MRTR: drive input_required manually to keep pending-request UX (#1704) (#1719)

* MRTR: drive input_required manually to keep pending-request UX (#1704)

Follow-up to #1627/#1705. Instead of letting the SDK auto-fulfil the modern
(2026-07-28) MRTR retry loop, InspectorClient now drives it itself so the
Inspector keeps its pending-request UX, owns the loop, and shows era-accurate
semantics.

Core (core/mcp/inspectorClient.ts):
- Construct the SDK Client with `inputRequired: { autoFulfill: false }`
  (unconditional; a no-op on legacy, which never returns input_required).
- New `requestWithInputRequired()` driver: issues the request with
  `allowInputRequired` + `withInputRequired(schema)`, and while the result is
  `input_required`, fulfils each embedded request through the SAME pending
  sampling/elicitation plumbing, then retries the original call with
  `inputResponses` + the echoed `requestState` on a fresh id, bounded by
  MRTR_MAX_ROUNDS.
- Route tools/call, prompts/get, and resources/read through the driver.
- Embedded roots/list is auto-answered from configured roots (no pending UX);
  decline/cancel is echoed to the server (not treated as an abort); a tool-call
  abort mid-round settles the pending request and surfaces
  ToolCallCancelledError.
- Extract shared `enqueuePendingSample`/`enqueuePendingElicitation` helpers used
  by both the legacy inbound handlers and the driver; add a per-request `origin`
  ("server-request" | "input-required") to the pending wrappers.

Web UI:
- New `MrtrOriginNote` element shows an "input_required — your answer returns as
  a retry" note on a modern MRTR round; legacy panels are unchanged.
- Thread `origin` App -> PendingClientRequestModal -> the sampling/elicitation
  panels (and the inline panels).

Test servers: new MRTR presets (multi-round, roots, sampling, loop, edge-case
param shaping). Integration tests cover the manual round-trip (asserting the
pending UI pauses and the retry carries inputResponses + requestState on a new
id), multi-round, roots auto-answer, sampling, decline-echoed, maxRounds bound,
abort mid-round, and requestState-only/inputRequests-only param shaping.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5

* Review: clarify sampling-reject and between-rounds abort comments (#1704)

Address review nits on PR #1719 (comment-only, no behavior change):
- enqueuePendingSample docstring: sampling has no decline/cancel action; the
  panel either sends a result (resolve) or Rejects (reject → fails the call).
  The shared "declined/cancelled resolves" wording was accurate only for the
  elicitation case.
- callToolWithRetries abort comment: note the between-rounds case — when the
  abort lands while an MRTR round awaits an embedded pending request there is no
  in-flight SDK request, so nothing is sent on the wire; the outcome
  (ToolCallCancelledError, no failed-call record) is identical.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5

* test-servers: add mrtr-showcase config exercising every MRTR preset (#1704)

A single modern-era streamable-HTTP server (port 3111) bundling all six MRTR
presets — mrtr_confirm, mrtr_two_step, mrtr_sample, mrtr_roots, mrtr_edge,
mrtr_loop — for manual testing of the manual-driving pending-request UX across
single-round, multi-round, sampling, roots, param-shaping, and maxRounds paths.
Document it in the README alongside modern-mrtr-http.json.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/web/src/components/groups/PendingClientRequestModal/PendingClientRequestModal.stories.tsx

@@ -112,7 +112,12 @@ type Story = StoryObj<typeof PendingClientRequestModal>;
 
 export const Sampling: Story = {
   args: {
-    request: { kind: "sampling", id: "sampling-1", request: samplingRequest },
+    request: {
+      kind: "sampling",
+      id: "sampling-1",
+      request: samplingRequest,
+      origin: "server-request",
+    },
   },
   play: async ({ canvasElement, args }) => {
     const body = within(canvasElement.ownerDocument.body);
@@ -125,12 +130,32 @@ export const Sampling: Story = {
   },
 };
 
+// A modern MRTR round: the sampling request was embedded in a tool-call
+// `input_required` result, so the panel shows the era-accurate note.
+export const SamplingInputRequired: Story = {
+  args: {
+    request: {
+      kind: "sampling",
+      id: "sampling-mrtr",
+      request: samplingRequest,
+      origin: "input-required",
+    },
+  },
+  play: async ({ canvasElement }) => {
+    const body = within(canvasElement.ownerDocument.body);
+    await body.findByText("Sampling Request");
+    expect(body.getByText("input_required")).toBeInTheDocument();
+    expect(body.getByText(/sent back as a retry/i)).toBeInTheDocument();
+  },
+};
+
 export const SamplingTall: Story = {
   args: {
     request: {
       kind: "sampling",
       id: "sampling-tall",
       request: tallSamplingRequest,
+      origin: "server-request",
     },
   },
 };
@@ -141,6 +166,7 @@ export const ElicitationForm: Story = {
       kind: "elicitation-form",
       id: "elicitation-1",
       request: formRequest,
+      origin: "server-request",
     },
   },
   play: async ({ canvasElement, args }) => {
@@ -163,6 +189,7 @@ export const ElicitationFormTall: Story = {
       kind: "elicitation-form",
       id: "elicitation-tall",
       request: tallFormRequest,
+      origin: "server-request",
     },
   },
 };
@@ -174,6 +201,7 @@ export const ElicitationUrl: Story = {
       id: "elicitation-2",
       message: "Authorize access in your browser to continue.",
       url: "https://example.com/authorize?token=abc123",
+      origin: "server-request",
     },
   },
   play: async ({ canvasElement }) => {