Validate context window against model capabilities in resolveApiModelId

cursoragent · cursoragent · commit bb8241aabeb9 · 2026-03-26T17:48:35.000Z
resolveApiModelId now accepts optional ModelCapabilities and uses
resolveContextWindow to validate context window values before appending
the [1m] suffix. This prevents invalid model IDs (e.g. claude-haiku-4-5[1m])
when a stale contextWindow option carries over from a model that supports
1M context to one that doesn't.

All three callers (ClaudeAdapter session start, ClaudeAdapter sendTurn,
ClaudeTextGeneration) now pass capabilities to resolveApiModelId.
diff --git a/apps/server/src/git/Layers/ClaudeTextGeneration.ts b/apps/server/src/git/Layers/ClaudeTextGeneration.ts
@@ -27,7 +27,10 @@ import {
   sanitizePrTitle,
   toJsonSchemaObject,
 } from "../Utils.ts";
-import { normalizeClaudeModelOptions } from "../../provider/Layers/ClaudeProvider.ts";
+import {
+  getClaudeModelCapabilities,
+  normalizeClaudeModelOptions,
+} from "../../provider/Layers/ClaudeProvider.ts";
 import { ServerSettingsService } from "../../serverSettings.ts";
 
 const CLAUDE_TIMEOUT_MS = 180_000;
@@ -104,7 +107,7 @@ const makeClaudeTextGeneration = Effect.gen(function* () {
             "--json-schema",
             jsonSchemaStr,
             "--model",
-            resolveApiModelId(modelSelection),
+            resolveApiModelId(modelSelection, getClaudeModelCapabilities(modelSelection.model)),
             ...(normalizedOptions?.effort ? ["--effort", normalizedOptions.effort] : []),
             ...(Object.keys(settings).length > 0 ? ["--settings", JSON.stringify(settings)] : []),
             "--dangerously-skip-permissions",
diff --git a/apps/server/src/provider/Layers/ClaudeAdapter.ts b/apps/server/src/provider/Layers/ClaudeAdapter.ts
@@ -2732,9 +2732,9 @@ function makeClaudeAdapter(options?: ClaudeAdapterLiveOptions) {
         const claudeBinaryPath = claudeSettings.binaryPath;
         const modelSelection =
           input.modelSelection?.provider === "claudeAgent" ? input.modelSelection : undefined;
-        const apiModelId = modelSelection ? resolveApiModelId(modelSelection) : undefined;
-        const requestedEffort = trimOrNull(modelSelection?.options?.effort ?? null);
         const caps = getClaudeModelCapabilities(modelSelection?.model);
+        const apiModelId = modelSelection ? resolveApiModelId(modelSelection, caps) : undefined;
+        const requestedEffort = trimOrNull(modelSelection?.options?.effort ?? null);
         const effort =
           requestedEffort && hasEffortLevel(caps, requestedEffort) ? requestedEffort : null;
         const fastMode = modelSelection?.options?.fastMode === true && caps.supportsFastMode;
@@ -2899,7 +2899,8 @@ function makeClaudeAdapter(options?: ClaudeAdapterLiveOptions) {
         }
 
         if (modelSelection?.model) {
-          const apiModelId = resolveApiModelId(modelSelection);
+          const caps = getClaudeModelCapabilities(modelSelection.model);
+          const apiModelId = resolveApiModelId(modelSelection, caps);
           yield* Effect.tryPromise({
             try: () => context.query.setModel(apiModelId),
             catch: (cause) => toRequestError(input.threadId, "turn/setModel", cause),
diff --git a/packages/shared/src/model.test.ts b/packages/shared/src/model.test.ts
@@ -179,6 +179,39 @@ describe("resolveApiModelId", () => {
     ).toBe("claude-opus-4-6");
   });
 
+  it("strips unsupported context window when capabilities are provided", () => {
+    const haikuCaps: ModelCapabilities = {
+      reasoningEffortLevels: [],
+      supportsFastMode: false,
+      supportsThinkingToggle: true,
+      contextWindowOptions: [],
+      promptInjectedEffortLevels: [],
+    };
+    expect(
+      resolveApiModelId(
+        {
+          provider: "claudeAgent",
+          model: "claude-haiku-4-5",
+          options: { contextWindow: "1m" },
+        },
+        haikuCaps,
+      ),
+    ).toBe("claude-haiku-4-5");
+  });
+
+  it("appends suffix when capabilities confirm support", () => {
+    expect(
+      resolveApiModelId(
+        {
+          provider: "claudeAgent",
+          model: "claude-opus-4-6",
+          options: { contextWindow: "1m" },
+        },
+        claudeCaps,
+      ),
+    ).toBe("claude-opus-4-6[1m]");
+  });
+
   it("returns the model as-is for Codex selections", () => {
     expect(resolveApiModelId({ provider: "codex", model: "gpt-5.4" })).toBe("gpt-5.4");
   });
diff --git a/packages/shared/src/model.ts b/packages/shared/src/model.ts
@@ -130,10 +130,14 @@ export function trimOrNull<T extends string>(value: T | null | undefined): T | n
   return trimmed || null;
 }
 
-export function resolveApiModelId(modelSelection: ModelSelection): string {
+export function resolveApiModelId(
+  modelSelection: ModelSelection,
+  capabilities?: ModelCapabilities,
+): string {
   switch (modelSelection.provider) {
     case "claudeAgent": {
-      const contextWindow = modelSelection.options?.contextWindow;
+      const raw = modelSelection.options?.contextWindow;
+      const contextWindow = capabilities ? resolveContextWindow(capabilities, raw) : raw;
       switch (contextWindow) {
         case "1m":
           return `${modelSelection.model}[1m]`;
