docs: add SDK defaults divergence notes to README

Document the actual retry, backoff, jitter, and timeout defaults of the Go, TypeScript, and Python SDKs with file and symbol references, so the drift between them is visible. No code defaults were changed.

Author: Patel230

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- **"Defaults & divergences across SDKs" README section** documenting how
+  retry, backoff, jitter, and timeout defaults differ between the Go,
+  TypeScript, and Python SDKs.
+
 ## [0.2.0] — 2026-07-14
 
 ### Changed

README.md

@@ -115,6 +115,23 @@ with HawkClient() as client:
             print(f"Tool: {call.name}({call.arguments})")
 ```
 
+## Defaults & divergences across SDKs
+
+The three Hawk SDKs (Go, TypeScript, Python) share wire behavior but have
+drifted in transport defaults. Actual current values:
+
+| Default | Python (this SDK) | Go | TypeScript |
+| --- | --- | --- | --- |
+| Retries | **On** — `retry_config or DEFAULT_RETRY_CONFIG` (`src/hawk/client.py`, both sync and async clients) | **Off** — opt in with `WithRetry(DefaultRetryConfig())` (`client.go`) | **Off** — opt in with `{ retry: defaultRetryConfig() }` (`src/client.ts`) |
+| Initial backoff | 0.5s (`src/hawk/retry.py`, `RetryConfig`) | 1s (`retry.go`, `DefaultRetryConfig`) | 1s (`src/retry.ts`, `defaultRetryConfig`) |
+| Backoff jitter | Equal + jitter: `backoff + rand(0, backoff/2)` (`src/hawk/retry.py`, `_compute_backoff`) | Full jitter: `rand(0, backoff)` (`retry.go`, `backoffDuration`) | Full jitter: `rand(0, backoff)` (`src/retry.ts`, `backoffDurationMs`) |
+| Request timeout | httpx timeout, 30s (`src/hawk/client.py`, `DEFAULT_TIMEOUT`) | `ResponseHeaderTimeout: 5s`, headers only (`client.go`) | Whole-request deadline, 30s, includes retries (`src/client.ts`, `timeoutMs`) |
+
+Max retries (3), max backoff (30s), retryable statuses (429/500/502/503/504),
+and the non-idempotent rule (only 429 is retried for POST `/v1/chat`) are
+identical in all three SDKs. This table documents current behavior; it is not
+a compatibility contract between the SDKs.
+
 ## API Reference
 
 ### HawkClient / AsyncHawkClient