fix(transcript): stop treating header-like content lines as file headers

Addresses review on #6158.

parseUnifiedDiff matched "---" / "+++" / "diff --git" / "index " at any
position, so a changed line whose *content* starts with a dash or plus was
silently discarded:

    parseUnifiedDiff("@@ -1 +1 @@\n--- old markdown\n+++ new markdown\n")
    // before: [{ kind: "gap", ... }] — both changed lines gone

A removal of "-- old markdown" is spelled "--- old markdown" on the wire, so
this hit Markdown rules, embedded patches, and comment banners.

File headers only exist ahead of the first hunk, so they are only recognised
there; once inside a hunk every line is parsed strictly by its first
character.

Also localizes the multi-file summary count, which was hardcoded English and
so leaked into the zh-Hans / ja / ko transcript rows. The presenter owns no
React and no i18n by design, so the phrasing is injected by the caller rather
than imported here, keeping the module unit-testable in isolation; the English
form remains the fallback. The three Chinese/Japanese/Korean truncation
strings now use "..." to match the English source they translate.

Verified: both new parser assertions fail against the previous
strip-anywhere behaviour and pass now; 47 presenter tests green, repo
typecheck and lint clean.

Co-authored-by: multica-agent <github@multica.ai>

packages/views/common/task-transcript/agent-transcript-dialog.tsx

@@ -65,7 +65,7 @@ import {
   traceEventSummary,
   traceEventSummaryIsMono,
 } from "./trace-event-presenter";
-import type { TraceDiffLine, TracePatchFile } from "./trace-event-presenter";
+import type { TraceDiffLine, TracePatchFile, TraceSummaryLabels } from "./trace-event-presenter";
 import { highlightBlock, highlightToLines, languageForPath } from "./diff-highlight";
 import { useT } from "../../i18n";
 import "../../editor/styles/code.css";
@@ -1102,7 +1102,14 @@ const TranscriptEventRow = ({
   const kind = traceEventKind(item);
   const color = getEventColor(item);
   const label = traceEventLabel(item);
-  const summary = traceEventSummary(item);
+  // The presenter stays i18n-free, so the localizable phrasing is injected.
+  const summaryLabels = useMemo<TraceSummaryLabels>(
+    () => ({
+      morePaths: (path, count) => t(($) => $.transcript.patch_summary_more, { path, count }),
+    }),
+    [t],
+  );
+  const summary = traceEventSummary(item, summaryLabels);
   const date = useMemo(
     () => (item.created_at ? new Date(item.created_at) : null),
     [item.created_at],

packages/views/common/task-transcript/trace-event-presenter.test.ts

@@ -308,7 +308,7 @@ describe("parseUnifiedDiff", () => {
     ]);
   });
 
-  it("drops file headers and no-newline metadata", () => {
+  it("drops file headers ahead of the first hunk", () => {
     const lines = parseUnifiedDiff(
       "diff --git a/x b/x\nindex 111..222 100644\n--- a/x\n+++ b/x\n@@ -1 +1 @@\n-a\n+b\n\\ No newline at end of file\n",
     );
@@ -319,6 +319,25 @@ describe("parseUnifiedDiff", () => {
     ]);
   });
 
+  // Inside a hunk, "---"/"+++" are ordinary changed lines whose content starts
+  // with a dash or plus — a Markdown rule, a nested patch, a comment banner.
+  // Treating them as file headers anywhere silently deleted real content.
+  it("keeps header-like content lines once inside a hunk", () => {
+    expect(parseUnifiedDiff("@@ -1 +1 @@\n--- old markdown\n+++ new markdown\n")).toEqual([
+      { kind: "gap", text: "@@ -1 +1 @@" },
+      { kind: "remove", text: "-- old markdown" },
+      { kind: "add", text: "++ new markdown" },
+    ]);
+  });
+
+  it("keeps a removed line that is exactly a Markdown rule", () => {
+    expect(parseUnifiedDiff("@@ -1,2 +1,1 @@\n---\n ok\n")).toEqual([
+      { kind: "gap", text: "@@ -1,2 +1,1 @@" },
+      { kind: "remove", text: "--" },
+      { kind: "context", text: "ok" },
+    ]);
+  });
+
   it("keeps an empty context line and does not invent a trailing one", () => {
     // " " is a blank unchanged line; the phantom element left by the trailing
     // newline is not.
@@ -475,6 +494,35 @@ describe("traceToolArgSummary / traceEventHasDetail — Codex changes[]", () =>
     ).toBe(".../d/e.go");
   });
 
