fix(seahorse): persist reasoning_content in sqlite history (#2707)

* fix(seahorse): persist reasoning_content in sqlite history

* fix(openai_compat): clarify DeepSeek reasoning replay rules

* style(seahorse): format files of seahorse

* fix(openai_compat): cover DeepSeek replay requirements

* fix(seahorse): repair missing reasoning_content during bootstrap

* fix(seahorse): repair reasoning_content on bootstrap prefix

pkg/providers/openai_compat/provider.go

@@ -270,6 +270,10 @@ func filterDeepSeekReasoningTurn(messages []Message) []Message {
 		}
 
 		cloned := msg
+		// DeepSeek thinking-mode replay only requires reasoning_content for
+		// turns that participate in a tool interaction round. For plain
+		// assistant turns between two user messages, the docs say the API will
+		// ignore reasoning_content on replay, so we strip it here.
 		if cloned.Role == "assistant" && strings.TrimSpace(cloned.ReasoningContent) != "" && !hasToolInteraction {
 			cloned.ReasoningContent = ""
 		}

pkg/providers/openai_compat/provider_test.go

@@ -526,6 +526,112 @@ func TestProviderChat_HistoryCanonicalizationMatrix(t *testing.T) {
 	})
 }
 
+func TestProviderChat_DeepSeekDocsReplayRequirements(t *testing.T) {
+	// DeepSeek's thinking-mode and multi-round chat docs distinguish two cases:
+	// - for a plain assistant turn between two user messages without tool calls,
+	//   reasoning_content does not need to be replayed and the API ignores it if sent;
+	// - for a turn that participates in a tool-interaction round, assistant
+	//   reasoning_content must be replayed on subsequent requests.
+	//
+	// Keep this behavior explicit here so future changes do not "fix" the
+	// non-tool stripping based on issue reports that are broader than the
+	// vendor documentation.
+	var requestBody map[string]any
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if err := json.NewDecoder(r.Body).Decode(&requestBody); err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+		resp := map[string]any{
+			"choices": []map[string]any{
+				{
+					"message":       map[string]any{"content": "ok"},
+					"finish_reason": "stop",
+				},
+			},
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer server.Close()
+
+	p := NewProvider("key", server.URL, "")
+	p.SetProviderName("deepseek")
+
+	messages := []Message{
+		{Role: "user", Content: "Who wrote The Hobbit?"},
+		{Role: "assistant", Content: "J.R.R. Tolkien.", ReasoningContent: "I know this from general knowledge."},
+		{Role: "user", Content: "What's the weather tomorrow?"},
+		{
+			Role:             "assistant",
+			Content:          "Let me check the date first.",
+			ReasoningContent: "I need tomorrow's date before checking the weather.",
+			ToolCalls: []ToolCall{{
+				ID:   "call_date",
+				Type: "function",
+				Function: &FunctionCall{
+					Name:      "get_date",
+					Arguments: "{}",
+				},
+			}},
+		},
+		{Role: "tool", ToolCallID: "call_date", Content: "2026-04-29"},
+		{
+			Role:             "assistant",
+			Content:          "Tomorrow is 2026-04-30.",
+			ReasoningContent: "Now I can continue with the weather request.",
+		},
+		{Role: "user", Content: "What about Guangzhou?"},
+	}
+
+	_, err := p.Chat(t.Context(), messages, nil, "deepseek-v4-flash", nil)
+	if err != nil {
+		t.Fatalf("Chat() error = %v", err)
+	}
+
+	reqMessages, ok := requestBody["messages"].([]any)
+	if !ok {
+		t.Fatalf("messages is not []any: %T", requestBody["messages"])
+	}
+	if len(reqMessages) != len(messages) {
+		t.Fatalf("len(messages) = %d, want %d", len(reqMessages), len(messages))
+	}
+
+	plainAssistant, ok := reqMessages[1].(map[string]any)
+	if !ok {
+		t.Fatalf("plain assistant message is not map[string]any: %T", reqMessages[1])
+	}
+	if _, exists := plainAssistant["reasoning_content"]; exists {
+		t.Fatalf(
+			"plain DeepSeek turn should omit reasoning_content on replay, got %v",
+			plainAssistant["reasoning_content"],
+		)
+	}
+
+	toolAssistant, ok := reqMessages[3].(map[string]any)
+	if !ok {
+		t.Fatalf("tool assistant message is not map[string]any: %T", reqMessages[3])
+	}
+	if toolAssistant["reasoning_content"] != "I need tomorrow's date before checking the weather." {
+		t.Fatalf(
+			"tool assistant reasoning_content = %v, want preserved",
+			toolAssistant["reasoning_content"],
+		)
+	}
+
+	finalAssistant, ok := reqMessages[5].(map[string]any)
+	if !ok {
+		t.Fatalf("final assistant message is not map[string]any: %T", reqMessages[5])
+	}
+	if finalAssistant["reasoning_content"] != "Now I can continue with the weather request." {
+		t.Fatalf(
+			"final assistant reasoning_content = %v, want preserved",
+			finalAssistant["reasoning_content"],
+		)
+	}
+}
+
 func TestProviderChat_HTTPError(t *testing.T) {
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "bad request", http.StatusBadRequest)

