Specify the plugin contract (todo §2); typed manifest + version/conflict rules in src/plugin.ts, authoritative docs/plugin-contract.md

README.md

@@ -164,7 +164,10 @@ is covered end-to-end; tests are independent and run **fully in parallel** for s
 ## Building a plugin _(planned)_
 
 A plugin is a folder under `plugins/`. The host discovers it at boot — no
-registration step, no central wiring.
+registration step, no central wiring. The full, authoritative API surface —
+manifest shape, handler/`RequestContext` contract, versioning, conflict rules,
+hooks, and the dev/test story — is **[docs/plugin-contract.md](docs/plugin-contract.md)**
+(`src/plugin.ts` holds the types). The sketch below is the shape.
 
 ```
 plugins/scheduling/
@@ -183,6 +186,7 @@ import { definePlugin } from "../../src/plugin.ts";
 import { listShifts } from "./shifts.ts";
 
 export default definePlugin({
+  apiVersion: 1,            // host contract this plugin targets; mismatch fails loud at boot
   id: "scheduling",
   basePath: "/scheduling",
 
@@ -386,11 +390,12 @@ src/icons.ts         Used-icon registry + sprite builder from lucide-static (reg
 src/list-query.ts    parseListQuery(): read a list URL → { q, filters, sort, page, pageSize }
 src/nav.ts           composeNav(): merge plugin nav fragments + central override, role-filter → nav-tree model
 src/paginate.ts      paginate(total,page,pageSize): page model (counts, row window, ellipsis sequence) for pagination.ejs
-src/plugin.ts        definePlugin() + the host's plugin discovery/router   (planned)
+src/plugin.ts        Plugin contract: manifest types, definePlugin(), version + conflict rules (discovery/router planned, §2)
 views/               Core EJS templates (index = the app-shell People dashboard, 403/404/500, partials/ incl. app shell, nav tree, filter bar, data table, pagination, form field, auth card, menu/popover, theme switch, icon sprite)
 public/              Static assets under /public/ (css/styles.css + auth.css, favicon, robots.txt)
 config/menu.ts       Central menu override + branding                      (planned)
 plugins/             Drop-in plugin folders, auto-discovered               (planned)
+docs/                Reference docs (plugin-contract.md — the authoritative plugin API)
 e2e/                 Playwright visual + functional E2E (Dockerfile.e2e + compose.e2e.yml run it)
 html-css-foundation/ HTML design mockups — the source for the building-block
                      partials; reference the stylesheets in public/css/.

docs/plugin-contract.md

@@ -0,0 +1,227 @@
+# The Plainpages plugin contract
+
+The authoritative reference for the plugin API — the product's main surface. A plugin is a
+self-contained folder under `plugins/` that the host discovers at boot; there is no
+registration step. The contract is **TypeScript** (`src/plugin.ts`), so the types here are the
+single source of truth — this document explains them, the guarantees around them, and the rules
+the host enforces.
+
+**Design stance.** The audience is experienced developers. The API optimises for being
+**powerful, predictable, and overloadable** — a plugin can take over as much of a page as it
+wants. The host **fails loud at boot/discovery** rather than sandboxing at runtime: a malformed
+manifest, a version mismatch, or a conflict stops startup with a clear message. Runtime
+crash-isolation (one bad plugin can't take the host down) is a *non-goal* — diagnose at deploy
+time, not in production.
+
+> **Status.** This is the contract the §2 host implements. The types and the pure rules
+> (`checkApiVersion`, `findConflicts`) exist today in `src/plugin.ts`; discovery, the router,
+> the per-plugin view resolver, and static serving are the next §2 items and wire this contract
+> to the filesystem and HTTP. Behaviour described as the host's is the target those items meet.
+
+## Anatomy of a plugin
+
+```
+plugins/scheduling/
+  plugin.ts            # default export: the manifest (definePlugin(...))
+  shifts.ts            # handlers, helpers — plain modules
+  views/               # EJS templates for this plugin's pages
+    shifts.ejs
+  public/              # static assets, served at /public/scheduling/
+    scheduling.css
+```
+
+Installing a plugin is "drop the folder, restart." Removing one is "delete the folder, restart."
+Nothing else references it; the operator stays in control through the central menu override
+(`config/menu.ts`, §2).
