diff --git a/apps/aether-gateway/.aether-windsurf-binary-test-03d740bc-64f1-49cb-b13d-4e5234e5de31/language-server b/apps/aether-gateway/.aether-windsurf-binary-test-03d740bc-64f1-49cb-b13d-4e5234e5de31/language-server
new file mode 100755
index 000000000..f8b18e900
--- /dev/null
+++ b/apps/aether-gateway/.aether-windsurf-binary-test-03d740bc-64f1-49cb-b13d-4e5234e5de31/language-server
@@ -0,0 +1 @@
+test binary
\ No newline at end of file
diff --git a/crates/aether-ai/formats/src/formats/openai/chat/response.rs b/crates/aether-ai/formats/src/formats/openai/chat/response.rs
index 69d503169..64a6589a2 100644
--- a/crates/aether-ai/formats/src/formats/openai/chat/response.rs
+++ b/crates/aether-ai/formats/src/formats/openai/chat/response.rs
@@ -1,6 +1,6 @@
 use std::collections::BTreeMap;
 
-use serde_json::{json, Value};
+use serde_json::{json, Map, Value};
 
 use crate::{
     formats::context::FormatContext,
@@ -13,6 +13,53 @@ use crate::{
     },
 };
 
+/// Reasoning text carried by one Chat Completions `message` or streaming
+/// `delta`, paired with the provider's reasoning block index where one exists.
+///
+/// The field name is not standardized.  DeepSeek-style upstreams send
+/// `reasoning_content`; OpenRouter sends `reasoning` alongside a structured
+/// `reasoning_details` array.  OpenRouter repeats the same text in both of its
+/// fields, so exactly one source is read per object and `reasoning_details`
+/// wins because only it carries the block index.
+pub(crate) fn openai_chat_reasoning_texts(
+    object: &Map<String, Value>,
+) -> Vec<(Option<usize>, String)> {
+    if let Some(details) = object.get("reasoning_details").and_then(Value::as_array) {
+        let texts = details
+            .iter()
+            .filter_map(Value::as_object)
+            .filter_map(|detail| {
+                // `reasoning.encrypted` carries opaque provider state rather
+                // than readable text, so it has nothing to hand downstream.
+                if detail.get("type").and_then(Value::as_str) == Some("reasoning.encrypted") {
+                    return None;
+                }
+                let text = detail
+                    .get("text")
+                    .or_else(|| detail.get("summary"))
+                    .and_then(Value::as_str)
+                    .filter(|text| !text.is_empty())?;
+                let index = detail
+                    .get("index")
+                    .and_then(Value::as_u64)
+                    .map(|index| index as usize);
+                Some((index, text.to_string()))
+            })
+            .collect::<Vec<_>>();
+        if !texts.is_empty() {
+            return texts;
+        }
+    }
+    // A provider may null out one spelling while filling the other, so skip
+    // past any key that is present but carries no string.