+  // The presenter stays i18n-free, so the caller injects the phrasing; the
+  // English form is only the fallback.
+  it("uses injected phrasing for the multi-file count", () => {
+    expect(
+      traceToolArgSummary(
+        {
+          changes: [
+            { path: "src/a.go", kind: "update", diff: "@@\n+x" },
+            { path: "src/b.go", kind: "add", content: "y" },
+          ],
+        },
+        { morePaths: (path, count) => `${path} 等 ${count} 个文件` },
+      ),
+    ).toBe("src/a.go 等 1 个文件");
+  });
+
+  it("does not consult the injected phrasing for a single file", () => {
+    expect(
+      traceToolArgSummary(
+        { changes: [{ path: "only.go", kind: "add", content: "x" }] },
+        {
+          morePaths: () => {
+            throw new Error("must not be called for a single-file patch");
+          },
+        },
+      ),
+    ).toBe("only.go");
+  });
+
   it("makes a patch row expandable — the bug was two blank unexpandable rows", () => {
     expect(
       traceEventHasDetail({

packages/views/common/task-transcript/trace-event-presenter.ts

@@ -95,18 +95,32 @@ function clip(value: string, max: number): string {
   return value.length > max ? value.slice(0, max) + "..." : value;
 }
 
+/**
+ * Localizable phrasing the presenter cannot produce on its own. This module
+ * stays free of React and i18n so it remains unit-testable in isolation, so the
+ * caller injects the wording instead. Omitting it falls back to English, which
+ * keeps the fallback safe rather than blank.
+ */
+export interface TraceSummaryLabels {
+  /** Phrase a multi-file patch, e.g. `src/a.go +2 more`. */
+  morePaths?: (path: string, count: number) => string;
+}
+
 /**
  * The single most informative argument of a tool call, as one line. Preference
  * order matches what a reviewer scans for first, falling back to the first
  * short string value.
  */
-export function traceToolArgSummary(input: Record<string, unknown> | undefined): string {
+export function traceToolArgSummary(
+  input: Record<string, unknown> | undefined,
+  labels?: TraceSummaryLabels,
+): string {
   if (!input) return "";
   const str = (v: unknown): string => (typeof v === "string" ? v : "");
   if (str(input.query)) return str(input.query);
   // A multi-file patch has no single path field; without this the row's
   // summary would fall through to the generic scan and come back empty.
-  const patch = readPatchSummary(input);
+  const patch = readPatchSummary(input, labels);
   if (patch) return patch;
   if (str(input.file_path)) return shortenTracePath(str(input.file_path));
   if (str(input.path)) return shortenTracePath(str(input.path));
@@ -135,12 +149,12 @@ function collapseWhitespace(value: string | undefined): string {
 }
 
 /** One-line summary for the collapsed row — never contains a newline. */
-export function traceEventSummary(event: TraceEvent): string {
+export function traceEventSummary(event: TraceEvent, labels?: TraceSummaryLabels): string {
   switch (traceEventKind(event)) {
     case "thinking":
       return clip(firstLine(event.content), 200);
     case "tool_use":
-      return traceToolArgSummary(event.input);
+      return traceToolArgSummary(event.input, labels);
     case "tool_result":
       // Unwrap first: the collapsed row is the one people read without
       // clicking, so it must not show transport escaping.
@@ -355,24 +369,33 @@ export function parseUnifiedDiff(diff: string): TraceDiffLine[] {
   if (raw.length > 0 && raw[raw.length - 1] === "") raw.pop();
 
