test(shell-completion): stabilize flaky zpty zsh completion tests

[dqn]

Summary

The zpty-based zsh interactive completion tests were intermittently
failing (~10–20%) with NMATCHES:-1. Root cause: a TAB-vs-ZLE race in
the test harness — TAB was sent before zsh's line editor finished
consuming the command, so it was inserted as a literal character instead
of triggering completion. Waiting for the command to be echoed back
(i.e. ZLE ingested the input) and letting ZLE settle before sending TAB
removes the race; no timeout extensions or retry logic were needed.

Main changes

• Wait for the command echo from zpty before sending TAB, plus a 0.1s
  ZLE settle delay
• Use the correct lowercase compprefuncs array; the previously used
  camelCase comppreFuncs is not a real zsh hook, so the pre-hook was
  silently inactive
• Add a _test_pre / _test_cap split using compprefuncs and
  comppostfuncs so diagnostics distinguish "TAB never triggered
  completion" (test infra race) from "completion ran but produced no
  matches" (potential politty bug)

Verification

• 20/20 consecutive runs of the zpty suite pass after the fix
• Full npm test (1290 tests) green

Notes

• The import-order tweak at the top of zsh.test.ts is an automatic
  reorder by lefthook's organize-imports-cli pre-commit hook. The hook
  only touches staged files, so older files drift out of sync until they
  are next edited — unrelated to the stabilization itself.

Code Metrics Report

	main (57b091d)	#436 (16100f3)	+/-
Coverage	87.8%	87.8%	0.0%
Test Execution Time	11s	11s	0s

Details

  |                     | main (57b091d) | #436 (16100f3) | +/-  |
  |---------------------|----------------|----------------|------|
  | Coverage            |          87.8% |          87.8% | 0.0% |
  |   Files             |             51 |             51 |    0 |
  |   Lines             |           4272 |           4272 |    0 |
  |   Covered           |           3753 |           3753 |    0 |
  | Test Execution Time |            11s |            11s |   0s |

---

Reported by octocov

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/politty@436

commit: a77c376

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 3 additional findings.