Bug fixes:
- Fix OSC8 format strings (backslash escape layering) in modern-backend.org
- Test format string had single backslash instead of double, causing
unclosed CL string that cascaded through 3 subsequent test forms
- Implementation format string had leading escaped quote (not a string
opener) and triple-backslash ending (also not a string terminator)
- Fix missing closing parens in border-char-rounded and border-char-double tests
- Fix ASDF input-tests pathname (file lives in tests/, not src/components/)
New features:
- Implement suspend-backend / resume-backend protocol methods
- modern-backend: exit/enter alt screen, re-enable mouse/kitty/bracketed-paste
- simple-backend: no-ops (no terminal state to preserve)
Infrastructure:
- Update test suite to cover suspend/resume (backend + modern-backend suites)
- 454 checks, 100% pass across 14 test suites
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