Support worker env vars before importing the server

[fzyzcjy]

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[gemini-code-assist]

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[guapisolo]

[P1][Unresolved through #2649] serve.py writes the complete own/worker argv, computed environment values, and exec argv to stdout; #2446 also wires this entrypoint into the Helm production launch path. Please log only non-sensitive phase metadata, identities, or counts, and add a sentinel-secret test proving neither argv nor environment values reach the logs.

[P2][Fixed only after checkpoint by #2345] This remains broken at the #2176 checkpoint. #2345 removes the hidden inner CLI contract by moving both entrypoints onto the shared --specs/--pool-id parser, so #2345 or an equivalent correction must land with the checkpoint.

[P2][Unresolved through #2649] The exec chain still rebuilds [sys.executable, "-m", ...], so Python flags such as -O, -u, -I, -E, and -X are dropped. Please preserve the interpreter-option prefix from sys.orig_argv while replacing only the module target, and cover one observable flag in a subprocess test.