diff --git a/backend/services/chat.py b/backend/services/chat.py
index c8bb3c3..ac1602f 100644
--- a/backend/services/chat.py
+++ b/backend/services/chat.py
@@ -90,8 +90,21 @@ class ChatService:
             total_prompt_tokens = 0
 
             for iteration in range(MAX_ITERATIONS):
+                # Helper to parse stream_result event
+                def parse_stream_result(event_str):
+                    """Parse stream_result SSE event and extract data dict."""
+                    # Format: "event: stream_result\ndata: {...}\n\n"
+                    try:
+                        for line in event_str.split('\n'):
+                            if line.startswith('data: '):
+                                return json.loads(line[6:])
+                    except Exception:
+                        pass
+                    return None
+
+                # Collect SSE events and extract final stream_result
                 try:
-                    stream_result = self._stream_llm_response(
+                    stream_gen = self._stream_llm_response(
                         app, messages, tools, tool_choice, step_index,
                         conv_model, conv_max_tokens, conv_temperature,
                         conv_thinking_enabled,
@@ -116,22 +129,37 @@ class ChatService:
                     yield _sse_event("error", {"content": f"Internal error: {e}"})
                     return
 
-                if stream_result is None:
-                    return  # Client disconnected
+                result_data = None
+                try:
+                    for event_str in stream_gen:
+                        # Check if this is a stream_result event (final event)
+                        if event_str.startswith("event: stream_result"):
+                            result_data = parse_stream_result(event_str)
+                        else:
+                            # Forward process_step events to client in real-time
+                            yield event_str
+                except Exception as e:
+                    logger.exception("Error during streaming")
+                    yield _sse_event("error", {"content": f"Stream error: {e}"})
+                    return
 
-                full_content, full_thinking, tool_calls_list, \
-                    thinking_step_id, thinking_step_idx, \
-                    text_step_id, text_step_idx, \
-                    completion_tokens, prompt_tokens, \
-                    sse_chunks = stream_result
+                if result_data is None:
+                    return  # Client disconnected or error
+
+                # Extract data from stream_result
+                full_content = result_data["full_content"]
+                full_thinking = result_data["full_thinking"]
+                tool_calls_list = result_data["tool_calls_list"]
+                thinking_step_id = result_data["thinking_step_id"]
+                thinking_step_idx = result_data["thinking_step_idx"]
+                text_step_id = result_data["text_step_id"]
+                text_step_idx = result_data["text_step_idx"]
+                completion_tokens = result_data["completion_tokens"]
+                prompt_tokens = result_data["prompt_tokens"]
 
                 total_prompt_tokens += prompt_tokens
                 total_completion_tokens += completion_tokens
 
-                # Yield accumulated SSE chunks to frontend
-                for chunk in sse_chunks:
-                    yield chunk
-
                 # Save thinking/text steps to all_steps for DB storage
                 if thinking_step_id is not None:
                     all_steps.append({
@@ -244,10 +272,16 @@ class ChatService:
         self, app, messages, tools, tool_choice, step_index,
         model, max_tokens, temperature, thinking_enabled,
     ):
-        """Call LLM streaming API and parse the response.
+        """Call LLM streaming API and yield SSE events in real-time.
 
-        Returns a tuple of parsed results, or None if the client disconnected.
-        Raises HTTPError / ConnectionError / Timeout for the caller to handle.
+        This is a generator that yields SSE event strings as they are received.
+        The final yield is a 'stream_result' event containing the accumulated data.
+
+        Yields:
+            str: SSE event strings (process_step events, then stream_result)
+
+        Raises:
+            HTTPError / ConnectionError / Timeout for the caller to handle.
         """
         full_content = ""
         full_thinking = ""
@@ -260,8 +294,6 @@ class ChatService:
         text_step_id = None
         text_step_idx = None
 
-        sse_chunks = []  # Collect SSE events to yield later
-
         with app.app_context():
             resp = self.llm.call(
                 model=model,
@@ -278,7 +310,7 @@ class ChatService:
         for line in resp.iter_lines():
             if _client_disconnected():
                 resp.close()
-                return None
+                return  # Client disconnected, stop generator
 
             if not line:
                 continue
@@ -304,37 +336,44 @@ class ChatService:
 
             delta = choices[0].get("delta", {})
 
