Render write() tool content as readable file text

components/MessageView.test.mjs

@@ -18,6 +18,7 @@ const {
 } = await jiti.import("./MessageView.tsx");
 const { I18nProvider } = await jiti.import("@/hooks/useI18n");
 const { splitFinalAssistantBlocks } = await jiti.import("@/lib/message-display");
+const { clearExpandedToolCalls, setToolCallExpanded } = await jiti.import("@/lib/tool-call-expansion");
 
 function renderMessage(message, props = {}) {
   return renderToStaticMarkup(
@@ -128,6 +129,50 @@ test("keeps streamed tool input out of collapsed markup while counting it", () =
   assert.equal(getTokenEstimateText(block), block.rawInput);
 });
 
+test("renders write tool content as readable file text", () => {
+  const block = {
+    type: "toolCall",
+    toolCallId: "call-write-file",
+    toolName: "write",
+    input: { path: "src/example.ts", content: "first line\nsecond line\n" },
+  };
+  clearExpandedToolCalls();
+  setToolCallExpanded(block.toolCallId, true);
+  try {
+    const html = renderMessage({
+      role: "assistant",
+      provider: "anthropic",
+      model: "claude-test",
+      content: [block],
+    });
+
+    assert.ok(html.includes("src/example.ts"));
+    assert.match(html, /first line\nsecond line\n/);
+    assert.doesNotMatch(html, /"content":/);
+  } finally {
+    clearExpandedToolCalls();
+  }
+});
+
+test("keeps the input JSON for a write with another argument, an empty file or streamed input", () => {
+  const cases = [
+    { id: "call-write-mode", input: { path: "notes.md", content: "text", mode: "append" } },
+    { id: "call-write-empty", input: { path: "empty.txt", content: "" } },
+    { id: "call-write-streaming", input: {}, rawInput: "{\"path\":\"a.ts\",\"content\":\"one\\ntwo" },
+  ];
+  for (const { id, input, rawInput } of cases) {
+    const block = { type: "toolCall", toolCallId: id, toolName: "write", input, ...(rawInput === undefined ? {} : { rawInput }) };
+    clearExpandedToolCalls();
+    setToolCallExpanded(id, true);
+    try {
+      const html = renderMessage({ role: "assistant", provider: "anthropic", model: "claude-test", content: [block] });
+      assert.equal(textOf(html).includes(getToolCallInputText(block)), true, id);
+    } finally {
+      clearExpandedToolCalls();
+    }
+  }
+});
+
 test("renders subagents as standard tool calls with only an extra session button", () => {
   const block = {
     type: "toolCall",
@@ -454,8 +499,6 @@ test("uses the unanswered truncation notice for an empty length reply", () => {
   assert.doesNotMatch(html, /follow-up/i);
 });
 
-const { setToolCallExpanded } = await jiti.import("@/lib/tool-call-expansion");
-
 function textOf(html) {
   return html.replace(/<[^>]+>/g, "").replace(/&quot;/g, "\"").replace(/&amp;/g, "&").replace(/&#x27;/g, "'");
 }

components/MessageView.tsx

@@ -11,7 +11,7 @@ import { parseCompactionSummary } from "@/lib/compaction-summary";
 import { getAssistantErrorMessage, getThinkingPreview, hasAssistantAnswer, isAssistantTruncated, isEmptyThinkingBlock } from "@/lib/message-display";
 import { parseUnifiedPatch, type SplitDiffCell, type SplitDiffFile } from "@/lib/patch";
 import { applyPatchPreviewToFiles, applyPatchResultHasFailures, extractApplyPatchPaths, getApplyPatchInputText, parseApplyPatchInput } from "@/lib/apply-patch";
-import { isApplyPatchToolName, isEditToolName } from "@/lib/tool-names";
+import { isApplyPatchToolName, isEditToolName, isWriteToolName } from "@/lib/tool-names";
 import { isToolCallExpanded, setToolCallExpanded } from "@/lib/tool-call-expansion";
 import { isThinkingExpandedByDefault, THINKING_EXPANDED_EVENT } from "@/lib/thinking-expansion-preference";
 import { TurnWrittenFiles } from "./TurnWrittenFiles";
@@ -1120,7 +1120,7 @@ function ToolCallBlock({ block, result, duration, onOpenSession }: { block: Tool
     setToolCallExpanded(block.toolCallId, next);
     setExpanded(next);
   };
-  const inputStr = getToolCallInputText(block);
+  const inputStr = getWrittenFileText(block) ?? getToolCallInputText(block);
   const isStreamingInput = block.rawInput !== undefined;
   const isEditTool = isEditToolName(block.toolName);
   const resultDiff = result && !result.isError ? getResultDiff(result) : null;
@@ -1911,6 +1911,18 @@ export function getToolCallInputText(block: ToolCallContent): string {
   return block.rawInput ?? JSON.stringify(block.input, null, 2);
 }
 
+const WRITE_VIEW_KEYS = new Set(["path", "file_path", "content"]);
+
+// A write's file text in place of its JSON. Streamed input is still incomplete
+// JSON, and any other argument (a mode, a title) would vanish from this view,
+// so those calls, and an empty file, keep the generic view.
+function getWrittenFileText(block: ToolCallContent): string | null {
+  if (block.rawInput !== undefined || !isWriteToolName(block.toolName)) return null;
+  const { content } = block.input;
+  if (typeof content !== "string" || content === "") return null;
+  return Object.keys(block.input).every((key) => WRITE_VIEW_KEYS.has(key)) ? content : null;
+}
+
 function formatCustomType(type: string): string {
   return type || "extension";
 }