Implements the non-SEP changes from the 2025-11-25 → draft spec diff tracked in #2202. Per-item breakdown:

(a) Deterministic tools/list ordering — already compliant, tests added

Servers SHOULD return tools in a deterministic order (i.e., the same ordering across requests when the underlying set of tools has not changed). — draft server/tools.mdx

McpServer lists tools via Object.entries(this._registeredTools), which is stable insertion order — no code change needed. Added regression tests (identical order across repeated tools/list calls, and stability across disable()/enable() toggles, including that re-enabling restores insertion position rather than appending) plus a short comment on the list handler documenting the guarantee.

(b) List responses when capability declared — the only behavioral change

Servers that declare the tools capability MUST respond to tools/list requests with the set of tools currently available to the requesting client. This set MAY be empty… — draft server/tools.mdx (equivalent language for resources/prompts)

Previously, McpServer installed list/call handlers lazily on first registerTool/registerResource/registerPrompt, so a server constructed with capabilities: { tools: {} } and zero registrations answered tools/list with -32601 (Method not found). The constructor now eagerly installs handlers for every primitive capability declared in ServerOptions.capabilities:

• tools → tools/list returns []; tools/call for an unknown tool returns -32602
• resources → resources/list / resources/templates/list return []; resources/read returns resource-not-found
• prompts → prompts/list returns []; prompts/get returns -32602

Undeclared capabilities with no registrations still return -32601, and lazy installation on first registration is unchanged for servers that don't declare capabilities up front. Low-level Server users remain responsible for their own handlers — documented on ServerOptions.capabilities.

Happy to split this item into its own PR if you'd prefer to keep behavioral and docs-only changes separate.

(c) Empty-string cursor — doc examples fixed

Don't make any determination based on cursor value other than whether a non-null value was provided (e.g. an empty string is a valid cursor and thus MUST NOT be treated as the end of results) — draft server/utilities/pagination.mdx

The SDK has no runtime pagination loop, but the pagination examples in client.examples.ts (and the JSDoc on listTools/listPrompts/listResources generated from them via sync:snippets) used } while (cursor);, which stops on an empty-string cursor. Fixed to while (cursor !== undefined) and re-ran pnpm sync:snippets.

(d) Resource path sanitization — docs only

Servers MUST sanitize file paths to prevent directory traversal attacks when serving file:// resources — draft server/resources.mdx (Security Considerations)

The SDK serves no files itself; added a security note to the Resources section of docs/server.md about sanitizing user-influenced paths (traversal sequences, encoded forms, symlink escapes).

(e) Completion value caps — already compliant, already tested

values: Array of suggestions (max 100) … hasMore: Additional results flag — draft server/utilities/completion.mdx

createCompletionResult in mcp.ts already slices to 100 and sets hasMore/total, and test/e2e/scenarios/completion.test.ts (requirement completion:result-shape, 150-item fixture) already asserts the 100-cap, total, and hasMore: true. No change needed.

Notes

• Potential rebase: (b) touches packages/server/src/server/mcp.ts near regions feat(core,server,client): implement SEP-2106 (tool schemas conform to JSON Schema 2020-12) #2249 (SEP-2106) also modifies; edits here are deliberately minimal and self-contained, but this PR may need a trivial rebase after feat(core,server,client): implement SEP-2106 (tool schemas conform to JSON Schema 2020-12) #2249 merges (or vice versa).
• Downstream impact: cloudflare/agents is unaffected by (b) since MCPAgent always registers primitives before connect, BUT agents has the same empty-string-cursor consumer bug in packages/agents/src/mcp/client-connection.ts (~L562-617, while (result.nextCursor)) — an agents-side fix issue should be filed.

Validation

• pnpm build:all, pnpm typecheck:all, pnpm lint:all (includes sync:snippets --check): pass
• Package tests: core 463/463, client 367/367, server 72/72
• Integration suite: 327/327 (includes 7 new tests in test/integration/test/server/declaredCapabilities.test.ts)
• Changeset: patch for @modelcontextprotocol/server and @modelcontextprotocol/client

Closes #2202