docs: add protovalidate to homepage, architecture, config, and interceptors howto

Index.md

@@ -38,6 +38,7 @@ A Kubernetes-native Go microservice framework for building production-grade gRPC
 | **gRPC Reflection** | Server reflection enabled by default — works with [grpcurl], [grpcui], and Postman |
 | **HTTP Compression** | Automatic gzip and [zstd] compression for all HTTP gateway responses (content-negotiated via `Accept-Encoding`) |
 | **Container-aware Runtime** | Auto-tunes GOMAXPROCS to match container CPU limits via [automaxprocs] |
+| **Request Validation** | [Protovalidate] annotations enforced automatically — define validation rules in your proto, get `InvalidArgument` errors for free |
 | **CI/CD Pipelines** | Ready-to-use [GitHub Actions] and [GitLab CI] workflows for build, test, lint, coverage, and benchmarks |
 
 ## Quick Start
@@ -100,7 +101,7 @@ Run `buf generate` — it creates typed Go interfaces from your proto definition
                     │  │ Gateway  │──► │                     │  │
                     │  │ (grpc-  │    │  ► Response Time    │  │
    gRPC Request ──► │  │ gateway)│    │  ► Trace ID         │  │
-                    │  └─────────┘    │  ► OpenTelemetry     │  │
+                    │  └─────────┘    │  ► Proto Validate   │  │
                     │       │         │  ► Prometheus        │  │
                     │       ▼         │  ► Error Notify      │  │
                     │  ┌─────────┐    │  ► Panic Recovery    │  │
@@ -188,3 +189,4 @@ ColdBrew composes proven Go libraries — not replacements:
 [GitLab CI]: https://docs.gitlab.com/ci/
 [slog]: https://pkg.go.dev/log/slog
 [zstd]: https://datatracker.ietf.org/doc/html/rfc8878
+[Protovalidate]: https://github.com/bufbuild/protovalidate

architecture.md

@@ -154,10 +154,11 @@ When a request arrives at a ColdBrew service, it flows through several layers:
   │  │                                           │   │
   │  │  1. Response Time Logging                 │   │
   │  │  2. Trace ID Injection                    │   │
-  │  │  3. Prometheus Metrics                    │   │
-  │  │  4. Error Notification (Sentry/Rollbar)   │   │
-  │  │  5. New Relic Transaction                 │   │
-  │  │  6. Panic Recovery                        │   │
+  │  │  3. Proto Validate                        │   │
+  │  │  4. Prometheus Metrics                    │   │
+  │  │  5. Error Notification (Sentry/Rollbar)   │   │
+  │  │  6. New Relic Transaction                 │   │
+  │  │  7. Panic Recovery                        │   │
   │  │  (OTEL tracing via gRPC stats handler)    │   │
   │  │                                           │   │
   │  └────────────────────┬─────────────────────┘   │
@@ -200,10 +201,11 @@ Interceptors are gRPC middleware that run on every request. ColdBrew chains them
 |-------|------------|---------|--------------|
 | 1 | Response Time Logging | `interceptors` | Logs method name, duration, and status code |
 | 2 | Trace ID | `interceptors` | Generates a trace ID (or reads it from the `x-trace-id` HTTP header or a `trace_id` proto field) and propagates it to structured logs, Sentry/Rollbar error reports, and OpenTelemetry spans (as the `coldbrew.trace_id` attribute) |
-| 3 | Prometheus | `interceptors` | Records request count, latency histogram, and status codes |
-| 4 | Error Notification | `interceptors` | Sends errors to Sentry/Rollbar/Airbrake asynchronously |
-| 5 | New Relic | `interceptors` | Creates a New Relic transaction for APM |
-| 6 | Panic Recovery | `interceptors` | Catches panics and converts them to gRPC errors |
+| 3 | Proto Validate | `interceptors` | Validates incoming messages using [protovalidate](https://github.com/bufbuild/protovalidate) annotations. Returns `InvalidArgument` on failure. Disable with `DISABLE_PROTO_VALIDATE` |
+| 4 | Prometheus | `interceptors` | Records request count, latency histogram, and status codes |
+| 5 | Error Notification | `interceptors` | Sends errors to Sentry/Rollbar/Airbrake asynchronously |
+| 6 | New Relic | `interceptors` | Creates a New Relic transaction for APM |
+| 7 | Panic Recovery | `interceptors` | Catches panics and converts them to gRPC errors |
 
 {: .note }
 OpenTelemetry tracing spans are created by the `otelgrpc` stats handler configured at the gRPC server/client level, not as an interceptor in the chain.

config-reference.md

@@ -51,6 +51,7 @@ cfg := config.GetColdBrewConfig()
 | `GRPC_MAX_SEND_MSG_SIZE` | int | `2147483647` | Maximum send message size in bytes (default: ~2GB, unlimited) |
 | `GRPC_MAX_RECV_MSG_SIZE` | int | `4194304` | Maximum receive message size in bytes (default: 4MB) |
 | `DISABLE_VT_PROTOBUF` | bool | `false` | Disable [vtprotobuf](https://github.com/planetscale/vtprotobuf) marshaller for gRPC. See [vtprotobuf guide](/howto/vtproto) |
+| `DISABLE_PROTO_VALIDATE` | bool | `false` | Disable [protovalidate](https://github.com/bufbuild/protovalidate) interceptor. When disabled, proto validation annotations are ignored |
 
 ## gRPC TLS
 

howto/interceptors.md

@@ -134,6 +134,42 @@ func main() {
 }
 ```
 
+## Proto Validation
+
+ColdBrew includes a [protovalidate](https://github.com/bufbuild/protovalidate) interceptor in the default chain. It validates incoming messages using annotations defined in your `.proto` files and returns `InvalidArgument` on failure.
+
+### Adding validation rules
+
+First, add `buf.build/bufbuild/protovalidate` to your `buf.yaml` deps and run `buf dep update`. Then add annotations to your proto:
+
+```protobuf
+import "buf/validate/validate.proto";
+
+message CreateUserRequest {
+    string email = 1 [(buf.validate.field).string.email = true];
+    string name = 2 [(buf.validate.field).string.min_len = 1];
+    int32 age = 3 [(buf.validate.field).int32 = {gte: 0, lte: 150}];
+}
+```
+
+No code changes needed — the interceptor validates automatically.
+
+### Custom constraints
+
+Add custom validation options during `init()`:
+
+```go
+func init() {
+    interceptors.SetProtoValidateOptions(
+        protovalidate.WithCustomConstraints(myConstraints...),
+    )
+}
+```
+
+### Disabling
+
+Set `DISABLE_PROTO_VALIDATE=true` to skip validation entirely.
+
 ## Adding custom interceptors to Default interceptors
 
 You can add your own interceptors to the [Default Interceptors] by appending to the list of interceptors.