Fix double-close of POSIX test-result FIFO descriptors

[Weidav]

Fixes #26173.

Remove the redundant fs.close(fd) call from the POSIX FIFO socket's close handler and the unused noop import. net.Socket already closes the descriptor, so closing it again can close an unrelated resource after descriptor reuse and crash the extension host. Add real-FIFO regression tests for normal closure and socket errors, isolated in child processes so descriptor reuse cannot affect the test runner.

Testing (Node 22.21.1 unless noted):

• npx gulp prePublishNonBundle — passed with Node 22.21.1.
• npm run lint and npm run format-check — passed.
• env -u VIRTUAL_ENV -u PS1 CI_PYTHON_PATH="$PWD/.venv/bin/python" npm run test:unittests — 5,206 passed, 38 pending/skipped.
• npm run test:functional -- --grep='POSIX named pipe reader' — 2 passed on Node 22.21.1 and Node 24.15.0/libuv 1.51.0. Both checks force descriptor reuse by another file and fail with EBADF on the original code. They also verify JSON-RPC delivery, error forwarding, reader cleanup, and repeated disposal.
• Built Linux x64 VSIX version 2026.7.26173; verified its archive, extension entrypoints, native environment helper, and bundled ownership fix.

Other:

• This overlaps with #26082. My fix retains focuses only on avoiding the crash and needs less changes.
• Thes probably fixes the Remote Extension Host crashes from repeated Remote Extension Host core dump  vscode#286663
• The regression tests use real POSIX FIFOs and are skipped on Windows. Each child process has a 10-second timeout.
• I tested the VSIX for two days in the linux remote-workspace, where I constantly run into this bug. No more crashes.

Suggested label: bug.

[Weidav]

@microsoft-github-policy-service agree

[Alex Rogozhnikov (arogozhnikov)]

empirically - after this patch no crash for a day, previously 2-3 times a day. So I guess this was it.

[Heejae Chang (heejaechang)]

🔒 Automated review in progress — Heejae Chang (@heejaechang) is auto-reviewing this PR.

[Heejae Chang (heejaechang)]

Result: ⚠️ partially-verified

Verification details

Verification: Isolated verification observed failures that were not classified as caused by this PR: Changed-file lint and formatting checks.

Summary: On Linux with Node 22.21.1, offline dependency installation and TypeScript compilation passed. Both new real-FIFO regressions passed, covering descriptor reuse, JSON-RPC delivery, error forwarding, cleanup, and repeated disposal. Three existing reader-consumer tests also passed. Changed-file lint passed, but formatting verification could not complete because my command used a Prettier 3 runner path while this repository specifies Prettier 2. All five targeted tests passed; broader suites and VSIX validation were not run.

Test runs: 5 passed, 1 failed

• ❌ Failed | unrelated to this PR | Changed-file lint and formatting checks | node ./node_modules/eslint/bin/eslint.js src/client/common/pipes/namedPipes.ts src/test/common/pipes/namedPipes.functional.test.ts src/test/common/pipes/namedPipesFixture.ts && node ./node_modules/prettier/bin/prettier.cjs --check src/client/common/pipes/namedPipes.ts src/test/common/pipes/namedPipes.functional.test.ts src/test/common/pipes/namedPipesFixture.ts
• ✅ Passed | POSIX named pipe reader regressions | node ./node_modules/mocha/bin/mocha.js --no-config --require ./out/test/unittests.js --require source-map-support/register --ui tdd --timeout 20000 --reporter spec --exit ./out/test/common/pipes/namedPipes.functional.test.js
• ✅ Passed | Existing named-pipe drain-on-cancel tests | node ./node_modules/mocha/bin/mocha.js --no-config --require ./out/test/unittests.js --require source-map-support/register --ui tdd --timeout 20000 --reporter spec --grep 'startRunResultNamedPipe drain-on-cancel tests' ./out/test/testing/testController/utils.unit.test.js
• ✅ Passed | Dependency and runner discovery | printf 'AUTOMATION_SANDBOX_PROFILE=%s\n' "$AUTOMATION_SANDBOX_PROFILE"; node --version; npm --version; command -v mkfifo; node -e "const fs=require('fs');const p=require('./package.json');console.log(JSON.stringify(p.scripts,null,2));for(const f of ['node_modules/typescript/lib/tsc.js','node_modules/mocha/bin/mocha.js','out/test/unittests.js','out/test/common/pipes/namedPipes.functional.test.js','package-lock.json'])console.log(f+': '+fs.existsSync(f));"; cat build/.mocha.functional.json build/.mocha.unittests.json .npmrc .nvmrc
• ✅ Passed | Offline dependency bootstrap | npm ci --offline
• ✅ Passed | TypeScript compilation | node ./node_modules/gulp/bin/gulp.js compileCore

❌ Changed-file lint and formatting checks diagnostic output

ESLint completed successfully; the subsequent formatting runner failed:
Error: Cannot find module '/workspace/node_modules/prettier/bin/prettier.cjs'
code: 'MODULE_NOT_FOUND'
Node.js v22.21.1

[Heejae Chang (heejaechang)]

Approved via Review Center.