AGENTS.md, so both harnesses find the same guidance

opencode discovers AGENTS.md and nothing else; claude code discovers CLAUDE.md.
this repo had neither, so an agent sent to change something here arrived with no
guidance at all under either.

it deliberately does NOT repeat README.md. that file says what the plugin is,
for someone deciding whether to install it. this one answers the other question:
i have to change something in here, what will i break.

the facts in it are read from the repository rather than recalled — the panel
keys from web/panels.ts, the tables from db/schema.ts, the permission keys, the
host binaries and the route claims from manifest.ts. presence is the declaration
everywhere in this system, so the file says what the platform will actually
conclude from these files existing.

CLAUDE.md beside it is a pointer, not a copy: two copies drift and the stale one
is the one somebody reads.

AGENTS.md

@@ -0,0 +1,52 @@
+# AGENTS.md
+
+Guidance for a coding agent working on **this plugin's own repository**. `CLAUDE.md` beside it only
+points here — the two harnesses discover different filenames and one set of instructions has to
+reach both.
+
+**This is not what the plugin is.** `README.md` answers that, for a person deciding whether to
+install it. This file answers "I have to change something in here — what will I break?"
+
+## Where you are
+
+A plugin repository, cloned into `~/officer-dev/plugins/iris`, its own git remote. It is **not**
+part of the platform's repository, and `platform/plugins/iris` is a different thing — that is
+where this plugin gets INSTALLED, by the installer cloning it from gitea. Never edit there; the
+next install overwrites it.
+
+Check the checkout with `bun run plugins:check` from the platform repo.
+
+## What it ships
+
+- `sidecar/index.ts` — a process, run by PM2 as `officer-iris`
+- `skills/` — read by every agent session, harness-agnostic
+- `affordances/` — read by every agent session, harness-agnostic
+
+Presence is the declaration: the platform decides what this plugin has by what files exist. Adding
+`db/schema.ts` gives it tables; deleting `api/router.ts` removes its routes. There is no field to
+keep in step.
+
+## What must not change without knowing why
+
+- **Host binaries** (`cargo`, `cc`) — declared in the manifest so an install can get them. Shelling out to something undeclared works on this machine and nowhere else.
+- **`appName`** — the directory name IS the id: route segment, table prefix, sidecar suffix, install key.
+
+## Verifying
+
+From the platform repo, which is where the toolchain lives:
+
+```bash
+bunx tsgo                 # a red typecheck is not done
+bun test                  # 1 known failure: ModelSelector, unrelated
+bun run plugins:check
+bunx prettier --write <the files you touched>
+```
+
+A sidecar change needs `pm2 restart officer-iris`; anything in `api/` or `web/` needs
+`pm2 restart officer`.
+
+## Related
+
+- `README.md` — what it is and what it claims, for someone installing it
+- `PLUGIN.md` — this plugin's own reference: conventions and API surface
+- `skills/` — how an agent USES this, as opposed to changing it