+            # Yield thinking content in real-time
             reasoning = delta.get("reasoning_content", "")
             if reasoning:
                 full_thinking += reasoning
                 if thinking_step_id is None:
                     thinking_step_id = f"step-{step_index}"
                     thinking_step_idx = step_index
-                sse_chunks.append(_sse_event("process_step", {
+                yield _sse_event("process_step", {
                     "id": thinking_step_id, "index": thinking_step_idx,
                     "type": "thinking", "content": full_thinking,
-                }))
+                })
 
+            # Yield text content in real-time
             text = delta.get("content", "")
             if text:
                 full_content += text
                 if text_step_id is None:
                     text_step_idx = step_index + (1 if thinking_step_id is not None else 0)
                     text_step_id = f"step-{text_step_idx}"
-                sse_chunks.append(_sse_event("process_step", {
+                yield _sse_event("process_step", {
                     "id": text_step_id, "index": text_step_idx,
                     "type": "text", "content": full_content,
-                }))
+                })
 
             tool_calls_list = self._process_tool_calls_delta(delta, tool_calls_list)
 
-        return (
-            full_content, full_thinking, tool_calls_list,
-            thinking_step_id, thinking_step_idx,
-            text_step_id, text_step_idx,
-            token_count, prompt_tokens,
-            sse_chunks,
-        )
+        # Final yield: stream_result event with accumulated data
+        yield _sse_event("stream_result", {
+            "full_content": full_content,
+            "full_thinking": full_thinking,
+            "tool_calls_list": tool_calls_list,
+            "thinking_step_id": thinking_step_id,
+            "thinking_step_idx": thinking_step_idx,
+            "text_step_id": text_step_id,
+            "text_step_idx": text_step_idx,
+            "completion_tokens": token_count,
+            "prompt_tokens": prompt_tokens,
+        })
 
     def _execute_tools_safe(self, app, executor, tool_calls_list, context):
         """Execute tool calls with top-level error wrapping.
diff --git a/frontend/src/App.vue b/frontend/src/App.vue
index efc4ccd..602f537 100644
--- a/frontend/src/App.vue
+++ b/frontend/src/App.vue
@@ -121,6 +121,11 @@ import ModalDialog from './components/ModalDialog.vue'
 import ToastContainer from './components/ToastContainer.vue'
 import { icons } from './utils/icons'
 import { useModal } from './composables/useModal'
+import {
+  DEFAULT_CONVERSATION_PAGE_SIZE,
+  DEFAULT_MESSAGE_PAGE_SIZE,
+  LS_KEY_TOOLS_ENABLED,
+} from './constants'
 
 const SettingsPanel = defineAsyncComponent(() => import('./components/SettingsPanel.vue'))
 const StatsPanel = defineAsyncComponent(() => import('./components/StatsPanel.vue'))
@@ -226,7 +231,7 @@ function updateStreamField(convId, field, ref, valueOrUpdater) {
 // -- UI state --
 const showSettings = ref(false)
 const showStats = ref(false)
-const toolsEnabled = ref(localStorage.getItem('tools_enabled') !== 'false')
+const toolsEnabled = ref(localStorage.getItem(LS_KEY_TOOLS_ENABLED) !== 'false')
 const currentProject = ref(null)
 const showFileExplorer = ref(false)
 const showCreateModal = ref(false)
@@ -250,7 +255,7 @@ async function loadConversations(reset = true) {
   if (loadingConvs.value) return
   loadingConvs.value = true
   try {
-    const res = await conversationApi.list(reset ? null : nextConvCursor.value, 20)
+    const res = await conversationApi.list(reset ? null : nextConvCursor.value, DEFAULT_CONVERSATION_PAGE_SIZE)
     if (reset) {
       conversations.value = res.data.items
     } else {
@@ -436,7 +441,7 @@ function createStreamCallbacks(convId, { updateConvList = true } = {}) {
         }
       } else {
         try {
-          const res = await messageApi.list(convId, null, 50)
+          const res = await messageApi.list(convId, null, DEFAULT_MESSAGE_PAGE_SIZE)
           const idx = conversations.value.findIndex(c => c.id === convId)
           if (idx >= 0) {
             const conv = conversations.value[idx]
@@ -557,7 +562,7 @@ async function saveSettings(data) {
 // -- Update tools enabled --
 function updateToolsEnabled(val) {
   toolsEnabled.value = val
-  localStorage.setItem('tools_enabled', String(val))
+  localStorage.setItem(LS_KEY_TOOLS_ENABLED, String(val))
 }
 
