fix: keep @ file mention responsive on very large projects (#600)

Typing @ in the chat input to reference a file froze the app on huge
workspaces. Two compounding causes:

1. The autocomplete hook fed fileFilterQuery straight into the React
   Query key, so every keystroke fired a new directory_suggestions
   request and a fresh BFS scan on the daemon. Added a 180 ms debounce
   that mirrors the existing pattern in new-workspace-screen so rapid
   typing coalesces into one request.

2. searchWorkspaceEntries only ignored node_modules, so dist, build,
   target, out, coverage, vendor and __pycache__ each consumed the
   5,000-entry scan budget before any real source file was reached.
   Extended WORKSPACE_IGNORED_DIRECTORY_NAMES with those names and
   added a regression test that proves a deep source file is still
   reachable when those directories are full of bait entries.

Refs #599

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/app/src/hooks/use-agent-autocomplete.ts

@@ -1,4 +1,4 @@
-import { useCallback, useMemo } from "react";
+import { useCallback, useEffect, useMemo, useState } from "react";
 import { keepPreviousData, useQuery } from "@tanstack/react-query";
 import type { AutocompleteOption } from "@/components/ui/autocomplete";
 import { useAgentCommandsQuery, type DraftCommandConfig } from "./use-agent-commands-query";
@@ -185,6 +185,12 @@ export function useAgentAutocomplete(input: UseAgentAutocompleteInput): AgentAut
   );
   const showFileAutocomplete = activeFileMention !== null;
   const fileFilterQuery = activeFileMention?.query ?? "";
+  const [debouncedFileFilterQuery, setDebouncedFileFilterQuery] = useState(fileFilterQuery);
+
+  useEffect(() => {
+    const timer = setTimeout(() => setDebouncedFileFilterQuery(fileFilterQuery), 180);
+    return () => clearTimeout(timer);
+  }, [fileFilterQuery]);
 
   const normalizedDraftConfig = useMemo(
     () => normalizeDraftCommandConfig(draftConfig),
@@ -229,14 +235,21 @@ export function useAgentAutocomplete(input: UseAgentAutocompleteInput): AgentAut
   });
 
   const fileSuggestionsQuery = useQuery({
-    queryKey: ["directorySuggestions", serverId, autocompleteCwd, fileFilterQuery, true, true],
+    queryKey: [
+      "directorySuggestions",
+      serverId,
+      autocompleteCwd,
+      debouncedFileFilterQuery,
+      true,
+      true,
+    ],
     queryFn: async (): Promise<DirectorySuggestionEntry[]> => {
       if (!client) {
         throw new Error("Daemon client unavailable");
       }
       const response = await client.getDirectorySuggestions({
         cwd: autocompleteCwd,
-        query: fileFilterQuery,
+        query: debouncedFileFilterQuery,
         limit: 50,
         includeFiles: true,
         includeDirectories: true,

packages/server/src/utils/directory-suggestions.test.ts

@@ -265,4 +265,34 @@ describe("searchWorkspaceEntries", () => {
     });
     expect(results.some((entry) => entry.path.startsWith("node_modules/"))).toBe(false);
   });
+
+  it("ignores common build/cache directories so large generated trees do not exhaust scan budget", async () => {
+    mkdirSync(path.join(workspaceDir, "packages", "app", "src"), { recursive: true });
+    writeFileSync(path.join(workspaceDir, "packages", "app", "src", "needle.ts"), "");
+
+    const heavyDirs = ["dist", "build", "target", "out", "coverage", "vendor", "__pycache__"];
+    for (const heavyDir of heavyDirs) {
+      for (let index = 0; index < 30; index += 1) {
+        mkdirSync(path.join(workspaceDir, heavyDir, `bundle-${index}`), { recursive: true });
+        writeFileSync(path.join(workspaceDir, heavyDir, `bundle-${index}`, "needle.ts"), "");
+      }
+    }
+
+    const results = await searchWorkspaceEntries({
+      cwd: workspaceDir,
+      query: "needle.ts",
+      limit: 20,
+      includeFiles: true,
+      includeDirectories: true,
+      maxEntriesScanned: 80,
+    });
+
+    expect(results).toContainEqual({
+      path: "packages/app/src/needle.ts",
+      kind: "file",
+    });
+    for (const heavyDir of heavyDirs) {
+      expect(results.some((entry) => entry.path.startsWith(`${heavyDir}/`))).toBe(false);
+    }
+  });
 });

packages/server/src/utils/directory-suggestions.ts

@@ -73,7 +73,16 @@ const directoryListCache = new Map<string, DirectoryListCacheEntry>();
 const workspaceEntryListCache = new Map<string, WorkspaceEntryListCacheEntry>();
 const NO_SEGMENT_INDEX = Number.MAX_SAFE_INTEGER;
 const NO_MATCH_OFFSET = Number.MAX_SAFE_INTEGER;
-const WORKSPACE_IGNORED_DIRECTORY_NAMES = new Set(["node_modules"]);
+const WORKSPACE_IGNORED_DIRECTORY_NAMES = new Set([
+  "node_modules",
+  "dist",
+  "build",
+  "target",
+  "out",
+  "coverage",
+  "vendor",
+  "__pycache__",
+]);
 
 export async function searchHomeDirectories(
   options: SearchHomeDirectoriesOptions,