   const out: TraceDiffLine[] = [];
+  // File headers only exist ahead of the first hunk. Past that point every
+  // line belongs to the file, and "---"/"+++" are ordinary changed lines whose
+  // content happens to start with a dash or plus — a Markdown rule, a nested
+  // patch, a comment banner. Treating them as headers anywhere deleted real
+  // content from the diff.
+  let inHunk = false;
   for (const line of raw) {
-    // File headers carry no content and the path is reported alongside.
-    if (
-      line.startsWith("diff --git") ||
-      line.startsWith("index ") ||
-      line.startsWith("--- ") ||
-      line.startsWith("+++ ") ||
-      line === "---" ||
-      line === "+++"
-    ) {
-      continue;
-    }
-    // "\ No newline at end of file" is metadata, not a line of the file.
-    if (line.startsWith("\\")) continue;
     if (line.startsWith("@@")) {
+      inHunk = true;
       out.push({ kind: "gap", text: line });
       continue;
     }
+    if (!inHunk) {
+      if (
+        line.startsWith("diff --git") ||
+        line.startsWith("index ") ||
+        line.startsWith("--- ") ||
+        line.startsWith("+++ ") ||
+        line === "---" ||
+        line === "+++"
+      ) {
+        continue;
+      }
+    }
+    // "\ No newline at end of file" is metadata, not a line of the file: a
+    // real line starting with a backslash carries a +/-/space prefix first.
+    if (line.startsWith("\\")) continue;
     if (line.startsWith("+")) {
       out.push({ kind: "add", text: line.slice(1) });
       continue;
@@ -443,14 +466,19 @@ function readPatchChanges(input: Record<string, unknown>): TracePatchFile[] | nu
 }
 
 /** First path plus a count, for the collapsed one-line summary. */
-function readPatchSummary(input: Record<string, unknown> | undefined): string {
+function readPatchSummary(
+  input: Record<string, unknown> | undefined,
+  labels?: TraceSummaryLabels,
+): string {
   if (!input) return "";
   const files = readPatchChanges(input);
   if (files === null) return "";
   const first = files[0];
   if (first === undefined) return "";
   const head = shortenTracePath(first.path);
-  return files.length > 1 ? `${head} +${files.length - 1} more` : head;
+  if (files.length === 1) return head;
+  const extra = files.length - 1;
+  return labels?.morePaths?.(head, extra) ?? `${head} +${extra} more`;
 }
 
 function readFileMutation(input: Record<string, unknown>): FileMutation | null {

packages/views/locales/en/agents.json

@@ -792,6 +792,7 @@
     "patch_truncated": "... (truncated)",
     "patch_body_truncated": "... (body truncated)",
     "patch_no_content": "(no content reported)",
+    "patch_summary_more": "{{path}} +{{count}} more",
     "status_queued": "Queued",
     "status_dispatched": "Dispatched",
     "status_cancelled": "Cancelled",

packages/views/locales/ja/agents.json

@@ -667,9 +667,10 @@
     "density_collapsed_desc": "1 行 1 イベントの最もコンパクトな表示",
     "no_output": "出力なし",
     "show_all": "すべて表示",
-    "patch_truncated": "…（切り詰め済み）",
-    "patch_body_truncated": "…（本文を切り詰めました）",
+    "patch_truncated": "...（切り詰め済み）",
+    "patch_body_truncated": "...（本文を切り詰めました）",
     "patch_no_content": "（内容の記録なし）",
+    "patch_summary_more": "{{path}} 他 {{count}} 件",
     "status_queued": "待機列",
     "status_dispatched": "ディスパッチ済み",
     "status_cancelled": "キャンセル",

packages/views/locales/ko/agents.json

@@ -675,9 +675,10 @@
     "density_collapsed_desc": "이벤트당 한 줄, 가장 간결한 보기",
     "no_output": "출력 없음",
     "show_all": "모두 보기",
-    "patch_truncated": "…(잘림)",
-    "patch_body_truncated": "…(본문 잘림)",
+    "patch_truncated": "...(잘림)",
+    "patch_body_truncated": "...(본문 잘림)",
     "patch_no_content": "(기록된 내용 없음)",
+    "patch_summary_more": "{{path}} 외 {{count}}개",
     "status_queued": "대기열",
     "status_dispatched": "디스패치됨",
     "status_cancelled": "취소됨",

packages/views/locales/zh-Hans/agents.json

@@ -774,9 +774,10 @@
     "density_collapsed_desc": "一行一事件，最紧凑的扫读视图",
     "no_output": "无输出",
     "show_all": "显示全部",
-    "patch_truncated": "……（已截断）",
-    "patch_body_truncated": "……（内容已截断）",
+    "patch_truncated": "...（已截断）",
+    "patch_body_truncated": "...（内容已截断）",
     "patch_no_content": "（未记录内容）",
+    "patch_summary_more": "{{path}} 等 {{count}} 个文件",
     "status_queued": "排队中",
     "status_dispatched": "已派发",
     "status_cancelled": "已取消",