pkg/seahorse/schema.go

@@ -46,6 +46,7 @@ func runSchema(db *sql.DB) error {
 			conversation_id INTEGER NOT NULL REFERENCES conversations(conversation_id),
 			role            TEXT NOT NULL,
 			content         TEXT NOT NULL DEFAULT '',
+			reasoning_content TEXT NOT NULL DEFAULT '',
 			token_count     INTEGER NOT NULL DEFAULT 0,
 			created_at      TEXT NOT NULL DEFAULT (datetime('now'))
 		)`,
@@ -157,9 +158,57 @@ func runSchema(db *sql.DB) error {
 			return err
 		}
 	}
+
+	if err := ensureMessagesReasoningContentColumn(db); err != nil {
+		return err
+	}
 	return nil
 }
 
+func ensureMessagesReasoningContentColumn(db *sql.DB) error {
+	hasColumn, err := tableHasColumn(db, "messages", "reasoning_content")
+	if err != nil {
+		return fmt.Errorf("check messages.reasoning_content: %w", err)
+	}
+	if hasColumn {
+		return nil
+	}
+
+	if _, err := db.Exec(`ALTER TABLE messages ADD COLUMN reasoning_content TEXT NOT NULL DEFAULT ''`); err != nil {
+		return fmt.Errorf("add messages.reasoning_content: %w", err)
+	}
+	return nil
+}
+
+func tableHasColumn(db *sql.DB, tableName, columnName string) (bool, error) {
+	rows, err := db.Query(fmt.Sprintf(`PRAGMA table_info(%s)`, tableName))
+	if err != nil {
+		return false, err
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		var (
+			cid        int
+			name       string
+			columnType string
+			notNull    int
+			defaultVal sql.NullString
+			pk         int
+		)
+		if err := rows.Scan(&cid, &name, &columnType, &notNull, &defaultVal, &pk); err != nil {
+			return false, err
+		}
+		if name == columnName {
+			return true, nil
+		}
+	}
+	if err := rows.Err(); err != nil {
+		return false, err
+	}
+	return false, nil
+}
+
 // checkFTS5Support verifies that SQLite has FTS5 with trigram tokenizer enabled.
 // This is required for full-text search with CJK (Chinese, Japanese, Korean) support.
 func checkFTS5Support(db *sql.DB) error {

pkg/seahorse/schema_test.go

@@ -91,6 +91,53 @@ func TestRunMigrationsIdempotent(t *testing.T) {
 	}
 }
 
+func TestRunSchemaAddsMessagesReasoningContentColumn(t *testing.T) {
+	db := openTestDB(t)
+
+	_, err := db.Exec(`CREATE TABLE messages (
+		message_id INTEGER PRIMARY KEY AUTOINCREMENT,
+		conversation_id INTEGER NOT NULL,
+		role TEXT NOT NULL,
+		content TEXT NOT NULL DEFAULT '',
+		token_count INTEGER NOT NULL DEFAULT 0,
+		created_at TEXT NOT NULL DEFAULT (datetime('now'))
+	)`)
+	if err != nil {
+		t.Fatalf("create legacy messages table: %v", err)
+	}
+
+	err = runSchema(db)
+	if err != nil {
+		t.Fatalf("runSchema: %v", err)
+	}
+
+	var count int
+	err = db.QueryRow(`SELECT count(*) FROM pragma_table_info('messages') WHERE name = 'reasoning_content'`).
+		Scan(&count)
+	if err != nil {
+		t.Fatalf("query pragma_table_info: %v", err)
+	}
+	if count != 1 {
+		t.Fatalf("reasoning_content column count = %d, want 1", count)
+	}
+
+	_, err = db.Exec(
+		`INSERT INTO conversations (session_key, created_at, updated_at) VALUES (?, datetime('now'), datetime('now'))`,
+		"reasoning-column-test",
+	)
+	if err != nil {
+		t.Fatalf("insert conversation: %v", err)
+	}
+
+	_, err = db.Exec(
+		`INSERT INTO messages (conversation_id, role, content, reasoning_content, token_count)
+		 VALUES (1, 'assistant', 'answer', 'thinking', 1)`,
+	)
+	if err != nil {
+		t.Fatalf("insert message with reasoning_content: %v", err)
+	}
+}
+
 func TestMigrationConversationUnique(t *testing.T) {
 	db := openTestDB(t)
 	if err := runSchema(db); err != nil {

