diff --git a/src/lib/components/events/event-trace-tree.svelte b/src/lib/components/events/event-trace-tree.svelte
index bd8eef8..5dfc2c4 100644
--- a/src/lib/components/events/event-trace-tree.svelte
+++ b/src/lib/components/events/event-trace-tree.svelte
@@ -53,27 +53,30 @@
   }
 </script>
 
-<div class="flex min-h-0 flex-col">
-  <div class="flex shrink-0 items-center gap-3 border-b border-border px-4 py-2.5 text-xs sm:px-5">
+<div class="flex min-h-0 min-w-0 flex-col overflow-hidden">
+  <div class="flex shrink-0 items-center gap-3 whitespace-nowrap border-b border-border px-4 py-2.5 text-xs sm:px-5">
     <button
       type="button"
       onclick={onCollapse}
       title={t('收起事件列表')}
       aria-label={t('收起事件列表')}
-      class="-ml-1 hidden text-faint transition-colors hover:text-foreground lg:block"
+      class="-ml-1 hidden shrink-0 text-faint transition-colors hover:text-foreground lg:block"
       ><PanelLeftClose class="size-4" /></button
     >
     <span class={failedCount ? 'text-destructive' : 'text-muted-foreground'}>{failedCount} {t('失败')}</span>
     <span class="text-faint">·</span>
     <span class="text-muted-foreground">{succeededCount} {t('成功')}</span>
-    <label class="ml-auto flex cursor-pointer items-center gap-1.5 text-muted-foreground">
+    <label
+      class="ml-auto flex min-w-0 cursor-pointer items-center gap-1.5 text-muted-foreground"
+      title={t('折叠成功的执行')}
+    >
       <input
         type="checkbox"
         checked={folded}
         onchange={(event) => onToggleFold(event.currentTarget.checked)}
-        class="accent-foreground"
+        class="shrink-0 accent-foreground"
       />
-      {t('折叠成功的执行')}
+      <span class="truncate">{t('折叠成功的执行')}</span>
     </label>
   </div>
   <div data-scroll-surface class="min-h-0 flex-1 overflow-y-auto pb-4">
diff --git a/src/lib/components/run-log-viewer.svelte b/src/lib/components/run-log-viewer.svelte
index a49fb32..5be5355 100644
--- a/src/lib/components/run-log-viewer.svelte
+++ b/src/lib/components/run-log-viewer.svelte
@@ -15,7 +15,6 @@
     loadingEarlier = false,
     downloading = false,
     preserveLine = 0,
-    horizontalScroll = true,
     onQuery,
     onDownload,
     onLoadEarlier,
@@ -32,8 +31,6 @@
      * Callers must not count rows inserted below that anchor.
      */
     preserveLine?: number;
-    /** Keep long lines scrollable in the full-page viewer; embedded event logs fit their pane. */
-    horizontalScroll?: boolean;
     onQuery: (value: string) => void;
     onDownload: () => void;
     onLoadEarlier?: () => void;
@@ -177,17 +174,10 @@
     data-scroll-surface
     data-log-viewport
     onscroll={trackScroll}
-    class="min-h-0 min-w-0 flex-1 overflow-y-auto rounded-lg border border-border bg-muted font-mono text-xs leading-5 text-foreground"
-    style:overflow-x={horizontalScroll ? 'auto' : 'hidden'}
+    class="min-h-0 min-w-0 flex-1 overflow-auto rounded-lg border border-border bg-muted font-mono text-xs leading-5 text-foreground"
   >
     {#if lines.length}
-      <div
-        class:min-w-full={!horizontalScroll}
-        class:w-max={horizontalScroll}
-        class:max-w-full={!horizontalScroll}
-        class:overflow-hidden={!horizontalScroll}
-        style:height="{totalHeight}px"
-      >
+      <div class="w-max min-w-full" style:height="{totalHeight}px">
         <div style:transform="translateY({startIndex * LINE_HEIGHT}px)">
           {#each visibleLines as line, offset (startIndex + offset)}
             {@const index = startIndex + offset}
