feat(profiler/behave_shell): emit environmental.numpad_usage

Sliding-window scan over single-char digit input events. A run of
NUMPAD_RUN_MIN (4) consecutive digit events whose pairwise IATs are
all ≤ NUMPAD_FAST_IAT_S (50ms) → detected. Otherwise → not_detected.
Skips below NUMPAD_MIN_TYPED_CHARS (50) typed chars. Confidence cap
0.50 per the registry's weak-signal flag.

decnet/profiler/behave_shell/_features/__init__.py

@@ -27,6 +27,7 @@ from decnet.profiler.behave_shell._features.cognitive import (
 from decnet.profiler.behave_shell._features.environmental import (
     keyboard_layout,
     locale,
+    numpad_usage,
     shell_type,
     terminal_multiplexer,
 )
@@ -77,4 +78,5 @@ FEATURES: tuple[FeatureFn, ...] = (
     terminal_multiplexer,
     locale,
     keyboard_layout,
+    numpad_usage,
 )

decnet/profiler/behave_shell/_features/environmental.py

@@ -9,6 +9,7 @@ Step F.1: ``environmental.shell_type``.
 Step F.2: ``environmental.terminal_multiplexer``.
 Step F.3: ``environmental.locale``.
 Step F.4: ``environmental.keyboard_layout``.
+Step F.5: ``environmental.numpad_usage``.
 """
 from __future__ import annotations
 
@@ -30,6 +31,10 @@ from decnet.profiler.behave_shell._thresholds import (
     LAYOUT_QWERTZ_Z_MIN,
     LAYOUT_TOP_ENG_BIGRAMS,
     LOCALE_MIN_VALUE_LENGTH,
+    NUMPAD_FAST_IAT_S,
+    NUMPAD_MIN_TYPED_CHARS,
+    NUMPAD_RUN_MIN,
+    PASTE_MIN_CHARS_PER_EVENT,
     SHELL_TYPE_MIN_PROMPTS,
 )
 
@@ -297,3 +302,51 @@ def keyboard_layout(ctx: SessionContext) -> Iterator[Observation]:
         value=value,
         confidence=confidence,
     )
+
+
+def numpad_usage(ctx: SessionContext) -> Iterator[Observation]:
+    """Emit ``environmental.numpad_usage`` ∈ {detected, not_detected}.
+
+    A digit run is ``NUMPAD_RUN_MIN`` (4) consecutive single-character
+    digit input events whose pairwise IATs are all
+    ≤ ``NUMPAD_FAST_IAT_S`` (50ms). Numpad muscle memory produces
+    faster digit cadence than touch-typing the top row.
+
+    Skip emission below ``NUMPAD_MIN_TYPED_CHARS`` (50) typed chars —
+    no honest signal in a tiny session. Confidence cap 0.50 (registry
+    flags as weak signal).
+    """
+    if not ctx.commands:
+        return
+
+    digit_events: list[float] = []
+    typed_count = 0
+    for t, _kind, data in ctx.input_events:
+        if len(data) >= PASTE_MIN_CHARS_PER_EVENT:
+            continue
+        typed_count += len(data)
+        if len(data) == 1 and data.isdigit():
+            digit_events.append(t)
+
+    if typed_count < NUMPAD_MIN_TYPED_CHARS:
+        return
+
+    detected = False
+    if len(digit_events) >= NUMPAD_RUN_MIN:
+        # Sliding window: any contiguous run of NUMPAD_RUN_MIN digit
+        # events whose internal IATs are ALL fast → numpad.
+        for i in range(len(digit_events) - NUMPAD_RUN_MIN + 1):
+            window_iats = [
+                digit_events[i + j + 1] - digit_events[i + j]
+                for j in range(NUMPAD_RUN_MIN - 1)
+            ]
+            if all(x <= NUMPAD_FAST_IAT_S for x in window_iats):
+                detected = True
+                break
+
+    yield make_observation(
+        ctx,
+        primitive="environmental.numpad_usage",
+        value="detected" if detected else "not_detected",
+        confidence=0.50,
+    )

decnet/profiler/behave_shell/_thresholds.py

@@ -263,6 +263,15 @@ LAYOUT_QWERTZ_Z_MIN: float = 0.030      # high `z` rate (German content / QWERTZ
 LAYOUT_QWERTZ_Y_MAX: float = 0.010      # AND `y` swap signature
 LAYOUT_QWERTY_ENG_MIN: float = 0.080    # English-bigram saturation floor
 
+# ── environmental.numpad_usage (Step F.5) ──────────────────────────────────
+# A digit run = NUMPAD_RUN_MIN consecutive single-char digit events
+# whose pairwise IATs are all ≤ NUMPAD_FAST_IAT_S. Numpad muscle memory
+# produces faster digit IATs than touch-typing on the top row.
+NUMPAD_FAST_IAT_S: float = 0.050
+NUMPAD_RUN_MIN: int = 4
+# Below this many typed chars total, skip emission (no honest signal).
+NUMPAD_MIN_TYPED_CHARS: int = 50
+
 # ── 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