fix: clean up Codex thinking level handling

- Remove per-thinking-level model variants (gpt-5.2-codex-high, etc.)
- Remove thinkingLevels from Model type
- Provider clamps reasoning effort internally
- Omit reasoning field when thinking is off

fixes #472

packages/coding-agent/src/core/model-resolver.ts

@@ -102,18 +102,6 @@ export interface ParsedModelResult {
 	warning: string | undefined;
 }
 
-const THINKING_SUFFIXES = ["-none", "-minimal", "-low", "-medium", "-high", "-xhigh"];
-
-function stripThinkingSuffix(pattern: string): string {
-	const normalized = pattern.toLowerCase();
-	for (const suffix of THINKING_SUFFIXES) {
-		if (normalized.endsWith(suffix)) {
-			return pattern.slice(0, pattern.length - suffix.length);
-		}
-	}
-	return pattern;
-}
-
 /**
  * Parse a pattern to extract model and thinking level.
  * Handles models with colons in their IDs (e.g., OpenRouter's :exacto suffix).
@@ -134,14 +122,6 @@ export function parseModelPattern(pattern: string, availableModels: Model<Api>[]
 		return { model: exactMatch, thinkingLevel: "off", warning: undefined };
 	}
 
-	const normalizedPattern = stripThinkingSuffix(pattern);
-	if (normalizedPattern !== pattern) {
-		const normalizedMatch = tryMatchModel(normalizedPattern, availableModels);
-		if (normalizedMatch) {
-			return { model: normalizedMatch, thinkingLevel: "off", warning: undefined };
-		}
-	}
-
 	// No match - try splitting on last colon if present
 	const lastColonIndex = pattern.lastIndexOf(":");
 	if (lastColonIndex === -1) {