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/tool-call-without-result.test.ts

@@ -3,6 +3,7 @@ import { describe, expect, it } from "vitest";
 import { getModel } from "../src/models.js";
 import { complete } from "../src/stream.js";
 import type { Api, Context, Model, OptionsForApi, Tool } 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)
@@ -170,6 +171,14 @@ describe("Tool Call Without Result Tests", () => {
 		});
 	});
 
+	describe.skipIf(!hasBedrockCredentials())("Amazon Bedrock Provider", () => {
+		const model = getModel("amazon-bedrock", "global.anthropic.claude-sonnet-4-5-20250929-v1:0");
+
+		it("should filter out tool calls without corresponding tool results", { retry: 3, timeout: 30000 }, async () => {
+			await testToolCallWithoutResult(model);
+		});
+	});
+
 	// =========================================================================
 	// OAuth-based providers (credentials from ~/.pi/agent/oauth.json)
 	// =========================================================================