fix(rivetkit): surface native runtime load failures instead of masking them with wasm

[MasterPtato]

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[MasterPtato]

Stack for rivet-dev/actors

• #5670 fix(rivetkit): surface native runtime load failures instead … 👈
• #5667 fix(envoy-client): fail sent vfs sqlite requests on disconne …
• #5666 fix(rivetkit-core): report actor crashes as a sleep intent i …
• #5668 fix(envoy-client): ack start commands immediately instead of …
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Get stack: forklift get 5670
Push local edits: forklift submit
Merge when ready: forklift merge 5670

_{change mputlvxy}

[claude]

Code Review

Small, well-scoped fix. Reviewed rivetkit-typescript/packages/rivetkit/src/registry/native.ts and the new tests in runtime.test.ts.

Summary

Previously, loadAutoRuntime silently swallowed the native-runtime load error whenever the wasm fallback succeeded, and if wasm also failed, the caller only ever saw the wasm error (with zero context about why native failed). This PR:

• Captures the native error and logs it via logger().warn(...) before falling back to wasm, so a silently-skipped platform binding is no longer invisible when wasm happens to succeed.
• When both native and wasm fail, throws a single RivetError("config", "runtime_unavailable", ...) that includes both underlying error messages instead of only the (usually irrelevant) wasm file:// fetch error.

Correctness

Control flow is correct: nativeError is unconditionally assigned in the first catch before the second try block can run, so there is no uninitialized-use path. The edge-like host short-circuit is untouched, and the explicit native/wasm request paths in loadConfiguredRuntime are unaffected, this change only touches the auto fallback path. No bugs found.

Style / conventions

• Structured logging (logger().warn({ msg, error: stringifyError(error) })) matches the existing pattern used elsewhere in this file.
• Comments are written as complete sentences per CLAUDE.md conventions.
• The new RivetError group/code (config/runtime_unavailable) is consistent with neighboring TS-only errors in the same file (unknown_runtime, wasm_local_sqlite). Since this is a TS-native RivetError, not a Rust #[derive(RivetError)] type, no generated-artifact update is needed.

Test coverage

Good coverage in runtime.test.ts via an injectable RuntimeLoaders: native success, native failure with wasm fallback, both failing (asserts both error messages are present in the thrown error), and the edge-host path never touching native. These are solid, deterministic unit tests with no mocking of real infra, consistent with the repo testing conventions.

Minor nits (non-blocking)

• The combined error message concatenates the two error strings with only a space separating "Native runtime: ..." and "Wasm runtime: ...". If stringifyError includes a stack trace (gated by the getLogErrorStack() debug flag), the boundary between the two sections becomes harder to read. A newline or semicolon separator would improve readability.
• This new error is constructed with public: true, so stringifyError output, including a stack trace when the debug flag is enabled, can propagate to the client. This mirrors existing sibling errors in the file, so it is likely intentional, but worth double-checking that this is the desired exposure for this code path.

Nothing blocking, looks safe to merge.