## Problem
`prompts/get` for a name that is not registered responds with JSON-RPC
`-32603` (INTERNAL_ERROR).
`handleGetPrompt` in `Server.kt` throws a bare
`IllegalArgumentException` when the prompt is missing.
`Protocol.respondWithError` maps any non-`McpException` cause to
`INTERNAL_ERROR`, so the client receives `-32603` for what is a
client-side bad parameter.
The sibling handler `handleReadResource` in the same file already throws
a typed `McpException(RESOURCE_NOT_FOUND)` for the equivalent not-found
case, which reaches the client as `-32002`. The two not-found paths are
inconsistent.
In JSON-RPC, `-32603` means the server hit an internal fault. Requesting
a prompt name that does not exist is a client error (an invalid `name`
parameter), so a client cannot tell "the prompt does not exist" apart
from "the server failed" and may retry a request that can never succeed.
## Change
Throw a typed `McpException(INVALID_PARAMS)` from `handleGetPrompt`,
consistent with `handleReadResource`. The message is unchanged.
`AbstractPromptIntegrationTest.testNonExistentPrompt` asserted `-32603`;
it now asserts `INVALID_PARAMS`.
If you would prefer a dedicated error code for this case instead of
`INVALID_PARAMS`, I am glad to adjust.
b7047e77cf