fix: keep browse/src/bun-child-config.ts unchanged so the native cookie qualification still binds

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

CHANGELOG.md

@@ -6,7 +6,7 @@
 
 ### Security
 - **Every bun entry point starts isolated:** all 123 bun shebangs are now `#!/usr/bin/env -S bun --no-env-file --config=/dev/null`. `bun run <file>` ignores the shebang, so the callers carry the flags too: skill templates, generated skill docs, resolvers, hook wrappers, `setup` and the bash bins pass `bun --no-env-file --config=/dev/null` for every `run`, `-e`, `-p` and script path.
-- **TypeScript spawns use `bunIsolationArgs()`** from `lib/bun-isolation.ts`, which now owns browse's `emptyBunConfig()`. This covers `scriptInvocation` (how TypeScript launches gstack's own bins), restamp, qa-deadline, the timeline hook's repair child, gbrain sync's ingest child, the agents-digest regen and the Claude Code migration. Native Windows has no `/dev/null`, so there the helper passes a private zero-byte bunfig. Under Git Bash, MSYS rewrites the shebang's `/dev/null` to `nul`, which Bun 1.4.2 reads as an empty config. A windows-latest run verified both.
+- **TypeScript spawns use `bunIsolationArgs()`** from `lib/bun-isolation.ts`, which follows browse's `emptyBunConfig()`. This covers `scriptInvocation` (how TypeScript launches gstack's own bins), restamp, qa-deadline, the timeline hook's repair child, gbrain sync's ingest child, the agents-digest regen and the Claude Code migration. Native Windows has no `/dev/null`, so there the helper passes a private zero-byte bunfig. Under Git Bash, MSYS rewrites the shebang's `/dev/null` to `nul`, which Bun 1.4.2 reads as an empty config. A windows-latest run verified both.
 - **Compiled builds:** `build:gates` and `scripts/build-app.sh` now pass `--no-compile-autoload-dotenv --no-compile-autoload-bunfig`, as `scripts/build.sh` already did. Without them, compiled binaries load both files.
 - **A ratchet and regressions:**
   - `test/bun-entry-isolation.test.ts` fails on any bun shebang, shell or skill caller, TypeScript spawn or `build --compile` that drops the flags.

browse/src/bun-child-config.ts

@@ -1,2 +1,35 @@
-/** The empty `--config` for every Bun child browse spawns (#3085); lib/bun-isolation.ts owns it. */
-export { emptyBunConfig } from '../../lib/bun-isolation';
+/**
+ * The `--config` file for every Bun child browse spawns (#3085). The child
+ * runs in the user's project, where Bun would otherwise load that project's
+ * bunfig.toml, whose preload runs code. POSIX passes /dev/null. Windows has no
+ * /dev/null and `--config=NUL` panicked Bun 1.3.10 while parsing the flag, so
+ * Windows gets an empty bunfig created exclusively in a private directory and
+ * re-checked to be a zero-byte regular file before each spawn; anything else
+ * is replaced, so the file cannot become a preload vector.
+ */
+import * as fs from 'fs';
+import * as os from 'os';
+import * as path from 'path';
+
+let emptyConfig: string | null = null;
+
+function isEmptyRegularFile(file: string): boolean {
+  try {
+    const stat = fs.lstatSync(file);
+    return stat.isFile() && stat.size === 0;
+  } catch {
+    return false;
+  }
+}
+
+export function emptyBunConfig(platform: NodeJS.Platform = process.platform): string {
+  if (platform !== 'win32') return '/dev/null';
+  if (emptyConfig && isEmptyRegularFile(emptyConfig)) return emptyConfig;
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-bunfig-'));
+  const file = path.join(dir, 'bunfig.toml');
+  fs.closeSync(fs.openSync(file, 'wx', 0o600));
+  if (!isEmptyRegularFile(file)) throw new Error(`empty Bun config ${file} is not a zero-byte file`);
+  process.once('exit', () => fs.rmSync(dir, { recursive: true, force: true }));
+  emptyConfig = file;
+  return file;
+}

lib/bun-isolation.ts

@@ -14,6 +14,9 @@
  * Windows gets an empty bunfig created exclusively in a private directory and
  * re-checked to be a zero-byte regular file before each spawn; anything else
  * is replaced, so the file cannot become a preload vector.
+ * browse/src/bun-child-config.ts keeps its own copy of emptyBunConfig(): the
+ * Windows native cookie qualification binds that file's bytes and bundles it
+ * without lib/.
  */
 import * as fs from 'fs';
 import * as os from 'os';

test/bun-entry-isolation.test.ts

@@ -22,6 +22,7 @@ import * as fs from 'node:fs';
 import * as path from 'node:path';
 import { bunIsolationArgs, emptyBunConfig } from '../lib/bun-isolation';
 import { scriptInvocation } from '../lib/script-invocation';
+import { emptyBunConfig as browseEmptyBunConfig } from '../browse/src/bun-child-config';
 
 const ROOT = path.resolve(import.meta.dir, '..');
 const FLAGS = '--no-env-file --config=/dev/null';
@@ -154,6 +155,9 @@ describe('GSTA-56: gstack never takes configuration from the audited repository'
     expect(inv).toEqual({ ok: true, cmd: 'bun', argv: [...bunIsolationArgs(), path.join(ROOT, 'bin', 'gstack-decision-log'), '--help'] });
     expect(bunIsolationArgs('linux')).toEqual(['--no-env-file', '--config=/dev/null']);
     expect(bunIsolationArgs('win32')).toEqual(['--no-env-file', `--config=${emptyBunConfig('win32')}`]);
+    expect(browseEmptyBunConfig('linux')).toBe(emptyBunConfig('linux'));
+    expect(fs.statSync(browseEmptyBunConfig('win32')).size).toBe(0);
+    expect(fs.statSync(emptyBunConfig('win32')).size).toBe(0);
   });
 
   test('every bun build --compile disables .env and bunfig autoload', () => {