+    ["reasoning_content", "reasoning"]
+        .iter()
+        .find_map(|key| object.get(*key).and_then(Value::as_str))
+        .filter(|text| !text.is_empty())
+        .map(|text| vec![(None, text.to_string())])
+        .unwrap_or_default()
+}
+
 pub fn from(body: &Value, _ctx: &FormatContext) -> Option<CanonicalResponse> {
     from_raw(body)
 }
@@ -40,21 +87,18 @@ pub fn from_raw(body_json: &Value) -> Option<CanonicalResponse> {
             .iter()
             .any(|block| matches!(block, CanonicalContentBlock::Thinking { .. }))
         {
-            if let Some(reasoning_content) = message
-                .get("reasoning_content")
-                .and_then(Value::as_str)
-                .filter(|value| !value.trim().is_empty())
-            {
-                content.insert(
-                    0,
-                    CanonicalContentBlock::Thinking {
-                        text: reasoning_content.to_string(),
-                        signature: None,
-                        encrypted_content: None,
-                        extensions: BTreeMap::new(),
-                    },
-                );
-            }
+            let thinking = openai_chat_reasoning_texts(message)
+                .into_iter()
+                .map(|(_, text)| text)
+                .filter(|text| !text.trim().is_empty())
+                .map(|text| CanonicalContentBlock::Thinking {
+                    text,
+                    signature: None,
+                    encrypted_content: None,
+                    extensions: BTreeMap::new(),
+                })
+                .collect::<Vec<_>>();
+            content.splice(0..0, thinking);
         }
         let stop_reason =
             openai_finish_reason_to_canonical(choice.get("finish_reason").and_then(Value::as_str));
@@ -179,3 +223,161 @@ pub fn to_raw(canonical: &CanonicalResponse) -> Value {
     }
     response
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::protocol::canonical::CanonicalContentBlock;
+
+    fn thinking_texts(response: &CanonicalResponse) -> Vec<String> {
+        response
+            .content
+            .iter()
+            .filter_map(|block| match block {
+                CanonicalContentBlock::Thinking { text, .. } => Some(text.clone()),
+                _ => None,
+            })
+            .collect()
+    }
+
+    #[test]
+    fn openrouter_reasoning_details_become_thinking_blocks() {
+        let response = from_raw(&json!({
+            "id": "gen-openrouter-123",
+            "model": "stealth/ox-alpha",
+            "choices": [{
+                "index": 0,
+                "message": {
+                    "role": "assistant",
+                    "content": "done",
+                    "reasoning": "step onestep two",
+                    "reasoning_details": [
+                        {"type": "reasoning.text", "text": "step one", "index": 0},
+                        {"type": "reasoning.text", "text": "step two", "index": 1}
+                    ]
+                },
+                "finish_reason": "stop"
+            }]
+        }))
+        .expect("openrouter response should convert");
+
+        // `reasoning` repeats the same text the details already carry, so the
+        // details win and the provider's own segmentation survives.
+        assert_eq!(thinking_texts(&response), vec!["step one", "step two"]);
+    }
+
+    #[test]
+    fn openrouter_reasoning_string_becomes_a_thinking_block() {
+        let response = from_raw(&json!({
+            "id": "gen-openrouter-123",
+            "model": "stealth/ox-alpha",
+            "choices": [{
+                "index": 0,
+                "message": {
+                    "role": "assistant",
+                    "content": "done",
+                    "reasoning": "thought about it"
+                },
+                "finish_reason": "stop"
+            }]
+        }))
+        .expect("openrouter response should convert");
+
+        assert_eq!(thinking_texts(&response), vec!["thought about it"]);
+    }
+
+    #[test]
+    fn deepseek_reasoning_content_still_becomes_a_thinking_block() {
+        let response = from_raw(&json!({
+            "id": "chatcmpl-deepseek",
+            "model": "deepseek-reasoner",
+            "choices": [{
+                "index": 0,
+                "message": {
+                    "role": "assistant",
+                    "content": "42",
+                    "reasoning_content": "let me work it out"
+                },
+                "finish_reason": "stop"
+            }]
+        }))
+        .expect("deepseek response should convert");