+
+## The manifest
+
+```ts
+import { definePlugin, HOST_API_VERSION } from "../../src/plugin.ts";
+import { listShifts, createShift } from "./shifts.ts";
+
+export default definePlugin({
+  apiVersion: HOST_API_VERSION,       // the host contract this plugin targets
+  basePath: "/scheduling",            // unique mount prefix
+  id: "scheduling",                   // globally unique; namespaces views/static/tokens
+
+  // Nav fragment, merged into the global menu and permission-filtered per user.
+  nav: [{
+    icon: "i-cal", id: "scheduling:root", label: "Scheduling",
+    children: [{ href: "/scheduling/shifts", id: "scheduling:shifts", label: "Shifts", permission: "scheduling:read" }],
+  }],
+
+  // Permission tokens this plugin introduces (for docs + Keto seeding). Optional.
+  permissions: [
+    { token: "scheduling:read", description: "View shifts" },
+    { token: "scheduling:write", description: "Create and edit shifts" },
+  ],
+
+  // Route handlers, mounted under basePath. `permission` gates before the handler runs.
+  routes: [
+    { method: "GET",  path: "/shifts", permission: "scheduling:read",  handler: listShifts },
+    { method: "POST", path: "/shifts", permission: "scheduling:write", handler: createShift },
+  ],
+});
+```
+
+`definePlugin()` only types the object and returns it unchanged — a manifest may equally be a
+plain typed object. All validation happens at discovery.
+
+| Field | Required | Notes |
+| --- | --- | --- |
+| `apiVersion` | yes | Host contract major version the plugin targets — see [Versioning](#contract-versioning). |
+| `basePath` | yes | Absolute, no trailing slash (`/scheduling`). Unique; must not prefix-overlap another plugin's. |
+| `id` | yes | Globally unique slug. Namespaces `views/`, `/public/<id>/`, and (by convention) nav/permission tokens. |
+| `nav` | no | `NavNode[]` fragment (same shape `composeNav` consumes). Node `id`s must be globally unique. |
+| `permissions` | no | Tokens this plugin introduces; declared for documentation and seeding. |
+| `routes` | no | See [Routes & handlers](#routes--handlers). |
+| `hooks` | no | See [Hooks](#hooks). |
+
+A plugin may be routes-only, nav-only, or hooks-only — every collection field is optional.
+
+## Routes & handlers
+
+A route is `{ method, path, permission?, handler }`. `path` is **relative to `basePath`**; the
+host matches `method` + the resolved full path, extracts `:name` segments into
+`ctx.params.name`, runs the `permission` gate (a coarse JWT-claim check — see the README), and
+only then calls the handler with the [request context](#requestcontext).
+
+`method` is one of `GET HEAD POST PUT PATCH DELETE`. A `GET` route also answers `HEAD`.
+
+A handler returns a **`RouteResult`** (or a `Promise` of one); the host turns it into the HTTP
+response. Returning `void` is the escape hatch — the handler wrote to `ctx.res` itself.
+
+```ts
+type RouteResult =
+  | { view: string; data?: Record<string, unknown>; status?: number; headers?: Record<string, string> }
+  | { html: string;  status?: number; headers?: Record<string, string> }
+  | { json: unknown;  status?: number; headers?: Record<string, string> }  // opt-in JS enhancement
+  | { redirect: string; status?: number };                                  // 303 unless status set
+```
+
+```ts
+// shifts.ts
+import type { RequestContext } from "../../src/context.ts";
+import { parseListQuery } from "../../src/list-query.ts";
+
+export async function listShifts(ctx: RequestContext) {
+  const q = parseListQuery(ctx.url);
+  const rows = await fetch(`${upstream}/shifts?${ctx.url.searchParams}`).then((r) => r.json());
+  return { view: "shifts", data: { rows, q } }; // renders plugins/scheduling/views/shifts.ejs
+}
+```
+
+- **`view`** resolves against the plugin's own `views/` (the per-plugin view resolver, §2). The
+  template may `include()` the core building-block partials (app shell, nav tree, data table, …)
+  to render a full page — exactly as the built-in screens do.
+- The handler **fetches its own data** from upstream and renders it; plugins hold no state
+  (see the README's *Stateless* section). The partials only need rows.
+- `default` status: `200` for `view`/`html`/`json`, `303` for `redirect`.
