fix: custom OPENAI_BASE_URL always wins over Codex model alias detection (#222)

* feat: add --provider CLI flag for multi-provider support

Adds a --provider flag that maps friendly provider names to the
environment variables the codebase uses for provider detection.
No more manual env-var configuration — users can now simply run:

  openclaude --provider openai --model gpt-4o
  openclaude --provider gemini --model gemini-2.0-flash
  openclaude --provider ollama --model llama3.2
  openclaude --provider bedrock
  openclaude --provider vertex

Implementation details:
- providerFlag.ts: core logic — maps provider names to env vars,
  uses ??= so explicit env vars always win over the flag defaults
- providerFlag.test.ts: 18 tests covering all 7 providers,
  error messages, model passthrough, and env-var precedence
- cli.tsx: early fast-path (mirrors --bare pattern) — sets env
  vars before Commander option-building and module constants run
- main.tsx: adds --provider to Commander option chain for --help

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix: custom OPENAI_BASE_URL always wins over Codex model alias detection

When OPENAI_MODEL=gpt-5.4 (or gpt-5.4-mini) and a custom OPENAI_BASE_URL
is set (Azure, OpenRouter, etc), the transport was incorrectly forced to
codex_responses because gpt-5.4 is in CODEX_ALIAS_MODELS. This caused
requests to be sent with Codex auth instead of the user's API key,
resulting in 401 Unauthorized errors.

Fix: only use codex_responses when the base URL is explicitly the Codex
endpoint, OR when no custom base URL is set and the model is a Codex
alias. An explicit OPENAI_BASE_URL always takes priority over model-name
based Codex detection.

Verified locally: gpt-5.4 via OpenRouter now correctly shows
Provider=OpenRouter, Endpoint=https://openrouter.ai/api/v1 instead of
routing to chatgpt.com/backend-api/codex.

Fixes #200, #203

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

src/utils/providerFlag.ts

@@ -0,0 +1,107 @@
+/**
+ * --provider CLI flag support.
+ *
+ * Maps the user-friendly provider name to the environment variables
+ * that the rest of the codebase uses for provider detection.
+ *
+ * Usage:
+ *   openclaude --provider openai --model gpt-4o
+ *   openclaude --provider gemini --model gemini-2.0-flash
+ *   openclaude --provider ollama --model llama3.2
+ *   openclaude --provider anthropic   (default, no-op)
+ */
+
+export const VALID_PROVIDERS = [
+  'anthropic',
+  'openai',
+  'gemini',
+  'github',
+  'bedrock',
+  'vertex',
+  'ollama',
+] as const
+
+export type ProviderFlagName = (typeof VALID_PROVIDERS)[number]
+
+/**
+ * Extract the value of --provider from argv.
+ * Returns null if the flag is absent or has no value.
+ */
+export function parseProviderFlag(args: string[]): string | null {
+  const idx = args.indexOf('--provider')
+  if (idx === -1) return null
+  const value = args[idx + 1]
+  if (!value || value.startsWith('--')) return null
+  return value
+}
+
+/**
+ * Extract the value of --model from argv.
+ * Returns null if absent.
+ */
+function parseModelFlag(args: string[]): string | null {
+  const idx = args.indexOf('--model')
+  if (idx === -1) return null
+  const value = args[idx + 1]
+  if (!value || value.startsWith('--')) return null
+  return value
+}
+
+/**
+ * Apply a provider name to process.env.
+ * Sets the required CLAUDE_CODE_USE_* flag and any provider-specific
+ * defaults (Ollama base URL, model routing). Does NOT overwrite values
+ * that are already set — explicit env vars always win.
+ *
+ * Returns { error } if the provider name is not recognized.
+ */
+export function applyProviderFlag(
+  provider: string,
+  args: string[],
+): { error?: string } {
+  if (!(VALID_PROVIDERS as readonly string[]).includes(provider)) {
+    return {
+      error: `Unknown provider "${provider}". Valid providers: ${VALID_PROVIDERS.join(', ')}`,
+    }
+  }
+
+  const model = parseModelFlag(args)
+
+  switch (provider as ProviderFlagName) {
+    case 'anthropic':
+      // Default — no env vars needed
+      break
+
+    case 'openai':
+      process.env.CLAUDE_CODE_USE_OPENAI = '1'
+      if (model) process.env.OPENAI_MODEL ??= model
+      break
+
+    case 'gemini':
+      process.env.CLAUDE_CODE_USE_GEMINI = '1'
+      if (model) process.env.GEMINI_MODEL ??= model
+      break
+
+    case 'github':
+      process.env.CLAUDE_CODE_USE_GITHUB = '1'
+      if (model) process.env.OPENAI_MODEL ??= model
+      break
+
+    case 'bedrock':
+      process.env.CLAUDE_CODE_USE_BEDROCK = '1'
+      break
+
+    case 'vertex':
+      process.env.CLAUDE_CODE_USE_VERTEX = '1'
+      break
+
+    case 'ollama':
+      process.env.CLAUDE_CODE_USE_OPENAI = '1'
+      process.env.OPENAI_BASE_URL ??= 'http://localhost:11434/v1'
+      process.env.OPENAI_API_KEY ??= 'ollama'
+      if (model) process.env.OPENAI_MODEL ??= model
+      break
+  }
+
+  return {}
+}