 // -- Browse project files --
diff --git a/frontend/src/api/index.js b/frontend/src/api/index.js
index fa32b1c..669f236 100644
--- a/frontend/src/api/index.js
+++ b/frontend/src/api/index.js
@@ -1,4 +1,11 @@
-const BASE = '/api'
+import {
+  API_BASE_URL,
+  CONTENT_TYPE_JSON,
+  LS_KEY_MODELS_CACHE,
+  DEFAULT_CONVERSATION_PAGE_SIZE,
+  DEFAULT_MESSAGE_PAGE_SIZE,
+  DEFAULT_PROJECT_PAGE_SIZE,
+} from '../constants'
 
 // Cache for models list
 let modelsCache = null
@@ -13,8 +20,8 @@ function buildQueryParams(params) {
 }
 
 async function request(url, options = {}) {
-  const res = await fetch(`${BASE}${url}`, {
-    headers: { 'Content-Type': 'application/json' },
+  const res = await fetch(`${API_BASE_URL}${url}`, {
+    headers: { 'Content-Type': CONTENT_TYPE_JSON },
     ...options,
     body: options.body ? JSON.stringify(options.body) : undefined,
   })
@@ -37,9 +44,9 @@ function createSSEStream(url, body, { onProcessStep, onDone, onError }) {
 
   const promise = (async () => {
     try {
-      const res = await fetch(`${BASE}${url}`, {
+      const res = await fetch(`${API_BASE_URL}${url}`, {
         method: 'POST',
-        headers: { 'Content-Type': 'application/json' },
+        headers: { 'Content-Type': CONTENT_TYPE_JSON },
         body: JSON.stringify(body),
         signal: controller.signal,
       })
@@ -107,7 +114,7 @@ export const modelApi = {
     }
 
     // Try localStorage cache first
-    const cached = localStorage.getItem('models_cache')
+    const cached = localStorage.getItem(LS_KEY_MODELS_CACHE)
     if (cached) {
       try {
         modelsCache = JSON.parse(cached)
@@ -118,7 +125,7 @@ export const modelApi = {
     // Fetch from server
     const res = await this.list()
     modelsCache = res.data
-    localStorage.setItem('models_cache', JSON.stringify(modelsCache))
+    localStorage.setItem(LS_KEY_MODELS_CACHE, JSON.stringify(modelsCache))
     return res
   },
 
@@ -131,7 +138,7 @@ export const statsApi = {
 }
 
 export const conversationApi = {
-  list(cursor, limit = 20, projectId = null) {
+  list(cursor, limit = DEFAULT_CONVERSATION_PAGE_SIZE, projectId = null) {
     return request(`/conversations${buildQueryParams({ cursor, limit, project_id: projectId })}`)
   },
 
@@ -159,7 +166,7 @@ export const conversationApi = {
 }
 
 export const messageApi = {
-  list(convId, cursor, limit = 50) {
+  list(convId, cursor, limit = DEFAULT_MESSAGE_PAGE_SIZE) {
     return request(`/conversations/${convId}/messages${buildQueryParams({ cursor, limit })}`)
   },
 
@@ -186,7 +193,7 @@ export const messageApi = {
 }
 
 export const projectApi = {
-  list(cursor, limit = 20) {
+  list(cursor, limit = DEFAULT_PROJECT_PAGE_SIZE) {
     return request(`/projects${buildQueryParams({ cursor, limit })}`)
   },
 
