refactor(rpc): preserve structured error responses

[crystalt]

Makes the internal rpc_call retain the complete JSON-RPC error response, including optional structured data. Existing public RPC methods continue converting errors to the current RpcError shape, so their behavior and API remain unchanged.

This provides a lossless internal boundary for callers that need to interpret structured errors.

---

Note

Low Risk
Refactor of internal RPC error typing with public APIs unchanged; risk is limited to subtle error-handling regressions inside rpc_call.

Overview
Internal rpc_call now keeps full JSON-RPC errors instead of collapsing them into RpcError::RpcResponseError immediately. JSON-RPC failures return RpcCallError::Response carrying JsonRpcError (renamed from ErrorPayload), including optional structured data.

Public RPC helpers still surface RpcError via map_err(RpcError::from), so external behavior stays the same: RpcResponseError only exposes code and message (data is dropped at the API boundary). From<JsonRpcError> for RpcError encodes that mapping.

custom_bundler parsing follows the JsonRpcError rename. Tests add a stub HTTP client and assert rpc_call preserves error.data for structured declines (e.g. policy/retry hints).

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[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-03T19:11:51.146081Z	be8c473	Manual request

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[crystalt]

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