feat(security): harden the HTTP transport against SSRF and unsafe redirects

CHANGELOG.md

@@ -14,6 +14,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   default), and return a clear `DevkitError::RateLimited` when the cap would be
   exceeded.
 
+### Security
+
+- `devkit-rpc`: harden the HTTP transport against SSRF. Endpoint validation now
+  refuses private, link-local, and other non-public address literals, DNS
+  answers are filtered before connection, and only re-validated same-host
+  redirects are followed. The final URL is checked again before reading the
+  response. See `docs/NETWORK_SECURITY.md`.
+
 ## [Unreleased]
 
 ### Added

SECURITY.md

@@ -44,7 +44,10 @@ Out of scope:
 
 ## Security model
 
-- No network access is performed by default. No network features exist yet.
+- No network access is performed by default. Network access is explicit, and
+  `HttpTransport` enforces a fail-closed SSRF policy: non-public addresses are
+  refused, DNS answers are filtered, and only same-host redirects are followed.
+  See [docs/NETWORK_SECURITY.md](docs/NETWORK_SECURITY.md).
 - Decoding is bounded; malformed input is handled with structured errors, not
   panics.
 - No secrets are read, logged, or committed.