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feat(apps): negotiated app-rendered form elicitations

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Let a server hand a form `elicitation/create` to an MCP App and return the
app's ordinary `ElicitResult`, with the native elicitation form as the
fallback on every failure.

No second extension, no custom method, and no custom result shape: the only
new wire surface is a nested `elicitation` flag on the existing
`io.modelcontextprotocol/ui` extension on each side, plus
`_meta.ui.resourceUri` on the request. App rendering is selected only when
all four gates hold — client `elicitation.form`, client MCP Apps MIME type,
the nested `elicitation` setting on BOTH peers, and a valid absolute `ui://`
URI on the request.

Only the web client advertises the nested client-side setting, and only
because it has a sandbox renderer: supplying
`InspectorClientOptions.appElicitation` is what opts a client in, so CLI and
TUI keep advertising the MIME type without ever claiming they can resolve an
elicitation through an app.

Routing lives in the one funnel both entry points already use
(`enqueuePendingElicitation`), so the inbound handler and the MRTR driver
cannot diverge. Ownership is request-scoped — a per-request id keys the
renderer, iframe and bridge — so two concurrent elicitations can never
resolve through each other's bridges. An explicit `decline`/`cancel` is a
completed elicitation and goes back to the server; everything else (absent or
malformed metadata, resource/sandbox/bridge failure, an app with no
elicitation capability, a timeout, an invalid result or one that fails the
requested schema) falls back.

The Inspector speaks the ext-apps#733 / SEP-3118 wire protocol but cannot yet
consume its helpers — the released `@modelcontextprotocol/ext-apps` (1.7.5)
predates that PR. `core/mcp/appElicitation.ts` and
`AppRenderer/requestAppElicitation.ts` mirror it exactly and are marked for
deletion once a release containing it ships. One consequence needed its own
seam: ext-apps 1.7.5 parses the view's `ui/initialize` through a schema that
strips `elicitation`, so an app that correctly advertises it would look like
one that did not, silently turning every negotiated elicitation into a
fallback. `AppRenderer/appCapabilities.ts` records the raw frame instead, and
prefers the bridge's own value once it carries the key.

`AppRenderer` now takes an `AppRenderSource` union rather than a `Tool`, so
the same renderer and bridge factory serve an App tool and an elicitation
without either faking the other's shape.

Adds the public fixture (`app_choose_option` + a self-contained
`ui://demo/choose-option.html` app covering accept/decline/cancel), its two
showcase configs, and `smoke:web:elicit`, which drives the negotiated path
end to end in headless Chromium and then the same tool against a server that
never advertised the capability, asserting the native form takes it.