pkg/seahorse/short_engine.go

@@ -253,9 +253,23 @@ func (e *Engine) Ingest(ctx context.Context, sessionKey string, messages []Messa
 		var added *Message
 		var err error
 		if len(msg.Parts) > 0 {
-			added, err = e.store.AddMessageWithParts(ctx, conv.ConversationID, msg.Role, msg.Parts, msg.TokenCount)
+			added, err = e.store.AddMessageWithPartsAndReasoning(
+				ctx,
+				conv.ConversationID,
+				msg.Role,
+				msg.Parts,
+				msg.ReasoningContent,
+				msg.TokenCount,
+			)
 		} else {
-			added, err = e.store.AddMessage(ctx, conv.ConversationID, msg.Role, msg.Content, msg.TokenCount)
+			added, err = e.store.AddMessageWithReasoning(
+				ctx,
+				conv.ConversationID,
+				msg.Role,
+				msg.Content,
+				msg.ReasoningContent,
+				msg.TokenCount,
+			)
 		}
 		if err != nil {
 			return nil, fmt.Errorf("add message: %w", err)
@@ -420,7 +434,7 @@ func (e *Engine) Bootstrap(ctx context.Context, sessionKey string, messages []Me
 	// Fast path: DB has same count and exact match → no-op
 	if len(dbMsgs) == len(messages) {
 		matched := true
-		for i := 0; i < len(messages); i++ {
+		for i := range messages {
 			if !messageMatches(dbMsgs[i], messages[i]) {
 				matched = false
 				break
@@ -431,14 +445,21 @@ func (e *Engine) Bootstrap(ctx context.Context, sessionKey string, messages []Me
 		}
 	}
 
-	// Find longest matching prefix from the start
-	anchor := -1
-	compareLen := len(dbMsgs)
-	if compareLen > len(messages) {
-		compareLen = len(messages)
+	// Migration repair path: old SeaHorse rows may be missing reasoning_content
+	// even though the canonical JSONL history already has it. Backfill those
+	// rows in place so we do not treat this as edited history and leave stale
+	// summaries/context behind after a partial raw-message rebuild.
+	if repaired, err := e.repairBootstrapReasoningContent(ctx, dbMsgs, messages); err != nil {
+		return fmt.Errorf("bootstrap: repair reasoning_content: %w", err)
+	} else if repaired && len(dbMsgs) == len(messages) {
+		return nil
 	}
 
-	for i := 0; i < compareLen; i++ {
+	// Find longest matching prefix from the start
+	anchor := -1
+	compareLen := min(len(dbMsgs), len(messages))
+
+	for i := range compareLen {
 		if messageMatches(dbMsgs[i], messages[i]) {
 			anchor = i
 		} else {
@@ -524,6 +545,57 @@ func (e *Engine) Bootstrap(ctx context.Context, sessionKey string, messages []Me
 	return nil
 }
 
+func (e *Engine) repairBootstrapReasoningContent(ctx context.Context, dbMsgs, messages []Message) (bool, error) {
+	if len(dbMsgs) == 0 || len(messages) == 0 {
+		return false, nil
+	}
+
+	overlap := min(len(messages), len(dbMsgs))
+
+	var updates []struct {
+		index            int
+		messageID        int64
+		reasoningContent string
+	}
+
+	for i := range overlap {
+		if !messageMatchesIgnoringReasoning(dbMsgs[i], messages[i]) {
+			return false, nil
+		}
+		if dbMsgs[i].ReasoningContent == messages[i].ReasoningContent {
+			continue
+		}
+		if dbMsgs[i].ReasoningContent != "" || messages[i].ReasoningContent == "" {
+			return false, nil
+		}
+		updates = append(updates, struct {
+			index            int
+			messageID        int64
+			reasoningContent string
+		}{
+			index:            i,
+			messageID:        dbMsgs[i].ID,
+			reasoningContent: messages[i].ReasoningContent,
+		})
+	}
+
+	if len(updates) == 0 {
+		return false, nil
+	}
+
+	for _, update := range updates {
+		if err := e.store.UpdateMessageReasoningContent(ctx, update.messageID, update.reasoningContent); err != nil {
+			return false, err
+		}
+		dbMsgs[update.index].ReasoningContent = update.reasoningContent
+	}
+
+	logger.InfoCF("seahorse", "bootstrap: repaired missing reasoning_content", map[string]any{
+		"messages": len(updates),
+	})
+	return true, nil
+}
+
 // truncate shortens a string for logging.
 func truncate(s string, maxLen int) string {
 	if len(s) <= maxLen {
@@ -532,12 +604,19 @@ func truncate(s string, maxLen int) string {
 	return s[:maxLen] + "..."
 }
 
-// messageMatches compares two messages using (role, content) or (role, parts).
-// TokenCount is NOT compared because it may be re-estimated differently
-// during bootstrap (e.g., via tokenizer.EstimateMessageTokens).
+// messageMatches compares two messages using role + reasoning_content and then
+// either content or parts. TokenCount is NOT compared because it may be
+// re-estimated differently during bootstrap (e.g., via tokenizer.EstimateMessageTokens).
 // For messages with Parts (tool_use, tool_result), compare Parts instead of Content
-// since AddMessageWithParts stores empty Content in DB.
+// because structured messages are matched by their parts payload.
 func messageMatches(a, b Message) bool {
+	if a.Role != b.Role || a.ReasoningContent != b.ReasoningContent {
+		return false
+	}
+	return messageMatchesIgnoringReasoning(a, b)
+}
+
+func messageMatchesIgnoringReasoning(a, b Message) bool {
 	if a.Role != b.Role {
 		return false
 	}

