fix(web): keep a file-to-symlink type change from crashing the diff view

apps/web/src/components/diffs/DiffFileTree.test.tsx

@@ -5,7 +5,10 @@ import { act, type MouseEvent, type ReactNode } from "react";
 import { create, type ReactTestRenderer } from "react-test-renderer";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vite-plus/test";
 
+import type { FileDiffMetadata } from "@pierre/diffs";
+
 import { DiffFileTree, type DiffFileTreeEntry } from "./DiffFileTree";
+import { diffFileTreeEntries } from "./diffFileTree.logic";
 import { useCodeViewFileReveal } from "./useCodeViewFileReveal";
 
 vi.mock("../../hooks/useTheme", () => ({ useTheme: () => ({ resolvedTheme: "dark" }) }));
@@ -112,6 +115,22 @@ describe("diff tree file activation", () => {
     vi.unstubAllGlobals();
   });
 
+  it("mounts a file-to-symlink type change as one tree row", async () => {
+    // Git carries a type change as a deletion and an addition of the same path.
+    const typeChange = diffFileTreeEntries([
+      { type: "deleted", name: "AGENTS.md", prevName: "AGENTS.md" } as FileDiffMetadata,
+      { type: "new", name: "AGENTS.md", prevName: "AGENTS.md" } as FileDiffMetadata,
+      { type: "change", name: "CLAUDE.md", prevName: "CLAUDE.md" } as FileDiffMetadata,
+    ]);
+    await mount({ files: [...typeChange] });
+
+    const tree = model();
+    expect(tree.getItem("AGENTS.md")?.isDirectory()).toBe(false);
+    expect(tree.getItem("CLAUDE.md")?.isDirectory()).toBe(false);
+    await activate("AGENTS.md");
+    expect(targets).toEqual([{ type: "item", id: "AGENTS.md\u0000AGENTS.md", align: "start" }]);
+  });
+
   it("reissues the reveal when the sole selected file is activated again", async () => {
     await mount();
     await activate("02-short.ts");

apps/web/src/components/diffs/diffFileTree.logic.test.ts

@@ -34,6 +34,23 @@ describe("diffFileTreeEntries", () => {
   });
 });
 
+describe("diffFileTreeEntries", () => {
+  it("folds a file-to-symlink type change into one modified entry", () => {
+    expect(
+      diffFileTreeEntries([
+        file("change", "CLAUDE.md"),
+        file("deleted", "AGENTS.md"),
+        file("new", "AGENTS.md"),
+        file("new", "docs/new.md"),
+      ]),
+    ).toEqual([
+      { path: "CLAUDE.md", status: "modified" },
+      { path: "AGENTS.md", status: "modified" },
+      { path: "docs/new.md", status: "added" },
+    ]);
+  });
+});
+
 describe("collectDirectoryPaths", () => {
   it("lists every ancestor once, parents first, with Pierre's trailing slash", () => {
     expect(collectDirectoryPaths(["apps/web/src/a.ts", "apps/web/b.ts", "README.md"])).toEqual([

apps/web/src/components/diffs/diffFileTree.logic.ts

@@ -23,11 +23,22 @@ function toGitStatus(file: FileDiffMetadata): GitStatus {
   }
 }
 
-/** Maps parsed diff files to tree entries, keeping the diff's own order. */
+/**
+ * Maps parsed diff files to tree entries, keeping the diff's own order. A path
+ * appears once: a type change (regular file to symlink) is a deletion plus an
+ * addition of the same path, and the tree shows the surviving file as modified.
+ */
 export function diffFileTreeEntries(
   files: ReadonlyArray<FileDiffMetadata>,
 ): ReadonlyArray<DiffFileTreeEntry> {
-  return files.map((file) => ({ path: resolveFileDiffPath(file), status: toGitStatus(file) }));
+  const statusByPath = new Map<string, GitStatus>();
+  for (const file of files) {
+    const path = resolveFileDiffPath(file);
+    const status = toGitStatus(file);
+    const previous = statusByPath.get(path);
+    statusByPath.set(path, previous === undefined || previous === status ? status : "modified");
+  }
+  return [...statusByPath].map(([path, status]) => ({ path, status }));
 }
 