@@ -210,7 +217,7 @@ export const projectApi = {
   },
 
   readFileRaw(projectId, filepath) {
-    return fetch(`${BASE}/projects/${projectId}/files/${filepath}`).then(res => {
+    return fetch(`${API_BASE_URL}/projects/${projectId}/files/${filepath}`).then(res => {
       if (!res.ok) throw new Error(`HTTP ${res.status}`)
       return res
     })
diff --git a/frontend/src/components/MessageInput.vue b/frontend/src/components/MessageInput.vue
index 9e90e3d..e00c2c6 100644
--- a/frontend/src/components/MessageInput.vue
+++ b/frontend/src/components/MessageInput.vue
@@ -24,7 +24,7 @@
         <input
           ref="fileInputRef"
           type="file"
-          accept=".txt,.md,.json,.xml,.html,.css,.js,.ts,.jsx,.tsx,.py,.java,.c,.cpp,.h,.hpp,.yaml,.yml,.toml,.ini,.csv,.sql,.sh,.bat,.log,.vue,.svelte,.go,.rs,.rb,.php,.swift,.kt,.scala,.lua,.r,.dart"
+          accept=ALLOWED_UPLOAD_EXTENSIONS
           @change="handleFileUpload"
           style="display: none"
         />
@@ -65,6 +65,7 @@
 <script setup>
 import { ref, computed, nextTick } from 'vue'
 import { icons } from '../utils/icons'
+import { TEXTAREA_MAX_HEIGHT_PX, ALLOWED_UPLOAD_EXTENSIONS } from '../constants'
 
 const props = defineProps({
   disabled: { type: Boolean, default: false },
@@ -83,7 +84,7 @@ function autoResize() {
   const el = textareaRef.value
   if (!el) return
   el.style.height = 'auto'
-  el.style.height = Math.min(el.scrollHeight, 200) + 'px'
+  el.style.height = Math.min(el.scrollHeight, TEXTAREA_MAX_HEIGHT_PX) + 'px'
 }
 
 function onKeydown(e) {
diff --git a/frontend/src/components/MessageNav.vue b/frontend/src/components/MessageNav.vue
index 4d4ce3d..29d188d 100644
--- a/frontend/src/components/MessageNav.vue
+++ b/frontend/src/components/MessageNav.vue
@@ -17,6 +17,7 @@
 
 <script setup>
 import { computed } from 'vue'
+import { DEFAULT_TRUNCATE_LENGTH } from '../constants'
 
 const props = defineProps({
   messages: { type: Array, required: true },
@@ -30,7 +31,7 @@ const userMessages = computed(() => props.messages.filter(m => m.role === 'user'
 function preview(msg) {
   if (!msg.text) return '...'
   const clean = msg.text.replace(/[#*`~>\-\[\]()]/g, '').replace(/\s+/g, ' ').trim()
-  return clean.length > 60 ? clean.slice(0, 60) + '...' : clean
+  return clean.length > DEFAULT_TRUNCATE_LENGTH ? clean.slice(0, DEFAULT_TRUNCATE_LENGTH) + '...' : clean
 }
 </script>
 
diff --git a/frontend/src/components/ProcessBlock.vue b/frontend/src/components/ProcessBlock.vue
index 17c0062..e09a04b 100644
--- a/frontend/src/components/ProcessBlock.vue
+++ b/frontend/src/components/ProcessBlock.vue
@@ -41,7 +41,10 @@
             </div>
             <div v-if="item.result" class="tool-detail">
               <span class="detail-label">返回结果:</span>
-              <pre>{{ item.result }}</pre>
+              <pre>{{ expandedResultKeys[item.key] ? item.result : item.resultPreview }}</pre>
+              <button v-if="item.resultTruncated" class="btn-expand-result" @click.stop="toggleResultExpand(item.key)">
+                {{ expandedResultKeys[item.key] ? '收起' : `展开全部 (${item.resultLength} 字符)` }}
+              </button>
             </div>
           </div>
         </div>
@@ -67,6 +70,19 @@ import { ref, computed, watch } from 'vue'
 import { renderMarkdown } from '../utils/markdown'
 import { formatJson, truncate } from '../utils/format'
 import { useCodeEnhancement } from '../composables/useCodeEnhancement'
+import { RESULT_PREVIEW_LIMIT } from '../constants'
+
+function buildResultFields(rawContent) {
+  const formatted = formatJson(rawContent)
+  const len = formatted.length
+  const truncated = len > RESULT_PREVIEW_LIMIT
+  return {
+    result: formatted,
+    resultPreview: truncated ? formatted.slice(0, RESULT_PREVIEW_LIMIT) + '\n...' : formatted,
+    resultTruncated: truncated,
+    resultLength: len,
+  }
+}
 
