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>

pr-screenshots/README.md

@@ -1,3 +1,47 @@
+# x-mcp-header Tools tooling (#1632) — proof screenshots
+
+End-to-end verification of the SEP-2243 `x-mcp-header` Tools tooling against a
+real modern (2026-07-28) HTTP test server
+(`test-servers/configs/xmcpheader-modern-http.json` on port 3120), driven in a
+real browser through the web client's remote-proxy transport.
+
+![Excluded tools in the sidebar](xmcpheader-excluded-tools.png)
+
+Connected with **Protocol Era = Modern**. `invalid_header_tool` is dropped from
+`tools/list` by the SDK (its `x-mcp-header` annotation is invalid), so the
+Inspector re-lists the raw list and surfaces it struck-through under an
+**"Excluded (SEP-2243)"** divider — showing _why_ a tool vanished rather than
+silently omitting it.
+
+![Exclusion reason on hover](xmcpheader-excluded-reason.png)
+
+Hovering the excluded tool shows the exact scan reason: the header name
+`"Bad Header"` contains a space, so it is not a valid RFC 9110 token.
+
+![Mirrored request headers](xmcpheader-mirrored-headers.png)
+
+`get_weather`'s detail panel shows the **"Mirrored request headers (SEP-2243)"**
+section: its `city` argument mirrors to `Mcp-Param-City`, with the note that the
+SDK omits `Mcp-Param-*` on the browser transport.
+
+![Unknown tool -32602](xmcpheader-unknown-tool.png)
+
+Calling a tool the server no longer recognizes rejects with **`-32602`** (SDK v2)
+instead of an `isError` result, and renders as an **"Unknown Tool"** error panel
+with a targeted hint (reproduced by swapping the sessionless server to one
+without `echo` while the cached list still showed it).
+
+![Invalid params -32602](xmcpheader-invalid-params.png)
+
+`-32602` is the generic _Invalid params_ code, so a **known** tool rejected for
+bad arguments throws the same code as an unknown tool. The panel disambiguates
+from the message: a `-32602` that does not name an unknown tool renders under
+**"Invalid Parameters"** (with a schema hint) rather than "Unknown Tool".
+Triggered live via the `trigger_invalid_params` tool, which returns a real
+`-32602` JSON-RPC error whose message is not about a missing tool.
+
+---
+
 # Tasks extension era fork (#1631) — proof screenshots
 
 End-to-end verification of the Tasks era fork against two real test servers
@@ -27,8 +71,8 @@ blocking `tasks/result`) — shown both in the Results panel and the Tasks card.
 `modern_input_task` moves to **`input_required`**: the `tasks/get` response's
 `inputRequests` map (visible in the task's Full Task Object) carries an embedded
 `elicitation/create`, surfaced through the same pending-request modal the MRTR
-path uses — note the accurate wording *"your answer is submitted via a
-tasks/update request (SEP-2663), not a retry"*. Answering it sends
+path uses — note the accurate wording _"your answer is submitted via a
+tasks/update request (SEP-2663), not a retry"_. Answering it sends
 **`tasks/update`** with the `inputResponses`, and the next poll completes the
 task: