feat(ai): Add Amazon Bedrock provider (#494)

Adds support for Amazon Bedrock with Claude models including:
- Full streaming support via Converse API
- Reasoning/thinking support for Claude models
- Cross-region inference model ID handling
- Multiple AWS credential sources (profile, IAM keys, API keys)
- Image support in messages and tool results
- Unicode surrogate sanitization

Also adds 'Adding a New Provider' documentation to AGENTS.md and README.

Co-authored-by: nickchan2 <nickchan2@users.noreply.github.com>

packages/ai/test/total-tokens.test.ts

@@ -16,6 +16,7 @@ import { describe, expect, it } from "vitest";
 import { getModel } from "../src/models.js";
 import { complete } from "../src/stream.js";
 import type { Api, Context, Model, OptionsForApi, Usage } from "../src/types.js";
+import { hasBedrockCredentials } from "./bedrock-utils.js";
 import { resolveApiKey } from "./oauth.js";
 
 // Resolve OAuth tokens at module level (async, runs before tests)
@@ -535,6 +536,25 @@ describe("totalTokens field", () => {
 		);
 	});
 
+	describe.skipIf(!hasBedrockCredentials())("Amazon Bedrock", () => {
+		it(
+			"claude-sonnet-4-5 - should return totalTokens equal to sum of components",
+			{ retry: 3, timeout: 60000 },
+			async () => {
+				const llm = getModel("amazon-bedrock", "global.anthropic.claude-sonnet-4-5-20250929-v1:0");
+
+				console.log(`\nAmazon Bedrock / ${llm.id}:`);
+				const { first, second } = await testTotalTokensWithCache(llm);
+
+				logUsage("First request", first);
+				logUsage("Second request", second);
+
+				assertTotalTokensEqualsComponents(first);
+				assertTotalTokensEqualsComponents(second);
+			},
+		);
+	});
+
 	// =========================================================================
 	// OpenAI Codex (OAuth)
 	// =========================================================================