Summary

Give optional engines and version-sensitive operations explicit capability boundaries while preserving ordinary operations on supported older daemons. Implement this separately from the core tmux 3.3a minimum.

Motivation

Control acquisition, output observation, buffer cleanup and version-sensitive commands have different requirements. One whole-product minimum or reduced CI coverage cannot express those guarantees accurately.

Proposal

• Require daemon tmux 3.7 or verified initialization-fix backports before library-managed control acquisition, including internal watches, mirrors and streams; make the decision before attachment.
• Preserve supported subprocess and polling operations, and return explicit per-operation refusals where no qualified fallback exists.
• Protect exact named-buffer deletion and temporary-buffer cleanup below tmux 3.4 where these operations are exposed.
• Preserve exact-3.7 break-pane handling and other still-required codecs, layout validation, readiness, buffering and cleanup.
• Update capability documentation, examples and focused CI coverage, distinguishing unsupported, timing-sensitive and unverified behavior.
• Demonstrate that regression gates fail when their protection is deliberately removed, and obtain independent review.

References

• README.md.
• AGENTS.md.