pkg/seahorse/short_engine_test.go

@@ -320,6 +320,108 @@ func TestEngineIngestWithParts(t *testing.T) {
 	}
 }
 
+func TestEngineIngestPreservesReasoningContent(t *testing.T) {
+	eng := newTestEngine(t)
+	ctx := context.Background()
+
+	msgs := []Message{
+		{
+			Role:             "assistant",
+			Content:          "world",
+			ReasoningContent: "let me think this through",
+			TokenCount:       4,
+		},
+	}
+
+	_, err := eng.Ingest(ctx, "agent:reasoning", msgs)
+	if err != nil {
+		t.Fatalf("Ingest: %v", err)
+	}
+
+	conv, _ := eng.store.GetOrCreateConversation(ctx, "agent:reasoning")
+	stored, err := eng.store.GetMessages(ctx, conv.ConversationID, 10, 0)
+	if err != nil {
+		t.Fatalf("GetMessages: %v", err)
+	}
+	if len(stored) != 1 {
+		t.Fatalf("stored messages = %d, want 1", len(stored))
+	}
+	if stored[0].ReasoningContent != "let me think this through" {
+		t.Errorf(
+			"stored[0].ReasoningContent = %q, want %q",
+			stored[0].ReasoningContent,
+			"let me think this through",
+		)
+	}
+
+	result, err := eng.Assemble(ctx, "agent:reasoning", AssembleInput{Budget: 1000})
+	if err != nil {
+		t.Fatalf("Assemble: %v", err)
+	}
+	if len(result.Messages) != 1 {
+		t.Fatalf("assembled messages = %d, want 1", len(result.Messages))
+	}
+	if result.Messages[0].ReasoningContent != "let me think this through" {
+		t.Errorf(
+			"assembled reasoning = %q, want %q",
+			result.Messages[0].ReasoningContent,
+			"let me think this through",
+		)
+	}
+}
+
+func TestEngineIngestWithPartsPreservesReasoningContent(t *testing.T) {
+	eng := newTestEngine(t)
+	ctx := context.Background()
+
+	msgs := []Message{
+		{
+			Role:             "assistant",
+			ReasoningContent: "I need to inspect the file first",
+			TokenCount:       10,
+			Parts: []MessagePart{
+				{Type: "tool_use", Name: "read_file", Arguments: `{"path":"/tmp/test"}`, ToolCallID: "tc_123"},
+			},
+		},
+	}
+
+	_, err := eng.Ingest(ctx, "agent:parts-reasoning", msgs)
+	if err != nil {
+		t.Fatalf("Ingest: %v", err)
+	}
+
+	conv, _ := eng.store.GetOrCreateConversation(ctx, "agent:parts-reasoning")
+	stored, err := eng.store.GetMessages(ctx, conv.ConversationID, 10, 0)
+	if err != nil {
+		t.Fatalf("GetMessages: %v", err)
+	}
+	if len(stored) != 1 {
+		t.Fatalf("stored messages = %d, want 1", len(stored))
+	}
+	if stored[0].ReasoningContent != "I need to inspect the file first" {
+		t.Errorf(
+			"stored reasoning = %q, want %q",
+			stored[0].ReasoningContent,
+			"I need to inspect the file first",
+		)
+	}
+
+	result, err := eng.Assemble(ctx, "agent:parts-reasoning", AssembleInput{Budget: 1000})
+	if err != nil {
+		t.Fatalf("Assemble: %v", err)
+	}
+	if len(result.Messages) != 1 {
+		t.Fatalf("assembled messages = %d, want 1", len(result.Messages))
+	}
+	if result.Messages[0].ReasoningContent != "I need to inspect the file first" {
+		t.Errorf(
+			"assembled reasoning = %q, want %q",
+			result.Messages[0].ReasoningContent,
+			"I need to inspect the file first",
+		)
+	}
+}
+
 func TestEngineIngestAssemblePreservesParts(t *testing.T) {
 	eng := newTestEngine(t)
 	ctx := context.Background()
@@ -514,6 +616,216 @@ func TestEngineBootstrapIdempotent(t *testing.T) {
 	}
 }
 
