fix: gate Titan embedding dimensions to v2

Addresses PR review (Codex P2). Titan v1 (G1) rejects any InvokeModel body
field other than inputText, so serializing `dimensions` for it — e.g. from
an embedding config shared with v2 — would fail the request. Only set
dimensions for amazon.titan-embed-text-v2 and ignore it for v1 (which
returns its fixed-size embedding). Adds a regression test.

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

Author: claude

packages/engine/internal/connector/provider_bedrock.go

@@ -261,9 +261,14 @@ func (p *BedrockEmbeddingProvider) Embeddings(ctx context.Context, req *Embeddin
 	out := make([][]float64, len(req.Inputs))
 	totalTokens := 0
 
+	// dimensions is only accepted by Titan v2; Titan v1 (G1) rejects any field
+	// 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")
+
 	for i, text := range req.Inputs {
 		body := titanEmbedRequest{InputText: text}
-		if req.Dimensions > 0 {
+		if req.Dimensions > 0 && supportsDimensions {
 			body.Dimensions = req.Dimensions
 		}
 		bodyJSON, err := json.Marshal(body)

packages/engine/internal/connector/provider_bedrock_embed_test.go

@@ -69,6 +69,31 @@ func TestBedrockEmbeddingProvider_Titan(t *testing.T) {
 	}
 }
 
+func TestBedrockEmbeddingProvider_V1IgnoresDimensions(t *testing.T) {
+	mock := &mockBedrockInvokeClient{
+		InvokeFunc: func(ctx context.Context, input *bedrockruntime.InvokeModelInput, opts ...func(*bedrockruntime.Options)) (*bedrockruntime.InvokeModelOutput, error) {
+			var body titanEmbedRequest
+			if err := json.Unmarshal(input.Body, &body); err != nil {
+				t.Fatalf("unmarshaling request body: %v", err)
+			}
+			// Titan v1 must not receive dimensions even when requested.
+			if body.Dimensions != 0 {
+				t.Errorf("dimensions = %d, want 0 (omitted) for titan v1", body.Dimensions)
+			}
+			resp, _ := json.Marshal(titanEmbedResponse{Embedding: []float64{1}, InputTextTokenCount: 1})
+			return &bedrockruntime.InvokeModelOutput{Body: resp}, nil
+		},
+	}
+	p := &BedrockEmbeddingProvider{Client: mock}
+	if _, err := p.Embeddings(context.Background(), &EmbeddingRequest{
+		Model:      "amazon.titan-embed-text-v1",
+		Inputs:     []string{"x"},
+		Dimensions: 512,
+	}); err != nil {
+		t.Fatalf("Embeddings() error: %v", err)
+	}
+}
+
 func TestBedrockEmbeddingProvider_UnsupportedModel(t *testing.T) {
 	p := &BedrockEmbeddingProvider{Client: &mockBedrockInvokeClient{}}
 	_, err := p.Embeddings(context.Background(), &EmbeddingRequest{