feat(entrypoint): non-destructively merge new template keys into settings.json

The settings.json bootstrap only fires when the file is ABSENT, so a
settings.json on a preserved named volume never picks up config added in a
later image (e.g. the observational-memory / pi-fork blocks, a newly-enabled
model). Users had to hand-merge after every upgrade.

On start, when settings.json already exists, deep-merge the template into it
with 'jq -s ".[0] * .[1]"' (template first, live second) so the user's values
always win and only MISSING keys are filled from the template. Arrays are
leaves (a model the user removed is not re-added). Rewrites only when the
merge changes something, backs up the original first, and skips safely (no
clobber) if either file is invalid JSON. Opt out with PI_SETTINGS_MERGE=0.

Add a recreate-sanity-check assertion that settings.json carries the
observational-memory + pi-fork blocks after recreate.

scripts/recreate-sanity-check.sh

@@ -187,6 +187,18 @@ else
   fail "~/.pi/agent/settings.json missing"
 fi
 
+# settings.json merge: the entrypoint deep-merges new template keys into a
+# preserved settings.json on every start, so config added in an image upgrade
+# (e.g. the observational-memory / pi-fork blocks) reaches existing volumes.
+# Assert those blocks are present and that the file is still valid JSON.
+if command -v jq >/dev/null 2>&1 && [ -f "$HOME/.pi/agent/settings.json" ]; then
+  if jq -e 'has("observational-memory") and has("pi-fork")' "$HOME/.pi/agent/settings.json" >/dev/null 2>&1; then
+    pass "settings.json has observational-memory + pi-fork blocks (template merge)"
+  else
+    fail "settings.json missing observational-memory and/or pi-fork blocks (template merge did not land)"
+  fi
+fi
+
 # pi package registrations (pi install <local-path> → recorded in settings.json)
 if [ -f "$HOME/.pi/agent/settings.json" ]; then
   for pkg in pi-fork pi-observational-memory; do