+func TestBootstrapRepairsMissingReasoningContent(t *testing.T) {
+	eng := newTestEngine(t)
+	ctx := context.Background()
+	sessionKey := "agent:repair-reasoning"
+
+	conv, err := eng.store.GetOrCreateConversation(ctx, sessionKey)
+	if err != nil {
+		t.Fatalf("GetOrCreateConversation: %v", err)
+	}
+
+	userMsg, err := eng.store.AddMessage(ctx, conv.ConversationID, "user", "hello", 3)
+	if err != nil {
+		t.Fatalf("AddMessage user: %v", err)
+	}
+
+	assistantMsg, err := eng.store.AddMessage(ctx, conv.ConversationID, "assistant", "world", 3)
+	if err != nil {
+		t.Fatalf("AddMessage assistant: %v", err)
+	}
+
+	err = eng.store.AppendContextMessages(
+		ctx,
+		conv.ConversationID,
+		[]int64{userMsg.ID, assistantMsg.ID},
+	)
+	if err != nil {
+		t.Fatalf("AppendContextMessages: %v", err)
+	}
+
+	err = eng.Bootstrap(ctx, sessionKey, []Message{
+		{Role: "user", Content: "hello", TokenCount: 3},
+		{Role: "assistant", Content: "world", ReasoningContent: "let me think this through", TokenCount: 3},
+	})
+	if err != nil {
+		t.Fatalf("Bootstrap: %v", err)
+	}
+
+	stored, err := eng.store.GetMessages(ctx, conv.ConversationID, 10, 0)
+	if err != nil {
+		t.Fatalf("GetMessages: %v", err)
+	}
+	if len(stored) != 2 {
+		t.Fatalf("stored messages = %d, want 2", len(stored))
+	}
+	if stored[1].ReasoningContent != "let me think this through" {
+		t.Errorf(
+			"stored[1].ReasoningContent = %q, want %q",
+			stored[1].ReasoningContent,
+			"let me think this through",
+		)
+	}
+}
+
+func TestBootstrapRepairsMissingReasoningContentWithoutDroppingSummaries(t *testing.T) {
+	eng := newTestEngine(t)
+	ctx := context.Background()
+	sessionKey := "agent:repair-reasoning-summary"
+
+	conv, err := eng.store.GetOrCreateConversation(ctx, sessionKey)
+	if err != nil {
+		t.Fatalf("GetOrCreateConversation: %v", err)
+	}
+
+	userMsg, err := eng.store.AddMessage(ctx, conv.ConversationID, "user", "hello", 3)
+	if err != nil {
+		t.Fatalf("AddMessage user: %v", err)
+	}
+	assistantMsg, err := eng.store.AddMessage(ctx, conv.ConversationID, "assistant", "world", 3)
+	if err != nil {
+		t.Fatalf("AddMessage assistant: %v", err)
+	}
+
+	err = eng.store.AppendContextMessages(
+		ctx,
+		conv.ConversationID,
+		[]int64{userMsg.ID, assistantMsg.ID},
+	)
+	if err != nil {
+		t.Fatalf("AppendContextMessages: %v", err)
+	}
+
+	summary, err := eng.store.CreateSummary(ctx, CreateSummaryInput{
+		ConversationID: conv.ConversationID,
+		Kind:           SummaryKindLeaf,
+		Depth:          0,
+		Content:        "summary before repair",
+		TokenCount:     10,
+	})
+	if err != nil {
+		t.Fatalf("CreateSummary: %v", err)
+	}
+
+	err = eng.store.AppendContextSummary(ctx, conv.ConversationID, summary.SummaryID)
+	if err != nil {
+		t.Fatalf("AppendContextSummary: %v", err)
+	}
+
+	err = eng.Bootstrap(ctx, sessionKey, []Message{
+		{Role: "user", Content: "hello", TokenCount: 3},
+		{Role: "assistant", Content: "world", ReasoningContent: "let me think this through", TokenCount: 3},
+	})
+	if err != nil {
+		t.Fatalf("Bootstrap: %v", err)
+	}
+
+	stored, err := eng.store.GetMessages(ctx, conv.ConversationID, 10, 0)
+	if err != nil {
+		t.Fatalf("GetMessages: %v", err)
+	}
+	if len(stored) != 2 {
+		t.Fatalf("stored messages = %d, want 2", len(stored))
+	}
+	if stored[1].ReasoningContent != "let me think this through" {
+		t.Errorf(
+			"stored[1].ReasoningContent = %q, want %q",
+			stored[1].ReasoningContent,
+			"let me think this through",
+		)
+	}
+
+	summaries, err := eng.store.GetSummariesByConversation(ctx, conv.ConversationID)
+	if err != nil {
+		t.Fatalf("GetSummariesByConversation: %v", err)
+	}
+	if len(summaries) != 1 {
+		t.Fatalf("summaries = %d, want 1", len(summaries))
+	}
+	if summaries[0].SummaryID != summary.SummaryID {
+		t.Errorf("SummaryID = %q, want %q", summaries[0].SummaryID, summary.SummaryID)
+	}
+
+	items, err := eng.store.GetContextItems(ctx, conv.ConversationID)
+	if err != nil {
+		t.Fatalf("GetContextItems: %v", err)
+	}
+	if len(items) != 3 {
+		t.Fatalf("context items = %d, want 3", len(items))
+	}
+	if items[2].ItemType != "summary" || items[2].SummaryID != summary.SummaryID {
+		t.Errorf("summary context item = %+v, want summary %q", items[2], summary.SummaryID)
+	}
+}
+
+func TestBootstrapRepairsMissingReasoningContentOnPrefixBeforeAppendingDelta(t *testing.T) {
+	eng := newTestEngine(t)
+	ctx := context.Background()
+	sessionKey := "agent:repair-reasoning-prefix"
+
+	conv, err := eng.store.GetOrCreateConversation(ctx, sessionKey)
+	if err != nil {
+		t.Fatalf("GetOrCreateConversation: %v", err)
+	}
+
+	userMsg, err := eng.store.AddMessage(ctx, conv.ConversationID, "user", "hello", 3)
+	if err != nil {
+		t.Fatalf("AddMessage user: %v", err)
+	}
+	assistantMsg, err := eng.store.AddMessage(ctx, conv.ConversationID, "assistant", "world", 3)
+	if err != nil {
+		t.Fatalf("AddMessage assistant: %v", err)
+	}
+
+	err = eng.store.AppendContextMessages(
+		ctx,
+		conv.ConversationID,
+		[]int64{userMsg.ID, assistantMsg.ID},
+	)
+	if err != nil {
+		t.Fatalf("AppendContextMessages: %v", err)
+	}
+
+	err = eng.Bootstrap(ctx, sessionKey, []Message{
+		{Role: "user", Content: "hello", TokenCount: 3},
+		{Role: "assistant", Content: "world", ReasoningContent: "let me think this through", TokenCount: 3},
+		{Role: "user", Content: "follow-up", TokenCount: 2},
+	})
+	if err != nil {
+		t.Fatalf("Bootstrap: %v", err)
+	}
+
+	stored, err := eng.store.GetMessages(ctx, conv.ConversationID, 10, 0)
+	if err != nil {
+		t.Fatalf("GetMessages: %v", err)
+	}
+	if len(stored) != 3 {
+		t.Fatalf("stored messages = %d, want 3", len(stored))
+	}
+	if stored[1].ReasoningContent != "let me think this through" {
+		t.Errorf(
+			"stored[1].ReasoningContent = %q, want %q",
+			stored[1].ReasoningContent,
+			"let me think this through",
+		)
+	}
+	if stored[2].Content != "follow-up" {
+		t.Errorf("stored[2].Content = %q, want %q", stored[2].Content, "follow-up")
+	}
+
+	items, err := eng.store.GetContextItems(ctx, conv.ConversationID)
+	if err != nil {
+		t.Fatalf("GetContextItems: %v", err)
+	}
+	if len(items) != 3 {
+		t.Fatalf("context items = %d, want 3", len(items))
+	}
+	if items[2].ItemType != "message" || items[2].MessageID != stored[2].ID {
+		t.Errorf("last context item = %+v, want appended message %d", items[2], stored[2].ID)
+	}
+}
+
 func TestEngineBootstrapDelta(t *testing.T) {
 	eng := newTestEngine(t)
 	ctx := context.Background()

