diff --git a/ui/src/components/IssueChatThread.test.tsx b/ui/src/components/IssueChatThread.test.tsx
index f292646a..17ea34d6 100644
--- a/ui/src/components/IssueChatThread.test.tsx
+++ b/ui/src/components/IssueChatThread.test.tsx
@@ -52,13 +52,19 @@ vi.mock("./MarkdownEditor", () => ({
     value = "",
     onChange,
     placeholder,
+    className,
+    contentClassName,
   }: {
     value?: string;
     onChange?: (value: string) => void;
     placeholder?: string;
+    className?: string;
+    contentClassName?: string;
   }) => (
     <textarea
       aria-label="Issue chat editor"
+      data-class-name={className}
+      data-content-class-name={contentClassName}
       placeholder={placeholder}
       value={value}
       onChange={(event) => onChange?.(event.target.value)}
@@ -240,6 +246,39 @@ describe("IssueChatThread", () => {
     });
   });
 
+  it("keeps the composer pinned with a capped editor height", () => {
+    const root = createRoot(container);
+
+    act(() => {
+      root.render(
+        <MemoryRouter>
+          <IssueChatThread
+            comments={[]}
+            linkedRuns={[]}
+            timelineEvents={[]}
+            liveRuns={[]}
+            onAdd={async () => {}}
+            enableLiveTranscriptPolling={false}
+          />
+        </MemoryRouter>,
+      );
+    });
+
+    const composer = container.querySelector('[data-testid="issue-chat-composer"]') as HTMLDivElement | null;
+    expect(composer).not.toBeNull();
+    expect(composer?.className).toContain("sticky");
+    expect(composer?.className).toContain("bottom-0");
+    expect(composer?.className).toContain("pb-[calc(env(safe-area-inset-bottom)+0.75rem)]");
+
+    const editor = container.querySelector('textarea[aria-label="Issue chat editor"]') as HTMLTextAreaElement | null;
+    expect(editor?.dataset.contentClassName).toContain("max-h-[40dvh]");
+    expect(editor?.dataset.contentClassName).toContain("overflow-y-auto");
+
+    act(() => {
+      root.unmount();
+    });
+  });
+
   it("folds chain-of-thought when the same message transitions from running to complete", () => {
     expect(resolveAssistantMessageFoldedState({
       messageId: "message-1",
diff --git a/ui/src/components/IssueChatThread.tsx b/ui/src/components/IssueChatThread.tsx
index 220de8ec..f535b9cf 100644
--- a/ui/src/components/IssueChatThread.tsx
+++ b/ui/src/components/IssueChatThread.tsx
@@ -1488,92 +1488,99 @@ function IssueChatComposer({
   }
 
   return (
-    <div className="space-y-2">
-      <MarkdownEditor
-        ref={editorRef}
-        value={body}
-        onChange={setBody}
-        placeholder="Reply"
-        mentions={mentions}
-        onSubmit={handleSubmit}
-        imageUploadHandler={onImageUpload}
-        contentClassName="min-h-[72px] text-sm"
-      />
+    <div
+      data-testid="issue-chat-composer"
+      className="sticky bottom-0 z-10 bg-gradient-to-t from-background via-background/95 to-background/70 pt-4 pb-[calc(env(safe-area-inset-bottom)+0.75rem)] backdrop-blur supports-[backdrop-filter]:from-background/92 supports-[backdrop-filter]:via-background/82"
+    >
+      <div className="space-y-3 rounded-2xl border border-border/70 bg-background/95 p-3 shadow-sm">
+        <MarkdownEditor
+          ref={editorRef}
+          value={body}
+          onChange={setBody}
+          placeholder="Reply"
+          mentions={mentions}
+          onSubmit={handleSubmit}
+          imageUploadHandler={onImageUpload}
+          bordered
+          className="rounded-xl border-border/70 bg-background/95"
+          contentClassName="min-h-[72px] max-h-[40dvh] overflow-y-auto pr-1 text-sm scrollbar-auto-hide"
+        />
 