+
+## RequestContext
+
+Every handler receives one argument, the `RequestContext` (`src/context.ts`), built once per
+request:
+
+```ts
+interface RequestContext {
+  params: Record<string, string>;   // path params from the route match, e.g. /shifts/:id → { id }
+  query: URLSearchParams;            // alias of url.searchParams
+  req: IncomingMessage;
+  res: ServerResponse;
+  roles: string[];                   // user?.roles ?? [] — coarse gate without a null-check
+  url: URL;
+  user: User | null;                 // { id, email, roles } from the verified session JWT, or null
+}
+```
+
+**Stability guarantee.** The fields above are the stable contract — present and non-breaking
+across a major `apiVersion`. New fields may be **added** within a major version (additive, never
+breaking). `req`/`res` are the raw Node objects and the full escape hatch; reading them is fine,
+but prefer the typed fields so a handler keeps working as the host evolves. `user`/`roles` come
+from the §4 JWT middleware and are `null`/`[]` until a session exists.
+
+## Nav & permissions
+
+A plugin's `nav` fragment is merged into the global menu by `composeNav` (`src/nav.ts`), which
+applies the central override and then **filters per user** by the roles in the session JWT — a
+node shows iff it declares no `permission` or the user's roles include that token. Use arbitrary
+depth, counts, and icons; see `composeNav` for the node shape.
+
+Permission tokens are a **shared global namespace** — that's deliberate, so an operator grants
+`scheduling:read` once in Keto and every plugin referencing it is gated consistently. Namespace
+your tokens as `<id>:<action>` to avoid accidental clashes. Declaring them in `permissions` is
+optional but recommended (it documents them and lets the bootstrap seed Keto, §3).
+
+## Contract versioning
+
+Each manifest declares `apiVersion` — the host contract major version it targets — and the host
+exposes the current `HOST_API_VERSION`. At discovery the host runs `checkApiVersion`:
+
+| Plugin `apiVersion` vs host | Result | Host action |
+| --- | --- | --- |
+| equal | `ok` | load |
+| less than host | `warn` | load, log — review for deprecated behaviour |
+| greater than host | `refuse` | **abort boot** — the plugin needs a newer host |
+| missing / not a positive integer | `refuse` | **abort boot** — must be declared |
+
+The version is a single integer bumped only on a **breaking** manifest/handler change; additive
+changes don't bump it (hence "older → warn, still load"). There are no semver ranges — pinned,
+explicit, in keeping with the project's versioning rules.
+
+## Conflict rules
+
+Plugins are independent folders, so the host detects collisions across all discovered manifests
+with `findConflicts` and resolves them **loudly — never last-write-wins**. `error` aborts boot;
+`warn` logs and continues.
+
+| Kind | Level | Rule |
+| --- | --- | --- |
+| `id` | error | Two plugins share an `id`. Ids must be globally unique (they namespace views/static/tokens). |
+| `basePath` | error | Two `basePath`s are equal, or one is a path-prefix of the other (`/x` vs `/x/y`) — routes would shadow. |
+| `route` | error | Two routes resolve to the same `method` + full path (within or across plugins). |
+| `nav-id` | error | A nav node `id` is used more than once — the central override targets ids, so they must be unique. |
+| `permission` | warn | A permission token is declared by more than one plugin. Sharing is legitimate (shared role); namespace as `<id>:<action>` if unintended. |
+
+`permission` is the one intentional overlap, so it warns rather than aborts; everything else is
+an error an author fixes before the host will start.
+
+## Hooks
+
+Optional, for reacting to system actions. A plugin's `hooks` may implement:
+
+| Hook | When | May |
+| --- | --- | --- |
+| `onBoot()` | after discovery, before the server listens | warm caches, validate upstream config |
+| `onRequest(ctx)` | before route matching | inspect, or **short-circuit** by returning a `RouteResult` |
+| `onResponse(ctx, result)` | after the handler | observe/log; cannot change the response |
+
+Hooks run with no sandbox — a throwing hook fails loud (boot for `onBoot`, the request for the
+others). Keep them cheap; `onRequest` is on the hot path. This surface is intentionally small and
+may grow additively within the major version.
+
+## Local dev & test story
+
+A plugin is a normal folder of TypeScript, so an author tests it the same way the core is tested
+— everything in Docker, no host tooling.
+
+1. **Unit-test handlers as pure functions.** Keep a handler thin: parse `ctx`, fetch upstream,
+   return a `RouteResult`. Test the data-shaping in isolation (mock `fetch`/upstream) with
+   `node --test`, exactly like `src/dashboard.test.ts` tests the dashboard model. No host needed.