 /**

apps/web/src/lib/diffRendering.test.ts

@@ -35,10 +35,10 @@ describe("buildPatchCacheKey", () => {
 
 describe("getRenderablePatch", () => {
   it.each([
-    ["a/example.ts", "a/example.ts"],
-    ["b/example.ts", "b/example.ts"],
-    ["a/before.ts", "b/after.ts"],
-  ])("preserves repository paths from %s to %s", (previousPath, path) => {
+    ["a/example.ts", "a/example.ts", "change"],
+    ["b/example.ts", "b/example.ts", "change"],
+    ["a/before.ts", "b/after.ts", "rename-changed"],
+  ])("preserves repository paths from %s to %s", (previousPath, path, type) => {
     const parsed = getRenderablePatch(
       [
         `diff --git a/${previousPath} b/${path}`,
@@ -59,7 +59,7 @@ describe("getRenderablePatch", () => {
     if (!file) return;
     expect(resolveFileDiffPath(file)).toBe(path);
     expect(resolveFileDiffPreviousPath(file)).toBe(previousPath);
-    expect(buildFileDiffIdentityKey(file)).toBe(`${previousPath}\0${path}`);
+    expect(buildFileDiffIdentityKey(file)).toBe(`${previousPath}\0${path}\0${type}`);
   });
 
   it("compacts partial hunk render offsets for virtualized review diffs", () => {
@@ -137,6 +137,33 @@ describe("diff file reconciliation", () => {
     expect(buildFileDiffRenderKey(file)).toBe(key);
   });
 
+  it("gives a type change its own identity per block", () => {
+    const patch = [
+      "diff --git a/AGENTS.md b/AGENTS.md",
+      "deleted file mode 100644",
+      "--- a/AGENTS.md",
+      "+++ /dev/null",
+      "@@ -1 +0,0 @@",
+      "-duplicated instructions",
+      "diff --git a/AGENTS.md b/AGENTS.md",
+      "new file mode 120000",
+      "--- /dev/null",
+      "+++ b/AGENTS.md",
+      "@@ -0,0 +1 @@",
+      "+CLAUDE.md",
+    ].join("\n");
+    const parsed = getRenderablePatch(patch, "type-change");
+    expect(parsed?.kind).toBe("files");
+    if (parsed?.kind !== "files") return;
+    const [deleted, added] = parsed.files;
+    expect(deleted?.type).toBe("deleted");
+    expect(added?.type).toBe("new");
+    if (!deleted || !added) return;
+
+    expect(buildFileDiffIdentityKey(deleted)).not.toBe(buildFileDiffIdentityKey(added));
+    expect(new Set(parsed.files.map(buildFileDiffIdentityKey)).size).toBe(parsed.files.length);
+  });
+
   it("keeps identities stable and versions local to the changed file", () => {
     const patch = (secondLine: string) =>
       [

apps/web/src/lib/diffRendering.ts

@@ -166,8 +166,13 @@ export function resolveFileDiffPreviousPath(fileDiff: FileDiffMetadata): string
   return fileDiffPath(fileDiff.prevName ?? fileDiff.name ?? "");
 }
 
+/**
+ * Stable across re-renders of the same file, distinct for every block in a
+ * patch. A type change (regular file to symlink) arrives as a deletion and an
+ * addition of the same path, so the change type is part of the identity.
+ */
 export function buildFileDiffIdentityKey(fileDiff: FileDiffMetadata): string {
-  return `${resolveFileDiffPreviousPath(fileDiff)}\u0000${resolveFileDiffPath(fileDiff)}`;
+  return `${resolveFileDiffPreviousPath(fileDiff)}\u0000${resolveFileDiffPath(fileDiff)}\u0000${fileDiff.type}`;
 }
 
 export function buildFileDiffRenderKey(fileDiff: FileDiffMetadata): string {