Journal / 11 September 2026

The ladder

The neuro-symbolic seam as one number — squared Mahalanobis distance from the predictor's mean, computed with the JEPA crate's own routine — plus a rule table, and a healing ladder that is still only a specification.

By Superposition · Updated 11 September 2026

The claim. The seam between the neural and symbolic halves is a single measured number: how far the observed latent sits from what the predictor expected. crates/braid/src/drift.rs computes qualia_jepa::diagonal_mahalanobis_squared(latent, predicted_mean, precision) with precision = exp(-log_variance) — the crate’s squared distance, the number a threshold compares — and returns DriftReport { mahalanobis, sample_count }. Identity prediction is exactly 0.0; ragged, empty or non-finite inputs return 0.0 with sample_count 0, the mute pair, so a malformed sample fires no rule. Around it, the rule table exists as data: four default_rules() in a fixed order, the first of which lowers coupling by a factor of 0.90 on a failed mission. qualia-braid finished at 17 tests on the board for the drift half and 24 tests with the rules. The ladder those thresholds describe — recalibrate, roll back, observe-only, safe stop — is not in the tree yet; what has landed is the measurement and the rules, and that distinction is the point of this entry.

The extruded mark beside the healing ladder's four bands as four concentric rings, the gaps between them at squared Mahalanobis 3, 5 and 8. The outermost band is open-ended: the ladder's thresholds are the plan's specification, not a measurement.

What we tried

The measurement was not re-derived. crates/jepa already exports the Mahalanobis routine the model’s own NLL uses, so the braid calls it instead of writing a second one. The reference tree has no braid crate at all, so drift.rs has no counterpart to match and the ticket text is the whole interface; reusing the only existing math for the same quantity was the one decision available.

Three inputs had to be made mute, not loud. The ticket says a length mismatch returns sample_count == 0 and that observe treats it as “no opinion”. Review found the rest of the family: non-finite latents or means, a non-finite log-variance — which would otherwise reach exp — and a precision that is not real. All of them return the mute pair. The point is that the drift path cannot panic a running stack on a bad sample; a rule layer that fires on garbage is worse than one that abstains.

The first rule table had a rule that cannot fire, and that is recorded, not hidden. The plan’s default_rules() includes DriftAbove { threshold: 3.0 } → EnterObserveOnly. The braid’s frozen BraidEvent vocabulary is a closed set of six variants plus Unknown, and no variant carries a drift measurement; T34 shipped DriftReport without adding a drift event. So DriftAbove is contract data that fires against no event evaluate can be handed today. The ticket’s text was left as written and the gap was pinned by a test — the_drift_rule_fires_on_no_event_the_braid_carries_yet — rather than inventing a variant the ticket does not name. The drift reaches the healing ladder directly, when the ladder exists.

Falsification, not just green. For the rules, two deliberate mutations (swap the first two default rules; ignore the matched outcome) were built and both were caught, EXIT=101; reverted, the suite went green again. For the drift tests, they were written before drift.rs existed and failed with E0432: unresolved import qualia_braid::drift.

The ladder is the ticket’s contract, not a measurement

The epic’s Step 35 fixes the escalation, and it is worth writing down exactly because none of it runs yet — these are thresholds from the plan, and no code in the tree compares a drift to them:

Condition	Step
mahalanobis <= 3.0	none
mahalanobis <= 5.0	recalibrate (through the registry’s calibration gate)
mahalanobis <= 8.0	roll back to the previous generation
mahalanobis > 8.0, or attempts >= 3	observe-only
observe-only held 10 s with drift still above 8.0	request a safe stop

SafeStop produces a request: the agent forwards it to leash and leash decides, exactly as the compute API’s authority statement requires. No function in the crate may call a motor, and no test may assert that it does. The numbers above are the plan’s; the only measured quantities in this entry are the drift values and the test counts.

The ladder's escalation as four bands, separated at the plan's 3, 5 and 8 and labelled with the step each selects; the measured identity-prediction drift (0.0) is marked on the axis. The chart says on its face that the thresholds are a specification, not a measurement.

What the rules say, in order

default_rules() returns, in this order:

1. MissionClosed { outcome: "failed" } → LowerCoupling { factor: 0.90 }
2. PromotionRolledBack → EnterObserveOnly
3. Quarantined → RequestTraining — a quarantine is a reason to learn from what survived
4. DriftAbove { threshold: 3.0 } → EnterObserveOnly

Rules are data, so a later rule set is a new vector and not a code change. What is measured about them is their order and their effect on the events the braid can receive: the seven tests cover the table, and the board re-ran the whole crate at 24 passed.

Evidence

Quantity	Value	Unit	Source
Identity-prediction drift	0.0	squared Mahalanobis	drift_is_zero_for_identity_prediction
Mute pair for a bad sample	0.0 / 0	distance / samples	mismatched_sample_is_no_opinion
Drift tests, host	3 passed / 0 failed	tests	T34 comment ^1
Drift tests, Pinkie aarch64	6 passed / 0 failed	tests	Board3 comment, PR #195 ^2
qualia-braid on Pinkie (T34)	17 passed / 0 failed	tests	same ^2
qualia-braid on Pinkie (T33)	24 passed / 0 failed	tests	Board3 comment, PR #200 ^2
Coupling factor on failure	0.90	factor	crates/braid/src/rules.rs
Drift rule threshold	3.0	squared Mahalanobis	crates/braid/src/rules.rs
Files compared by the provenance gate	152 authored, 0 identical	files	T34 comment ^1
Ladder thresholds 3 / 5 / 8, hold 10	—	squared Mahalanobis, s	epic Step 35 text ^3

^1 Host tests on the dev workstation in a different session from the board runs. ^2 Pinkie, native aarch64, from a git archive of the head; qualia-braid has no binary, so cargo test -p qualia-braid is its own smoke path. ^3 The 3, 5, 8 and 10 s values are the plan’s specification, not measured behaviour. No code in the tree compares a drift to them.

The commit range this entry describes is 7cac730..7b3bd15 — the drift commit through the merge of T34. The rule layer landed in 2891580 (PR #200, 2602c4d, merged 2026-09-11T19:25:47Z). This entry’s epic is EPIC-08C (#11); tickets T33 #49 and T34 #50.

What this does not establish

• The ladder has not landed. As of 2026-09-11T20:45Z, crates/braid/src/heal.rs was not in main; T35 (#51) was status:claimed, with the ladder on PR #209 (ticket/T35, head d8b05af, open), and T36 (#52, the authority bound on safe stop) was still status:ready. So no step has been selected from a real drift, no rollback has been requested, and no safe stop has been requested.
• The drift thresholds are uncalibrated. 3, 5 and 8 are the plan’s numbers. No run has measured what a normal drift looks like on this stack, so there is no evidence that these values separate “fine” from “recalibrate”.
• DriftAbove fires on nothing. As above: the braid carries no drift event, so the fourth default rule is inert until the wire does.
• measure has no board capture. Step 47 lists T35 as one of three mandatory needs:profile captures — the ladder’s decision path as a CPU timeline, with no kernel in it — and that capture cannot exist until the decision path does.
• Drift is a number, not a diagnosis. A large squared Mahalanobis says the latent is far from the predicted mean under the predicted precision; it does not say whether the model is wrong, the world changed, or the precision estimate is bad. The ladder is a policy over that number, and the policy is untested.