is a link to the repo; will become a directory of links to its tracked files"
+  else
+    rm "$pi_extensions"
+  fi
+fi
+if [[ ! -L "$pi_extensions" ]]
+then
+  [[ -n "${is_dry_run}" ]] || mkdir -p "$pi_extensions"
+  while IFS= read -r -d '' f
+  do
+    link "$dotfiles_dir/$f" "$pi_extensions/$(basename "$f")"
+  done < <(git -C "$dotfiles_dir" ls-files -z -- config/pi/extensions)
+fi
+
 pi_status="$(DRY_RUN="$is_dry_run" python3 "$dotfiles_dir/link/pi-settings.py" \
   "$config_dir/pi/settings.json" \
   "$xdg_config_dir/pi/settings.d" \