✨ add custom HTTP headers support via OCO_API_CUSTOM_HEADERS

Add OCO_API_CUSTOM_HEADERS variable to README, config enum,
and env parsing to allow JSON string of custom headers.
Validate that custom headers are valid JSON in config validator.
Extend AiEngineConfig with customHeaders and pass headers to
OllamaEngine and OpenAiEngine clients when creating requests.
Parse custom headers in utils/engine and warn on invalid format.
Add unit tests to ensure OCO_API_CUSTOM_HEADERS is handled
correctly and merged from env over global config.

This enables users to send additional headers such as
Authorization or tracing headers with LLM API calls.

src/commands/config.ts

@@ -25,6 +25,7 @@ export enum CONFIG_KEYS {
   OCO_ONE_LINE_COMMIT = 'OCO_ONE_LINE_COMMIT',
   OCO_TEST_MOCK_TYPE = 'OCO_TEST_MOCK_TYPE',
   OCO_API_URL = 'OCO_API_URL',
+  OCO_API_CUSTOM_HEADERS = 'OCO_API_CUSTOM_HEADERS',
   OCO_OMIT_SCOPE = 'OCO_OMIT_SCOPE',
   OCO_GITPUSH = 'OCO_GITPUSH' // todo: deprecate
 }
@@ -204,6 +205,22 @@ export const configValidators = {
     return value;
   },
 
+  [CONFIG_KEYS.OCO_API_CUSTOM_HEADERS](value) {
+    try {
+      // Custom headers must be a valid JSON string
+      if (typeof value === 'string') {
+        JSON.parse(value);
+      }
+      return value;
+    } catch (error) {
+      validateConfig(
+        CONFIG_KEYS.OCO_API_CUSTOM_HEADERS,
+        false,
+        'Must be a valid JSON string of headers'
+      );
+    }
+  },
+
   [CONFIG_KEYS.OCO_TOKENS_MAX_INPUT](value: any) {
     value = parseInt(value);
     validateConfig(
@@ -380,6 +397,7 @@ export type ConfigType = {
   [CONFIG_KEYS.OCO_TOKENS_MAX_INPUT]: number;
   [CONFIG_KEYS.OCO_TOKENS_MAX_OUTPUT]: number;
   [CONFIG_KEYS.OCO_API_URL]?: string;
+  [CONFIG_KEYS.OCO_API_CUSTOM_HEADERS]?: string;
   [CONFIG_KEYS.OCO_DESCRIPTION]: boolean;
   [CONFIG_KEYS.OCO_EMOJI]: boolean;
   [CONFIG_KEYS.OCO_WHY]: boolean;
@@ -462,6 +480,7 @@ const getEnvConfig = (envPath: string) => {
     OCO_MODEL: process.env.OCO_MODEL,
     OCO_API_URL: process.env.OCO_API_URL,
     OCO_API_KEY: process.env.OCO_API_KEY,
+    OCO_API_CUSTOM_HEADERS: process.env.OCO_API_CUSTOM_HEADERS,
     OCO_AI_PROVIDER: process.env.OCO_AI_PROVIDER as OCO_AI_PROVIDER_ENUM,
 
     OCO_TOKENS_MAX_INPUT: parseConfigVarValue(process.env.OCO_TOKENS_MAX_INPUT),