Planner.fetchBaseKey ignores structured platform base keys #430

Summary

Reported with OpenTDF Java SDK 0.19.1: Planner.fetchBaseKey does not parse the platform's structured configuration.base_key response and returns Optional.empty() for a valid base key.

Reproduction

Return the following shape from GetWellKnownConfiguration (values are illustrative):

{
  "configuration": {
    "base_key": {
      "kas_id": "00000000-0000-0000-0000-000000000001",
      "kas_uri": "https://kas.example.com/kas",
      "public_key": {
        "algorithm": "rsa:2048",
        "kid": "example-key-id",
        "pem": "-----BEGIN PUBLIC KEY-----\n...\n-----END PUBLIC KEY-----\n"
      }
    }
  }
}

Call Planner.fetchBaseKey with that configuration. The protobuf Value is a struct, so getStringValue() returns "" and Gson produces no base key. The old mapping also expects kas_url instead of kas_uri and a protobuf algorithm enum name instead of the wire-format rsa:2048.

Expected behavior

Read the nested struct, use kas_uri, and convert wire-format algorithms such as rsa:2048 to the corresponding policy enum. A valid base key should remain available to the planner.

The Go SDK demonstrates this behavior:

• Object parsing and algorithm conversion
• Algorithm mapping
• Success test using the platform response shape

Affected Java implementation: Planner.java at v0.19.1.

Fix

Tracked for posterity; the fix is proposed in #429 (currently open). That PR reads structured configuration, uses kas_uri, maps wire-format algorithms, and adds regression tests. This issue does not imply that the fix has already shipped.