+
+        assert_eq!(thinking_texts(&response), vec!["let me work it out"]);
+    }
+
+    #[test]
+    fn deepseek_reasoning_content_wins_over_a_bare_reasoning_field() {
+        let response = from_raw(&json!({
+            "id": "chatcmpl-deepseek",
+            "model": "deepseek-reasoner",
+            "choices": [{
+                "index": 0,
+                "message": {
+                    "role": "assistant",
+                    "content": "42",
+                    "reasoning_content": "the real one",
+                    "reasoning": "the other spelling"
+                },
+                "finish_reason": "stop"
+            }]
+        }))
+        .expect("deepseek response should convert");
+
+        assert_eq!(thinking_texts(&response), vec!["the real one"]);
+    }
+
+    #[test]
+    fn blank_reasoning_content_produces_no_thinking_block() {
+        let response = from_raw(&json!({
+            "id": "chatcmpl-deepseek",
+            "model": "deepseek-reasoner",
+            "choices": [{
+                "index": 0,
+                "message": {"role": "assistant", "content": "42", "reasoning_content": "   "},
+                "finish_reason": "stop"
+            }]
+        }))
+        .expect("deepseek response should convert");
+
+        assert!(thinking_texts(&response).is_empty());
+    }
+
+    #[test]
+    fn plain_openai_response_without_reasoning_is_unchanged() {
+        let response = from_raw(&json!({
+            "id": "chatcmpl-openai",
+            "model": "gpt-4o",
+            "choices": [{
+                "index": 0,
+                "message": {"role": "assistant", "content": "hello"},
+                "finish_reason": "stop"
+            }]
+        }))
+        .expect("openai response should convert");
+
+        assert!(thinking_texts(&response).is_empty());
+    }
+
+    #[test]
+    fn encrypted_reasoning_details_carry_no_thinking_text() {
+        let response = from_raw(&json!({
+            "id": "gen-openrouter-123",
+            "model": "stealth/ox-alpha",
+            "choices": [{
+                "index": 0,
+                "message": {
+                    "role": "assistant",
+                    "content": "done",
+                    "reasoning_details": [
+                        {"type": "reasoning.encrypted", "data": "b3BhcXVl", "index": 0}
+                    ]
+                },
+                "finish_reason": "stop"
+            }]
+        }))
+        .expect("openrouter response should convert");
+
+        assert!(thinking_texts(&response).is_empty());
+    }
+}
diff --git a/crates/aether-ai/formats/src/formats/openai/chat/stream.rs b/crates/aether-ai/formats/src/formats/openai/chat/stream.rs
index a5a29524e..6f5655fd0 100644
--- a/crates/aether-ai/formats/src/formats/openai/chat/stream.rs
+++ b/crates/aether-ai/formats/src/formats/openai/chat/stream.rs
@@ -3,6 +3,7 @@ use std::collections::{BTreeMap, BTreeSet};
 use serde_json::{json, Map, Value};
 use sha2::{Digest, Sha256};
 
+use crate::formats::openai::chat::response::openai_chat_reasoning_texts;
 use crate::formats::openai::namespace::NamespaceToolAliases;
 use crate::formats::openai::responses::{
     encode_gemini_tool_signature_carrier_with_direction, openai_responses_message_item_id,
@@ -41,6 +42,7 @@ pub struct OpenAIChatProviderState {
     started: bool,
     finished: bool,
     pending_finish_reason: Option<String>,
+    last_reasoning_index: Option<usize>,
     tool_calls: BTreeMap<usize, OpenAIChatProviderToolState>,
 }
 
@@ -271,24 +273,39 @@ impl OpenAIChatProviderState {
             } else if delta.contains_key("content") {
                 recognized_delta = true;
             }
-            if let Some(reasoning_content) = delta.get("reasoning_content").and_then(Value::as_str)
+            if delta.contains_key("reasoning_content")
+                || delta.contains_key("reasoning_details")
+                || delta.contains_key("reasoning")
             {
                 recognized_delta = true;
-                if !reasoning_content.is_empty() {
+                for (reasoning_index, text) in openai_chat_reasoning_texts(delta) {
                     self.ensure_started(report_context, &mut out);
                     if !self.terminal_only {
                         let (id, model) = self.identity(report_context);
+                        // A change of reasoning block index closes the part that
+                        // is open, so downstream summaries keep the provider's
+                        // own segmentation instead of collapsing into one
+                        // paragraph.
