fix: guard small context windows

src/agents/context-window-guard.ts

@@ -0,0 +1,84 @@
+import type { ClawdbotConfig } from "../config/config.js";
+
+export const CONTEXT_WINDOW_HARD_MIN_TOKENS = 16_000;
+export const CONTEXT_WINDOW_WARN_BELOW_TOKENS = 32_000;
+
+export type ContextWindowSource =
+  | "model"
+  | "modelsConfig"
+  | "agentContextTokens"
+  | "default";
+
+export type ContextWindowInfo = {
+  tokens: number;
+  source: ContextWindowSource;
+};
+
+function normalizePositiveInt(value: unknown): number | null {
+  if (typeof value !== "number" || !Number.isFinite(value)) return null;
+  const int = Math.floor(value);
+  return int > 0 ? int : null;
+}
+
+export function resolveContextWindowInfo(params: {
+  cfg: ClawdbotConfig | undefined;
+  provider: string;
+  modelId: string;
+  modelContextWindow?: number;
+  defaultTokens: number;
+}): ContextWindowInfo {
+  const fromModel = normalizePositiveInt(params.modelContextWindow);
+  if (fromModel) return { tokens: fromModel, source: "model" };
+
+  const fromModelsConfig = (() => {
+    const providers = params.cfg?.models?.providers as
+      | Record<
+          string,
+          { models?: Array<{ id?: string; contextWindow?: number }> }
+        >
+      | undefined;
+    const providerEntry = providers?.[params.provider];
+    const models = Array.isArray(providerEntry?.models)
+      ? providerEntry.models
+      : [];
+    const match = models.find((m) => m?.id === params.modelId);
+    return normalizePositiveInt(match?.contextWindow);
+  })();
+  if (fromModelsConfig)
+    return { tokens: fromModelsConfig, source: "modelsConfig" };
+
+  const fromAgentConfig = normalizePositiveInt(
+    params.cfg?.agents?.defaults?.contextTokens,
+  );
+  if (fromAgentConfig)
+    return { tokens: fromAgentConfig, source: "agentContextTokens" };
+
+  return { tokens: Math.floor(params.defaultTokens), source: "default" };
+}
+
+export type ContextWindowGuardResult = ContextWindowInfo & {
+  shouldWarn: boolean;
+  shouldBlock: boolean;
+};
+
+export function evaluateContextWindowGuard(params: {
+  info: ContextWindowInfo;
+  warnBelowTokens?: number;
+  hardMinTokens?: number;
+}): ContextWindowGuardResult {
+  const warnBelow = Math.max(
+    1,
+    Math.floor(params.warnBelowTokens ?? CONTEXT_WINDOW_WARN_BELOW_TOKENS),
+  );
+  const hardMin = Math.max(
+    1,
+    Math.floor(params.hardMinTokens ?? CONTEXT_WINDOW_HARD_MIN_TOKENS),
+  );
+  const tokens = Math.max(0, Math.floor(params.info.tokens));
+  return {
+    ...params.info,
+    tokens,
+    shouldWarn: tokens > 0 && tokens < warnBelow,
+    shouldBlock: tokens > 0 && tokens < hardMin,
+  };
+}