fix(models): match model names on version boundary, not bare prefix

A bare startsWith let an unlisted future minor collapse into the base entry
(gpt-5.6 -> "GPT-5"), the same mis-bucketing class as #420 but for non-Claude
families. Require an exact match or a key-plus-dash boundary in both
getShortModelName and the Codex provider so new versions fall through to their
raw id instead of a wrong name and pricing tier.

src/models.ts

@@ -478,7 +478,10 @@ export function getShortModelName(model: string): string {
   const claude = deriveClaudeShortName(canonical)
   if (claude) return claude
   for (const [key, name] of SORTED_SHORT_NAMES) {
-    if (canonical.startsWith(key)) return name
+    // Match on a version boundary, not a bare prefix: an unlisted future minor
+    // (e.g. gpt-5.6) must NOT collapse into the base "gpt-5" entry — it should
+    // fall through to its raw id rather than show a wrong name/tier.
+    if (canonical === key || canonical.startsWith(key + '-')) return name
   }
   return canonical
 }

src/providers/codex.ts

@@ -23,6 +23,10 @@ const modelDisplayNames: Record<string, string> = {
   'gpt-4o': 'GPT-4o',
 }
 
+// Longest-first + version-boundary match so an unlisted future minor (gpt-5.6)
+// falls through to its raw id instead of collapsing into the base "GPT-5" entry.
+const modelDisplayEntries = Object.entries(modelDisplayNames).sort((a, b) => b[0].length - a[0].length)
+
 const toolNameMap: Record<string, string> = {
   exec_command: 'Bash',
   read_file: 'Read',
@@ -589,8 +593,8 @@ export function createCodexProvider(codexDir?: string): Provider {
     displayName: 'Codex',
 
     modelDisplayName(model: string): string {
-      for (const [key, name] of Object.entries(modelDisplayNames)) {
-        if (model.startsWith(key)) return name
+      for (const [key, name] of modelDisplayEntries) {
+        if (model === key || model.startsWith(key + '-')) return name
       }
       return model
     },