 const props = defineProps({
   toolCalls: { type: Array, default: () => [] },
@@ -75,10 +91,12 @@ const props = defineProps({
 })
 
 const expandedKeys = ref({})
+const expandedResultKeys = ref({})
 
 // Auto-collapse all items when a new stream starts
 watch(() => props.streaming, (v) => {
   if (v) expandedKeys.value = {}
+  expandedResultKeys.value = {}
 })
 
 const processRef = ref(null)
@@ -87,6 +105,10 @@ function toggleItem(key) {
   expandedKeys.value[key] = !expandedKeys.value[key]
 }
 
+function toggleResultExpand(key) {
+  expandedResultKeys.value[key] = !expandedResultKeys.value[key]
+}
+
 function getResultSummary(result) {
   try {
     const parsed = typeof result === 'string' ? JSON.parse(result) : result
@@ -138,7 +160,7 @@ const processItems = computed(() => {
         const summary = getResultSummary(step.content)
         const match = items.findLast(it => it.type === 'tool_call' && it.id === toolId)
         if (match) {
-          match.result = formatJson(step.content)
+          Object.assign(match, buildResultFields(step.content))
           match.resultSummary = summary.text
           match.isSuccess = summary.success
           match.loading = false
@@ -165,7 +187,8 @@ const processItems = computed(() => {
     if (props.toolCalls && props.toolCalls.length > 0) {
       props.toolCalls.forEach((call, i) => {
         const toolName = call.function?.name || '未知工具'
-        const result = call.result ? getResultSummary(call.result) : null
+        const resultSummary = call.result ? getResultSummary(call.result) : null
+        const resultFields = call.result ? buildResultFields(call.result) : { result: null, resultPreview: null, resultTruncated: false, resultLength: 0 }
         items.push({
           type: 'tool_call',
           toolName,
@@ -174,9 +197,9 @@ const processItems = computed(() => {
           id: call.id,
           key: `tool_call-${call.id || i}`,
           loading: !call.result && props.streaming,
-          result: call.result ? formatJson(call.result) : null,
-          resultSummary: result ? result.text : null,
-          isSuccess: result ? result.success : undefined,
+          ...resultFields,
+          resultSummary: resultSummary ? resultSummary.text : null,
+          isSuccess: resultSummary ? resultSummary.success : undefined,
         })
       })
     }
@@ -345,6 +368,23 @@ watch(() => props.processSteps?.length, () => {
   word-break: break-word;
 }
 
+.btn-expand-result {
+  display: inline-block;
+  margin-top: 6px;
+  padding: 3px 10px;
+  font-size: 11px;
+  color: var(--tool-color);
+  background: var(--tool-bg);
+  border: 1px solid var(--tool-border);
+  border-radius: 4px;
+  cursor: pointer;
+  transition: background 0.15s;
+}
+
+.btn-expand-result:hover {
+  background: var(--tool-bg-hover);
+}
+
 /* Text content — rendered as markdown */
 .text-content {
   padding: 0;
diff --git a/frontend/src/components/SettingsPanel.vue b/frontend/src/components/SettingsPanel.vue
index 186ac41..8b089e7 100644
--- a/frontend/src/components/SettingsPanel.vue
+++ b/frontend/src/components/SettingsPanel.vue
@@ -126,6 +126,7 @@ import { reactive, ref, watch, onMounted } from 'vue'
 import { conversationApi } from '../api'
 import { useTheme } from '../composables/useTheme'
 import { icons } from '../utils/icons'
+import { SETTINGS_AUTO_SAVE_DEBOUNCE_MS } from '../constants'
 