+                        if let Some(reasoning_index) = reasoning_index {
+                            if self
+                                .last_reasoning_index
+                                .is_some_and(|last| last != reasoning_index)
+                            {
+                                out.push(CanonicalStreamFrame {
+                                    id: id.clone(),
+                                    model: model.clone(),
+                                    event: CanonicalStreamEvent::ReasoningSummaryDone,
+                                });
+                            }
+                            self.last_reasoning_index = Some(reasoning_index);
+                        }
                         out.push(CanonicalStreamFrame {
                             id,
                             model,
-                            event: CanonicalStreamEvent::ReasoningDelta(
-                                reasoning_content.to_string(),
-                            ),
+                            event: CanonicalStreamEvent::ReasoningDelta(text),
                         });
                     }
                 }
-            } else if delta.contains_key("reasoning_content") {
-                recognized_delta = true;
             }
 
             if let Some(tool_calls) = delta.get("tool_calls").and_then(Value::as_array) {
@@ -4287,6 +4304,175 @@ mod tests {
         )));
     }
 
+    #[test]
+    fn openai_chat_provider_state_reads_openrouter_reasoning_once() {
+        let mut state = OpenAIChatProviderState::default();
+        let report_context = json!({});
+        let frames = state
+            .push_line(
+                &report_context,
+                data_line(json!({
+                    "id": "gen-openrouter-123",
+                    "model": "stealth/ox-alpha",
+                    "choices": [{
+                        "index": 0,
+                        "delta": {
+                            "content": "",
+                            "role": "assistant",
+                            "reasoning": " me translate the",
+                            "reasoning_details": [{
+                                "type": "reasoning.text",
+                                "text": " me translate the",
+                                "format": "unknown",
+                                "index": 0
+                            }]
+                        },
+                        "finish_reason": Value::Null
+                    }]
+                })),
+            )
+            .expect("openrouter reasoning delta should parse");
+
+        let reasoning = frames
+            .iter()
+            .filter_map(|frame| match frame.event {
+                CanonicalStreamEvent::ReasoningDelta(ref text) => Some(text.as_str()),
+                _ => None,
+            })
+            .collect::<Vec<_>>();
+        // `reasoning` and `reasoning_details` repeat the same text, so only one
+        // of the two may reach the client.
+        assert_eq!(reasoning, vec![" me translate the"]);
+        assert!(!frames
+            .iter()
+            .any(|frame| matches!(frame.event, CanonicalStreamEvent::UnknownEvent(_))));
+    }
+
+    #[test]
+    fn openai_chat_provider_state_still_reads_deepseek_reasoning_content() {
+        let mut state = OpenAIChatProviderState::default();
+        let report_context = json!({});
+        let frames = state
+            .push_line(
+                &report_context,
+                data_line(json!({
+                    "id": "chatcmpl-deepseek",
+                    "model": "deepseek-reasoner",
+                    "choices": [{
+                        "index": 0,
+                        "delta": {"role": "assistant", "reasoning_content": "let me work it out"},
+                        "finish_reason": Value::Null
+                    }]
+                })),
+            )
+            .expect("deepseek reasoning delta should parse");
+
+        let reasoning = frames
+            .iter()
+            .filter_map(|frame| match frame.event {
+                CanonicalStreamEvent::ReasoningDelta(ref text) => Some(text.as_str()),
+                _ => None,
+            })
+            .collect::<Vec<_>>();
+        assert_eq!(reasoning, vec!["let me work it out"]);
+        // A single reasoning block carries no index, so nothing may close a part.