+
+   ```bash
+   docker compose run --rm web npm test
+   ```
+
+2. **Run one plugin against the host.** Drop the folder in `plugins/` and `docker compose up`;
+   the host discovers it. For an isolated harness, the §2 host exposes plugin injection
+   (`createApp({ plugins: [myPlugin] })`) so a test can mount a single manifest and assert its
+   routes, nav, and gating without the rest of the stack.
+
+3. **E2E the user-facing flow.** Per AGENTS.md §6, every plugin page/form ships *with* a
+   Playwright test in `e2e/`, side-effect-free so the suite stays `fullyParallel`. The test runs
+   against the live `web` service with the plugin mounted.
+
+The validation an author hits is the same the host runs: bad `apiVersion` or a conflict
+([above](#conflict-rules)) stops boot with a precise message naming the plugin(s) involved.

src/plugin.test.ts

@@ -0,0 +1,85 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import {
+  checkApiVersion,
+  definePlugin,
+  findConflicts,
+  HOST_API_VERSION,
+  type Plugin,
+} from "./plugin.ts";
+
+// A representative manifest exercising every field — its existence type-checks the contract
+// (handler return variants, nav fragment, permission decls, hooks). The README example.
+const scheduling: Plugin = definePlugin({
+  apiVersion: HOST_API_VERSION,
+  basePath: "/scheduling",
+  hooks: { onBoot: () => {} },
+  id: "scheduling",
+  nav: [{
+    children: [{ href: "/scheduling/shifts", id: "scheduling:shifts", label: "Shifts", permission: "scheduling:read" }],
+    icon: "i-cal", id: "scheduling:root", label: "Scheduling",
+  }],
+  permissions: [{ description: "View shifts", token: "scheduling:read" }],
+  routes: [
+    { handler: () => ({ data: { rows: [] }, view: "shifts" }), method: "GET", path: "/shifts", permission: "scheduling:read" },
+    { handler: () => ({ redirect: "/scheduling/shifts" }), method: "POST", path: "/shifts", permission: "scheduling:write" },
+    { handler: (ctx) => void ctx.res.end("raw"), method: "GET", path: "/raw" }, // void = handler wrote res itself
+  ],
+});
+
+test("definePlugin returns the manifest unchanged — it only types; validation is at discovery (§2)", () => {
+  const m: Plugin = { apiVersion: 1, basePath: "/x", id: "x" };
+  assert.equal(definePlugin(m), m); // identity, not a copy
+  assert.equal(scheduling.routes?.length, 3);
+});
+
+test("checkApiVersion: match ok, older warns, newer/malformed refuses (host refuses or warns, never silent)", () => {
+  assert.equal(checkApiVersion(HOST_API_VERSION).level, "ok");
+  assert.equal(checkApiVersion(1, 2).level, "warn"); // plugin targets an older host
+  assert.equal(checkApiVersion(HOST_API_VERSION + 1).level, "refuse"); // needs a newer host
+  for (const bad of [0, -1, 1.5, "1", undefined, null, Number.NaN]) {
+    assert.equal(checkApiVersion(bad).level, "refuse", `${String(bad)} must refuse`);
+  }
+});
+
+// Minimal valid plugin, overridable per case.
+const p = (over: Partial<Plugin> & Pick<Plugin, "id" | "basePath">): Plugin =>
+  definePlugin({ apiVersion: HOST_API_VERSION, ...over });
+
+test("findConflicts: a clean set has none", () => {
+  assert.deepEqual(findConflicts([p({ basePath: "/a", id: "a" }), p({ basePath: "/b", id: "b" })]), []);
+});
+
+test("findConflicts: duplicate id, overlapping basePath, and colliding route are loud errors", () => {
+  const dupId = findConflicts([p({ basePath: "/a", id: "a" }), p({ basePath: "/b", id: "a" })]);
+  assert.ok(dupId.some((c) => c.kind === "id" && c.level === "error"));
+
+  const sameBase = findConflicts([p({ basePath: "/x", id: "a" }), p({ basePath: "/x", id: "b" })]);
+  assert.ok(sameBase.some((c) => c.kind === "basePath" && c.level === "error"));
+
+  // A basePath that is a path-prefix of another also overlaps (routes would shadow).