pkg/seahorse/store.go

@@ -162,20 +162,31 @@ func (s *Store) getMessageTimeRange(ctx context.Context, convID int64) (time.Tim
 
 // AddMessage appends a message to a conversation.
 func (s *Store) AddMessage(ctx context.Context, convID int64, role, content string, tokenCount int) (*Message, error) {
+	return s.AddMessageWithReasoning(ctx, convID, role, content, "", tokenCount)
+}
+
+// AddMessageWithReasoning appends a message with reasoning content to a conversation.
+func (s *Store) AddMessageWithReasoning(
+	ctx context.Context,
+	convID int64,
+	role, content, reasoningContent string,
+	tokenCount int,
+) (*Message, error) {
 	result, err := s.db.ExecContext(ctx,
-		"INSERT INTO messages (conversation_id, role, content, token_count) VALUES (?, ?, ?, ?)",
-		convID, role, content, tokenCount,
+		"INSERT INTO messages (conversation_id, role, content, reasoning_content, token_count) VALUES (?, ?, ?, ?, ?)",
+		convID, role, content, reasoningContent, tokenCount,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("add message: %w", err)
 	}
 	id, _ := result.LastInsertId()
 	return &Message{
-		ID:             id,
-		ConversationID: convID,
-		Role:           role,
-		Content:        content,
-		TokenCount:     tokenCount,
+		ID:               id,
+		ConversationID:   convID,
+		Role:             role,
+		Content:          content,
+		ReasoningContent: reasoningContent,
+		TokenCount:       tokenCount,
 	}, nil
 }
 
@@ -212,6 +223,18 @@ func (s *Store) AddMessageWithParts(
 	role string,
 	parts []MessagePart,
 	tokenCount int,
+) (*Message, error) {
+	return s.AddMessageWithPartsAndReasoning(ctx, convID, role, parts, "", tokenCount)
+}
+
+// AddMessageWithPartsAndReasoning adds a message with structured parts and reasoning content.
+func (s *Store) AddMessageWithPartsAndReasoning(
+	ctx context.Context,
+	convID int64,
+	role string,
+	parts []MessagePart,
+	reasoningContent string,
+	tokenCount int,
 ) (*Message, error) {
 	tx, err := s.db.BeginTx(ctx, nil)
 	if err != nil {
@@ -223,8 +246,8 @@ func (s *Store) AddMessageWithParts(
 	readableContent := partsToReadableContent(parts)
 
 	result, err := tx.ExecContext(ctx,
-		"INSERT INTO messages (conversation_id, role, content, token_count) VALUES (?, ?, ?, ?)",
-		convID, role, readableContent, tokenCount,
+		"INSERT INTO messages (conversation_id, role, content, reasoning_content, token_count) VALUES (?, ?, ?, ?, ?)",
+		convID, role, readableContent, reasoningContent, tokenCount,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("add message: %w", err)
@@ -256,11 +279,12 @@ func (s *Store) AddMessageWithParts(
 
