merge: lane/sampled-restore-load-guard-20260819 @ 010869175e — SOLO admission for sampled restore, which is what makes the two lanes above safe to ship: the measured crossover sits between c1 and c2 (1.349x at c1, 0.668x at c2, worst 0.477x at c3, 0.813x at c16), so the watermark is SOLO and inert at c1 to 0.1%. Also: boundary-probe default 1.5 -> 4.0, the gemma runbook rewrite, and the MEMRA_DRAFT / MEMRA_MTP_DRAFT seam documentation. Fast-forwarded over the gate-tool branch 8297da4ca7.