#532 Copy explicitGlobalArgs before mutation in resolveOrCreateDefinition

Problem

In src/libswamp/models/direct_execution.ts:168, the new explicit globalArgs path (added in swamp-club#504 / PR #1491) mutates the caller's object in-place:

Object.assign(explicitGlobalArgs, coerced);

The implicit routing path creates a local {} (line 98) that the function owns, so mutation is safe there. But explicitGlobalArgs is the caller's task.globalArgs reference from the step task data.

Impact

Harmless today because (a) coercion is idempotent and (b) the task is consumed once. But it violates the ownership contract the implicit path follows — if executeModelMethod is ever refactored to re-read task.globalArgs after calling the resolver (e.g. for logging or retry), the coerced values would silently replace the original YAML values.

Fix

Create a local copy before mutating:

const globalArgs = { ...explicitGlobalArgs };
if (modelDef.globalArguments) {
  const coerced = coerceMethodArgs(globalArgs, modelDef.globalArguments);
  Object.assign(globalArgs, coerced);
}
routed = { globalArguments: globalArgs, methodArguments: inputs };

Flagged by the adversarial code review on PR #1491.