feat(profiler/behave_shell): emit motor.paste_burst_rate

BEHAVE-EXTRACTOR.md Phase A Step 3. Same paste-event ratio as
motor.input_modality but coarser-bucketed: this is the *habit*
signal (does the operator reach for paste at all?), where
input_modality is the dominant-channel signal.

* _features/motor.py:paste_burst_rate(ctx) emits one Observation
  per session in {none, occasional, habitual} with confidence
  0.70 / 0.70 / 0.80.
* Thresholds: PASTE_RATE_OCCASIONAL_MIN=0.10,
  PASTE_RATE_HABITUAL_MIN=0.50.

Splits YOU-sim from LW/CLAUDE-FF/CLAUDE-CL — LLM-driven sessions
paste habitually, real humans rarely paste.

Tests: pure-typed → none; 1-paste-in-10 → occasional;
paste-majority → habitual; output-only → no observation; habitual
confidence > occasional confidence.

tests/profiler/behave_shell/test_motor_paste_burst_rate.py

@@ -0,0 +1,53 @@
+"""Step 3: ``motor.paste_burst_rate`` — none / occasional / habitual."""
+from __future__ import annotations
+
+from decnet.profiler.behave_shell import extract_session
+from decnet.profiler.behave_shell._parse import AsciinemaEvent
+
+
+def _of(observations: list, primitive: str):
+    obs = [o for o in observations if o.primitive == primitive]
+    assert len(obs) == 1, f"expected exactly one {primitive}, got {len(obs)}"
+    return obs[0]
+
+
+def test_pure_typed_session_emits_none() -> None:
+    events: list[AsciinemaEvent] = [(i * 0.1, "i", c) for i, c in enumerate("ls -la\r")]
+    out = list(extract_session(events, sid="rate-typed"))
+    assert _of(out, "motor.paste_burst_rate").value == "none"
+
+
+def test_one_paste_in_ten_emits_occasional() -> None:
+    # 1 paste + 9 single-char typed events → ratio 0.10 → occasional
+    events: list[AsciinemaEvent] = [(0.0, "i", "echo paste\r")]
+    events += [(0.5 + i * 0.1, "i", c) for i, c in enumerate("ls -la\rp")]
+    out = list(extract_session(events, sid="rate-occasional"))
+    assert _of(out, "motor.paste_burst_rate").value == "occasional"
+
+
+def test_paste_majority_emits_habitual() -> None:
+    events: list[AsciinemaEvent] = [
+        (0.0, "i", "echo a\r"),
+        (1.0, "i", "echo b\r"),
+        (2.0, "i", "echo c\r"),
+        (3.0, "i", "x"),
+    ]
+    out = list(extract_session(events, sid="rate-habitual"))
+    assert _of(out, "motor.paste_burst_rate").value == "habitual"
+
+
+def test_zero_input_emits_nothing() -> None:
+    out = list(extract_session([(0.0, "o", "hi\r\n")], sid="rate-empty"))
+    assert [o for o in out if o.primitive == "motor.paste_burst_rate"] == []
+
+
+def test_confidence_higher_for_habitual_than_occasional() -> None:
+    pasted = [
+        (0.0, "i", "echo a\r"), (1.0, "i", "echo b\r"), (2.0, "i", "echo c\r"),
+    ]
+    occasional = [(0.0, "i", "echo a\r")] + [
+        (0.5 + i * 0.1, "i", c) for i, c in enumerate("ls -la\rps\r")
+    ]
+    h = _of(list(extract_session(pasted, sid="conf-h")), "motor.paste_burst_rate")
+    o = _of(list(extract_session(occasional, sid="conf-o")), "motor.paste_burst_rate")
+    assert h.confidence > o.confidence