Headless mode: ext_image_copy_capture session deadlocks in wlr_output_configure_primary_swapchain

[deepin-wm]

Description

Creating an ext_image_copy_capture capture session in headless mode (WLR_BACKENDS=headless, WLR_RENDERER=pixman) deadlocks inside wlr_output_configure_primary_swapchain.

Reproduction

1. Build treeland with headless backend
2. Run the wayland-ext-image-copy-capture-v1 protocol test with a full capture session (not just global presence)
3. The test hangs indefinitely inside wlr_output_configure_primary_swapchain

Environment

• Backend: headless (WLR_BACKENDS=headless)
• Renderer: pixman (WLR_RENDERER=pixman)
• Found during wayland-protocols test coverage work (PR tests/protocols: add 24 standard wayland-protocols tests served by Treeland #1336)

Impact

The ext-image-copy-capture protocol test can only verify global presence and create_source in headless CI, not a full end-to-end capture session. Full E-level coverage is blocked until this deadlock is resolved.

Workaround

The test creates and immediately destroys the source without starting a capture session, avoiding the deadlock path.