# Plugins `EXTRACTING-A-PLUGIN.md` is the runbook for turning a platform feature into a plugin, and `EXTRACT-A-PLUGIN-PROMPT.md` is the way to hand that to a fresh agent. This file is for the concepts a plugin author needs that are not procedure. **This directory holds documentation, not plugins.** Every plugin is its own repository; `plugins//` appears by `git clone` when somebody installs one, and is gitignored here. --- ## Affordances **DESIGN, NOT BUILT.** Agreed 2026-08-19. There is no registry, no API and nothing to call yet. It is written down now because the name and the boundary are the parts that are expensive to change later, and because a plugin author who invents a different word for this will be hard to merge with afterwards. ### What one is > **An affordance is something the surface on the other end of the conversation offers the agent — > declared by the code that implements it, and read by the agent at runtime.** > > Not what the agent can do. What the client will honour. ### Why it needs to exist The platform hosts the agent and never introduces itself. An agent gets a shell, a filesystem and a prompt; everything about the surface it is speaking _through_ has to be smuggled in as prose somebody maintains by hand. The worked example is images. Officer's chat renders markdown images — `ChatImage` is wired into `react-markdown` — but an `` carries no bearer token, so it can only load what the browser can fetch unauthenticated. A fresh agent knows none of that. It writes `![](/home/me/chart.png)`, nothing renders, and nothing tells it why. The knowledge currently lives in a hand-written `CLAUDE.md` on one machine, which says "use a public URL" — a workaround, one step removed from the actual constraint, with nothing keeping the two in sync. Three properties make prose the wrong container for this: - **It drifts.** The file describes a workaround; the code has a reason. Neither knows about the other. - **It is per-machine.** It lives in one repository, copied by hand. - **A plugin cannot contribute to it.** Install a plugin that adds a surface and no agent learns it exists — which is the case that matters here, because a plugin is exactly a new surface arriving at runtime. ### The boundary Three neighbours, easily confused: | | answers | | -------------- | ---------------------------------------------------- | | **tool** | what the agent can _do_ — it acts, something happens | | **permission** | what this _account_ may reach | | **skill** | instructions the agent _follows_ | | **affordance** | what the _client_ will render, accept or ignore | Two tests settle most cases: 1. **Would it change if the same agent talked to a different client?** A phone app, a terminal, a webhook, a cron run with no human at all. If yes, it is an affordance. Rendering an image is; reading a file is not. 2. **Does the agent have to guess it today?** If the honest answer is "it writes the markdown and hopes", that is a missing affordance. ### The rule that makes it worth having **An affordance is declared where it is implemented.** `ChatImage` declares that images render, because `ChatImage` is what makes them render. The moment it becomes a list maintained somewhere else, it is the hand-written `CLAUDE.md` problem again with a better name — and this time with a build step. Same posture as `permissions/registry.ts`, and for the same reason: one enumeration, owned by the code it describes, which cannot quietly disagree with reality. ### The file Markdown with YAML frontmatter, like every other item in `capabilities/`. Frontmatter is for the PLATFORM; the body is for the agent. ```markdown --- name: Image rendering description: Use when you have an image to show the user in chat. version: 1 --- `![alt](https://…)` renders as an image. **The user's device fetches the URL**, so it must be reachable from there — a local path, `file://`, or anything behind authentication renders nothing, and fails silently. ``` | field | | | ------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `name` | becomes the heading in the compiled block, so the agent can index it | | `description` | when to reach for it. Costs the agent nothing — it is not sent | | `version` | an INTEGER, not semver, matching `capabilities/agents/` (`agent-files.ts` parses it that way). A plugin-contributed affordance sits near two version numbers and they mean different things: this integer is the revision of _this text_, the plugin's semver is the plugin's. Do not reconcile them | **Keep the body short.** Every affordance is loaded into every conversation, so it is charged to the context budget of every turn. State the constraint, name the silent failures, say what to do instead. There is deliberately no `surface` field yet. It was drafted and dropped: for the image affordance it would mean _what the client renders_, and for the gitea one below _what tooling exists on the machine_ — two different axes wearing one name. Everything is loaded unconditionally until that is worked out, which is fine at two files and will not be at twenty. See `TODO.md`. ### Where they live ``` capabilities/affordances/ officer/core/ ← core, installed by the setup script image-rendering.md officer/gitea/ ← contributed by the gitea plugin on install gitea.md ``` `/`, taken from the manifest verbatim — so a plugin published by `officerdev` lands under `officerdev/`. `officer/core` is not a plugin: it is the platform's own, shipped by the setup script from the capabilities repository. The two spellings mark two different things and should not be normalised into one. A plugin ships an `affordances/` directory in its repository; installing copies it in, uninstalling removes it — the same shape as `assets/` and `publishAssets`. ### A plugin-contributed one, for reference This is the gitea plugin's, and it shows what these are for: the agent cannot discover from the filesystem that `tea` is authenticated, or that it should prefer `git` for the things git already does. ```markdown --- name: Gitea description: Use when working with git repositories, or with Gitea issues and pull requests. version: 1 --- For anything git already does — clone, fetch, pull, push, branches, tags — use plain `git`. It talks to the server directly. For anything git does not — pull requests, issues, comments, releases, creating a repository — use `tea`. It is already logged in as the current user, with that user's own permissions. Do not configure it, and do not ask the user for a token. ``` ### On the word `capability` was taken — `CAPABILITIES` is the permission registry. `skill` was taken twice: by `capabilities/skills/` here and by the wider AI ecosystem. `affordance` is the exact term for what an environment offers an actor, and the precision earns the slight awkwardness: rendering an image is not a skill the agent has, it is something the client on the other end permits. Keeping that distinction in the name saves explaining it every time.