fix(oauth): pass the raw challenge scopes to the step-up scope filter

Copilot review round 10 on #2114 — a defect in round 8's fix, and the
precise loop that fix's extra argument was added to prevent.

`enrichChallengeWithScopes` narrows `requiredScopes` to the *missing*
subset, so a challenge requiring `offline_access tools:write` against a
stored scope that already carries `offline_access` arrives as just
`["tools:write"]`. Passing that narrowed list made the filter read the
server's explicit requirement as inherited and strip it, so
re-authorization would earn the same challenge forever.

Passes `challenge.requiredScopes` — the raw list — instead. The mixed
case is now covered, and fails against the narrowed list.

Also stops the checkbox promising more than the setting delivers: it
does not register anything for a preconfigured or CIMD client, and the
authorization server decides issuance either way. It now says it
declares the grant so the server *may* issue a refresh token.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013hzwzS8UvBsr4yZm7o7sev
Signed-off-by: cliffhall <cliff@futurescale.com>

core/mcp/oauthManager.ts

@@ -804,7 +804,15 @@ export class OAuthManager {
         ? scopeForDeclinedRefreshGrant(
             requestedScopeForAuth,
             this.oauthConfig.scope,
-            enriched.requiredScopes,
+            // The RAW challenge scopes, not `enriched.requiredScopes`:
+            // `enrichChallengeWithScopes` narrows that to the *missing* subset,
+            // so a challenge requiring `offline_access tools:write` against a
+            // stored scope that already has `offline_access` arrives here as
+            // just `["tools:write"]`. Passing the narrowed list would read the
+            // server's explicit requirement as inherited and strip it — then
+            // re-authorization earns the same challenge forever, which is the
+            // loop this argument exists to prevent.
+            challenge.requiredScopes,
           )
         : requestedScopeForAuth;