Propose append-only typed output API

[zikolach]

Summary

• propose a callback-completed, TUI-owned append operation for typed normal-screen scrollback output
• preserve the existing non-waiting contended/reentrant flushRender() contract
• require a running normal-screen TUI with NormalResizeClearPolicy.PreserveScrollback and a committed live frame
• render detached one-shot components with a restricted context and retry only unpublished resize-invalidated candidates
• reject cursor and cleanup authority, remap Kitty IDs, and bound append ownership to a 4096-ID redacted ledger
• serialize append output with existing runtime work, redraw the retained frame, and restore hardware cursor and mouse frame origin
• separate automated protocol/PTY guarantees from manual Kitty and iTerm2 emulator persistence checks

OpenSpec

• change: add-append-only-output-api
• proposal, design, specification, and 32 implementation tasks are complete
• implementation is intentionally deferred pending proposal review

Validation

• openspec validate --all --strict — 14 passed, 0 failed
• git diff --check
• confirmed the change artifacts contain no Sigma references