 	// Return message with parts
 	msg := &Message{
-		ID:             msgID,
-		ConversationID: convID,
-		Role:           role,
-		TokenCount:     tokenCount,
-		Parts:          make([]MessagePart, len(parts)),
+		ID:               msgID,
+		ConversationID:   convID,
+		Role:             role,
+		ReasoningContent: reasoningContent,
+		TokenCount:       tokenCount,
+		Parts:            make([]MessagePart, len(parts)),
 	}
 	for i, p := range parts {
 		p.MessageID = msgID
@@ -271,7 +295,7 @@ func (s *Store) AddMessageWithParts(
 
 // GetMessages retrieves messages for a conversation.
 func (s *Store) GetMessages(ctx context.Context, convID int64, limit int, beforeID int64) ([]Message, error) {
-	query := "SELECT message_id, conversation_id, role, content, token_count, created_at FROM messages WHERE conversation_id = ?"
+	query := "SELECT message_id, conversation_id, role, content, reasoning_content, token_count, created_at FROM messages WHERE conversation_id = ?"
 	args := []any{convID}
 	if beforeID > 0 {
 		query += " AND message_id < ?"
@@ -298,6 +322,7 @@ func (s *Store) GetMessages(ctx context.Context, convID int64, limit int, before
 			&msg.ConversationID,
 			&msg.Role,
 			&msg.Content,
+			&msg.ReasoningContent,
 			&msg.TokenCount,
 			&createdAt,
 		); err != nil {
@@ -335,10 +360,11 @@ func (s *Store) GetMessageCount(ctx context.Context, convID int64) (int, error)
 func (s *Store) GetMessageByID(ctx context.Context, messageID int64) (*Message, error) {
 	var msg Message
 	var createdAt string
-	err := s.db.QueryRowContext(ctx,
-		"SELECT message_id, conversation_id, role, content, token_count, created_at FROM messages WHERE message_id = ?",
+	err := s.db.QueryRowContext(
+		ctx,
+		"SELECT message_id, conversation_id, role, content, reasoning_content, token_count, created_at FROM messages WHERE message_id = ?",
 		messageID,
-	).Scan(&msg.ID, &msg.ConversationID, &msg.Role, &msg.Content, &msg.TokenCount, &createdAt)
+	).Scan(&msg.ID, &msg.ConversationID, &msg.Role, &msg.Content, &msg.ReasoningContent, &msg.TokenCount, &createdAt)
 	if err == sql.ErrNoRows {
 		return nil, fmt.Errorf("message %d not found", messageID)
 	}
@@ -350,6 +376,28 @@ func (s *Store) GetMessageByID(ctx context.Context, messageID int64) (*Message,
 	return &msg, nil
 }
 
+// UpdateMessageReasoningContent updates reasoning_content for an existing message.
+func (s *Store) UpdateMessageReasoningContent(ctx context.Context, messageID int64, reasoningContent string) error {
+	result, err := s.db.ExecContext(
+		ctx,
+		"UPDATE messages SET reasoning_content = ? WHERE message_id = ?",
+		reasoningContent,
+		messageID,
+	)
+	if err != nil {
+		return fmt.Errorf("update message reasoning_content: %w", err)
+	}
+
+	rowsAffected, err := result.RowsAffected()
+	if err != nil {
+		return fmt.Errorf("update message reasoning_content rows affected: %w", err)
+	}
+	if rowsAffected == 0 {
+		return fmt.Errorf("message %d not found", messageID)
+	}
+	return nil
+}
+
 func (s *Store) loadMessageParts(ctx context.Context, msgID int64) ([]MessagePart, error) {
 	rows, err := s.db.QueryContext(ctx,
 		`SELECT part_id, message_id, type, text, name, arguments, tool_call_id, media_uri, mime_type
@@ -534,7 +582,7 @@ func (s *Store) LinkSummaryToMessages(ctx context.Context, summaryID string, mes
 // GetSummarySourceMessages retrieves source messages for a summary.
 func (s *Store) GetSummarySourceMessages(ctx context.Context, summaryID string) ([]Message, error) {
 	rows, err := s.db.QueryContext(ctx,
-		`SELECT m.message_id, m.conversation_id, m.role, m.content, m.token_count, m.created_at
+		`SELECT m.message_id, m.conversation_id, m.role, m.content, m.reasoning_content, m.token_count, m.created_at
 		 FROM summary_messages sm
 		 JOIN messages m ON m.message_id = sm.message_id
 		 WHERE sm.summary_id = ?
@@ -555,6 +603,7 @@ func (s *Store) GetSummarySourceMessages(ctx context.Context, summaryID string)
 			&msg.ConversationID,
 			&msg.Role,
 			&msg.Content,
+			&msg.ReasoningContent,
 			&msg.TokenCount,
 			&createdAt,
 		); err != nil {

