Era-aware connection model & capability gating (#1626) (#1697)

* Era-aware connection model & capability gating (#1626)

Make protocol era (SEP §7.8) a first-class, per-server connection dimension,
orthogonal to the transport type, and drive the SDK Client's versionNegotiation
from it.

Config
- Add `ServerProtocolEra` ("legacy" | "auto" | "modern"), `DEFAULT_PROTOCOL_ERA`
  (legacy, per the SDK's don't-auto-probe guidance), `MODERN_PROTOCOL_VERSION`,
  and `eraToVersionNegotiation()` in core/mcp/types.ts.
- Persist `protocolEra` on `StoredMCPServer` / `InspectorServerSettings`,
  round-tripping through serverList.ts (omitting the default on disk) and the
  `/api/servers` read + write validators.

InspectorClient / state
- Thread `versionNegotiation` through `InspectorClientOptions` (default legacy),
  replacing the hardcoded pin. After connect, read `getProtocolEra()` /
  `getDiscoverResult()` / `getNegotiatedProtocolVersion()`, expose them via
  getters, dispatch `protocolEraChange` / `discoverResultChange`, and clear on
  disconnect. `useInspectorClient` surfaces `protocolEra` / `discoverResult`.

Web UI
- ServerSettingsForm: a Protocol Era selector bound to the per-server setting.
- ConnectionInfoContent: era-aware — Era badge, Session ("Sessionless" on
  modern), and a Discovery section (supported versions + extensions) from the
  `server/discover` result.

CLI/TUI also map the mcp.json `protocolEra` into versionNegotiation so the field
applies uniformly. Version negotiation stays fully client-side; modern connect
works over the existing remote tunnel and disconnect is sessionless (the SDK
skips DELETE when there is no session id). Mcp-* header fidelity is left to the
History/Network card.

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

* Address @claude review: era docstrings, era validation, stdio session label, AGENTS.md rule

- Fix stale docstrings/comments in inspectorClient.ts, useInspectorClient.ts,
  inspectorClientEventTarget.ts, and ConnectionInfoContent.tsx: getProtocolEra()
  returns "legacy" (not undefined) on a plain legacy connect; it is undefined
  only when not connected.
- Validate protocolEra at the storedFieldsToInspectorSettings read boundary
  (new shared isProtocolEra guard) so a hand-edited mcp.json read directly by
  the CLI/TUI drops an unknown era instead of passing it to
  eraToVersionNegotiation. Keeps the exhaustive switch intact.
- ConnectionInfoContent: the Session row is HTTP-only — show "N/A (stdio)" for
  stdio instead of the misleading "Session-based".
- AGENTS.md: add a rule against unjustified `as unknown as` double casts, and
  drop the one such cast introduced in the serverList test.

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

* Address re-review: dedupe isProtocolEra guard in remote server

Replace the local isProtocolEra in remote/node/server.ts with the shared guard
now exported from serverList.ts (already imported here), so the era literal set
lives in one place and can't drift.

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/ServerSettingsModal/ServerSettingsModal.test.tsx

@@ -118,6 +118,27 @@ describe("ServerSettingsModal", () => {
     );
   });
 
+  it("maps the selected protocol era into settings (#1626)", async () => {
+    const user = userEvent.setup();
+    const onSettingsChange = vi.fn();
+    renderWithMantine(
+      <ServerSettingsModal
+        opened
+        settings={emptySettings}
+        serverType="streamable-http"
+        isStdio={false}
+        onClose={vi.fn()}
+        onSettingsChange={onSettingsChange}
+      />,
+    );
+    // The Options section (with Protocol Era) is expanded by default.
+    await user.click(screen.getByDisplayValue("Legacy (2025-11-25 handshake)"));
+    await user.click(screen.getByText("Modern (2026-07-28, sessionless)"));
+    expect(onSettingsChange).toHaveBeenCalledWith(
+      expect.objectContaining({ protocolEra: "modern" }),
+    );
+  });
+
   it("calls onSettingsChange when adding a header after expanding the section", async () => {
     const user = userEvent.setup();
     const onSettingsChange = vi.fn();

clients/web/src/components/groups/ServerSettingsModal/ServerSettingsModal.tsx

@@ -3,6 +3,7 @@ import { CloseButton, Group, Modal, Stack } from "@mantine/core";
 import type {
   InspectorServerSettings,
   OAuthSettings,
+  ServerProtocolEra,
   ServerType,
 } from "@inspector/core/mcp/types.js";
 import { isOAuthCapableServerType } from "@inspector/core/mcp/config.js";
@@ -165,6 +166,10 @@ export function ServerSettingsModal({
     onSettingsChange({ ...settings, maxFetchRequests: value });
   }
 
+  function handleProtocolEraChange(value: ServerProtocolEra) {
+    onSettingsChange({ ...settings, protocolEra: value });
+  }
+
   function handleAddRoot() {
     onSettingsChange({
       ...settings,
@@ -228,6 +233,7 @@ export function ServerSettingsModal({
           onTimeoutChange={handleTimeoutChange}
           onAutoRefreshChange={handleAutoRefreshChange}
           onMaxFetchRequestsChange={handleMaxFetchRequestsChange}
+          onProtocolEraChange={handleProtocolEraChange}
           onOAuthChange={handleOAuthChange}
           onClearStoredOAuth={onClearStoredOAuth}
           onAddRoot={handleAddRoot}