[RomainROCH]

What this PR does

Make the developer-check fixture accept Windows PowerShell line wrapping in the
expected Cargo failure, including wrapping inside an argument. Require the full
diagnostic with exit code 7 and exactly one fmt --all -- --check trace entry.
The process-level failure check remains unchanged.

Why

On a long checkout path, Windows PowerShell 5.1 splits --all across output
lines. The original contiguous-string assertion fails even though the fake
Cargo correctly failed at the first command. Whitespace tolerance is limited to
this diagnostic; the trace check also rejects repeated or additional commands.

Base: main at 8c459778b4fc726ef6b62d03e150adfcbbac3eda, matching the accepted
one-file correction. This is a separate draft for review. The v0.2.1 candidate
and its tag target remain at that base; this PR does not change the release.

How it was tested

• Reproduced the original failure on Windows PowerShell 5.1.26100.9444.

• 20 synthetic cases exercise the actual assertion ASTs: accepted formatting,
  wrong/missing failure diagnostics, extra/repeated commands, and the unchanged
  process-level success/failure guard.

• Developer suite: exit 0 on script paths of 80, 109 and 192 characters, including
  spaces. Copied scripts were byte-identical; temporary fixtures were removed.

• Docs: exit 0, 27 Markdown files; local anchors are outside checker coverage.

• Smoke-safety: exit 0, seven preflight cases and the safety suite with fake
  process/task/build callbacks. All five native suite stderr logs are empty.

• Whitespace, local content/metadata privacy and secret checks passed.

• No general local build, real protection runtime or hardware acceptance was
  run for this test-only change. Hosted PR CI is tracked separately.

• scripts/check.ps1 -Mode Full locally (not run: no Rust changes)

• tests/developer_checks.ps1 passes for the developer-tooling change

• tests/smoke_safety.ps1 passes

• Relevant local checks run with synthetic fixtures; runtime/manual limits stated

• Product documentation needs no change: only test assertions change

Checklist

• Base and draft-only integration scope stated above
• No architecture, production, dependency or CI/release-infrastructure change
• No business-model change