Expand Windows integration coverage

[dinsley]

Summary

Priority: P1

Expand Windows-specific automated and manual integration coverage beyond the current cross-platform unit and build checks.

CI already runs the project check on windows-latest, and executable resolution has a Windows unit test. The remaining risk is at the process and desktop-integration boundary: real installation locations, paths containing spaces, CRLF streaming, detached child behavior, timeouts, and Stream Deck's runtime environment.

Proposed scope

• Add a Windows subprocess test fixture that behaves like the relevant Amp commands without requiring an Amp account.
• Exercise:
  • executable discovery and explicit paths;
  • paths containing spaces and non-ASCII characters;
  • argument passing without shell interpolation;
  • CRLF and chunked JSONL output;
  • stdout/stderr bounds;
  • acknowledgement parsing;
  • timeout and child termination;
  • detached command lifetime after acknowledgement; and
  • plugin shutdown while a child or retry is active.
• Document expected Amp installation discovery on Windows.
• Add a repeatable manual smoke-test checklist for a real Windows Stream Deck installation and authenticated Amp CLI.
• Record which behaviors cannot be established in hosted CI because they require hardware, Stream Deck, or user authentication.

Acceptance criteria

• Windows CI runs the subprocess compatibility suite using a disposable fake Amp executable.
• No command path relies on shell quoting or an interactive terminal environment.
• CRLF and arbitrarily chunked stream records are covered.
• Timeout, process exit, spawn error, and accepted-then-failed cases are covered.
• The manual checklist verifies status monitoring, selection, open, review, ship, archive, restart, and log collection.
• README.md or troubleshooting documentation clearly describes supported Windows setup and known limitations.
• At least one real Windows test result is recorded before Windows support is considered fully verified for a release.