From 64d1cffd8951c2b18b064baec9c2c2a506ec2581 Mon Sep 17 00:00:00 2001
From: Eric Rakestraw <eric@rakestraw.us>
Date: Tue, 25 Aug 2026 09:42:28 +0000
Subject: [PATCH] Preserve explicit empty model responses

---
 docs/roadmap/implementation.md                |  2 +
 internal/llm/openai_compatible_client.go      | 10 ++--
 internal/llm/openai_compatible_client_test.go | 51 +++++++++++++++++++
 3 files changed, 58 insertions(+), 5 deletions(-)

diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index d575bca..4f5ef77 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -230,6 +230,8 @@ Stage 2 is complete when content presence is distinguishable from content
 emptiness and all malformed successful-envelope cases retain their prior error
 identity.
 
+**Status:** Complete.
+
 ## Stage 3: Build Full-Context, Prompt-Safe Corrective Requests
 
 ### Objective
diff --git a/internal/llm/openai_compatible_client.go b/internal/llm/openai_compatible_client.go
index 3247a09..ba0c760 100644
--- a/internal/llm/openai_compatible_client.go
+++ b/internal/llm/openai_compatible_client.go
@@ -179,12 +179,12 @@ func (c *OpenAICompatibleClient) Generate(ctx context.Context, req domain.Genera
 		return nil, fmt.Errorf("%w: no choices returned", ErrMalformedResponse)
 	}
 	content := wireResp.Choices[0].Message.Content
-	if content == "" {
-		return nil, fmt.Errorf("%w: first choice has empty message content", ErrMalformedResponse)
+	if content == nil {
+		return nil, fmt.Errorf("%w: first choice has missing message content", ErrMalformedResponse)
 	}
 
 	return &domain.GenerateResponse{
-		Content: content,
+		Content: *content,
 		Usage: domain.TokenUsage{
 			PromptTokens:     wireResp.Usage.PromptTokens,
 			CompletionTokens: wireResp.Usage.CompletionTokens,
@@ -379,8 +379,8 @@ type openAICacheControl struct {
 }
 
 type openAIChatResponseMessage struct {
-	Role    string `json:"role"`
-	Content string `json:"content"`
+	Role    string  `json:"role"`
+	Content *string `json:"content"`
 }
 
 type openAIChatResponse struct {
diff --git a/internal/llm/openai_compatible_client_test.go b/internal/llm/openai_compatible_client_test.go
index 0877e01..f76c7da 100644
--- a/internal/llm/openai_compatible_client_test.go
+++ b/internal/llm/openai_compatible_client_test.go
@@ -765,6 +765,7 @@ func TestOpenAICompatibleClientResponseFraming(t *testing.T) {
 		run  func(*testing.T)
 	}{
 		{name: "usage mapping", run: checkCacheUsageMapping},
+		{name: "content presence", run: checkContentPresence},
 		{name: "common response failures", run: checkCommonResponseFailures},
 		{name: "successful response byte boundary", run: checkSuccessfulResponseByteBoundary},
 		{name: "continuing oversized response", run: checkContinuingOversizedResponse},
@@ -776,6 +777,53 @@ func TestOpenAICompatibleClientResponseFraming(t *testing.T) {
 	}
 }
 
+func checkContentPresence(t *testing.T) {
+	tests := []struct {
+		name    string
+		content string
+	}{
+		{name: "explicit empty string", content: ""},
+		{name: "whitespace string", content: " \n\t "},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			provider := newRecordingProvider(t)
+			provider.respond(http.StatusOK, `{
+  "choices": [{"message": {"content": `+strconv.Quote(tc.content)+`}}],
+  "usage": {
+    "prompt_tokens": 10,
+    "completion_tokens": 20,
+    "total_tokens": 30,
+    "prompt_tokens_details": {"cached_tokens": 4},
+    "cache_write_tokens": 5
+  }
+}`)
+			client := newProviderClient(t, provider, OpenAICompatibleConfig{Model: "model"})
+
+			response, err := client.Generate(context.Background(), ordinaryGenerateRequest())
+			if err != nil {
+				t.Fatalf("generate: %v", err)
+			}
+			if response == nil {
+				t.Fatal("expected response")
+			}
+			if response.Content != tc.content {
+				t.Fatalf("content = %q, want %q", response.Content, tc.content)
+			}
+			if response.Usage != (domain.TokenUsage{
+				PromptTokens:     10,
+				CompletionTokens: 20,
+				TotalTokens:      30,
+				CachedTokens:     4,
+				CacheWriteTokens: 5,
+			}) {
+				t.Fatalf("usage = %+v", response.Usage)
+			}
+		})
+	}
+}
+
 func checkCacheUsageMapping(t *testing.T) {
 	provider := newRecordingProvider(t)
 	provider.respond(http.StatusOK, `{
@@ -1129,6 +1177,9 @@ func checkCommonResponseFailures(t *testing.T) {
 		},
 		{name: "invalid JSON", statusCode: http.StatusOK, body: `{not valid json`, wantErr: ErrMalformedResponse},
 		{name: "missing choices", statusCode: http.StatusOK, body: `{"choices": []}`, wantErr: ErrMalformedResponse},
+		{name: "missing content", statusCode: http.StatusOK, body: `{"choices": [{"message": {}}]}`, wantErr: ErrMalformedResponse},
+		{name: "null content", statusCode: http.StatusOK, body: `{"choices": [{"message": {"content": null}}]}`, wantErr: ErrMalformedResponse},
+		{name: "non-string content", statusCode: http.StatusOK, body: `{"choices": [{"message": {"content": 1}}]}`, wantErr: ErrMalformedResponse},
 	}
 
 	for _, tc := range tests {