fix(client): detect authorization-server migration from fresh PRM

[mattzcarey]

Previously unaddressed

#2358 isolated credentials by issuer once the current authorization server was known, but cached discovery could keep the client pinned to AS-A after a fresh resource_metadata challenge selected AS-B. Existing tests had to clear discovery manually before migration was detected.

This PR

• re-probes cached discovery only for a fresh resource-metadata challenge
• compares the newly PRM-validated AS with the recorded identity
• discards old-AS tokens and non-portable client credentials before continuing
• preserves portable CIMD client IDs
• avoids false migration on legacy fallback, transient discovery failure, or the authorization-code callback

Verification

• client: 735 tests, including migration, fallback, CIMD, and callback cases
• pnpm check:all
• pnpm build:all

Follow-up to #2271, #2358, and #2286.

[changeset-bot]

🦋 Changeset detected

Latest commit: e4de221

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@modelcontextprotocol/client	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[pkg-pr-new]

Open in StackBlitz

@modelcontextprotocol/client

npm i https://pkg.pr.new/@modelcontextprotocol/client@2450

@modelcontextprotocol/codemod

npm i https://pkg.pr.new/@modelcontextprotocol/codemod@2450

@modelcontextprotocol/core

npm i https://pkg.pr.new/@modelcontextprotocol/core@2450

@modelcontextprotocol/server

npm i https://pkg.pr.new/@modelcontextprotocol/server@2450

@modelcontextprotocol/server-legacy

npm i https://pkg.pr.new/@modelcontextprotocol/server-legacy@2450

@modelcontextprotocol/express

npm i https://pkg.pr.new/@modelcontextprotocol/express@2450

@modelcontextprotocol/fastify

npm i https://pkg.pr.new/@modelcontextprotocol/fastify@2450

@modelcontextprotocol/hono

npm i https://pkg.pr.new/@modelcontextprotocol/hono@2450

@modelcontextprotocol/node

npm i https://pkg.pr.new/@modelcontextprotocol/node@2450

commit: e4de221