fix: REPL display, /compact panic, identity leak, DeepSeek reasoning, thinking blocks

Five interrelated fixes from parallel Hephaestus sessions:

1. fix(repl): display assistant text after spinner (#2981, #2982, #2937)
   - Added final_assistant_text() call after run_turn spinner completes
   - REPL now shows response text like run_prompt_json does

2. fix(compact): handle Thinking content blocks (#2985)
   - Added ContentBlock::Thinking variant throughout compact summarizer
   - Prevents panic when /compact encounters thinking blocks

3. fix(prompt): provider-aware model identity (#2822)
   - New ModelFamilyIdentity enum (Claude vs Generic)
   - Non-Anthropic models no longer say 'I am Claude'
   - model_family_identity_for() detects provider and sets identity

4. fix(openai): preserve DeepSeek reasoning_content (#2821)
   - Stream parser now captures reasoning_content from OpenAI-compat
   - Emits ThinkingDelta/SignatureDelta events for reasoning models
   - Thinking blocks included in conversation history for re-send

5. feat(runtime): Thinking block support across codebase
   - AssistantEvent::Thinking variant in conversation.rs
   - ContentBlock::Thinking in session serialization
   - Thinking-aware compact summarization
   - Tests for thinking block ordering and content

Closes #2981, #2982, #2937, #2985, #2822, #2821

rust/crates/runtime/src/compact.rs

@@ -213,6 +213,7 @@ fn summarize_messages(messages: &[ConversationMessage]) -> String {
             ContentBlock::ToolUse { name, .. } => Some(name.as_str()),
             ContentBlock::ToolResult { tool_name, .. } => Some(tool_name.as_str()),
             ContentBlock::Text { .. } => None,
+            ContentBlock::Thinking { .. } => None,
         })
         .collect::<Vec<_>>();
     tool_names.sort_unstable();
@@ -317,6 +318,9 @@ fn merge_compact_summaries(existing_summary: Option<&str>, new_summary: &str) ->
 fn summarize_block(block: &ContentBlock) -> String {
     let raw = match block {
         ContentBlock::Text { text } => text.clone(),
+        ContentBlock::Thinking { thinking, .. } => {
+            format!("thinking ({} chars)", thinking.chars().count())
+        }
         ContentBlock::ToolUse { name, input, .. } => format!("tool_use {name}({input})"),
         ContentBlock::ToolResult {
             tool_name,
@@ -378,6 +382,7 @@ fn collect_key_files(messages: &[ConversationMessage]) -> Vec<String> {
             ContentBlock::Text { text } => text.as_str(),
             ContentBlock::ToolUse { input, .. } => input.as_str(),
             ContentBlock::ToolResult { output, .. } => output.as_str(),
+            ContentBlock::Thinking { thinking, .. } => thinking.as_str(),
         })
         .flat_map(extract_file_candidates)
         .collect::<Vec<_>>();
@@ -400,6 +405,7 @@ fn first_text_block(message: &ConversationMessage) -> Option<&str> {
         ContentBlock::Text { text } if !text.trim().is_empty() => Some(text.as_str()),
         ContentBlock::ToolUse { .. }
         | ContentBlock::ToolResult { .. }
+        | ContentBlock::Thinking { .. }
         | ContentBlock::Text { .. } => None,
     })
 }
@@ -450,6 +456,10 @@ fn estimate_message_tokens(message: &ConversationMessage) -> usize {
             ContentBlock::ToolResult {
                 tool_name, output, ..
             } => (tool_name.len() + output.len()) / 4 + 1,
+            ContentBlock::Thinking {
+                thinking,
+                signature,
+            } => thinking.len() / 4 + signature.as_ref().map_or(0, |value| value.len() / 4 + 1),
         })
         .sum()
 }

