test(runtime): tolerate node18 warning in prepare-runtime output

[mikeylong]

Summary

• harden the prepare-runtime test helper to parse the trailing JSON payload when Node 18 emits an experimental JSON-module warning first
• keep the missing-runtime-bundle assertion stable across local and CI Node versions

Validation

• node --test packages/interfacectl-cli/test/prepare-runtime.test.mjs
• npx -y node@18 --test packages/interfacectl-cli/test/prepare-runtime.test.mjs

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Parse trailing JSON block instead of individual lines

The fallback in parseJsonFromOutput only tries JSON.parse on each single line, which cannot parse the pretty-printed error object emitted by runPrepareRuntimeCommand (JSON.stringify(..., null, 2)), so the new logic still fails whenever a Node 18 experimental warning is prepended to stderr. In that scenario JSON.parse(trimmed) fails because of the warning prefix, each individual JSON line also fails, and the test throws Unable to parse JSON output instead of asserting on payload.code.

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