S2.1 Minimal Metabolism Loop — REFUTE

Date: 2026-07-02 Pre-registered spec: research/11-s2-minimal-metabolism-loop.md (incl. the 2026-07-02 amendment repairing the degenerate stage-0 holdout split) Model: Qwen/Qwen2.5-0.5B-Instruct (HFDriver, CPU float32, greedy) Stage: stage_0_grounding (8 episodes; 3 holdout probes post-repair) Seeds: 5 (seed-shuffled teaching order + cortex init) Checkpoints: K ∈ {0, 1, 2, 4, 8} Code: src/oczy/experiments/minimal_loop.py (uv run python -m oczy.experiments.minimal_loop --seeds 5) Wall clock: 745 s. verify_manifest() OK before and after.

Verdict

REFUTE H-LOOP. The minimal organism (HFDriver + fast-weight cortex + hippocampus-as-replay-buffer) does not close the loop on this substrate under the pre-registered design:

• loop_delta_holdout = 0.0000 (need > 0, CI excluding 0) — every seed scored 0/3 holdout at K=N, exactly matching vanilla (0.0).
• loop_compounding_rho = nan (endpoint series not monotone; need ≥ 0.6).
• Validity gate PASSED: vanilla holdout accuracy 0.0 < 0.5, so this is a true refutation, not an invalid run.

Per-checkpoint holdout accuracy (mean ± 95% CI, n=5)

Vanilla column: 0.0000 (all seeds). Per-seed K=N accuracy: 0.0 × 5.

Mechanistic reading (exploratory, does not alter the verdict)

The trajectory is not noise-flat: at K=4, 2 of 5 seed orderings answered one holdout probe correctly; at K=8 all effect vanishes. This is the prefix budget eviction signature: ~13 tokens per correction means the spec's 48-token budget holds ~3.7 corrections. At K=4 most taught corrections still fit; at K=8 the oldest are dropped (prefix_overflow > 0) and the probes' facts are usually evicted. The content channel demonstrably can carry a correction into changed holdout behavior — but only while its fact survives the budget, and it does not compound; it crowds out.

Live-debug observations (single organism, seed 0, K=8): the consolidated prefix compiled correctly ('model' means fashion model. … 'log' means the captain's journal., 48/48 tokens, 3 corrections evicted); answers were coherent but the 0.5B raw-completion model paraphrases or rambles instead of applying the sense mapping ("Deploy the model." → a classification list containing "fashion" but never "fashion model").

Invalid first run + implementation deviations (all recorded)

1. Run 1 (INVALID, implementation bug): flat 0.0 at every checkpoint because emit_all_cvecs() pushed warm-state cvecs at combined norm ~140 (~29/layer × 24 layers), collapsing every generation into a repeated garbage token — the S2.4 magnitude pathology as a bug, masking the content channel entirely. Fixed in d9702fc.
2. Cvec posture disabled (spec: "optional cvec posture"). Even clamped to combined norm 1.0 the posture still degraded some probes into token noise; the working amplitude on this substrate is uncalibrated. Posture defaults OFF; the clamp path remains for a future calibration experiment. The s2-5 fanout agent hit the same failure independently and made the same call — convergent diagnosis.
3. Prefix gains a \n separator (was bare-concatenated into the probe text).
4. HFDriver.load() no-arg default repaired (39454d7) — the S1.1/S1.2 parallel-development name mismatch (HF_MODEL_ID vs DEFAULT_MODEL_ID) had never been exercised before this experiment.

Consequences for the dependent specs (adjudicated per their gates)

• research/12 (S2.2 KV content path): BLOCKED. The spec's validity gate — "if research/11 REFUTED H-LOOP (C1 itself produces no effect), this experiment is reported as BLOCKED, not run to a fake verdict" — now binds. The KV channel implementation + tests are merged and remain valid code.
• research/13 (S2.5 forgetting test): BLOCKED. Validity gate A_full − A_none ≥ 0.10 cannot hold when the loop does not close. Deletion APIs + harness are merged and remain valid code.

What would have to change before a re-attempt (future specs, not tweaks)

1. Chat-template prompting. Qwen2.5-Instruct is chat-trained; raw completion severely underuses it (research/17 already anticipates template use for the second model). A new spec (research/18 candidate) would re-pose H-LOOP under the template, identically for vanilla.
2. Content budget scaling law. The K=4 bump suggests measuring holdout effect vs budget (16/48/128 tokens) — is eviction the binding constraint?
3. KV-channel capacity. S1.3 showed KV-splice ≡ prefix rank-for-rank at zero visible tokens; whether KV entries escape the visible-token budget trade-off is now the interesting question, but it needs a design that works at C1 first.

An honest REFUTE is a successful outcome; this one comes with a mechanism.

See also

Conceptual post-mortem of why the steering/posture channel failed here and across S1.3/S1.4/S2.4 — the three broken assumptions and what survives: notes/2026-07-03_steering_vs_posture_postmortem.md. The surviving mechanism (consolidation as context distillation) is pre-registered as research/18-consolidation-as-distillation.md.