 const props = defineProps({
   visible: { type: Boolean, default: false },
@@ -218,7 +219,7 @@ let saveTimer = null
 watch(form, () => {
   if (props.visible && props.conversation && syncedConvId === props.conversation.id && !isSyncing) {
     if (saveTimer) clearTimeout(saveTimer)
-    saveTimer = setTimeout(saveChanges, 500)
+    saveTimer = setTimeout(saveChanges, SETTINGS_AUTO_SAVE_DEBOUNCE_MS)
   }
 }, { deep: true })
 
diff --git a/frontend/src/components/Sidebar.vue b/frontend/src/components/Sidebar.vue
index 9a31bef..c5c3e00 100644
--- a/frontend/src/components/Sidebar.vue
+++ b/frontend/src/components/Sidebar.vue
@@ -113,6 +113,7 @@
 import { computed, reactive } from 'vue'
 import { formatTime } from '../utils/format'
 import { icons } from '../utils/icons'
+import { INFINITE_SCROLL_THRESHOLD_PX } from '../constants'
 
 const props = defineProps({
   conversations: { type: Array, required: true },
@@ -171,7 +172,7 @@ function toggleGroup(id) {
 
 function onScroll(e) {
   const el = e.target
-  if (el.scrollTop + el.clientHeight >= el.scrollHeight - 50) {
+  if (el.scrollTop + el.clientHeight >= el.scrollHeight - INFINITE_SCROLL_THRESHOLD_PX) {
     emit('loadMore')
   }
 }
diff --git a/frontend/src/composables/useCodeEnhancement.js b/frontend/src/composables/useCodeEnhancement.js
index ffe53c7..0ffbb73 100644
--- a/frontend/src/composables/useCodeEnhancement.js
+++ b/frontend/src/composables/useCodeEnhancement.js
@@ -1,5 +1,6 @@
 import { watch, onMounted, nextTick, onUnmounted } from 'vue'
 import { enhanceCodeBlocks } from '../utils/markdown'
+import { CODE_ENHANCE_DEBOUNCE_MS } from '../constants'
 
 /**
  * Composable for enhancing code blocks in a container element.
@@ -18,7 +19,7 @@ export function useCodeEnhancement(templateRef, dep, watchOpts) {
 
   function debouncedEnhance() {
     if (debounceTimer) clearTimeout(debounceTimer)
-    debounceTimer = setTimeout(() => nextTick(enhance), 150)
+    debounceTimer = setTimeout(() => nextTick(enhance), CODE_ENHANCE_DEBOUNCE_MS)
   }
 
   onMounted(enhance)
diff --git a/frontend/src/composables/useToast.js b/frontend/src/composables/useToast.js
index e380b04..b4afff7 100644
--- a/frontend/src/composables/useToast.js
+++ b/frontend/src/composables/useToast.js
@@ -1,4 +1,5 @@
 import { reactive } from 'vue'
+import { TOAST_DEFAULT_DURATION } from '../constants'
 
 const state = reactive({
   toasts: [],
@@ -6,7 +7,7 @@ const state = reactive({
 })
 
