Suggested test: copilot/custom-safe-outputs-zero-default-input

## Motivation

github/gh-aw PR #58... "Preserve zero-valued input defaults" — fixed a bug where numeric `default: 0` on custom safe-output job inputs was treated as missing due to truthiness-based fallback instead of nullish coalescing. No regression test exercises a numeric-zero default end-to-end.

## Proposed test

- **Workflow file**: `test-copilot-custom-safe-outputs-zero-default.md`
- **Trigger**: `workflow_dispatch`
- **Engine**: copilot
- **Safe output**: custom `safe-outputs.jobs` (similar to existing `test-copilot-custom-safe-outputs.md`)
- **Variant**: standard

## Minimal test prompt sketch

Define a custom safe-output job with an input of `type: number` and `default: 0`, where the agent does not set the input explicitly. The job step should assert the received value is literally `0` (not empty/missing) and write it to the step summary, failing the job if the value is blank.

## New fixtures or secrets needed

None — reuses the existing custom-safe-outputs job pattern.

## Notes

Distinct from `test-copilot-custom-safe-outputs.md` (which uses a required string input, no default). Not present in `fails.txt` or open suggestions.

> Generated by [🔍 Suggest New E2E Tests](https://github.com/githubnext/gh-aw-test/actions/runs/33854350934) · copilot · auto · 41 AIC · ⌖ 12.2 AIC · ⊞ 8.8K · [◷](https://github.com/search?q=repo%3Agithubnext%2Fgh-aw-test+is%3Aissue+%22gh-aw-workflow-call-id%3A+githubnext%2Fgh-aw-test%2Fsuggest-new-e2e-tests%22&type=issues)

Start with test-copilot-custom-safe-outputs.md to understand the existing custom safe-outputs job pattern, then use test-copilot-custom-safe-outputs-zero-default.md as the new workflow fixture. Exercise the workflow_dispatch path with the copilot engine and verify the numeric input remains 0 when unset, appears in the step summary, and causes failure if blank.

Written by the indexing model from the issue text.