settings: give pi-fork a capability floor (extensions: [])

A fork child inherits the parent's whole session branch by design, and has
twice written to the shared palace under the parent's identity. extensions: []
runs children with --no-extensions; the mempalace bridge is an extension, so
the write path is gone by construction rather than by instruction. Costs forks
their palace search and recall; set to null to restore normal loading.

settings.example.json

@@ -20,6 +20,8 @@
   },
 
   "pi-fork": {
+    "_comment_extensions": "extensions:[] makes every fork child run with `pi --no-extensions`. This is a CAPABILITY FLOOR, not a style preference: the mempalace bridge is a pi EXTENSION, so with [] a fork physically cannot file drawers or diary entries under your identity. Measured on mbp-m1-2020 2026-09-01 and 2026-09-06: forks ignored their brief, answered in the user's voice, fabricated self-referential measurements, and one filed a diary entry as agent_name=pi (landing in wing_pi, where a wing-scoped diary_read never sees it). Root cause is upstream and by design, not a bug to wait out: the child is handed getHeader()+getBranch(), i.e. the WHOLE active session branch, with the brief appended as the final user message and the system prompt untouched (pi-fork src/index.ts) - so in a long session the parent narrative outweighs the task. Proven by control: the SAME model as the 'fast' profile below (haiku, thinking off) obeyed the identical brief perfectly when run as `pi -p --mode json --session-id <fresh> --no-extensions`, i.e. with no inherited context. COST of []: no palace search and no recall inside a fork. Set to null to restore normal extension loading.",
+    "extensions": [],
     "defaultEffort": "balanced",
     "effortProfiles": {
       "fast":     { "provider": "amazon-bedrock", "id": "eu.anthropic.claude-haiku-4-5-20251001-v1:0", "thinking": "off" },