+  const prefix = findConflicts([p({ basePath: "/x", id: "a" }), p({ basePath: "/x/y", id: "b" })]);
+  assert.ok(prefix.some((c) => c.kind === "basePath" && c.level === "error" && c.plugins.includes("a") && c.plugins.includes("b")));
+
+  const noop = () => {};
+  const dupRoute = findConflicts([p({
+    basePath: "/a", id: "a",
+    routes: [{ handler: noop, method: "GET", path: "/t" }, { handler: noop, method: "GET", path: "/t" }],
+  })]);
+  assert.ok(dupRoute.some((c) => c.kind === "route" && c.level === "error"));
+});
+
+test("findConflicts: duplicate nav id is an error, a shared permission token only warns", () => {
+  const navDup = findConflicts([
+    p({ basePath: "/a", id: "a", nav: [{ id: "dup", label: "A" }] }),
+    p({ basePath: "/b", id: "b", nav: [{ id: "dup", label: "B" }] }),
+  ]);
+  assert.ok(navDup.some((c) => c.kind === "nav-id" && c.level === "error" && c.plugins.includes("a") && c.plugins.includes("b")));
+
+  // Sharing a permission across plugins is legitimate (shared role) → warn, not error.
+  const permDup = findConflicts([
+    p({ basePath: "/a", id: "a", permissions: [{ token: "shared:read" }] }),
+    p({ basePath: "/b", id: "b", permissions: [{ token: "shared:read" }] }),
+  ]);
+  assert.ok(permDup.some((c) => c.kind === "permission" && c.level === "warn"));
+});

src/plugin.ts

@@ -0,0 +1,159 @@
+// The plugin contract (todo §2) — the product's main API surface. This module is the
+// authoritative, machine-readable shape; `docs/plugin-contract.md` is the prose reference.
+// It only declares types + pure rules; the §2 discovery/router wire them to the filesystem
+// and HTTP. Philosophy: a powerful, predictable, overload-friendly API that fails loud at
+// boot/discovery rather than sandboxing at runtime.
+
+import type { RequestContext } from "./context.ts";
+import type { NavNode } from "./nav.ts";
+
+// Host contract major version. Bump on a breaking manifest/handler change; a plugin pins the
+// version it targets via `apiVersion` and the host refuses/warns on mismatch (checkApiVersion).
+export const HOST_API_VERSION = 1;
+
+export type HttpMethod = "DELETE" | "GET" | "HEAD" | "PATCH" | "POST" | "PUT";
+
+// A handler's return value; the host turns it into the HTTP response. Returning void is the
+// escape hatch — the handler wrote to `ctx.res` itself (streaming, custom headers, etc.).
+export type RouteResult =
+  | { headers?: Record<string, string>; html: string; status?: number }
+  | { headers?: Record<string, string>; json: unknown; status?: number } // for opt-in JS enhancement
+  | { data?: Record<string, unknown>; headers?: Record<string, string>; status?: number; view: string }
+  | { redirect: string; status?: number };
+
+export type RouteHandler = (ctx: RequestContext) => Promise<RouteResult | void> | RouteResult | void;
+
+export interface Route {
+  handler: RouteHandler;
+  method: HttpMethod;
+  path: string; // relative to basePath; ":name" segments become ctx.params.name
+  permission?: string; // coarse gate (a role token); checked before the handler runs
+}
+
+// A permission token this plugin introduces — declared for docs/seeding. Tokens are a shared
+// global namespace (so an operator grants them in Keto); namespace as `<id>:<action>`.
+export interface PermissionDecl {
+  description?: string;
+  token: string;
+}
+
+// Optional hooks on system actions. Crash-isolation is a non-goal — a throwing hook fails loud.
+export interface PluginHooks {
+  onBoot?: () => Promise<void> | void; // after discovery, before the server listens
+  onRequest?: (ctx: RequestContext) => Promise<RouteResult | void> | RouteResult | void; // may short-circuit
+  onResponse?: (ctx: RequestContext, result: RouteResult | null) => Promise<void> | void;
+}
+
+export interface Plugin {
+  apiVersion: number; // host contract version this plugin targets (= HOST_API_VERSION)
+  basePath: string; // unique mount prefix, e.g. "/scheduling"; must not overlap another plugin's
+  hooks?: PluginHooks;
+  id: string; // globally unique; namespaces views, /public/<id>/, and nav/permission tokens
+  nav?: NavNode[]; // fragment merged into the global menu (composeNav); ids must be globally unique
+  permissions?: PermissionDecl[];
+  routes?: Route[];
+}
+
+// Identity helper: types the manifest, returns it unchanged. Validation happens at discovery
+// (§2), so a plugin may equally be a plain typed object. Mirrors Vite's `defineConfig`.
