# `imp_stiff_low` — cocarry_partners@v2

<!-- Generated by scripts/render_partner_cards.py from chamber.partners.sets + the fingerprint archive — do not edit by hand. -->

**Set.** `cocarry_partners@v2` (task `cocarry@v1`) · **Stratum.** scripted · **Split.** public · **Role.** partner_arm

**Identity.** `partner_id` `2551311d47ba8e57` · parameter digest `a5d61ee76a1a7a8a7f9241d25fca8db825215da0babb8fcda096e2bec36073a0` · `weights_uri` `member://cocarry_impedance/a5d61ee76a1a7a8a7f9241d25fca8db825215da0babb8fcda096e2bec36073a0`

## What this partner does

A deterministic end-effector-space PI impedance controller for one co-carry arm (ADR-026 §Decision 1): it drives its bar-end toward the cooperative goal along a straight Cartesian path through a damped pseudo-inverse Jacobian, sharing the bar load compliantly with the ego arm. `kp`/`ki` set the Cartesian PI gains, `step_max` the per-step command clip (response speed), `damping` the pseudo-inverse regularisation, and `lag_steps` a bounded transport delay (a sluggish-but-competent member: delayed but convergent tracking).

## Construction provenance

Built from registry class `cocarry_impedance` (`PartnerSpec(seed=0, checkpoint_step=None)`). Public member: the exact values below were drawn from the committed box under the maintainer-held derivation seed and are committed next to their digest.

| parameter | committed box | value |
| --- | --- | --- |
| `damping` | [0.035, 0.045] | 0.0442 |
| `ki` | [0.5, 0.7] | 0.6616 |
| `kp` | [1.1, 1.6] | 1.1991 |
| `lag_steps` | [0, 0] (int) | 0 |
| `step_max` | [0.028, 0.032] | 0.0286 |

## Behavioural fingerprint

Committed probe suite: seeds [7000, 7001, 7002, 7003] x 5 episodes against the task's reference ego (archive: `spikes/results/partner-fingerprints/cocarry_partners-v2/imp_stiff_low/`, an ADR-028 v3 bundle). Summary statistics of the member's action distribution and the dyad's stress channel — enough to tell members apart without policy access (ADR-018/I3).

| statistic | value |
| --- | --- |
| `action_abs_mean` | 0.313 |
| `action_abs_p90` | 1 |
| `action_std` | 0.4232 |
| `n_episodes` | 20 |
| `stress_max` | 103.9 |
| `stress_mean` | 81.57 |
| `stress_p50` | 80.36 |
| `stress_p90` | 97.9 |
| `success_rate` | 1 |

**Competence floor.** floor probe `fingerprint` — success 1 vs committed floor 0.75 → **PASS**