Extract shared logic, avoid dead code

When the same logic appears in multiple places—across files (e.g., duplicated repairDuplicatedJsonArguments/appendToolArgs in two translator modules) or across branches within the same function (e.g., duplicated finish-reason computation in flush vs. response.completed paths)—extract it into a single shared helper function or module. This prevents the implementations from drifting apart as one copy is updated without the other. For example, move shared utilities into a common module (concerns/toolArgs.js) and import it everywhere needed, or factor duplicated branch logic into a named helper like computeFinishReason(state).

Likewise, avoid adding parameters, options, or code paths that aren’t actually wired up or used yet (e.g., an onProgress callback with no caller). Speculative, unused code adds cognitive overhead and signals functionality that doesn’t exist; add it only when it’s actually needed and exercised. If behavior depends on non-obvious state (such as sticky flags carried across calls), add a short comment explaining why, so future readers don’t mistake it for an oversight.