feat(curator): tool extension, generated prompt check, two pi findings

curator-tools.ts registers no schema of its own: it fetches the specs from the
backend bridge, so contracts.py stays the single owner and there is no TypeScript
copy to drift. It refuses to activate without a bridge URL and token, because an
agent that silently loses its tools still answers -- from the model's memory of
what a media library might contain.

deploy-scenario.sh now vendors listed shared/extensions modules into
.pi/extensions/_shared/. A tracked extension importing from shared/ cannot
resolve that path once installed outside the repository, so the deployed tree has
to be self-contained; this overwrites rather than merges, keeping the repository
authoritative. common.sh gains toml_list, using tomllib rather than more awk
because an array can span lines or carry comments.

verify-generated.sh checks that generated regions in tracked prompts match the
backend that generates them, and is wired into the pre-commit hook. This is
needed because of finding 22 below: the tool list has to be copied into the
prompt, and a copy drifts silently.

Two findings recorded in docs/pi-runtime-notes.md, both measured:

  21. An extension that fails to import is silent -- exit 0, empty stderr, no
      tools. A missing --extension path exits 1 with a clear message, but a
      module that throws while loading reports nothing. The agent then invented a
      complete library listing with plausible episode counts, quality and size.
      A later identical run said it had no data instead, so the failure is both
      silent and inconsistent.

  22. --system-prompt suppresses the tool list. The customPrompt branch returns
      before toolsList and guidelines are built, so promptSnippet and
      promptGuidelines are inert. The tools stay callable over the provider API,
      so tool use becomes a coin flip: one run in four looked at the library and
      three said they had not been given any results.

SYSTEM.phase3.md is staged alongside the deployed SYSTEM.md rather than replacing
it: profile.toml still describes the phase-0 configuration that is actually
running, and the live service is untouched.

scripts/lib/common.sh

@@ -64,6 +64,24 @@ toml_get() {
 
 # Print a unified diff between a tracked file and its live counterpart.
 # Returns 0 when identical, 1 when different or missing.
+# Read a TOML array of strings, one element per line.
+#
+# Uses Python's tomllib rather than more awk: an array can span lines, hold
+# comments, or be empty, and a hand-rolled parser that mostly works is worse
+# than none because it fails on the one profile that formats it differently.
+toml_list() {
+  local file="$1" section="$2" key="$3"
+  python3 - "$file" "$section" "$key" <<'PYEOF'
+import sys, tomllib, pathlib
+data = tomllib.loads(pathlib.Path(sys.argv[1]).read_text())
+value = data.get(sys.argv[2], {}).get(sys.argv[3]) or []
+if isinstance(value, str):
+    value = [value]
+for item in value:
+    print(item)
+PYEOF
+}
+
 diff_file() {
   local tracked="$1" live="$2" label="$3"
   if [ ! -f "$live" ]; then