 export function useToast() {
-  function add(type, message, duration = 1500) {
+  function add(type, message, duration = TOAST_DEFAULT_DURATION) {
     const id = ++state._id
     state.toasts.push({ id, type, message })
     setTimeout(() => {
diff --git a/frontend/src/constants.js b/frontend/src/constants.js
new file mode 100644
index 0000000..3724089
--- /dev/null
+++ b/frontend/src/constants.js
@@ -0,0 +1,37 @@
+/**
+ * Frontend constants
+ */
+
+// === Tool Result Display ===
+/** Max characters shown in tool result preview before truncation */
+export const RESULT_PREVIEW_LIMIT = 2048
+
+// === API ===
+export const API_BASE_URL = '/api'
+export const CONTENT_TYPE_JSON = 'application/json'
+
+// === Pagination ===
+export const DEFAULT_CONVERSATION_PAGE_SIZE = 20
+export const DEFAULT_MESSAGE_PAGE_SIZE = 50
+export const DEFAULT_PROJECT_PAGE_SIZE = 20
+
+// === Timers (ms) ===
+export const TOAST_DEFAULT_DURATION = 1500
+export const CODE_ENHANCE_DEBOUNCE_MS = 150
+export const SETTINGS_AUTO_SAVE_DEBOUNCE_MS = 500
+export const COPY_BUTTON_RESET_MS = 1500
+
+// === Truncation ===
+export const DEFAULT_TRUNCATE_LENGTH = 60
+
+// === UI Limits ===
+export const TEXTAREA_MAX_HEIGHT_PX = 200
+export const INFINITE_SCROLL_THRESHOLD_PX = 50
+
+// === LocalStorage Keys ===
+export const LS_KEY_THEME = 'theme'
+export const LS_KEY_TOOLS_ENABLED = 'tools_enabled'
+export const LS_KEY_MODELS_CACHE = 'models_cache'
+
+// === File Upload ===
+export const ALLOWED_UPLOAD_EXTENSIONS = '.txt,.md,.json,.xml,.html,.css,.js,.ts,.jsx,.tsx,.py,.java,.c,.cpp,.h,.hpp,.yaml,.yml,.toml,.ini,.csv,.sql,.sh,.bat,.log,.vue,.svelte,.go,.rs,.rb,.php,.swift,.kt,.scala,.lua,.r,.dart'
diff --git a/frontend/src/main.js b/frontend/src/main.js
index 7641951..a7ef148 100644
--- a/frontend/src/main.js
+++ b/frontend/src/main.js
@@ -3,9 +3,10 @@ import App from './App.vue'
 import './styles/global.css'
 import './styles/highlight.css'
 import 'katex/dist/katex.min.css'
+import { LS_KEY_THEME } from './constants'
 
 // Initialize theme before app mounts to avoid flash when lazy-loading useTheme
-const savedTheme = localStorage.getItem('theme')
+const savedTheme = localStorage.getItem(LS_KEY_THEME)
 if (savedTheme === 'dark' || savedTheme === 'light') {
   document.documentElement.setAttribute('data-theme', savedTheme)
 }
diff --git a/frontend/src/utils/format.js b/frontend/src/utils/format.js
index 6b83c49..478b68f 100644
--- a/frontend/src/utils/format.js
+++ b/frontend/src/utils/format.js
@@ -1,3 +1,5 @@
+import { DEFAULT_TRUNCATE_LENGTH } from '../constants'
+
 /**
  * Format ISO date string to a short time string.
  * - Today: "14:30"
@@ -36,7 +38,7 @@ export function formatJson(value) {
 /**
  * Truncate text to max characters with ellipsis.
  */
-export function truncate(text, max = 60) {
+export function truncate(text, max = DEFAULT_TRUNCATE_LENGTH) {
   if (!text) return ''
   const str = text.replace(/\s+/g, ' ').trim()
   return str.length > max ? str.slice(0, max) + '\u2026' : str
diff --git a/frontend/src/utils/markdown.js b/frontend/src/utils/markdown.js
index ff6eded..5c72d7e 100644
--- a/frontend/src/utils/markdown.js
+++ b/frontend/src/utils/markdown.js
@@ -2,6 +2,7 @@ import { marked } from 'marked'
 import { markedHighlight } from 'marked-highlight'
 import katex from 'katex'
 import { highlightCode } from './highlight'
+import { COPY_BUTTON_RESET_MS } from '../constants'
 
 function renderMath(text, displayMode) {
   try {
@@ -108,7 +109,7 @@ export function enhanceCodeBlocks(container) {
 
     copyBtn.addEventListener('click', () => {
       const raw = code?.textContent || ''
-      const copy = () => { copyBtn.innerHTML = CHECK_SVG; setTimeout(() => { copyBtn.innerHTML = COPY_SVG }, 1500) }
+      const copy = () => { copyBtn.innerHTML = CHECK_SVG; setTimeout(() => { copyBtn.innerHTML = COPY_SVG }, COPY_BUTTON_RESET_MS) }
       if (navigator.clipboard) {
         navigator.clipboard.writeText(raw).then(copy)
       } else {