SDK parity gaps: endpoint headers and OSSFS support are inconsistent across languages

[ninan-nn]

There are still cross-language SDK parity gaps around two areas:

1. Execd endpoint headers are not applied consistently in Code Interpreter SDKs.

• Python async was fixed in PR fix: critical bugs across execd, server, and SDKs #468
• Python sync still appears to miss endpoint headers
• JavaScript code-interpreter also appears to only use connection-level headers
• C# / Kotlin already handle endpoint headers

2. OSSFS volume support is inconsistent across sandbox SDKs.

• Python converter was fixed in PR fix: critical bugs across execd, server, and SDKs #468
• Kotlin volume converter still does not serialize ossfs
• C# volume models do not appear to expose ossfs yet

[ninan-nn]

Additional parity notes from a broader static scan:

• Python remains the most complete SDK overall because it has both async and sync surfaces for sandbox and code-interpreter.
• JavaScript sandbox high-level models still expose only host/pvc volumes even though generated lifecycle types already include ossfs.
• Kotlin sandbox domain/converter layer also does not currently model/serialize ossfs.
• C# sandbox models likewise only expose Host/Pvc volume backends today.

Code Interpreter specific gaps:

• Python async endpoint-header support was fixed in PR fix: critical bugs across execd, server, and SDKs #468, but the sync adapter still appears to miss endpoint headers.
• JavaScript code-interpreter also appears to use only connection-level headers, not endpoint headers.
• Kotlin code-interpreter appears to have two issues: endpoint headers are not added in run(), and deleteContexts() recursively calls itself instead of the API method.
• C# code-interpreter appears ahead here: endpoint headers are wired through already.

So the remaining work is not just one missing fix in one SDK; it is broader cross-language parity drift between generated spec coverage, domain models, and high-level adapters.