Implement SEP-2164: Standardize resource not found error code (-32602)

[felixweinberger]

This is a tracking issue for implementation of SEP-2164.

[mattzcarey]

Status — SEP-2164 (Standardize resource not-found error code)

Track: C — independent, starts now. Smallest issue in the project.
Spec: seps/2164-resource-not-found-error.md · merged

What's done — pointed in the WRONG direction

The spec says: -32602 (Invalid Params). main is currently set to -32002 (ResourceNotFound):

• packages/core/src/types/enums.ts:

  ResourceNotFound = -32_002,

• packages/core/CHANGELOG.md / packages/server/CHANGELOG.md:

  Resources: Unknown resource reads now return error code -32002 (ResourceNotFound) instead of -32602 (InvalidParams).
  Added ProtocolErrorCode.ResourceNotFound.

This was the right move pre-SEP-2164, but SEP-2164 walks it back to -32602 for spec conformance with JSON-RPC. The SDK is currently regressing against the new spec.

Outstanding (acceptance criteria, summary)

• R-2164-1 (wire): resources/read for unknown URI MUST return -32602 Invalid Params
• R-2164-2 (wire): error data SHOULD include the URI
• R-2164-4 (wire): server MUST NOT return an empty contents array for a non-existent resource — must be a JSON-RPC error
• R-2164-5 (sdk): Client SHOULD accept -32002 as a resource-not-found error for BC with earlier protocol versions — map it to the same ResourceNotFound error type as -32602

Suggested first PR (tiny)

1. Server: switch resources/read unknown-URI path to throw -32602 with data: { uri }
2. Keep ProtocolErrorCode.ResourceNotFound = -32002 for the legacy/BC client mapping (R-2164-5)
3. Update the two CHANGELOG entries to reflect the spec change
4. Update tests

Coordination

• No dependencies. Drop-in fix. ~30 LOC.