-      <div className="mt-3 flex items-center justify-end gap-3">
-        {(onImageUpload || onAttachImage) ? (
-          <div className="mr-auto flex items-center gap-3">
+        <div className="flex flex-wrap items-center justify-end gap-3 border-t border-border/60 pt-2">
+          {(onImageUpload || onAttachImage) ? (
+            <div className="mr-auto flex items-center gap-3">
+              <input
+                ref={attachInputRef}
+                type="file"
+                accept="image/png,image/jpeg,image/webp,image/gif"
+                className="hidden"
+                onChange={handleAttachFile}
+              />
+              <Button
+                variant="ghost"
+                size="icon-sm"
+                onClick={() => attachInputRef.current?.click()}
+                disabled={attaching}
+                title="Attach image"
+              >
+                <Paperclip className="h-4 w-4" />
+              </Button>
+            </div>
+          ) : null}
+
+          <label className="flex items-center gap-1.5 text-xs text-muted-foreground cursor-pointer select-none">
             <input
-              ref={attachInputRef}
-              type="file"
-              accept="image/png,image/jpeg,image/webp,image/gif"
-              className="hidden"
-              onChange={handleAttachFile}
+              type="checkbox"
+              checked={reopen}
+              onChange={(event) => setReopen(event.target.checked)}
+              className="rounded border-border"
             />
-            <Button
-              variant="ghost"
-              size="icon-sm"
-              onClick={() => attachInputRef.current?.click()}
-              disabled={attaching}
-              title="Attach image"
-            >
-              <Paperclip className="h-4 w-4" />
-            </Button>
-          </div>
-        ) : null}
+            Re-open
+          </label>
 
-        <label className="flex items-center gap-1.5 text-xs text-muted-foreground cursor-pointer select-none">
-          <input
-            type="checkbox"
-            checked={reopen}
-            onChange={(event) => setReopen(event.target.checked)}
-            className="rounded border-border"
-          />
-          Re-open
-        </label>
+          {enableReassign && reassignOptions.length > 0 ? (
+            <InlineEntitySelector
+              value={reassignTarget}
+              options={reassignOptions}
+              placeholder="Assignee"
+              noneLabel="No assignee"
+              searchPlaceholder="Search assignees..."
+              emptyMessage="No assignees found."
+              onChange={setReassignTarget}
+              className="h-8 text-xs"
+              renderTriggerValue={(option) => {
+                if (!option) return <span className="text-muted-foreground">Assignee</span>;
+                const agentId = option.id.startsWith("agent:") ? option.id.slice("agent:".length) : null;
+                const agent = agentId ? agentMap?.get(agentId) : null;
+                return (
+                  <>
+                    {agent ? (
+                      <AgentIcon icon={agent.icon} className="h-3.5 w-3.5 shrink-0 text-muted-foreground" />
+                    ) : null}
+                    <span className="truncate">{option.label}</span>
+                  </>
+                );
+              }}
+              renderOption={(option) => {
+                if (!option.id) return <span className="truncate">{option.label}</span>;
+                const agentId = option.id.startsWith("agent:") ? option.id.slice("agent:".length) : null;
+                const agent = agentId ? agentMap?.get(agentId) : null;
+                return (
+                  <>
+                    {agent ? (
+                      <AgentIcon icon={agent.icon} className="h-3.5 w-3.5 shrink-0 text-muted-foreground" />
+                    ) : null}
+                    <span className="truncate">{option.label}</span>
+                  </>
+                );
+              }}
+            />
+          ) : null}
 
-        {enableReassign && reassignOptions.length > 0 ? (
-          <InlineEntitySelector
-            value={reassignTarget}
-            options={reassignOptions}
-            placeholder="Assignee"
-            noneLabel="No assignee"
-            searchPlaceholder="Search assignees..."
-            emptyMessage="No assignees found."
-            onChange={setReassignTarget}
-            className="h-8 text-xs"
-            renderTriggerValue={(option) => {
-              if (!option) return <span className="text-muted-foreground">Assignee</span>;
-              const agentId = option.id.startsWith("agent:") ? option.id.slice("agent:".length) : null;
-              const agent = agentId ? agentMap?.get(agentId) : null;
-              return (
-                <>
-                  {agent ? (
-                    <AgentIcon icon={agent.icon} className="h-3.5 w-3.5 shrink-0 text-muted-foreground" />
-                  ) : null}
-                  <span className="truncate">{option.label}</span>
-                </>
-              );
-            }}
-            renderOption={(option) => {
-              if (!option.id) return <span className="truncate">{option.label}</span>;
-              const agentId = option.id.startsWith("agent:") ? option.id.slice("agent:".length) : null;
-              const agent = agentId ? agentMap?.get(agentId) : null;
-              return (
-                <>
-                  {agent ? (
-                    <AgentIcon icon={agent.icon} className="h-3.5 w-3.5 shrink-0 text-muted-foreground" />
-                  ) : null}
-                  <span className="truncate">{option.label}</span>
-                </>
-              );
-            }}
-          />
-        ) : null}
-
-        <Button size="sm" disabled={!canSubmit} onClick={() => void handleSubmit()}>
-          {submitting ? "Posting..." : "Send"}
-        </Button>
+          <Button size="sm" disabled={!canSubmit} onClick={() => void handleSubmit()}>
+            {submitting ? "Posting..." : "Send"}
+          </Button>
+        </div>
       </div>
     </div>
   );