+export function definePlugin(plugin: Plugin): Plugin {
+  return plugin;
+}
+
+export interface VersionCheck {
+  level: "ok" | "refuse" | "warn";
+  message: string;
+}
+
+// The versioning rule: equal → ok; plugin older than host → warn (load, review); plugin newer
+// or not a positive integer → refuse. Discovery maps refuse→throw, warn→log.
+export function checkApiVersion(pluginVersion: unknown, hostVersion: number = HOST_API_VERSION): VersionCheck {
+  if (typeof pluginVersion !== "number" || !Number.isInteger(pluginVersion) || pluginVersion < 1) {
+    return { level: "refuse", message: `apiVersion must be a positive integer; got ${JSON.stringify(pluginVersion)}` };
+  }
+  if (pluginVersion > hostVersion) {
+    return { level: "refuse", message: `plugin targets apiVersion ${pluginVersion} but host is ${hostVersion}; upgrade the host` };
+  }
+  if (pluginVersion < hostVersion) {
+    return { level: "warn", message: `plugin targets apiVersion ${pluginVersion}; host is ${hostVersion} — review for deprecated behaviour` };
+  }
+  return { level: "ok", message: `apiVersion ${pluginVersion}` };
+}
+
+export interface PluginConflict {
+  kind: "basePath" | "id" | "nav-id" | "permission" | "route";
+  level: "error" | "warn";
+  message: string;
+  plugins: string[]; // unique ids involved
+}
+
+// The conflict rules: defined, loud resolution — never last-write-wins. Pure over the discovered
+// manifests; discovery throws on any "error" and logs every "warn". Shared permission tokens are
+// the one intentional overlap, so they warn rather than error.
+export function findConflicts(plugins: Plugin[]): PluginConflict[] {
+  const out: PluginConflict[] = [];
+
+  const idCounts = new Map<string, number>();
+  for (const plugin of plugins) idCounts.set(plugin.id, (idCounts.get(plugin.id) ?? 0) + 1);
+  for (const [id, n] of idCounts) {
+    if (n > 1) out.push({ kind: "id", level: "error", message: `${n} plugins share id "${id}"; ids must be globally unique`, plugins: [id] });
+  }
+
+  for (let i = 0; i < plugins.length; i++) {
+    for (let j = i + 1; j < plugins.length; j++) {
+      const a = plugins[i] as Plugin;
+      const b = plugins[j] as Plugin;
+      if (basePathOverlap(a.basePath, b.basePath)) {
+        out.push({ kind: "basePath", level: "error", message: `basePath "${a.basePath}" (${a.id}) overlaps "${b.basePath}" (${b.id})`, plugins: uniq([a.id, b.id]) });
+      }
+    }
+  }
+
+  collect(plugins, (plugin, push) => {
+    for (const route of plugin.routes ?? []) push(`${route.method} ${joinPath(plugin.basePath, route.path)}`);
+  }).forEach((owners, key) => {
+    if (owners.length > 1) out.push({ kind: "route", level: "error", message: `${owners.length} routes resolve to "${key}"`, plugins: uniq(owners) });
+  });
+
+  collect(plugins, (plugin, push) => collectNavIds(plugin.nav, push)).forEach((owners, id) => {
+    if (owners.length > 1) out.push({ kind: "nav-id", level: "error", message: `nav id "${id}" used ${owners.length}×; override targets ids, so they must be unique`, plugins: uniq(owners) });
+  });
+
+  collect(plugins, (plugin, push) => {
+    for (const decl of plugin.permissions ?? []) push(decl.token);
+  }).forEach((owners, token) => {
+    if (owners.length > 1) out.push({ kind: "permission", level: "warn", message: `permission "${token}" declared by ${uniq(owners).length} plugins; namespace as "<id>:<action>" unless shared on purpose`, plugins: uniq(owners) });
+  });
+
+  return out;
+}
+
+// Map each emitted key → the plugin ids that emitted it (repeats kept, so within-plugin dups count).
