fix(context-window): prioritize config over model for context window resolution

resolveContextWindowInfo now uses config > model > default priority so
explicit --context-window flag overrides model defaults. Also adds
--context-window CLI option to the run command.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/cli/src/commands/run.ts

@@ -28,6 +28,7 @@ type RunOptions = {
   runLog?: boolean;
   toolsAllow?: string[];
   toolsDeny?: string[];
+  contextWindow?: number;
   help?: boolean;
 };
 
@@ -49,6 +50,7 @@ ${cyan("Options:")}
   ${yellow("--session")} ID        Session ID for persistence
   ${yellow("--debug")}             Enable debug logging
   ${yellow("--run-log")}           Enable structured run logging (run-log.jsonl)
+  ${yellow("--context-window")} N  Override context window token count
   ${yellow("--help")}, -h          Show this help
 
 ${cyan("Tools Configuration:")}
@@ -141,6 +143,11 @@ function parseArgs(argv: string[]): { opts: RunOptions; prompt: string } {
       opts.toolsDeny = value?.split(",").map((s) => s.trim()) ?? [];
       continue;
     }
+    if (arg === "--context-window") {
+      const value = args.shift();
+      opts.contextWindow = value ? parseInt(value, 10) : undefined;
+      continue;
+    }
     if (arg === "--") {
       promptParts.push(...args);
       break;
@@ -213,6 +220,7 @@ export async function runCommand(args: string[]): Promise<void> {
       debug: opts.debug,
       enableRunLog,
       tools: toolsConfig,
+      contextWindowTokens: opts.contextWindow,
     });
 
     const sessionDir = join(DATA_DIR, "sessions", agent.sessionId);

packages/core/src/agent/context-window/guard.test.ts

@@ -24,15 +24,15 @@ describe("guard", () => {
   });
 
   describe("resolveContextWindowInfo", () => {
-    it("should prioritize model context window", () => {
+    it("should prioritize config over model (explicit override wins)", () => {
       const result = resolveContextWindowInfo({
         modelContextWindow: 100_000,
         configContextTokens: 50_000,
         defaultTokens: 200_000,
       });
 
-      expect(result.tokens).toBe(100_000);
-      expect(result.source).toBe("model");
+      expect(result.tokens).toBe(50_000);
+      expect(result.source).toBe("config");
     });
 
     it("should fall back to config when model is undefined", () => {
@@ -105,13 +105,23 @@ describe("guard", () => {
       expect(result.source).toBe("config");
     });
 
-    it("should floor decimal values", () => {
+    it("should floor decimal values from model", () => {
       const result = resolveContextWindowInfo({
         modelContextWindow: 100_000.9,
       });
 
       expect(result.tokens).toBe(100_000);
     });
+
+    it("should use model when config is not provided", () => {
+      const result = resolveContextWindowInfo({
+        modelContextWindow: 100_000,
+        defaultTokens: 200_000,
+      });
+
+      expect(result.tokens).toBe(100_000);
+      expect(result.source).toBe("model");
+    });
   });
 
   describe("evaluateContextWindowGuard", () => {

packages/core/src/agent/context-window/guard.ts

@@ -27,28 +27,29 @@ function normalizePositiveInt(value: unknown): number | null {
 /**
  * Resolve context window information
  *
- * Priority: model > config > default
+ * Priority: config > model > default
+ * (Explicit config override always wins — allows capping context for testing/cost control)
  */
 export function resolveContextWindowInfo(params: {
   /** Model's contextWindow property */
   modelContextWindow?: number | undefined;
-  /** Context tokens specified in config */
+  /** Context tokens specified in config (explicit override, highest priority) */
   configContextTokens?: number | undefined;
   /** Default value */
   defaultTokens?: number | undefined;
 }): ContextWindowInfo {
-  // 1. Try getting from model
-  const fromModel = normalizePositiveInt(params.modelContextWindow);
-  if (fromModel) {
-    return { tokens: fromModel, source: "model" };
-  }
-
-  // 2. Try getting from config
+  // 1. Explicit config override always wins
   const fromConfig = normalizePositiveInt(params.configContextTokens);
   if (fromConfig) {
     return { tokens: fromConfig, source: "config" };
   }
 
+  // 2. Try getting from model
+  const fromModel = normalizePositiveInt(params.modelContextWindow);
+  if (fromModel) {
+    return { tokens: fromModel, source: "model" };
+  }
+
   // 3. Use default value
   return {
     tokens: Math.floor(params.defaultTokens ?? DEFAULT_CONTEXT_TOKENS),