feat(profiler/behave_shell): emit cognitive.cognitive_load

Composite over three [0, 1]-clipped sub-signals (chunking variance,
error rate from D.0's Command.errored, pace variability), mean-aggregated
and bucketed against COGNITIVE_LOAD_LOW_MAX / COGNITIVE_LOAD_MEDIUM_MAX.
Components missing data drop out of the mean rather than zeroing it.

v0.1 thresholds; D.8 re-tunes once D.2-D.7 are stable. Confidence
held at 0.60 (composite over soft sub-signals) and halved below the
5-command sample-size floor.

decnet/profiler/behave_shell/_features/__init__.py

@@ -12,6 +12,7 @@ from decnet_behave_core.spec.envelope import Observation
 
 from decnet.profiler.behave_shell._ctx import SessionContext
 from decnet.profiler.behave_shell._features.cognitive import (
+    cognitive_load,
     command_branch_diversity,
     feedback_loop_engagement,
     inter_command_consistency,
@@ -45,4 +46,5 @@ FEATURES: tuple[FeatureFn, ...] = (
     command_branch_diversity,
     feedback_loop_engagement,
     inter_command_consistency,
+    cognitive_load,
 )

decnet/profiler/behave_shell/_features/cognitive.py

@@ -4,6 +4,7 @@ Step 5: ``cognitive.inter_command_latency_class``.
 Step 6: ``cognitive.command_branch_diversity``.
 Step 7: ``cognitive.feedback_loop_engagement``.
 Step 8: ``cognitive.inter_command_consistency``.
+Step D.1: ``cognitive.cognitive_load``.
 """
 from __future__ import annotations
 
@@ -16,6 +17,10 @@ from decnet.profiler.behave_shell._ctx import SessionContext
 from decnet.profiler.behave_shell._features._emit import make_observation
 from decnet.profiler.behave_shell._thresholds import (
     BRANCH_DIVERSITY_LINEAR_MIN,
+    COGNITIVE_LOAD_CHUNKING_REF_CV,
+    COGNITIVE_LOAD_LOW_MAX,
+    COGNITIVE_LOAD_MEDIUM_MAX,
+    COGNITIVE_LOAD_PACE_REF_CV,
     FEEDBACK_CORRELATION_MIN,
     FEEDBACK_MIN_PAIRS,
     INTER_CMD_DELIBERATE_MAX,
@@ -29,6 +34,24 @@ from decnet.profiler.behave_shell._thresholds import (
 )
 
 
+def _clip01(x: float) -> float:
+    if x < 0.0:
+        return 0.0
+    if x > 1.0:
+        return 1.0
+    return x
+
+
+def _cv(xs: tuple[float, ...] | list[float]) -> float | None:
+    """Coefficient of variation; ``None`` if undefined (n<2 or mean==0)."""
+    if len(xs) < 2:
+        return None
+    mean = statistics.fmean(xs)
+    if mean <= 0.0:
+        return None
+    return statistics.stdev(xs) / mean
+
+
 def _bucket_inter_cmd_latency(median_iat: float) -> str:
     if median_iat <= INTER_CMD_INSTANT_MAX:
         return "instant"
@@ -156,6 +179,80 @@ def feedback_loop_engagement(ctx: SessionContext) -> Iterator[Observation]:
     )
 
