feat: enable permission-aware subagents

pi-subagents/test/fixtures/.pi/agents/memory-readonly.md

@@ -0,0 +1,13 @@
+---
+description: "memory read-only — an agent without write tools gets a read-only memory block."
+memory: project
+tools: read, grep
+expect_tools_present: "read, grep"
+expect_tools_absent: "write, edit"
+expect_prompt_contains: "Agent Memory (read-only), Memory scope: project"
+expect_prompt_absent: "persistent memory directory"
+---
+A read-only memory agent. Per the README, agents without write/edit tools
+auto-get a read-only memory fallback: existing memory is injected, no write
+access is granted, and no memory directory is created (so `project` scope is
+safe here — nothing is written into the repo).