feat(r12): sweep wrapper for KV-cache compression PPL headroom diagnostic (A'')

[synapticode-ai]

Summary

R12 v1.1 first-execution sweep wrapper (A''): orchestrates a b_mse ∈ {6,5,4,3,2,1} sweep against the R7-B v1.2 autoregressive harness with the β1a (make_b_mse_hook_uniform) KV-cache compression hook on MPS. Produces per-point JSONs conformant to ppl_headroom_kv_cache_point/1.0 and an aggregate manifest conformant to ppl_headroom_kv_cache_sweep/1.0 per R12 v1.1 §6.

Why

All upstream dependencies landed this week (B baseline, Cache-shape contract PR #32, R7-B v1.2 calibration gate PR #33, MPS Codebook fix in gamma-seeds/turboquant fork). The sweep wrapper is the last piece needed to characterise TurboQuant's PPL-vs-compression frontier under R7-B-conformant methodology. The 12 May TQ bench b_mse=3 anchor (PPL 7.82→8.14) was non-R7-B-conformant per R7-B §1.2; this sweep re-establishes the anchor and characterises the full grid under the valid methodology.

Changes

New file tools/tern_r12_sweep.py (683 lines):

• Schema constants for both per-point and sweep JSON formats
• SweepPointResult / SweepResult dataclasses
• run_sweep_point — single-point execution with branched error capture (hook construction failure, ppl eval failure, non-finite PPL)
• build_point_json / build_sweep_manifest — §6.1 and §6.2 schema assembly
• detect_termination — per-point termination classifier
• classify_recommended_operating_point — frontier search for most-aggressive b_mse passing the R7-B v1.2 §1.1 N-indexed calibration gate
• run_sweep — model-once / sequences-once orchestration loop with per-point JSON write for partial-progress preservation
• main — full CLI surface including --smoke mode

Dispositions (ratified Phase B)

#	Decision
Q1	Baseline anchor: B (R7-B@N=16 FP16 MPS, PPL=7.9367, run_id=20260516T065626Z)
Q2	Model loaded once, reused across all sweep points
Q3	Hook factory built per-point (b_mse differs; factory is closure over b_mse)
Q4	Termination: continue on ppl_eval_failure, halt on hook_construction_failure, halt at first ceiling_crossed per §8 canonical continue_past_ceiling=false
Q5	Smoke params: b_mse=[4,2], N=2, L=128
Q6	kv_cache_compression_ratio = theoretical 16/b_mse (β1a is round-trip — pre/post-bytes mechanism vacuous; theoretical ratio captures deployment-relevant compression). Per-point notes field documents derivation + flags R12 v1.2 amendment carry-forward

Phase E smoke results

Smoke 1 (default ceiling=2.0×):

• Single point completes (b_mse=4): PPL=9551.6, headroom=+120,247%, Fail band, ceiling_crossed=True
• Sweep correctly halts at point 0; recommended_operating_point correctly null-stubbed; both JSONs schema-conformant
• Wall: ~30s on MPS (model load 4.1s + factory 0.24s + eval 30.6s)

Smoke 2 (permissive ceiling=100000):

• Both points complete: b_mse=4 finite (same PPL as Smoke 1), b_mse=2 produces NaN
• Sweep correctly continues past ppl_eval_failure at b_mse=2 (less-aggressive b_mse can still succeed per Q4 disposition)
• Point 1 JSON populated with null PPL fields + theoretical compression ratio 8.0 retained + failure rationale in notes
• Wall: ~46s

Both smokes verify the wrapper's full schema-conformance + termination-branch coverage. High PPL values are artefacts of the smoke's tiny context (N=2 L=128 with aggressive compression); not indicative of canonical-config behaviour.

Full sweep launched

After this PR opens, the canonical sweep launches as a nohup background process:

--model-id TinyLlama/TinyLlama-1.1B-Chat-v1.0
--baseline-run-id 20260516T065626Z --baseline-ppl 7.9367
--b-mse-values "6,5,4,3,2,1" --num-sequences 16 --ar-seq-len 2048
--device mps --hook-spec uniform

Expected wall-time: ~3-12 hours on M4 Pro MPS (β1a per §8.2.3 estimated ~26 hr on CPU; MPS speedup uncertain at L=2048). Results land in results/ppl_headroom_kv_cache_sweep/ for next-session inspection. PID + log path captured in landing report.

Test plan

• Smoke 1 (default ceiling): ceiling_crossed termination + schema conformance verified
• Smoke 2 (permissive ceiling): multi-point aggregation + ppl_eval_failure non-halting + null-field schema conformance verified
• Per-point JSON conformance against §6.1 schema (all required keys present, enum values valid)
• Sweep manifest conformance against §6.2 schema (all required keys present including inputs, frontier, recommended_operating_point, termination, hardware sub-blocks)
• Full canonical sweep produces frontier covering b_mse=[6,5,4,3,2,1] or terminates at ceiling — verified next session from background-process output

Cross-references

• R12 v1.1 §6 (per-point + sweep schemas), §8 (canonical sweep parameters)
• R7-B v1.2 §1.1 N-indexed calibration gate (PR docs(r7-b): v1.2 calibration gate widening per D1 factor decomposition #33)
• β1a factory make_b_mse_hook_uniform (PR make_b_mse_hook_uniform: batched-uniform R12 factory (β1a) #27)
• Cache-shape DynamicCache contract (PR fix(tern_infer): factories return DynamicCache natively per R7-B §5.2 #32)
• MPS Codebook fix (gamma-seeds/turboquant fork; upstream PR OnlyTerp#5)

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