+        assert!(!frames
+            .iter()
+            .any(|frame| matches!(frame.event, CanonicalStreamEvent::ReasoningSummaryDone)));
+        assert!(!frames
+            .iter()
+            .any(|frame| matches!(frame.event, CanonicalStreamEvent::UnknownEvent(_))));
+    }
+
+    #[test]
+    fn openai_chat_provider_state_splits_reasoning_details_on_block_index() {
+        let mut state = OpenAIChatProviderState::default();
+        let report_context = json!({});
+        let reasoning_chunk = |index: u64, text: &str| {
+            data_line(json!({
+                "id": "gen-openrouter-123",
+                "model": "stealth/ox-alpha",
+                "choices": [{
+                    "index": 0,
+                    "delta": {
+                        "content": "",
+                        "role": "assistant",
+                        "reasoning_details": [{
+                            "type": "reasoning.text",
+                            "text": text,
+                            "index": index
+                        }]
+                    },
+                    "finish_reason": Value::Null
+                }]
+            }))
+        };
+        let mut frames = state
+            .push_line(&report_context, reasoning_chunk(0, "first"))
+            .expect("first reasoning block should parse");
+        frames.extend(
+            state
+                .push_line(&report_context, reasoning_chunk(1, "second"))
+                .expect("second reasoning block should parse"),
+        );
+
+        let reasoning = frames
+            .iter()
+            .filter_map(|frame| match frame.event {
+                CanonicalStreamEvent::ReasoningDelta(ref text) => Some(text.as_str()),
+                CanonicalStreamEvent::ReasoningSummaryDone => Some("<part-done>"),
+                _ => None,
+            })
+            .collect::<Vec<_>>();
+        assert_eq!(reasoning, vec!["first", "<part-done>", "second"]);
+    }
+
+    #[test]
+    fn openai_chat_reasoning_only_stream_reaches_responses_clients() {
+        // Regression: OpenRouter streams a long reasoning phase as chunks whose
+        // `delta.content` is an empty string and whose text sits under
+        // `reasoning`.  Dropping those chunks left Responses clients with
+        // nothing after `response.in_progress` until they timed the stream out.
+        let mut state = OpenAIChatProviderState::default();
+        let mut emitter = OpenAIResponsesClientEmitter::default();
+        let report_context = json!({});
+        let mut bytes = Vec::new();
+        for piece in ["Let", " me think."] {
+            let frames = state
+                .push_line(
+                    &report_context,
+                    data_line(json!({
+                        "id": "gen-openrouter-123",
+                        "model": "stealth/ox-alpha",
+                        "choices": [{
+                            "index": 0,
+                            "delta": {
+                                "content": "",
+                                "role": "assistant",
+                                "reasoning": piece,
+                                "reasoning_details": [{
+                                    "type": "reasoning.text",
+                                    "text": piece,
+                                    "format": "unknown",
+                                    "index": 0
+                                }]
+                            },
+                            "finish_reason": Value::Null
+                        }]
+                    })),
+                )
+                .expect("reasoning chunk should parse");
+            for frame in frames {
+                bytes.extend(emitter.emit(frame).expect("frame should encode"));
+            }
+        }
+
+        let sse = String::from_utf8(bytes).expect("sse should be utf8");
+        assert!(sse.contains("event: response.reasoning_summary_text.delta\n"));
+        assert!(sse.contains("\"delta\":\"Let\""));
+        assert!(sse.contains("\"delta\":\" me think.\""));
+    }
+
     #[test]
     fn openai_chat_provider_state_waits_for_real_tool_call_identity() {
         let mut state = OpenAIChatProviderState::default();
diff --git a/crates/aether-ai/formats/src/formats/shared/sync_products.rs b/crates/aether-ai/formats/src/formats/shared/sync_products.rs
index 4a20b159f..91285be78 100644