rust/crates/runtime/src/conversation.rs

@@ -28,6 +28,10 @@ pub struct ApiRequest {
 /// Streamed events emitted while processing a single assistant turn.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum AssistantEvent {
+    Thinking {
+        thinking: String,
+        signature: Option<String>,
+    },
     TextDelta(String),
     ToolUse {
         id: String,
@@ -721,6 +725,16 @@ fn build_assistant_message(
 
     for event in events {
         match event {
+            AssistantEvent::Thinking {
+                thinking,
+                signature,
+            } => {
+                flush_text_block(&mut text, &mut blocks);
+                blocks.push(ContentBlock::Thinking {
+                    thinking,
+                    signature,
+                });
+            }
             AssistantEvent::TextDelta(delta) => text.push_str(&delta),
             AssistantEvent::ToolUse { id, name, input } => {
                 flush_text_block(&mut text, &mut blocks);
@@ -1723,6 +1737,47 @@ mod tests {
             .contains("assistant stream produced no content"));
     }
 
+    #[test]
+    fn build_assistant_message_places_thinking_block_before_text_and_tool_use() {
+        // given
+        let events = vec![
+            AssistantEvent::Thinking {
+                thinking: "pondering".to_string(),
+                signature: Some("sig".to_string()),
+            },
+            AssistantEvent::TextDelta("hello".to_string()),
+            AssistantEvent::ToolUse {
+                id: "tool-1".to_string(),
+                name: "echo".to_string(),
+                input: "payload".to_string(),
+            },
+            AssistantEvent::MessageStop,
+        ];
+
+        // when
+        let (message, _, _) = build_assistant_message(events)
+            .expect("assistant message should preserve thinking, text, and tool blocks");
+
+        // then
+        assert_eq!(
+            message.blocks,
+            vec![
+                ContentBlock::Thinking {
+                    thinking: "pondering".to_string(),
+                    signature: Some("sig".to_string()),
+                },
+                ContentBlock::Text {
+                    text: "hello".to_string(),
+                },
+                ContentBlock::ToolUse {
+                    id: "tool-1".to_string(),
+                    name: "echo".to_string(),
+                    input: "payload".to_string(),
+                },
+            ]
+        );
+    }
+
     #[test]
     fn static_tool_executor_rejects_unknown_tools() {
         // given

rust/crates/runtime/src/lib.rs

@@ -131,8 +131,8 @@ pub use policy_engine::{
     PolicyEngine, PolicyRule, ReconcileReason, ReviewStatus,
 };
 pub use prompt::{
-    load_system_prompt, prepend_bullets, ContextFile, ProjectContext, PromptBuildError,
-    SystemPromptBuilder, FRONTIER_MODEL_NAME, SYSTEM_PROMPT_DYNAMIC_BOUNDARY,
+    load_system_prompt, prepend_bullets, ContextFile, ModelFamilyIdentity, ProjectContext,
+    PromptBuildError, SystemPromptBuilder, FRONTIER_MODEL_NAME, SYSTEM_PROMPT_DYNAMIC_BOUNDARY,
 };
 pub use recovery_recipes::{
     attempt_recovery, recipe_for, EscalationPolicy, FailureScenario, RecoveryContext,

rust/crates/runtime/src/prompt.rs

@@ -43,6 +43,24 @@ pub const FRONTIER_MODEL_NAME: &str = "Claude Opus 4.6";
 const MAX_INSTRUCTION_FILE_CHARS: usize = 4_000;
 const MAX_TOTAL_INSTRUCTION_CHARS: usize = 12_000;
 
+/// Neutral identity for the model family line in generated prompts.
+#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
+pub enum ModelFamilyIdentity {
+    #[default]
+    Claude,
+    Generic,
+}
+
+impl ModelFamilyIdentity {
+    #[must_use]
+    pub const fn family_label(self) -> &'static str {
+        match self {
+            Self::Claude => FRONTIER_MODEL_NAME,
+            Self::Generic => "an AI assistant",
+        }
+    }
+}
+
 /// Contents of an instruction file included in prompt construction.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ContextFile {
@@ -97,6 +115,7 @@ pub struct SystemPromptBuilder {
     output_style_prompt: Option<String>,
     os_name: Option<String>,
     os_version: Option<String>,
+    model_family: Option<ModelFamilyIdentity>,
     append_sections: Vec<String>,
     project_context: Option<ProjectContext>,
     config: Option<RuntimeConfig>,
@@ -122,6 +141,12 @@ impl SystemPromptBuilder {
         self
     }
 
