Index-topk sharing previously required editing model config or passing raw JSON overrides. Add first-class server args that merge into json_model_override_args before ModelConfig is read, preserving existing JSON overrides while letting launch scripts toggle index_topk_freq directly. Treat offset 0 as unset so wrappers can use 0 for default behavior without injecting a model-config override.
Constraint: Prefill and decode launch commands need the same effective model config without mutating /ssd model files.
Rejected: Require editing config.json | operationally fragile across g0034/g0035/g0036 model copies.
Rejected: Only use --json-model-override-args | works but is too error-prone for frequent launch-command tuning.
Confidence: high
Scope-risk: narrow
Directive: Keep these flags as model-config override shortcuts; apply them before any get_model_config() call.
Tested: Remote pytest in g0034 container for NSA index override parser tests: 2 passed.
Tested: py_compile for server_args.py and test_server_args.py.
Not-tested: Full prefill/decode ETE launch with --nsa-index-topk-freq enabled.
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