Tools: x-mcp-header annotation tooling + -32602 unknown-tool rendering (#1632) (#1735)

* Tools: x-mcp-header annotation tooling + -32602 unknown-tool rendering (#1632)

Card 9/10 of the SDK-v2 + New Spec stack. Adds SEP-2243 `x-mcp-header`
tooling to the Tools tab and adjusts result rendering for SDK v2's
unknown-tool behavior, and bumps the SDK to 2.0.0-beta.5.

- **`core/json/xMcpHeader.ts`**: a faithful port of the SDK's (non-public)
  `scanXMcpHeaderDeclarations` — validates every SEP-2243 constraint
  (primitive types incl. `number`, RFC 9110 token, case-insensitive
  uniqueness, statically-reachable `properties`-only chain) and derives the
  mirrored `Mcp-Param-{Name}` params for a kept tool.

- **Excluded tools**: the SDK silently drops tools with invalid annotations
  from `tools/list`. InspectorClient now re-lists the RAW (unfiltered) list
  and scans it to recompute the excluded set with reasons — gated to the
  modern non-stdio era (matching the SDK's gate), recomputed on every
  aggregate refresh, surfaced via a new `excludedToolsChange` event +
  `getExcludedTools()` and `useInspectorClient().excludedTools`. The Tools
  sidebar lists them struck-through under an "Excluded (SEP-2243)" divider
  with the reason on hover.

- **Mirrored args**: ToolDetailPanel shows a "Mirrored request headers"
  section listing each arg → `Mcp-Param-{Name}` (with the browser-omits note).

- **-32602 rendering**: SDK v2 rejects an unknown-tool call with `-32602`
  instead of an `isError` result, which previously rendered nothing. New
  ToolCallErrorPanel renders a thrown tool-call error, with a targeted
  "Unknown Tool" hint for `-32602`.

Adds unit + Storybook + integration coverage (a real modern server with an
invalid-header tool fixture) for every path. `npm run ci`-equivalent checks
green.

Closes #1632

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

* test-servers: x-mcp-header modern showcase config + preset (#1632)

Register the `invalid_header_tool` fixture as a preset and add
`xmcpheader-modern-http.json` — a modern HTTP showcase serving echo, a
valid-header `get_weather`, and the invalid-header tool — so the Tools-tab
x-mcp-header tooling (mirrored headers, excluded-tools surface, -32602
rendering) can be exercised manually. Documented in the README alongside the
other per-SEP showcase configs. Smoke-tested end to end in the web client.

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

* docs: add #1632 proof screenshots to pr-screenshots

End-to-end web-client verification of the x-mcp-header Tools tooling against
the modern showcase server: excluded-tools surface + reason, mirrored-headers
section, and the -32602 unknown-tool error panel.

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

* Respond to review: disambiguate -32602, doc/search nits (#1632)

Addresses the review on PR #1735:

1. -32602 "Unknown Tool" mislabel: `-32602` is generic Invalid params, so a
   known tool called with bad arguments hit the same code and rendered under
   the definitive "Unknown Tool" heading. Replace `isUnknownToolError` with
   `classifyToolCallError(code, message)` → "unknown-tool" only when the
   message names it (not found / unknown tool / …), else "invalid-params"
   (new "Invalid Parameters" heading + schema hint), else "generic".

2. Double pagination walk: expand the `listAllTools` comment to document that
   the excluded-tools recompute is a deliberately un-cached second raw walk
   (doubles list round-trips on modern non-stdio, runs even on a cache-served
   aggregate) — accepted for a debugging tool, no-op on legacy/stdio.

3. Doc nit: `scanXMcpHeaderDeclarations` no longer claims to visit "$ref
   targets" — reworded to note `$ref` is never followed (refs resolve into the
   unreachable `$defs` body).

4. Search nit: the excluded-list filter now matches name AND title, matching
   the main tools filter.

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

* Tighten unknown-tool matcher to be tool-scoped (#1632 re-review nit)

The re-review noted the -32602 disambiguation was symmetric: broad markers
("does not exist", "unrecognized") could inversely mislabel a genuine
invalid-params message (e.g. "property 'region' does not exist") as "Unknown
Tool". Scope the not-found/does-not-exist family to require the word "tool" in
the same clause (matching the SDK's "Tool <name> not found"); keep "unknown
tool" / "no such tool" as standalone unambiguous markers. Adds a
tool-less-"does not exist" test asserting it classifies as invalid-params.

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

* Add trigger_invalid_params showcase tool + Invalid Parameters screenshot (#1632)

Adds a `trigger_invalid_params` spec-error trigger to the modern showcase
server: the injector answers its `tools/call` with a real `-32602 Invalid
params` JSON-RPC error whose message does NOT name an unknown tool. This lets
the "Invalid Parameters" branch of the tool-call error panel (added in the
review response) be exercised live, distinct from the unknown-tool `-32602`.

- `SPEC_ERROR_TRIGGERS` gains the `trigger_invalid_params` entry (HTTP 200,
  in-band -32602) + preset registration.
- Enable `injectSpecErrors` on `xmcpheader-modern-http.json` and add the tool.
- README + pr-screenshots README document it; adds the live "Invalid
  Parameters" proof screenshot.

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/App.tsx

@@ -463,6 +463,18 @@ function errorMessage(err: unknown): string {
   return err instanceof Error ? err.message : String(err);
 }
 
+// The numeric JSON-RPC code of a thrown protocol error (e.g. a `ProtocolError`
+// carrying `-32602`), or undefined for a plain Error. Duck-typed like
+// `formatErrorDetails` so we don't couple to the SDK's error class here — the
+// only consumer is the Tools error panel's unknown-tool (`-32602`) hint (#1632).
+function errorCodeOf(err: unknown): number | undefined {
+  if (err && typeof err === "object") {
+    const code = (err as { code?: unknown }).code;
+    if (typeof code === "number") return code;
+  }
+  return undefined;
+}
+
 // Pretty-print a thrown error for the URL-elicitation details modal: a ProtocolError
 // carries a `code`/`data` worth showing alongside the message, so include them
 // when present; otherwise fall back to the plain message.
@@ -935,6 +947,7 @@ function App() {
     protocolVersion,
     protocolEra,
     discoverResult,
+    excludedTools,
     lastError,
   } = useInspectorClient(inspectorClient);
   const {
@@ -2933,6 +2946,7 @@ function App() {
         setToolCallState({
           status: "error",
           error: errorMessage(err),
+          errorCode: errorCodeOf(err),
         });
       }
     },
@@ -4198,6 +4212,7 @@ function App() {
           initializeResult={initializeResult}
           latencyMs={latencyMs}
           tools={tools}
+          excludedTools={excludedTools}
           prompts={prompts}
           resources={resources}
           resourceTemplates={resourceTemplates}