+    #[must_use]
+    pub fn with_model_family(mut self, model_family: ModelFamilyIdentity) -> Self {
+        self.model_family = Some(model_family);
+        self
+    }
+
     #[must_use]
     pub fn with_project_context(mut self, project_context: ProjectContext) -> Self {
         self.project_context = Some(project_context);
@@ -179,9 +204,10 @@ impl SystemPromptBuilder {
             || "unknown".to_string(),
             |context| context.current_date.clone(),
         );
+        let identity = self.model_family.unwrap_or_default();
         let mut lines = vec!["# Environment context".to_string()];
         lines.extend(prepend_bullets(vec![
-            format!("Model family: {FRONTIER_MODEL_NAME}"),
+            format!("Model family: {}", identity.family_label()),
             format!("Working directory: {cwd}"),
             format!("Date: {date}"),
             format!(
@@ -434,12 +460,14 @@ pub fn load_system_prompt(
     current_date: impl Into<String>,
     os_name: impl Into<String>,
     os_version: impl Into<String>,
+    model_family: ModelFamilyIdentity,
 ) -> Result<Vec<String>, PromptBuildError> {
     let cwd = cwd.into();
     let project_context = ProjectContext::discover_with_git(&cwd, current_date.into())?;
     let config = ConfigLoader::default_for(&cwd).load()?;
     Ok(SystemPromptBuilder::new()
         .with_os(os_name, os_version)
+        .with_model_family(model_family)
         .with_project_context(project_context)
         .with_runtime_config(config)
         .build())
@@ -522,7 +550,8 @@ mod tests {
     use super::{
         collapse_blank_lines, display_context_path, normalize_instruction_content,
         render_instruction_content, render_instruction_files, truncate_instruction_content,
-        ContextFile, ProjectContext, SystemPromptBuilder, SYSTEM_PROMPT_DYNAMIC_BOUNDARY,
+        ContextFile, ModelFamilyIdentity, ProjectContext, SystemPromptBuilder,
+        SYSTEM_PROMPT_DYNAMIC_BOUNDARY,
     };
     use crate::config::ConfigLoader;
     use std::fs;
@@ -804,13 +833,19 @@ mod tests {
         std::env::set_var("HOME", &root);
         std::env::set_var("CLAW_CONFIG_HOME", root.join("missing-home"));
         std::env::set_current_dir(&root).expect("change cwd");
-        let prompt = super::load_system_prompt(&root, "2026-03-31", "linux", "6.8")
-            .expect("system prompt should load")
-            .join(
-                "
+        let prompt = super::load_system_prompt(
+            &root,
+            "2026-03-31",
+            "linux",
+            "6.8",
+            ModelFamilyIdentity::Claude,
+        )
+        .expect("system prompt should load")
+        .join(
+            "
 
 ",
-            );
+        );
         std::env::set_current_dir(previous).expect("restore cwd");
         if let Some(value) = original_home {
             std::env::set_var("HOME", value);
@@ -828,6 +863,50 @@ mod tests {
         fs::remove_dir_all(root).expect("cleanup temp dir");
     }
 
