fix: Normalize 'minimal' to 'low' for gpt-5-codex

Codex CLI does not provide a 'minimal' reasoning effort preset for gpt-5-codex
(only low/medium/high - see model_presets.rs:20-40). When users configure
reasoningEffort: 'minimal' for gpt-5-codex, normalize it to 'low' to prevent
unsupported configuration.

- Add validation in getReasoningConfig() to detect and normalize
- Add test case to verify normalization works correctly
- Prevents potential errors when backend receives unsupported effort level

Addresses feedback from GPT-5 Codex code review.

lib/request-transformer.mjs

@@ -48,13 +48,23 @@ export function getModelConfig(modelName, userConfig = {}) {
 export function getReasoningConfig(originalModel, userConfig = {}) {
 	const isLightweight =
 		originalModel?.includes("nano") || originalModel?.includes("mini");
+	const isCodex = originalModel?.includes("codex");
 
 	// Default based on model type (Codex CLI defaults)
 	const defaultEffort = isLightweight ? "minimal" : "medium";
 
+	// Get user-requested effort
+	let effort = userConfig.reasoningEffort || defaultEffort;
+
+	// Normalize "minimal" to "low" for gpt-5-codex
+	// Codex CLI does not provide a "minimal" preset for gpt-5-codex
+	// (only low/medium/high - see model_presets.rs:20-40)
+	if (isCodex && effort === "minimal") {
+		effort = "low";
+	}
+
 	return {
-		// User config takes precedence, otherwise use defaults
-		effort: userConfig.reasoningEffort || defaultEffort,
+		effort,
 		summary: userConfig.reasoningSummary || "auto", // Changed from "detailed" to match Codex CLI
 	};
 }

test-config.mjs

@@ -87,9 +87,22 @@ console.log("Test 5: Lightweight model (gpt-5-nano)");
 const nanoReasoning = getReasoningConfig("gpt-5-nano", {});
 console.log("Nano reasoning:", nanoReasoning);
 console.log("Expected: effort='minimal' (lightweight default), summary='auto'");
-console.log("✓ Pass:", 
+console.log("✓ Pass:",
 	nanoReasoning.effort === "minimal" &&
 	nanoReasoning.summary === "auto"
 );
+console.log("\n");
+
+// Test 6: Normalize "minimal" to "low" for gpt-5-codex
+console.log("Test 6: Normalize minimal→low for gpt-5-codex (Codex CLI doesn't support minimal)");
+const codexMinimalConfig = { reasoningEffort: "minimal" };
+const codexMinimalReasoning = getReasoningConfig("gpt-5-codex", codexMinimalConfig);
+console.log("Config:", codexMinimalConfig);
+console.log("Reasoning result:", codexMinimalReasoning);
+console.log("Expected: effort='low' (normalized from minimal), summary='auto'");
+console.log("✓ Pass:",
+	codexMinimalReasoning.effort === "low" &&
+	codexMinimalReasoning.summary === "auto"
+);
 
 console.log("\n=== All Tests Complete ===");