fix: /model selection for shared-handle tiers (#859)

src/agent/model.ts

@@ -78,6 +78,55 @@ export function getModelInfo(modelIdentifier: string) {
   return null;
 }
 
+/**
+ * Get model info by handle + llm_config.
+ *
+ * This exists because many model "tiers" (e.g. gpt-5.2-none/low/medium/high)
+ * share the same handle and differ only by updateArgs like reasoning_effort.
+ *
+ * When resuming a session we want `/model` to highlight the tier that actually
+ * matches the agent configuration.
+ */
+export function getModelInfoForLlmConfig(
+  modelHandle: string,
+  llmConfig?: {
+    reasoning_effort?: string | null;
+    enable_reasoner?: boolean | null;
+  } | null,
+) {
+  // Try ID/handle direct resolution first.
+  const direct = getModelInfo(modelHandle);
+
+  // Collect all candidates that share this handle.
+  const candidates = models.filter((m) => m.handle === modelHandle);
+  if (candidates.length === 0) {
+    return direct;
+  }
+
+  const effort = llmConfig?.reasoning_effort ?? null;
+  if (effort) {
+    const match = candidates.find(
+      (m) =>
+        (m.updateArgs as { reasoning_effort?: unknown } | undefined)
+          ?.reasoning_effort === effort,
+    );
+    if (match) return match;
+  }
+
+  // Anthropic-style toggle (best-effort; llm_config may not always include it)
+  if (llmConfig?.enable_reasoner === false) {
+    const match = candidates.find(
+      (m) =>
+        (m.updateArgs as { enable_reasoner?: unknown } | undefined)
+          ?.enable_reasoner === false,
+    );
+    if (match) return match;
+  }
+
+  // Fall back to whatever models.json considers the default for this handle.
+  return direct ?? candidates[0] ?? null;
+}
+
 /**
  * Get updateArgs for a model by ID or handle
  * @param modelIdentifier - Can be either a model ID (e.g., "opus-4.5") or a full handle (e.g., "anthropic/claude-opus-4-5")

src/cli/App.tsx

@@ -2412,7 +2412,14 @@ export default function App({
             agent.llm_config.model_endpoint_type && agent.llm_config.model
               ? `${agent.llm_config.model_endpoint_type}/${agent.llm_config.model}`
               : agent.llm_config.model;
-          const modelInfo = getModelInfo(agentModelHandle || "");
+          const { getModelInfoForLlmConfig } = await import("../agent/model");
+          const modelInfo = getModelInfoForLlmConfig(
+            agentModelHandle || "",
+            agent.llm_config as unknown as {
+              reasoning_effort?: string | null;
+              enable_reasoner?: boolean | null;
+            },
+          );
           if (modelInfo) {
             setCurrentModelId(modelInfo.id);
           } else {
@@ -3303,28 +3310,53 @@ export default function App({
               const client = await getClient();
               const agent = await client.agents.retrieve(agentIdRef.current);
 
-              // Check if the model has changed by comparing llm_config
+              // Keep model UI in sync with the agent configuration.
+              // Note: many tiers share the same handle (e.g. gpt-5.2-none/high), so we
+              // must also treat reasoning settings as model-affecting.
               const currentModel = llmConfigRef.current?.model;
               const currentEndpoint = llmConfigRef.current?.model_endpoint_type;
+              const currentEffort = llmConfigRef.current?.reasoning_effort;
+              const currentEnableReasoner = (
+                llmConfigRef.current as unknown as {
+                  enable_reasoner?: boolean | null;
+                }
+              )?.enable_reasoner;
+
               const agentModel = agent.llm_config.model;
               const agentEndpoint = agent.llm_config.model_endpoint_type;
+              const agentEffort = agent.llm_config.reasoning_effort;
+              const agentEnableReasoner = (
+                agent.llm_config as unknown as {
+                  enable_reasoner?: boolean | null;
+                }
+              )?.enable_reasoner;
 
               if (
                 currentModel !== agentModel ||
-                currentEndpoint !== agentEndpoint
+                currentEndpoint !== agentEndpoint ||
+                currentEffort !== agentEffort ||
+                currentEnableReasoner !== agentEnableReasoner
               ) {
                 // Model has changed - update local state
                 setLlmConfig(agent.llm_config);
 
                 // Derive model ID from llm_config for ModelSelector
                 // Try to find matching model by handle in models.json
-                const { getModelInfo } = await import("../agent/model");
+                const { getModelInfoForLlmConfig } = await import(
+                  "../agent/model"
+                );
                 const agentModelHandle =
                   agent.llm_config.model_endpoint_type && agent.llm_config.model
                     ? `${agent.llm_config.model_endpoint_type}/${agent.llm_config.model}`
                     : agent.llm_config.model;
 
-                const modelInfo = getModelInfo(agentModelHandle || "");
+                const modelInfo = getModelInfoForLlmConfig(
+                  agentModelHandle || "",
+                  agent.llm_config as unknown as {
+                    reasoning_effort?: string | null;
+                    enable_reasoner?: boolean | null;
+                  },
+                );
                 if (modelInfo) {
                   setCurrentModelId(modelInfo.id);
                 } else {

src/tests/model-tier-selection.test.ts

@@ -0,0 +1,22 @@
+import { describe, expect, test } from "bun:test";
+
+import { getModelInfoForLlmConfig } from "../agent/model";
+
+describe("getModelInfoForLlmConfig", () => {
+  test("selects gpt-5.2 tier by reasoning_effort", () => {
+    const handle = "openai/gpt-5.2";
+
+    const high = getModelInfoForLlmConfig(handle, { reasoning_effort: "high" });
+    expect(high?.id).toBe("gpt-5.2-high");
+
+    const none = getModelInfoForLlmConfig(handle, { reasoning_effort: "none" });
+    expect(none?.id).toBe("gpt-5.2-none");
+  });
+
+  test("falls back to first handle match when effort missing", () => {
+    const handle = "openai/gpt-5.2";
+    const info = getModelInfoForLlmConfig(handle, null);
+    // models.json order currently lists gpt-5.2-none first.
+    expect(info?.id).toBe("gpt-5.2-none");
+  });
+});