--- a/crates/aether-ai/formats/src/formats/shared/sync_products.rs
+++ b/crates/aether-ai/formats/src/formats/shared/sync_products.rs
@@ -26,6 +26,7 @@ use serde_json::{json, Map, Value};
 use super::{decode_sync_report_body_base64, AiSurfaceFinalizeError};
 use crate::formats::claude::messages::stream::ClaudeProviderState;
 use crate::formats::gemini::generate_content::stream::GeminiProviderState;
+use crate::formats::openai::chat::response::openai_chat_reasoning_texts;
 use crate::formats::openai::chat::stream::{OpenAIChatProviderState, OpenAIResponsesProviderState};
 use crate::formats::shared::model_directives::model_directive_display_model_from_report_context;
 use crate::formats::shared::response::sanitize_claude_read_tool_inputs;
@@ -1827,6 +1828,7 @@ fn apply_report_context_model_fallback(model: &mut String, report_context: &Valu
 struct OpenAIChatChoiceState {
     role: Option<String>,
     content: String,
+    reasoning: String,
     finish_reason: Option<String>,
     tool_calls: BTreeMap<usize, OpenAIChatToolCallState>,
 }
@@ -2195,6 +2197,9 @@ pub fn aggregate_openai_chat_stream_sync_response(body: &[u8]) -> Option<Value>
             if let Some(content) = delta.get("content").and_then(Value::as_str) {
                 state.content.push_str(content);
             }
+            for (_, piece) in openai_chat_reasoning_texts(delta) {
+                state.reasoning.push_str(&piece);
+            }
             if let Some(tool_calls) = delta.get("tool_calls").and_then(Value::as_array) {
                 for tool_call in tool_calls {
                     let Some(tool_call_object) = tool_call.as_object() else {
@@ -2254,6 +2259,14 @@ pub fn aggregate_openai_chat_stream_sync_response(body: &[u8]) -> Option<Value>
             "role".to_string(),
             Value::String(state.role.unwrap_or_else(|| "assistant".to_string())),
         );
+        // Reassemble under the spelling this crate emits for Chat clients; the
+        // provider's own spelling was already normalized away by the parser.
+        if !state.reasoning.is_empty() {
+            message.insert(
+                "reasoning_content".to_string(),
+                Value::String(state.reasoning),
+            );
+        }
         if state.tool_calls.is_empty() {
             message.insert("content".to_string(), Value::String(state.content));
         } else {
@@ -4139,6 +4152,92 @@ mod tests {
         );
     }
 
+    #[test]
+    fn aggregates_openai_chat_stream_reasoning_into_sync_body() {
+        // The aggregator used to keep only `content` and `tool_calls`, so a
+        // stream downgraded to a sync response lost the reasoning entirely —
+        // for OpenRouter's `reasoning`/`reasoning_details` and for the
+        // DeepSeek-style `reasoning_content` alike.
+        let body = concat!(
+            "data: {\"id\":\"gen-openrouter-123\",\"object\":\"chat.completion.chunk\",\"model\":\"stealth/ox-alpha\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"\",\"role\":\"assistant\",\"reasoning\":\"Let me\",\"reasoning_details\":[{\"type\":\"reasoning.text\",\"text\":\"Let me\",\"index\":0}]},\"finish_reason\":null}]}\n\n",
+            "data: {\"id\":\"gen-openrouter-123\",\"object\":\"chat.completion.chunk\",\"model\":\"stealth/ox-alpha\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"\",\"role\":\"assistant\",\"reasoning\":\" think.\",\"reasoning_details\":[{\"type\":\"reasoning.text\",\"text\":\" think.\",\"index\":0}]},\"finish_reason\":null}]}\n\n",
+            "data: {\"id\":\"gen-openrouter-123\",\"object\":\"chat.completion.chunk\",\"model\":\"stealth/ox-alpha\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"Done.\",\"role\":\"assistant\"},\"finish_reason\":null}]}\n\n",
+            "data: {\"id\":\"gen-openrouter-123\",\"object\":\"chat.completion.chunk\",\"model\":\"stealth/ox-alpha\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"\",\"role\":\"assistant\",\"reasoning\":null},\"finish_reason\":\"stop\"}],\"usage\":{\"prompt_tokens\":1,\"completion_tokens\":2,\"total_tokens\":3}}\n\n",
+        );
+
+        let result = aggregate_openai_chat_stream_sync_response(body.as_bytes())
+            .expect("openrouter chat stream should aggregate into a sync body");
+
+        let message = &result["choices"][0]["message"];
+        assert_eq!(message["content"], "Done.");
+        // `reasoning` and `reasoning_details` repeat one another, so the
+        // reassembled text must not double up.
