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

src/endocrine/AGENTS.md

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+# AGENTS.md — endocrine organs (R / Octave)
+
+Local guide for `src/endocrine`. Repo-wide map and rules: [`../../AGENTS.md`](../../AGENTS.md);
+working agreements: [`../../CLAUDE.md`](../../CLAUDE.md).
+
+## What this is
+
+The **endocrine array** — slow-signal organs that modulate the system: the R
+**Drive-Box** (`drive_box.R`, `driver_*.R`, `endocrine_array.R`, `priors.R`) and
+the Octave **ETR** under `etr/`. See `Plan.md` here and `etr/etr_invariants.md`
+for design.
+
+## Build & run
+
+Toolchains (R 4.3.3, Octave 8.4) are installed each session by the SessionStart
+hook. Run the organ tests directly:
+
+```bash
+src/endocrine/run_tests.sh        # R Drive-Box + drivers
+src/endocrine/etr/run_etr_tests.sh   # Octave ETR
+```
+
+(Not yet wired into the top-level `run-sica-fondt` smoke driver — run them here.)
+
+## Local notes
+
+- Pure R/Octave; no compile step. Each `test_*.R` / `test_etr.m` pairs with its
+  `driver`/source file.
+- ETR invariants are documented in `etr/etr_invariants.md` — read before
+  changing `etr.m`.

src/ichor/AGENTS.md

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+# AGENTS.md — Ichor bus (Pony)
+
+Local guide for `src/ichor`. Repo-wide map and rules: [`../../AGENTS.md`](../../AGENTS.md);
+working agreements: [`../../CLAUDE.md`](../../CLAUDE.md).
+
+## What this is
+
+The **Ichor perfusion bus** — the outer transport that perfuses organs with
+messages. Pony. This is where inbound external traffic is first screened before
+anything reaches the Ada border (D1).
+
+## Build & run
+
+Run from the **repo root** (ponyc resolves the path from there):
+
+```bash
+export PATH=/root/.local/share/ponyup/bin:$PATH   # if ponyc not found
+ponyc src/ichor -o build && ./build/ichor
+```
+
+Or via the smoke driver: `.claude/skills/run-sica-fondt/smoke.sh`.
+
+## Local invariants
+
+- **S1 lives here.** The bus must `D1 REJECT` unscreened external payloads —
+  external traffic only reaches an organ via the Ada border. Never add a path
+  that perfuses an inner organ directly from `world`.
+- **S2:** never reclassify a message's provenance as it crosses the bus.