fix(cliproxy): preserve explicit Claude long-context intent

- centralize Anthropic model-key [1m] handling in shared helpers

- keep dashboard preset and editor writes consistent across all Claude tiers

- add explicit api create and help guidance for --1m/--no-1m

Refs #789

src/shared/extended-context-utils.ts

@@ -4,6 +4,16 @@
 
 /** Extended context suffix recognized by Claude Code. */
 export const EXTENDED_CONTEXT_SUFFIX = '[1m]';
+export const ANTHROPIC_MODEL_ENV_KEYS = [
+  'ANTHROPIC_MODEL',
+  'ANTHROPIC_DEFAULT_OPUS_MODEL',
+  'ANTHROPIC_DEFAULT_SONNET_MODEL',
+  'ANTHROPIC_DEFAULT_HAIKU_MODEL',
+] as const;
+
+export type AnthropicModelEnvKey = (typeof ANTHROPIC_MODEL_ENV_KEYS)[number];
+
+const ANTHROPIC_MODEL_ENV_KEY_SET = new Set<string>(ANTHROPIC_MODEL_ENV_KEYS);
 
 /** Check if model is a native Gemini model (auto-enabled behavior). */
 export function isNativeGeminiModel(modelId: string): boolean {
@@ -27,3 +37,64 @@ export function stripExtendedContextSuffix(model: string): string {
   if (!model) return model;
   return hasExtendedContextSuffix(model) ? model.slice(0, -EXTENDED_CONTEXT_SUFFIX.length) : model;
 }
+
+/** True when key belongs to Anthropic model mapping state. */
+export function isAnthropicModelEnvKey(key: string): key is AnthropicModelEnvKey {
+  return ANTHROPIC_MODEL_ENV_KEY_SET.has(key);
+}
+
+/** Strip transient config suffixes so model IDs can be checked against catalogs. */
+export function stripModelConfigurationSuffixes(modelId: string): string {
+  return stripExtendedContextSuffix(modelId.trim()).replace(/\([^)]+\)$/, '');
+}
+
+/** Whether any saved Anthropic model mapping explicitly requests [1m]. */
+export function hasAnthropicExtendedContextEnabled(
+  env: Partial<Record<string, string | undefined>>
+): boolean {
+  return ANTHROPIC_MODEL_ENV_KEYS.some((key) => {
+    const value = env[key];
+    return typeof value === 'string' && hasExtendedContextSuffix(value);
+  });
+}
+
+/** Apply or strip [1m] across Anthropic model mappings while honoring compatibility. */
+export function applyExtendedContextPreferenceToAnthropicModels<
+  T extends Record<string, string | undefined>,
+>(
+  env: T,
+  enabled: boolean,
+  options: {
+    supportsExtendedContext?: (modelId: string, key: AnthropicModelEnvKey) => boolean;
+  } = {}
+): T {
+  const nextEnv: Record<string, string | undefined> = { ...env };
+
+  for (const key of ANTHROPIC_MODEL_ENV_KEYS) {
+    const value = nextEnv[key];
+    if (typeof value !== 'string' || value.trim().length === 0) {
+      continue;
+    }
+
+    const modelId = stripModelConfigurationSuffixes(value);
+    const supported = options.supportsExtendedContext?.(modelId, key) ?? true;
+    nextEnv[key] =
+      enabled && supported ? applyExtendedContextSuffix(value) : stripExtendedContextSuffix(value);
+  }
+
+  return nextEnv as T;
+}
+
+/** Detect Claude model identifiers, regardless of transient [1m]/(thinking) suffixes. */
+export function isClaudeModelId(modelId: string): boolean {
+  return stripModelConfigurationSuffixes(modelId).toLowerCase().startsWith('claude-');
+}
+
+/**
+ * Conservative Claude long-context support heuristic for generic API profile flows.
+ * Haiku stays plain; Opus/Sonnet default to opt-in [1m].
+ */
+export function likelySupportsClaudeExtendedContext(modelId: string): boolean {
+  const baseModel = stripModelConfigurationSuffixes(modelId).toLowerCase();
+  return baseModel.startsWith('claude-') && !baseModel.startsWith('claude-haiku-');
+}