feat(profiler/behave_shell): emit motor.error_correction

BEHAVE-EXTRACTOR.md Phase B Step B.3. Replaces the prototype's
two-line "0 vs >0 backspaces" placeholder with a backspace-timing
classifier that honours the registry's full vocabulary.

* SessionContext gains backspace_count, backspace_iats (IAT from
  each backspace back to the preceding non-backspace input event),
  and kill_line_count (^U / ^W). Built by _scan_correction_signals,
  which retains only counts and timing aggregates — no character
  data leaves the helper, in line with the BEHAVE PII discipline.
* _features/motor.py:error_correction(ctx) emits one Observation
  in {immediate, deferred, absent, route_around}.
  - 0 backspaces + ≥1 ^U/^W → route_around (rewrite, not correct)
  - 0 backspaces + 0 kill-lines → absent
  - backspaces with median IAT ≤ 500 ms → immediate
  - slower → deferred
  Confidence 0.65 / 0.65 / 0.55 / 0.55.
* < 3 inputs → skip emit.
* Calibration grid widened to include motor.error_correction;
  green across all five shards.

Tests cover all four buckets, the < 3 inputs skip, and the PII
regression (raw command body never appears in the serialised
observation).

decnet/profiler/behave_shell/_features/__init__.py

@@ -18,6 +18,7 @@ from decnet.profiler.behave_shell._features.cognitive import (
     inter_command_latency_class,
 )
 from decnet.profiler.behave_shell._features.motor import (
+    error_correction,
     input_modality,
     keystroke_cadence,
     motor_stability,
@@ -31,6 +32,7 @@ FEATURES: tuple[FeatureFn, ...] = (
     paste_burst_rate,
     keystroke_cadence,
     motor_stability,
+    error_correction,
     inter_command_latency_class,
     command_branch_diversity,
     feedback_loop_engagement,

decnet/profiler/behave_shell/_features/motor.py

@@ -15,6 +15,7 @@ from decnet_behave_core.spec.envelope import Observation
 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 (
+    BACKSPACE_IMMEDIATE_MAX_S,
     CV_BURSTY_MAX,
     CV_MACHINE_MAX,
     CV_STEADY_MAX,
@@ -166,3 +167,41 @@ def motor_stability(ctx: SessionContext) -> Iterator[Observation]:
         value=value,
         confidence=confidence,
     )
+
+
+def error_correction(ctx: SessionContext) -> Iterator[Observation]:
+    """Emit ``motor.error_correction`` ∈ {immediate, deferred, absent, route_around}.
+
+    Backspace timing relative to the preceding non-backspace key:
+
+    * 0 backspaces + ≥1 ^U/^W → ``route_around`` (operator killed
+      the line and rewrote rather than correcting in place).
+    * 0 backspaces + 0 ^U/^W → ``absent`` (no correction observed).
+    * Backspaces with median IAT ≤ ``BACKSPACE_IMMEDIATE_MAX_S``
+      (500 ms) → ``immediate`` (caught the typo mid-keystroke).
+    * Slower → ``deferred`` (paused, noticed, then went back).
+
+    < 3 input events → skip emission.
+    """
+    if len(ctx.input_events) < 3:
+        return
+    if ctx.backspace_count == 0:
+        if ctx.kill_line_count > 0:
+            value, confidence = "route_around", 0.55
+        else:
+            value, confidence = "absent", 0.65
+    else:
+        if ctx.backspace_iats:
+            med = statistics.median(ctx.backspace_iats)
+        else:
+            med = float("inf")
+        if med <= BACKSPACE_IMMEDIATE_MAX_S:
+            value, confidence = "immediate", 0.65
+        else:
+            value, confidence = "deferred", 0.55
+    yield make_observation(
+        ctx,
+        primitive="motor.error_correction",
+        value=value,
+        confidence=confidence,
+    )