[copybara-service]

fix: add typed GAOS 4XX/5XX error responses and surface backend error messages in Java, Go, and CLI

Operations outside the core /interactions CRUD paths omitted 4XX and 5XX response mappings in the GAOS OpenAPI spec, causing generated SDKs to fall back to untyped generic errors; additionally, Speakeasy-generated Java, Go, and CLI error classes pass the placeholder "API error occurred" when error details are nested under {error: {message}}.

1. GAOS 4XX/5XX error response overlay (overlays/gaos/15-error-responses.yaml):

   • Defines shared ApiError (ApiErrorCode: integer | string, message: string with x-speakeasy-error-message: true, ApiErrorStatus: string | integer, details: array of object), ApiClientError (4XX), and ApiServerError (5XX) schemas, accepting both standard OnePlatform HTTP error envelopes (code: int, status: str, details: [...]) and Interactions HTTP error envelopes (code: str) without colliding with the SSE #/components/schemas/Error schema.
   • Applies 4XX -> ApiClientError and 5XX -> ApiServerError to all GAOS operations that lack 4XX responses (32 public operations and 47 internal operations, including POST /{api_version}/decisions, /feedback, /agents/{id}/triggers, and /interactions/{id}/auth_tokens).
   • Bridges non-interaction Java and .NET operations onto native ClientException/ServerException (ClientError/ServerError) and surfaces typed error.message directly in Python, TypeScript, Go (apierrors.ApiClientError / ApiServerError), and CLI (sdkerrors.ApiClientError / ApiServerError).

2. Backend error message surfacing in Java, Go, and CLI:

   • Java: Emits package-private GaosErrorBody (scripts/templates/error_body.java.tmpl) and forwards GaosErrorBody.status(body) (OnePlatform error.status, else Interactions string error.code, else "") and GaosErrorBody.message(message, body) to com.google.genai.errors.ApiException from GaosBaseException, GaosClientException, and GaosServerException when Speakeasy passes "API error occurred".
   • Go: Emits messageFromBody (scripts/templates/error_body.go.tmpl) in interactions/models/apierrors/errorbody.go and calls it from NewAPIError on fallback responses.
   • CLI: Emits messageFromBody in internal/sdk/models/sdkerrors/errorbody.go and calls it from NewSDKDefaultError (covering fallback responses, classic.openapi.json operations, and rawhttp.go).

3. Sync hardening & tests:

   • Switches Java error reparent replacements in sync_speakeasy_outputs.py (reparent_java_error) to _replace_once so generator template changes fail loudly at sync time, and adds patch_go_apierrors and patch_cli_sdkerrors.
   • Regenerates OAD goldens and all 6 SDKs + CLI, and adds/updates error compatibility and unit tests across Java, .NET, Go, CLI, and sync_speakeasy_outputs_test.py.

FUTURE_COPYBARA_INTEGRATE_REVIEW=#3249 from googleapis:release-please--branches--main 4b4b0f3