+        assert_eq!(message["reasoning_content"], "Let me think.");
+        assert_eq!(result["choices"][0]["finish_reason"], "stop");
+    }
+
+    #[test]
+    fn aggregates_deepseek_reasoning_content_into_sync_body() {
+        let body = concat!(
+            "data: {\"id\":\"chatcmpl-deepseek\",\"object\":\"chat.completion.chunk\",\"model\":\"deepseek-reasoner\",\"choices\":[{\"index\":0,\"delta\":{\"role\":\"assistant\",\"reasoning_content\":\"Let me\"},\"finish_reason\":null}]}\n\n",
+            "data: {\"id\":\"chatcmpl-deepseek\",\"object\":\"chat.completion.chunk\",\"model\":\"deepseek-reasoner\",\"choices\":[{\"index\":0,\"delta\":{\"reasoning_content\":\" think.\"},\"finish_reason\":null}]}\n\n",
+            "data: {\"id\":\"chatcmpl-deepseek\",\"object\":\"chat.completion.chunk\",\"model\":\"deepseek-reasoner\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"42\"},\"finish_reason\":\"stop\"}]}\n\n",
+        );
+
+        let result = aggregate_openai_chat_stream_sync_response(body.as_bytes())
+            .expect("deepseek chat stream should aggregate into a sync body");
+
+        let message = &result["choices"][0]["message"];
+        assert_eq!(message["content"], "42");
+        assert_eq!(message["reasoning_content"], "Let me think.");
+        assert_eq!(result["choices"][0]["finish_reason"], "stop");
+    }
+
+    #[test]
+    fn aggregated_chat_stream_without_reasoning_adds_no_reasoning_key() {
+        let body = "data: {\"id\":\"chatcmpl-openai\",\"object\":\"chat.completion.chunk\",\"model\":\"gpt-4o\",\"choices\":[{\"index\":0,\"delta\":{\"role\":\"assistant\",\"content\":\"hi\"},\"finish_reason\":\"stop\"}]}\n\n";
+
+        let result = aggregate_openai_chat_stream_sync_response(body.as_bytes())
+            .expect("plain chat stream should aggregate into a sync body");
+
+        let message = &result["choices"][0]["message"];
+        assert_eq!(message["content"], "hi");
+        assert!(
+            message.get("reasoning_content").is_none(),
+            "a stream with no reasoning must not gain a reasoning key: {message}"
+        );
+    }
+
+    #[test]
+    fn aggregated_openai_chat_reasoning_reaches_every_client_format() {
+        let body = concat!(
+            "data: {\"id\":\"gen-openrouter-123\",\"object\":\"chat.completion.chunk\",\"model\":\"stealth/ox-alpha\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"\",\"role\":\"assistant\",\"reasoning\":\"Thinking.\"},\"finish_reason\":null}]}\n\n",
+            "data: {\"id\":\"gen-openrouter-123\",\"object\":\"chat.completion.chunk\",\"model\":\"stealth/ox-alpha\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"Done.\",\"role\":\"assistant\"},\"finish_reason\":\"stop\"}]}\n\n",
+        );
+        let aggregated = aggregate_openai_chat_stream_sync_response(body.as_bytes())
+            .expect("openrouter chat stream should aggregate into a sync body");
+        let report_context = json!({});
+
+        for (client_api_format, marker) in [
+            ("openai:responses", "\"type\":\"reasoning\""),
+            ("claude:messages", "\"type\":\"thinking\""),
+            ("gemini:generate_content", "\"thought\":true"),
+        ] {
+            let converted = convert_standard_chat_response(
+                &aggregated,
+                "openai:chat",
+                client_api_format,
+                &report_context,
+            )
+            .unwrap_or_else(|| panic!("{client_api_format} should convert"));
+            let encoded = serde_json::to_string(&converted).expect("converted body should encode");
+            assert!(
+                encoded.contains(marker),
+                "{client_api_format} dropped the reasoning block: {encoded}"
+            );
+        }
+    }
+
     #[test]
     fn aggregates_openai_chat_stream_tool_usage_and_finish_into_sync_body() {
         let body = concat!(