Closes #1854

Signed-off-by: cliffhall <cliff@futurescale.com>
This commit is contained in:
cliffhall 2026-08-22 19:05:21 -04:00
commit 08fc20a22d
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README.md
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@ -140,6 +140,7 @@ Each config below is a ready-made server for exercising one feature by hand. Loa
| Config | Demonstrates | Issue |
| ----------------------------------------- | -------------------------------------------------- | ---------------------------------------------------------------------- |
| `mcp-app-http.json` **(legacy era)** | An MCP App (UI resource + app tool) in the Apps tab | [#1859](https://github.com/modelcontextprotocol/inspector/issues/1859) |
| `app-elicitation-http.json` **(legacy era)** | An MCP App rendering a form elicitation | [#1854](https://github.com/modelcontextprotocol/inspector/issues/1854) |
| `modern-mrtr-http.json` | A single MRTR round-trip | — |
| `mrtr-showcase-http.json` | Every MRTR preset in one server | [#1860](https://github.com/modelcontextprotocol/inspector/issues/1860) |
| `modern-network-http.json` | Network tab: `Mcp-*` headers + error taxonomy | [#1628](https://github.com/modelcontextprotocol/inspector/issues/1628) |
@ -162,6 +163,25 @@ Open the Apps tab, select `mcp_app_demo`, give it a title and click **Open App**
For the scripted version of the same flow (`--app-info` probe → deep link → rendered widget), see [Reviewing an MCP App](./docs/mcp-app-review.md).
#### App-rendered form elicitations
`app-elicitation-http.json` serves `app_choose_option` alongside the `choose_option_app` UI resource (`ui://demo/choose-option.html`). The tool sends a completely ordinary form `elicitation/create` — the only thing added is `_meta.ui.resourceUri` naming that app. Plain streamable-HTTP; connect with the **default (legacy)** protocol era.
Run `app_choose_option` from the Tools tab. The server's app renders in a modal instead of the built-in elicitation form, and clicking **Option A**, **Decline**, or **Cancel** returns the standard `ElicitResult` straight to the server, which echoes it into the tool result.
App rendering is selected only when **all four** conditions hold ([#1854](https://github.com/modelcontextprotocol/inspector/issues/1854), per [ext-apps#733](https://github.com/modelcontextprotocol/ext-apps/pull/733) / SEP-3118):
1. the client advertises `elicitation.form`;
2. the client advertises `extensions["io.modelcontextprotocol/ui"].mimeTypes` including `text/html;profile=mcp-app`;
3. **both** the client and the server advertise the nested `elicitation` setting on that same extension;
4. the request carries a valid absolute `ui://` URI in `_meta.ui.resourceUri`.
Only the **web** client advertises the nested client-side setting, and only because it has a sandbox renderer to back it; the CLI and TUI advertise the MIME type (they know what an App is) but never claim they can resolve an elicitation through one, so the same server falls back to their native prompts. Turning **Server Settings → Advertised Extensions → MCP Apps UI** off, or turning form elicitation off, removes the claim on web too.
Everything else falls back to the built-in elicitation form, by design: metadata that is absent or not an absolute `ui://` URI, a resource that fails to load, a sandbox or bridge that fails to initialize, an app that did not advertise `elicitation`, a request that times out, and any result that is not a valid `ElicitResult` for the requested schema. An explicit `decline` or `cancel` is **not** a fallback — it is a completed elicitation and goes back to the server as-is.
> The Inspector speaks the ext-apps#733 wire protocol but does not yet consume its helpers: the released `@modelcontextprotocol/ext-apps` (1.7.5) predates that PR. `core/mcp/appElicitation.ts` and `clients/web/src/components/elements/AppRenderer/requestAppElicitation.ts` mirror it exactly and are marked for deletion in favour of the package's own exports once a release containing it ships.
#### MRTR
`modern-mrtr-http.json` serves the `mrtr_confirm` tool (preset `mrtr_confirm`, `createMrtrTool`) over the modern leg. Its handler returns `inputRequired(...)` embedding a form elicitation, so invoking it produces a real round-trip: `input_required` → the client fulfils the embedded elicitation and retries with a new id → `complete`.
@ -343,7 +363,7 @@ Each client self-validates from its own folder; the root scripts chain them. The
| ----------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `npm run validate` | Runs the three durable guards first — `verify:format-coverage` (every tracked source file is format-gated), `verify:typecheck-coverage` (every one lands in a tsconfig project), `verify:dep-lockstep` (no dependency reaching one `tsc` program from two installs skews across them) — then `test:scripts` (the guards' own parser unit tests), then `validate:core` (the shared `core/` `format:check` + `lint` gate), then per client: `format:check` + `lint` + **`typecheck`** (cli/tui/launcher; web typechecks via `tsc -b` inside its `build`) + `build` + fast unit tests. The quick inner-loop check. |
| `npm run coverage` | The **per-file ≥90% gate** (lines/statements/functions/branches) under v8 instrumentation, per client. CI-enforced. For web this also runs the integration project and covers the shared `core/` runtime (including `core/json` and `core/client`). |
| `npm run smoke` | End-to-end smokes through the built launcher (`--help` dispatch + prod cli/tui/web), plus two headless-Chromium smokes: a boot smoke that runs the prod web bundle and asserts a clean first render (no uncaught error — sync exception or unhandled rejection, how a Node built-in reaching the browser bundle manifests), and an **MCP Apps** smoke (`smoke:web:app`) that drives connect → open app → `data-app-status="ready"` against a composable App server, covering the sandbox proxy and UI-protocol bridge. |
| `npm run smoke` | End-to-end smokes through the built launcher (`--help` dispatch + prod cli/tui/web), plus two headless-Chromium smokes: a boot smoke that runs the prod web bundle and asserts a clean first render (no uncaught error — sync exception or unhandled rejection, how a Node built-in reaching the browser bundle manifests), and an **MCP Apps** smoke (`smoke:web:app`) that drives connect → open app → `data-app-status="ready"` against a composable App server, covering the sandbox proxy and UI-protocol bridge. A third (`smoke:web:elicit`) drives an **app-rendered elicitation** end to end — call the tool, answer inside the sandboxed app, see the app's `ElicitResult` reach the server — and then the same tool against a server that never advertised the capability, which must fall back to the native elicitation form. |
| `npm run verify:build-gate` | Runs a real `vite build` with a Node built-in forced into the browser graph and asserts the build **fails** via the #1769 gate (which turns Vite's browser-externalization warning into a hard error). Guards against the warning phrasing drifting in a Vite bump and silently disabling the gate. Part of `npm run ci`. |
| `npm run verify:format-coverage` | Parses the `format:check` globs out of every `package.json` (only those reachable from `validate`), enumerates all tracked source files, and **fails** listing any not covered by a glob — the durable guard for the "every first-party source file is format-gated" invariant (#1792). Runs first in `validate`. |
| `npm run test:scripts` | Table-driven unit tests (`node --test`) for the guard's own pure parsers (`scripts/lib/npm-scripts.mjs`, `scripts/lib/tsc-program.mjs` + the exported helpers of `verify-typecheck-coverage.mjs` and `verify-dep-lockstep.mjs`), one case per rule they encode, plus `scripts/lib/resolve-node-bin.test.mjs` — the cross-platform bin resolver (#1939), pinned against the real `bin`/`exports` shapes of the packages the scripts actually spawn. Runs in `validate` — and `verify:typecheck-coverage` guards *this* gate in turn (reachable from `validate`, non-empty test set, every test file matched by the `test:scripts` glob), since `node --test` silently skips a file its glob misses and still exits 0. |