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>

core/mcp/elicitationCreateMessage.ts

@@ -1,5 +1,6 @@
 import type { ElicitRequest, ElicitResult } from "@modelcontextprotocol/client";
 import { RELATED_TASK_META_KEY } from "@modelcontextprotocol/client";
+import type { PendingRequestOrigin } from "./types.js";
 
 export type { ElicitRequest, ElicitResult };
 
@@ -13,6 +14,7 @@ export interface InspectorPendingElicitation {
   timestamp: Date;
   request: ElicitRequest;
   taskId?: string;
+  origin: PendingRequestOrigin;
 }
 
 /**
@@ -23,8 +25,19 @@ export class ElicitationCreateMessage {
   public readonly timestamp: Date;
   public readonly request: ElicitRequest;
   public readonly taskId?: string;
+  /**
+   * How this request reached the Inspector — a legacy server→client request or
+   * a modern MRTR `input_required` round. Drives era-accurate copy in the
+   * pending-request UI. Defaults to `"server-request"` so existing call sites
+   * (and stories) keep the legacy semantics unchanged.
+   */
+  public readonly origin: PendingRequestOrigin;
   private resolvePromise?: (result: ElicitResult) => void;
-  /** Set only for task-augmented elicit; used when user declines so server's tasks/result receives an error */
+  /**
+   * Rejects the originating call with an error. Set for task-augmented elicit
+   * (so the server's `tasks/result` receives the error on decline) and for
+   * MRTR-driven elicitations (so a genuine failure aborts the tool call).
+   */
   private rejectCallback?: (error: Error) => void;
   private onRemove: (id: string) => void;
 
@@ -33,6 +46,7 @@ export class ElicitationCreateMessage {
     resolve: (result: ElicitResult) => void,
     onRemove: (id: string) => void,
     reject?: (error: Error) => void,
+    origin: PendingRequestOrigin = "server-request",
   ) {
     this.onRemove = onRemove;
     this.id = `elicitation-${crypto.randomUUID()}`;
@@ -41,6 +55,7 @@ export class ElicitationCreateMessage {
     // Extract taskId from request params metadata if present
     const relatedTask = request.params?._meta?.[RELATED_TASK_META_KEY];
     this.taskId = relatedTask?.taskId;
+    this.origin = origin;
     this.resolvePromise = resolve;
     this.rejectCallback = reject;
   }