docs: nest organ-level AGENTS.md, root states the hierarchy

AGENTS.md is hierarchical (nearest-file-wins), so the root is the map and each
organ owns a scoped AGENTS.md with local build/run/invariants: src/ichor (Pony
bus, S1 membrane), src/endocrine (R/Octave organ tests), mafiabot_core (Ada
border + COBOL vault, alr-not-gprbuild, S3). Scopes kept non-overlapping to
avoid the divergence trap rather than sprinkling sync notes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015hmgREHNsxYCuim33yUF2c

mafiabot_core/AGENTS.md

@@ -0,0 +1,43 @@
+# AGENTS.md — Ada border (D1) + invariant vault
+
+Local guide for `mafiabot_core`. Repo-wide map and rules: [`../AGENTS.md`](../AGENTS.md);
+working agreements: [`../CLAUDE.md`](../CLAUDE.md).
+
+## What this is
+
+The **Ada/SPARK border — D1**. All traffic to the inner brain crosses here
+first. Built with **Alire**. Internal modules under `src/`: `trust` (incl. the
+COBOL invariant-law vault), `organs`, `network`, `protocol`, `daemons`, `core`,
+`types`, `payloads`. These are modules, not separate organs — they share this
+file.
+
+## Build & test
+
+Use **Alire**, not bare `gprbuild` (the project imports an Alire-generated
+config gpr):
+
+```bash
+cd mafiabot_core && alr -n build
+./bin/trust_tests && ./bin/config_tests && ./bin/engine_tests
+```
+
+`engine_tests` prints nothing on success (clean exit). Or run the whole repo
+via `.claude/skills/run-sica-fondt/smoke.sh`.
+
+## The COBOL invariant vault (`src/trust`)
+
+`src/trust/invariants-architecture.cobol` is **E1, the constitution** —
+Invariant 0 (the culpability anchor) and 01 (minimize harm). Compile/run free
+format:
+
+```bash
+cobc -x -free -o /tmp/inv src/trust/invariants-architecture.cobol && /tmp/inv
+```
+
+## Local invariants
+
+- **S1:** this is the border — never add a route that lets traffic reach the
+  inner brain without crossing here.
+- **S2:** never reclassify a message's provenance.
+- **S3:** the invariant vault is **immutable at runtime** — don't edit it
+  casually; it's the constitution, not config.