pkg/seahorse/store_test.go

@@ -199,6 +199,47 @@ func TestStoreAddAndGetMessages(t *testing.T) {
 	}
 }
 
+func TestStoreAddAndGetMessagesWithReasoningContent(t *testing.T) {
+	s := openTestStore(t)
+	ctx := context.Background()
+
+	conv, _ := s.GetOrCreateConversation(ctx, "agent:reasoning")
+
+	msg, err := s.AddMessageWithReasoning(
+		ctx,
+		conv.ConversationID,
+		"assistant",
+		"hello world",
+		"let me think",
+		5,
+	)
+	if err != nil {
+		t.Fatalf("AddMessageWithReasoning: %v", err)
+	}
+	if msg.ReasoningContent != "let me think" {
+		t.Fatalf("ReasoningContent = %q, want %q", msg.ReasoningContent, "let me think")
+	}
+
+	msgs, err := s.GetMessages(ctx, conv.ConversationID, 10, 0)
+	if err != nil {
+		t.Fatalf("GetMessages: %v", err)
+	}
+	if len(msgs) != 1 {
+		t.Fatalf("got %d messages, want 1", len(msgs))
+	}
+	if msgs[0].ReasoningContent != "let me think" {
+		t.Errorf("ReasoningContent = %q, want %q", msgs[0].ReasoningContent, "let me think")
+	}
+
+	found, err := s.GetMessageByID(ctx, msg.ID)
+	if err != nil {
+		t.Fatalf("GetMessageByID: %v", err)
+	}
+	if found.ReasoningContent != "let me think" {
+		t.Errorf("GetMessageByID ReasoningContent = %q, want %q", found.ReasoningContent, "let me think")
+	}
+}
+
 func TestStoreAddMessageWithParts(t *testing.T) {
 	s := openTestStore(t)
 	ctx := context.Background()
@@ -233,6 +274,43 @@ func TestStoreAddMessageWithParts(t *testing.T) {
 	}
 }
 
+func TestStoreAddMessageWithPartsAndReasoningContent(t *testing.T) {
+	s := openTestStore(t)
+	ctx := context.Background()
+
+	conv, _ := s.GetOrCreateConversation(ctx, "agent:parts-reasoning")
+
+	parts := []MessagePart{
+		{Type: "tool_use", Name: "read_file", Arguments: `{"path":"/tmp/test"}`, ToolCallID: "tc_123"},
+	}
+	_, err := s.AddMessageWithPartsAndReasoning(
+		ctx,
+		conv.ConversationID,
+		"assistant",
+		parts,
+		"need to inspect the file first",
+		10,
+	)
+	if err != nil {
+		t.Fatalf("AddMessageWithPartsAndReasoning: %v", err)
+	}
+
+	msgs, err := s.GetMessages(ctx, conv.ConversationID, 10, 0)
+	if err != nil {
+		t.Fatalf("GetMessages: %v", err)
+	}
+	if len(msgs) != 1 {
+		t.Fatalf("expected 1 message, got %d", len(msgs))
+	}
+	if msgs[0].ReasoningContent != "need to inspect the file first" {
+		t.Errorf(
+			"ReasoningContent = %q, want %q",
+			msgs[0].ReasoningContent,
+			"need to inspect the file first",
+		)
+	}
+}
+
 func TestStoreGetMessageCount(t *testing.T) {
 	s := openTestStore(t)
 	ctx := context.Background()
@@ -275,6 +353,31 @@ func TestStoreGetMessageByID(t *testing.T) {
 	}
 }
 
+func TestStoreUpdateMessageReasoningContent(t *testing.T) {
+	s := openTestStore(t)
+	ctx := context.Background()
+
+	conv, _ := s.GetOrCreateConversation(ctx, "agent:update-reasoning")
+
+	msg, err := s.AddMessage(ctx, conv.ConversationID, "assistant", "answer", 3)
+	if err != nil {
+		t.Fatalf("AddMessage: %v", err)
+	}
+
+	err = s.UpdateMessageReasoningContent(ctx, msg.ID, "thinking")
+	if err != nil {
+		t.Fatalf("UpdateMessageReasoningContent: %v", err)
+	}
+
+	found, err := s.GetMessageByID(ctx, msg.ID)
+	if err != nil {
+		t.Fatalf("GetMessageByID: %v", err)
+	}
+	if found.ReasoningContent != "thinking" {
+		t.Errorf("ReasoningContent = %q, want %q", found.ReasoningContent, "thinking")
+	}
+}
+
 // --- Summary Operations ---
 
 func TestStoreCreateAndGetSummary(t *testing.T) {