fix(chat): open file references in editor instead of new browser window

Clicking a file reference in a chat message (e.g. `useShellTerminal.ts`)
opened a new browser window because it was rendered as a plain anchor with
target="_blank" and an empty/relative href.

The markdown link renderer now intercepts file-path links — using the href,
or the link text when the href is empty — strips any `:line:col` suffix, and
opens the file in the in-app editor side panel while keeping the Chat tab
active (matching the inline edit view).

- useFileOpenResolver: resolves bare/partial references to real project
  files via the cached project file tree
- PaletteOpsContext: add `openFileInEditor` op that opens the editor without
  switching tabs

src/hooks/useFileOpenResolver.ts

@@ -0,0 +1,108 @@
+import { useCallback, useRef } from 'react';
+
+import { api } from '../utils/api';
+import type { Project } from '../types/app';
+
+type FileNode = {
+  type: 'file' | 'directory';
+  name: string;
+  path: string;
+  children?: FileNode[];
+};
+
+type FlatFile = {
+  name: string;
+  path: string;
+};
+
+// `diffInfo` is intentionally `any` so this resolver can wrap editor handlers
+// that expect a concrete diff payload type as well as generic callers.
+type OnFileOpen = (filePath: string, diffInfo?: any) => void;
+
+const normalize = (value: string): string => value.replace(/\\/g, '/');
+
+const flatten = (nodes: FileNode[], out: FlatFile[]): void => {
+  for (const node of nodes) {
+    if (node.type === 'file') {
+      out.push({ name: node.name, path: node.path });
+    } else if (node.children && node.children.length > 0) {
+      flatten(node.children, out);
+    }
+  }
+};
+
+// References inside chat messages are often bare basenames (`foo.ts`) or partial
+// paths (`utils/foo.ts`) rather than full paths, so match by path suffix and
+// fall back to filename equality.
+const findBestMatch = (files: FlatFile[], ref: string): string | null => {
+  const target = normalize(ref).replace(/^\.\//, '').replace(/^\/+/, '');
+  if (!target) {
+    return null;
+  }
+
+  const suffixMatch = files.find((file) => {
+    const filePath = normalize(file.path);
+    return filePath === target || filePath.endsWith(`/${target}`);
+  });
+  if (suffixMatch) {
+    return suffixMatch.path;
+  }
+
+  const base = target.split('/').pop() || target;
+  return files.find((file) => file.name === base)?.path ?? null;
+};
+
+/**
+ * Wraps an `onFileOpen` handler so a possibly bare/partial file reference is
+ * resolved against the project's file tree (cached per project) before the file
+ * is opened in the in-app editor.
+ */
+export function useFileOpenResolver(
+  selectedProject: Project | null | undefined,
+  onFileOpen: OnFileOpen,
+): OnFileOpen {
+  const projectId = selectedProject?.projectId;
+  const cacheRef = useRef<{ projectId?: string; files: Promise<FlatFile[]> | null }>({
+    projectId: undefined,
+    files: null,
+  });
+
+  const loadFiles = useCallback((): Promise<FlatFile[]> => {
+    if (!projectId) {
+      return Promise.resolve([]);
+    }
+    if (cacheRef.current.projectId === projectId && cacheRef.current.files) {
+      return cacheRef.current.files;
+    }
+
+    const filesPromise = (async () => {
+      try {
+        const response = await api.getFiles(projectId);
+        if (!response.ok) {
+          return [];
+        }
+        const data = await response.json();
+        const tree: FileNode[] = Array.isArray(data) ? data : [];
+        const flat: FlatFile[] = [];
+        flatten(tree, flat);
+        return flat;
+      } catch {
+        return [];
+      }
+    })();
+
+    cacheRef.current = { projectId, files: filesPromise };
+    return filesPromise;
+  }, [projectId]);
+
+  return useCallback(
+    (filePath: string, diffInfo?: any) => {
+      const ref = normalize(filePath).trim();
+      void loadFiles().then((files) => {
+        const match = findBestMatch(files, ref);
+        onFileOpen(match ?? filePath, diffInfo);
+      });
+    },
+    [loadFiles, onFileOpen],
+  );
+}