On a miss the draw first takes its pipeline without compiling (its base made or in the archive, then a specialization). Failing that it draws with the pair's pulling pipeline (<key>_bp: no vertex descriptor, the streams read through a per-draw layout block at buffer 16, pull_bind), specialized with the draw's colour state, while its own pipeline is built in the background; a later draw takes that one. Both compute the same positions (t_pull_inv), so a draw that switches does not flicker or z-fight. Only a pulling base already made or archived is used; otherwise it is built in the background for the pair's next miss and the draw waits. Merged passes, readable-tile and diagnostic fragments, and layer-writing or transform feedback vertex shaders have no stand-in. DM_PSO_HYBRID=0 turns it off; it needs the Metal 4 path, so it is on by default on the Mac only.
On main's demand-first pipelines (#75): pso_pend_kick stays the speculative admission (at most two running, at most two per prediction, the oldest finished entry reclaimed when the table is full). A draw with a stand-in queues its own pipeline before the prediction runs (pso_pend_demand): outside the speculative limit, on serial queues at utility QoS, one per two performance cores (pp_bg_queue), so a demanded build never waits behind speculation and speculation never waits behind it. The prediction spends its budget only on draws that will have no stand-in, since only those would wait. A draw that would wait for a build still queued makes the pipeline itself at once (pso_pend_take; Breath of the Wild's cold start waited 0.5-0.9 s for one pipeline behind a burst before). The first miss of a submission loads the shader libraries the rest of it binds in parallel (shader_prefetch_rest): 248 libraries in about 210 ms where one by one on the submit thread took about 1 s, in the hybrid and the waiting path alike.
Diagnostics: a "pipelines up to frame" line every 300 frames (submit-thread pipeline, library and prediction time, archive lookups, specializations, base compiles, hybrid draws, background builds, the draws that waited and why), DM_PSO_WAITLOG=1 (each wait over 20 ms with its pair), DM_PSO_PULL_ALL=1 (every draw with a pulling pipeline draws with it), and the longframe line's count of hybrid draws.
Breath of the Wild, Mac (M2 Max), steady state in Zora's Domain: mean GPU p50 over frames 2,400-5,100 was 8.98 ms with the hybrid, 8.98 ms on the Metal 4 path without it, 9.35 ms through the MTLDevice. Cold-start numbers are with the prebuild of the next change.
Tests: t_pull (346 checks, now also the layout block the host fills), t_pull_inv, t_pso_pending (48) and t_pso_archive (32) pass; the other graphics tests and the host unit tests give the results they give on main. docs/development.md ("Hybrid pipelines") and dm/gfx/README.md describe it.
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