@@ -198,11 +188,7 @@
                   ? 'active'
                   : 'true'
                 : undefined}
-              class:min-w-full={!horizontalScroll}
-              class:w-max={horizontalScroll}
-              class:max-w-full={!horizontalScroll}
-              class:overflow-hidden={!horizontalScroll}
-              class="h-5 px-4 whitespace-pre data-[log-match=true]:bg-amber-300/25 data-[log-match=active]:bg-orange-500/40"
+              class="h-5 w-max min-w-full px-4 whitespace-pre data-[log-match=true]:bg-amber-300/25 data-[log-match=active]:bg-orange-500/40"
               style:height="{LINE_HEIGHT}px"
               style:line-height="{LINE_HEIGHT}px"
             >
diff --git a/src/lib/components/sandbox-log-runs.svelte b/src/lib/components/sandbox-log-runs.svelte
index 8a210c6..59142c7 100644
--- a/src/lib/components/sandbox-log-runs.svelte
+++ b/src/lib/components/sandbox-log-runs.svelte
@@ -22,7 +22,6 @@
     events,
     activeStream,
     legacyCells = [],
-    horizontalScroll = true,
     onError,
   }: {
     sandboxId: string;
@@ -30,7 +29,6 @@
     events: RunEvent[];
     activeStream?: AgentStreamState;
     legacyCells?: SandboxHistoryCell[];
-    horizontalScroll?: boolean;
     onError?: (message: string) => void;
   } = $props();
 
@@ -293,7 +291,6 @@
     {loadingEarlier}
     {downloading}
     {preserveLine}
-    {horizontalScroll}
     onViewportLine={(line) => (anchorBeforeLine = line)}
     onQuery={(value) => (query = value)}
     onDownload={() => void download()}
diff --git a/src/lib/components/sandbox-workbench.svelte b/src/lib/components/sandbox-workbench.svelte
index ae1b82a..60945f5 100644
--- a/src/lib/components/sandbox-workbench.svelte
+++ b/src/lib/components/sandbox-workbench.svelte
@@ -556,7 +556,6 @@
             {runs}
             {events}
             {activeStream}
-            horizontalScroll={!embedded}
             legacyCells={historyCells.filter((cell) => !cell.runId && !cell.id.endsWith('-legacy-log'))}
             onError={(message) => (error = message)}
           />
@@ -564,7 +563,6 @@
             query={contextLogQuery}
             lines={fallbackLogLines}
             loadedLineCount={fallbackLogLines.length}
-            horizontalScroll={!embedded}
             onQuery={(value) => (contextLogQuery = value)}
             onDownload={downloadContextLog}
           />{/if}
diff --git a/src/routes/EventDetail.svelte b/src/routes/EventDetail.svelte
index 06ea02a..c9c0488 100644
--- a/src/routes/EventDetail.svelte
+++ b/src/routes/EventDetail.svelte
@@ -34,8 +34,9 @@
   /** 左侧事件栏收起后，右侧的日志占满宽度。 */
   let traceCollapsed = $state(false);
   // 左栏宽度占整行的百分比，拖动分隔线调整，记在浏览器里。
-  const TRACE_WIDTH_KEY = 'agent-compose:event-trace-width';
-  const TRACE_WIDTH_DEFAULT = 42;
+  // 改默认宽度时换一个 key，让旧的记忆值失效。
+  const TRACE_WIDTH_KEY = 'agent-compose:event-trace-width:v3';
+  const TRACE_WIDTH_DEFAULT = 28;
   const TRACE_WIDTH_MIN = 20;
   const TRACE_WIDTH_MAX = 70;
   let traceWidth = $state(clampTraceWidth(Number(localStorage.getItem(TRACE_WIDTH_KEY)) || TRACE_WIDTH_DEFAULT));
@@ -248,7 +249,9 @@
           >
         </div>
       {/if}
-      <div class="relative min-h-0 flex-col border-border lg:border-r {traceCollapsed ? 'flex lg:hidden' : 'flex'}">
+      <div
+        class="relative min-h-0 min-w-0 flex-col border-border lg:border-r {traceCollapsed ? 'flex lg:hidden' : 'flex'}"
+      >
         <!-- svelte-ignore a11y_no_noninteractive_tabindex, a11y_no_noninteractive_element_interactions -->
         <div
           data-trace-resizer