[Proposed] Special-token position ablation (prefix / suffix / middle)

From EXPERIMENT_QUEUE.md, added 2026-04-16

Follow-up to leakage v3 + A3b. All marker experiments to date place the special token at one fixed position (typically prepended or appended to the persona's response). Question: does marker position matter for adoption vs containment?

Factorial: marker position ∈ {prefix, suffix, middle-inserted} × contrastive / non-contrastive training × 2 source personas.

Hypothesis: prefix marker has strongest identity-conditioning effect (consistent with in-context learning literature on early-token dominance); suffix is most prone to leakage (token can be "detached" from persona cue); middle is weakest signal.

Falsifier: position-invariant adoption rates.

Compute: ~6 GPU-hours (6 conditions × ~1h each). Reuses leakage infrastructure.

Gate-keeper priority: MEDIUM (narrow but clean question; could sharpen the marker-leakage mechanism story).