+function collect(plugins: Plugin[], emit: (plugin: Plugin, push: (key: string) => void) => void): Map<string, string[]> {
+  const owners = new Map<string, string[]>();
+  for (const plugin of plugins) emit(plugin, (key) => owners.set(key, [...(owners.get(key) ?? []), plugin.id]));
+  return owners;
+}
+
+function collectNavIds(nodes: NavNode[] | undefined, push: (id: string) => void): void {
+  for (const node of nodes ?? []) {
+    if (node.id != null) push(node.id);
+    collectNavIds(node.children, push);
+  }
+}
+
+const trimSlash = (s: string): string => s.replace(/\/+$/, "");
+
+function basePathOverlap(a: string, b: string): boolean {
+  const x = trimSlash(a);
+  const y = trimSlash(b);
+  return x === y || y.startsWith(`${x}/`) || x.startsWith(`${y}/`);
+}
+
+function joinPath(basePath: string, path: string): string {
+  return `${trimSlash(basePath)}${path.startsWith("/") ? path : `/${path}`}`;
+}
+
+function uniq(xs: string[]): string[] {
+  return [...new Set(xs)];
+}

todo.md

@@ -45,7 +45,7 @@ everything via Docker.
 - [x] Add to principles that we should have full E2E coverage in the Playwright tests - make sure they can run in parallel to get up some speed. → Added **Full, parallel E2E** core principle (AGENTS.md §6 + README): every user-facing flow gets a Playwright test shipped with it, tests stay side-effect-free so the suite runs `fullyParallel` (already set; verified 7 tests / 7 workers). Led by example: added E2E coverage for the 404 page (the one user-facing gap). Fixed the documented run command to `--build` (the runner bakes in `e2e/`, so spec edits were silently ignored without it).
 
 ## 2. Plugin host
-- [ ] **Specify the plugin contract** (big job, do first — it's the product's main API surface). Write it down as the authoritative reference: the full manifest shape; the `RequestContext` handed to handlers and what's guaranteed stable; **contract versioning** (a `apiVersion`/`engines`-style field so a plugin declares the host it targets, and the host refuses or warns on mismatch); **conflict rules** (two plugins claiming the same `basePath`, nav slot, or `permission` name → defined, loud resolution, not last-write-wins); the **local dev/test story** (how an author runs + tests one plugin in isolation against the host). Audience is experienced devs: optimise for a powerful, predictable, clearly-documented API. Crash-isolation (a bad plugin can't take down the host) is a *nice-to-have*, not a blocker — fail loud at boot/discovery over sandboxing at runtime.
+- [x] **Specify the plugin contract** (big job, do first — it's the product's main API surface). Write it down as the authoritative reference: the full manifest shape; the `RequestContext` handed to handlers and what's guaranteed stable; **contract versioning** (a `apiVersion`/`engines`-style field so a plugin declares the host it targets, and the host refuses or warns on mismatch); **conflict rules** (two plugins claiming the same `basePath`, nav slot, or `permission` name → defined, loud resolution, not last-write-wins); the **local dev/test story** (how an author runs + tests one plugin in isolation against the host). Audience is experienced devs: optimise for a powerful, predictable, clearly-documented API. Crash-isolation (a bad plugin can't take down the host) is a *nice-to-have*, not a blocker — fail loud at boot/discovery over sandboxing at runtime. It is a target that plugins should be able to overload as much as possible. Hooks on actions in the system is not bad either, if it is possible. → `src/plugin.ts` is the typed, machine-readable contract (single source of truth: manifest `Plugin`, `Route`/`RouteResult`/`RouteHandler`, `PermissionDecl`, `PluginHooks`, `definePlugin()`, `HOST_API_VERSION`) plus the pure rules the §2 host enforces — `checkApiVersion` (equal→ok, older→warn, newer/malformed→refuse) and `findConflicts` (id/basePath-overlap/route = error, duplicate nav-id = error, shared permission token = warn; never last-write-wins). `docs/plugin-contract.md` is the prose reference (anatomy, manifest fields, handler/RouteResult, `RequestContext` stability guarantee, nav/permission namespacing, versioning, conflicts, hooks, dev/test story). README links it + example gained `apiVersion`. Tests-first (`plugin.test.ts`); typecheck + 80 units green. Discovery/router/view-resolver/static stay as the next §2 items that wire this to FS+HTTP.
 - [ ] Discovery: scan `plugins/`, import each `plugin.ts` default export, validate.
 - [ ] Router: match method+path under `basePath`, resolve path params, run permission gate, call handler with context.
 - [ ] Per-plugin view resolver (`plugins/<id>/views/*.ejs`).