Remove per-row runtime_error from CastInputsToJson in aggregate functions

[Copilot]

CastInputsToJson threw a std::runtime_error when context_columns was absent, but this was called on every row during aggregation — meaning a bad prompt would produce one exception per row at execution time rather than failing once at bind time.

Changes

• src/functions/aggregate/aggregate.cpp: Removed the else { throw std::runtime_error(...) } branch from CastInputsToJson. The context_columns presence check is already enforced at bind time by ValidatePromptStructFields, making the per-row throw unreachable dead code.

// Before
if (prompt_context_json.contains("context_columns")) {
    context_columns = prompt_context_json["context_columns"];
    prompt_context_json.erase("context_columns");
} else {
    throw std::runtime_error("Missing 'context_columns' in second argument...");
}

// After — bind-time validation in ValidatePromptStructFields is sufficient
if (prompt_context_json.contains("context_columns")) {
    context_columns = prompt_context_json["context_columns"];
    prompt_context_json.erase("context_columns");
}

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[Copilot]

Pull request overview

This PR adjusts Flock’s aggregate-function input parsing to avoid throwing a runtime exception during aggregation when context_columns is absent, relying instead on bind-time validation.

Changes:

• Removed the runtime std::runtime_error branch in AggregateFunctionBase::CastInputsToJson when context_columns is missing.
• Leaves enforcement of context_columns presence to bind-time checks (ValidatePromptStructFields).

[Copilot]

ValidatePromptStructFields only guarantees the prompt STRUCT type contains a context_columns field, but CastVectorOfStructsToJson currently omits the context_columns key when the list is empty (and also returns an empty object when count == 0). With this change, those cases will silently produce context_columns = [] instead of throwing, which can change aggregate behavior (often resulting in NULL output). Consider ensuring CastVectorOfStructsToJson always materializes context_columns as an empty array when present-but-empty, or add an explicit validation/error here if empty context is not supported.

[anasdorbani]

@copilot apply changes based on this feedback

[Copilot]

This change alters runtime behavior when context_columns is empty/missing in the JSON produced at execution time. Please add a unit/integration test that exercises an aggregate call with context_columns := [] (and/or an empty input chunk) to lock in the intended behavior (error vs NULL result).