 
+def cognitive_load(ctx: SessionContext) -> Iterator[Observation]:
+    """Emit ``cognitive.cognitive_load`` ∈ {low, medium, high}.
+
+    Composite of three [0, 1]-clipped sub-signals, mean-aggregated:
+
+    * **chunking** — median CV of intra-command IATs / reference CV.
+      Fragmented mid-command typing → high contribution.
+    * **errors** — fraction of commands whose post-execution output
+      matched a canonical error fingerprint (``Command.errored`` from
+      Step D.0). Failures pile load.
+    * **pace variability** — CV of inter-command IATs / reference CV.
+      A spread of think-pause durations → unsettled cadence → load.
+
+    Components missing data contribute 0.0 (no penalty for an absent
+    signal), and the composite normalises by *available* component
+    count so a session with zero inter-command pauses isn't punished
+    for the silence. Skip emission entirely when no commands at all
+    exist — there's no honest answer.
+
+    v0.1 thresholds; D.8 re-tunes once the rest of Phase D is stable.
+    """
+    if not ctx.commands:
+        return
+
+    # Component A: chunking variance — median within-command CV
+    per_cmd_cvs: list[float] = []
+    for cmd_iats in ctx.intra_command_iats:
+        cv = _cv(cmd_iats)
+        if cv is not None:
+            per_cmd_cvs.append(cv)
+    if per_cmd_cvs:
+        chunking_load: float | None = _clip01(
+            statistics.median(per_cmd_cvs) / COGNITIVE_LOAD_CHUNKING_REF_CV
+        )
+    else:
+        chunking_load = None
+
+    # Component B: error rate
+    error_load: float = sum(1 for c in ctx.commands if c.errored) / len(ctx.commands)
+    error_load = _clip01(error_load)
+
+    # Component C: pace variability — CV of inter-command IATs
+    pace_cv = _cv(ctx.inter_cmd_iats)
+    if pace_cv is not None:
+        pace_load: float | None = _clip01(pace_cv / COGNITIVE_LOAD_PACE_REF_CV)
+    else:
+        pace_load = None
+
+    components = [c for c in (chunking_load, error_load, pace_load) if c is not None]
+    if not components:
+        return
+    load = sum(components) / len(components)
+
+    if load < COGNITIVE_LOAD_LOW_MAX:
+        value = "low"
+    elif load < COGNITIVE_LOAD_MEDIUM_MAX:
+        value = "medium"
+    else:
+        value = "high"
+
+    if len(ctx.commands) < MIN_COMMANDS_FOR_FULL_CONFIDENCE:
+        confidence = 0.40
+    else:
+        # Composite over three soft sub-signals — held below the
+        # cap of single-source primitives. D.8 re-tunes.
+        confidence = 0.60
+    yield make_observation(
+        ctx,
+        primitive="cognitive.cognitive_load",
+        value=value,
+        confidence=confidence,
+    )
+
+
 def inter_command_consistency(ctx: SessionContext) -> Iterator[Observation]:
     """Emit ``cognitive.inter_command_consistency``.
 

decnet/profiler/behave_shell/_thresholds.py

@@ -87,6 +87,27 @@ PAUSE_CV_BIMODAL_MIN: float = 1.50
 # ``cognitive_load`` must be reflected by editing the patterns tuple
 # (not a constant, so no boundary-band logic applies).
 
+# ── cognitive.cognitive_load (Step D.1) ─────────────────────────────────────
+# Composite ∈ [0, 1] over three sub-signals (each clipped to [0, 1]):
+#
+#   A = chunking_load         = median_intra_cmd_cv / CHUNKING_REF_CV
+#   B = error_load            = errored_cmds / total_cmds
+#   C = pace_variability_load = (stdev / mean of inter_cmd_iats) / PACE_REF_CV
+#
+# load = mean(A, B, C); bucket:
+#   load <  COGNITIVE_LOAD_LOW_MAX     → low
+#   load <  COGNITIVE_LOAD_MEDIUM_MAX  → medium
+#   else                               → high
+#
+# v0.1 thresholds — D.8 re-tunes once D.1-D.7 are stable. The reference
+# CVs (CHUNKING_REF_CV / PACE_REF_CV) are the value at which that single
+# component saturates to a load contribution of 1.0; anything past
+# saturates the term but doesn't double-count.
+COGNITIVE_LOAD_CHUNKING_REF_CV: float = 1.00
+COGNITIVE_LOAD_PACE_REF_CV: float = 1.50
+COGNITIVE_LOAD_LOW_MAX: float = 0.33
+COGNITIVE_LOAD_MEDIUM_MAX: float = 0.67
+
 # ── motor.keystroke_cadence (Step B.1) ──────────────────────────────────────
 # Typing bursts split at gaps > IKI_THINK_MAX_S so think-pauses between
 # commands don't inflate the within-burst CV. Mirrors the prototype's