🐛 export: fix free_buffers memory leak on single-plane exports

[devin-ai-integration]

📝 Description

Fixes the OOM crash reported when running exports on tauri:dev (memory allocation of 7570752 bytes failed → STATUS_STACK_BUFFER_OVERRUN).

Root cause: in feed_cursor_frames the writer recycles every finished ProducedFrame::Bytes into the free_buffers pool, but buffers are only ever popped back out inside the dual_plane producer branch. On a single-plane stream — cursor-only or items-only — nothing consumes the pool, so it grows by one plate (~7–8 MiB) per frame. A 60 s export at 30 fps leaks ~14 GB of dead Vecs until the allocator fails — matching the reported ~7.5 MB failed allocation (a screen-rect plane) exactly.

The bug came in with the overlay worker-pool refactor (929c9d1), one commit before #3 — it is not caused by the screen-rect plate change, which only shrinks each leaked buffer slightly.

Fix: gate the recycle push on dual_plane. Single-plane frames are dropped after the write as before; dual-plane recycling is unchanged. One-word gate, no behavioural change to output.

🎯 Type of Change

• 🐛 Bug fix (non-breaking change fixing an issue)

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🧪 Validation & Testing

• cargo fmt --check — clean

• cargo clippy -- -D warnings — clean

• cargo check — clean

• bun run typecheck / bun run test — Rust-only diff; covered by CI

• Tested on target operating systems:

  • Windows (compile-verified; the export loop itself needs a real export run)
  • macOS
  • Linux

📋 Checklist

• Style follows existing conventions
• Non-obvious decision commented at free_buffers (why pushes are gated on dual_plane)
• No raw frames/secrets across Tauri boundaries
• No telemetry added

Link to Devin session: https://app.devin.ai/sessions/52c7ba7f829f4aecbefa2f889efc8dc5
Open in Devin Desktop: https://app.devin.ai/desktop/session/52c7ba7f829f4aecbefa2f889efc8dc5?variant=devin
Requested by: @jeandedieuH

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring