fix: harden Metal presentation lifetimes

[x90skysn3k]

Retains the exact tokened Metal frame until host presentation acknowledgement, preventing remote-terminal typing updates from waiting behind recycled or stalled frames. Covers replacement, reordering, and teardown lifetimes without adding an app-level draw loop.\n\nRebased directly onto current manaflow-ai/ghostty main. Local zig build test passes with Zig 0.15.2.

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Summary by cubic

Hardened Metal presentation by tracking a per-frame presentation lifetime and generation, so stale or resized IOSurfaces never overwrite current contents. This fixes remote-terminal typing latency and flicker during resize or layer teardown.

• Bug Fixes
  • Retains the exact tokened IOSurface until host ack; queues presentation on main to avoid recycled or stalled frames blocking input.
  • Validates updates by size and monotonic generation; discards stale/wrong-size surfaces and advances generation on resize/teardown.
  • Splits presentation lifetime from renderer/layer ownership to avoid touching detached UI or callback userdata.
  • Sync completion on macOS now returns delivery to caller after draw lock releases; iOS path stays async to keep queued behavior.

^{Written for commit cce098d. Summary will update on new commits.}

[x90skysn3k]

@lawrencecchen This is the minimal 3-file rebase onto current fork main. Full zig build test passes with Zig 0.15.2; parent macOS/iOS integration was already green against the equivalent patch. Please merge when checks clear.

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📥 Commits

Reviewing files that changed from the base of the PR and between 0b1734f and cce098d.

📒 Files selected for processing (3)

• src/renderer/Metal.zig
• src/renderer/metal/Frame.zig
• src/renderer/metal/IOSurfaceLayer.zig

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🧪 Generate unit tests (beta)

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[x90skysn3k]

@lawrencecchen All available checks are now green/skipped, the full Ghostty renderer suite is green, and the parent macOS/iOS integration has been built and dogfooded. The parent repository is temporarily pinned to the equivalent fork-main commit; merging this PR is the remaining step needed to restore the configured manaflow-ai/ghostty main-branch ancestry contract.