fix: thread ctx + validate Titan v2 dimensions in ai/embed

Addresses CodeRabbit review on the Bedrock embeddings PR:

- Thread the request context through EmbeddingConnector.getProvider into
  NewAWSConfig instead of context.Background(), so cancellation/deadlines
  aren't dropped during AWS config resolution (Major).
- Validate Titan v2 dimensions up front — only 256, 512, or 1024 are
  accepted, so reject other values with a clear error instead of a cryptic
  Bedrock runtime failure (Minor).
- Tests: cover the ai/embed bedrock provider path via a stubbed
  AWSConfigFunc (region resolution + [bedrock] error wrapping) and reject
  invalid v2 dimensions. (v1 dimension-ignoring is already covered by
  TestBedrockEmbeddingProvider_V1IgnoresDimensions.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WnKgCRfMvFcZAkoVbr8k79

Author: claude

packages/engine/internal/connector/embed.go

@@ -48,7 +48,7 @@ func (c *EmbeddingConnector) Execute(ctx context.Context, params map[string]any)
 		return nil, fmt.Errorf("ai/embed: %w", err)
 	}
 
-	provider, err := c.getProvider(providerName, params)
+	provider, err := c.getProvider(ctx, providerName, params)
 	if err != nil {
 		return nil, fmt.Errorf("ai/embed: %w", err)
 	}
@@ -80,7 +80,7 @@ func (c *EmbeddingConnector) Execute(ctx context.Context, params map[string]any)
 }
 
 // getProvider returns the EmbeddingProvider for the given provider name.
-func (c *EmbeddingConnector) getProvider(name string, params map[string]any) (EmbeddingProvider, error) {
+func (c *EmbeddingConnector) getProvider(ctx context.Context, name string, params map[string]any) (EmbeddingProvider, error) {
 	switch name {
 	case "openai":
 		baseURL := "https://api.openai.com/v1"
@@ -102,7 +102,7 @@ func (c *EmbeddingConnector) getProvider(name string, params map[string]any) (Em
 		if configFunc == nil {
 			configFunc = NewAWSConfig
 		}
-		awsCfg, err := configFunc(context.Background(), cred, defaultRegion)
+		awsCfg, err := configFunc(ctx, cred, defaultRegion)
 		if err != nil {
 			return nil, fmt.Errorf("[bedrock]: %w", err)
 		}

packages/engine/internal/connector/embed_test.go

@@ -3,9 +3,13 @@ package connector
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
+
+	"github.com/aws/aws-sdk-go-v2/aws"
 )
 
 // embedTestServer returns an httptest server that emits `n` deterministic
@@ -144,6 +148,32 @@ func TestEmbeddingConnector_IncompleteResponseFailsFast(t *testing.T) {
 	}
 }
 
+func TestEmbeddingConnector_BedrockRegionAndErrorWrapping(t *testing.T) {
+	var gotRegion string
+	c := &EmbeddingConnector{
+		DefaultRegion: "us-west-2",
+		AWSConfigFunc: func(ctx context.Context, cred map[string]string, defaultRegion string) (aws.Config, error) {
+			gotRegion = defaultRegion
+			return aws.Config{}, errors.New("boom")
+		},
+	}
+	_, err := c.Execute(context.Background(), map[string]any{
+		"model":    "amazon.titan-embed-text-v2:0",
+		"input":    "x",
+		"provider": "bedrock",
+		"region":   "eu-central-1", // params region overrides DefaultRegion
+	})
+	if err == nil {
+		t.Fatal("expected error from stubbed AWS config")
+	}
+	if !strings.Contains(err.Error(), "[bedrock]") {
+		t.Errorf("error not wrapped with [bedrock]: %v", err)
+	}
+	if gotRegion != "eu-central-1" {
+		t.Errorf("resolved region = %q, want eu-central-1 (params override)", gotRegion)
+	}
+}
+
 func TestEmbeddingConnector_UnknownProvider(t *testing.T) {
 	c := &EmbeddingConnector{}
 	_, err := c.Execute(context.Background(), map[string]any{

packages/engine/internal/connector/provider_bedrock.go

@@ -265,6 +265,13 @@ func (p *BedrockEmbeddingProvider) Embeddings(ctx context.Context, req *Embeddin
 	// other than inputText, so ignore it there rather than failing a request
 	// that reuses a shared embedding config.
 	supportsDimensions := strings.Contains(req.Model, "titan-embed-text-v2")
+	if req.Dimensions > 0 && supportsDimensions {
+		switch req.Dimensions {
+		case 256, 512, 1024:
+		default:
+			return nil, fmt.Errorf("bedrock: %s supports dimensions 256, 512, or 1024, got %d", req.Model, req.Dimensions)
+		}
+	}
 
 	for i, text := range req.Inputs {
 		body := titanEmbedRequest{InputText: text}

packages/engine/internal/connector/provider_bedrock_embed_test.go

@@ -94,6 +94,24 @@ func TestBedrockEmbeddingProvider_V1IgnoresDimensions(t *testing.T) {
 	}
 }
 
+func TestBedrockEmbeddingProvider_V2InvalidDimensions(t *testing.T) {
+	mock := &mockBedrockInvokeClient{
+		InvokeFunc: func(ctx context.Context, input *bedrockruntime.InvokeModelInput, opts ...func(*bedrockruntime.Options)) (*bedrockruntime.InvokeModelOutput, error) {
+			t.Fatal("InvokeModel should not be called for invalid dimensions")
+			return nil, nil
+		},
+	}
+	p := &BedrockEmbeddingProvider{Client: mock}
+	_, err := p.Embeddings(context.Background(), &EmbeddingRequest{
+		Model:      "amazon.titan-embed-text-v2:0",
+		Inputs:     []string{"x"},
+		Dimensions: 999, // only 256/512/1024 are valid
+	})
+	if err == nil {
+		t.Error("expected error for unsupported Titan v2 dimensions")
+	}
+}
+
 func TestBedrockEmbeddingProvider_UnsupportedModel(t *testing.T) {
 	p := &BedrockEmbeddingProvider{Client: &mockBedrockInvokeClient{}}
 	_, err := p.Embeddings(context.Background(), &EmbeddingRequest{