+    #[test]
+    fn renders_default_claude_model_family_identity() {
+        // given: a prompt builder without an explicit model family override
+        let project_context = ProjectContext {
+            cwd: PathBuf::from("/tmp/project"),
+            current_date: "2026-03-31".to_string(),
+            ..ProjectContext::default()
+        };
+
+        // when: rendering the system prompt environment section
+        let prompt = SystemPromptBuilder::new()
+            .with_os("linux", "6.8")
+            .with_project_context(project_context)
+            .render();
+
+        // then: the Claude model family label is preserved by default
+        assert!(prompt.contains("Model family: Claude Opus 4.6"));
+    }
+
+    #[test]
+    fn renders_generic_model_family_identity_without_claude_label() {
+        // given: a prompt builder with generic model family identity
+        let project_context = ProjectContext {
+            cwd: PathBuf::from("/tmp/project"),
+            current_date: "2026-03-31".to_string(),
+            ..ProjectContext::default()
+        };
+
+        // when: rendering the system prompt environment section
+        let prompt = SystemPromptBuilder::new()
+            .with_os("linux", "6.8")
+            .with_model_family(ModelFamilyIdentity::Generic)
+            .with_project_context(project_context)
+            .render();
+        let model_family_line = prompt
+            .lines()
+            .find(|line| line.contains("Model family:"))
+            .expect("model family line should render");
+
+        // then: the model family line is neutral and excludes Claude Opus 4.6
+        assert_eq!(model_family_line, " - Model family: an AI assistant");
+        assert!(!model_family_line.contains("Claude Opus 4.6"));
+    }
+
     #[test]
     fn renders_claude_code_style_sections_with_project_context() {
         let root = temp_dir();

rust/crates/runtime/src/session.rs

@@ -30,6 +30,10 @@ pub enum ContentBlock {
     Text {
         text: String,
     },
+    Thinking {
+        thinking: String,
+        signature: Option<String>,
+    },
     ToolUse {
         id: String,
         name: String,
@@ -737,6 +741,22 @@ impl ContentBlock {
                 object.insert("type".to_string(), JsonValue::String("text".to_string()));
                 object.insert("text".to_string(), JsonValue::String(text.clone()));
             }
+            Self::Thinking {
+                thinking,
+                signature,
+            } => {
+                object.insert(
+                    "type".to_string(),
+                    JsonValue::String("thinking".to_string()),
+                );
+                object.insert("thinking".to_string(), JsonValue::String(thinking.clone()));
+                if let Some(signature) = signature {
+                    object.insert(
+                        "signature".to_string(),
+                        JsonValue::String(signature.clone()),
+                    );
+                }
+            }
             Self::ToolUse { id, name, input } => {
                 object.insert(
                     "type".to_string(),
@@ -783,6 +803,13 @@ impl ContentBlock {
             "text" => Ok(Self::Text {
                 text: required_string(object, "text")?,
             }),
+            "thinking" => Ok(Self::Thinking {
+                thinking: required_string(object, "thinking")?,
+                signature: object
+                    .get("signature")
+                    .and_then(JsonValue::as_str)
+                    .map(String::from),
+            }),
             "tool_use" => Ok(Self::ToolUse {
                 id: required_string(object, "id")?,
                 name: required_string(object, "name")?,
@@ -1208,6 +1235,36 @@ mod tests {
         assert_eq!(restored.session_id, session.session_id);
     }
 
+    #[test]
+    fn persists_assistant_thinking_block_round_trip_through_jsonl() {
+        // given
+        let mut session = Session::new();
+        session
+            .push_message(ConversationMessage::assistant(vec![
+                ContentBlock::Thinking {
+                    thinking: "trace the path through session persistence".to_string(),
+                    signature: Some("sig-123".to_string()),
+                },
+            ]))
+            .expect("thinking block should append");
+        let path = temp_session_path("thinking-jsonl");
+
+        // when
+        session.save_to_path(&path).expect("session should save");
+        let restored = Session::load_from_path(&path).expect("session should load");
+        fs::remove_file(&path).expect("temp file should be removable");
+
+        // then
+        assert_eq!(restored, session);
+        assert_eq!(
+            restored.messages[0].blocks[0],
+            ContentBlock::Thinking {
+                thinking: "trace the path through session persistence".to_string(),
+                signature: Some("sig-123".to_string()),
+            }
+        );
+    }
+
     #[test]
     fn loads_legacy_session_json_object() {
         let path = temp_session_path("legacy");