fix(ai): remove global process.env.ANTHROPIC_API_KEY deletion (#164)

* fix(ai): remove global process.env.ANTHROPIC_API_KEY deletion

The code was deleting process.env.ANTHROPIC_API_KEY to prevent the SDK
from using it when OAuth tokens were provided. However, this was a global
mutation that affected the entire Node.js process, causing the API key to
be unavailable after the first prompt.

The Anthropic SDK constructor already handles credential selection via
parameters (apiKey: null, authToken: token for OAuth vs apiKey: key for
regular keys), so the environment variable deletion was unnecessary.

* Update CHANGELOG.md for API key fix

packages/ai/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed bug where `ANTHROPIC_API_KEY` environment variable was deleted globally after first OAuth token usage, causing subsequent prompts to fail
+
 ## [0.17.0] - 2025-12-09
 
 ### Added

packages/ai/src/providers/anthropic.ts

@@ -289,11 +289,6 @@ function createClient(
 			...(model.headers || {}),
 		};
 
-		// Clear the env var if we're in Node.js to prevent SDK from using it
-		if (typeof process !== "undefined" && process.env) {
-			delete process.env.ANTHROPIC_API_KEY;
-		}
-
 		const client = new Anthropic({
 			apiKey: null,
 			authToken: apiKey,