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).

tests/profiler/behave_shell/test_calibration_grid.py

@@ -42,6 +42,7 @@ PHASE_AB_PRIMITIVES: frozenset[str] = frozenset({
     # Phase B — motor.* completion (lands one primitive per commit)
     "motor.keystroke_cadence",
     "motor.motor_stability",
+    "motor.error_correction",
 })
 
 

tests/profiler/behave_shell/test_motor_error_correction.py

@@ -0,0 +1,79 @@
+"""Step B.3: ``motor.error_correction``."""
+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_too_few_inputs_no_emission() -> None:
+    events: list[AsciinemaEvent] = [(0.0, "i", "a"), (0.1, "i", "b")]
+    out = list(extract_session(events, sid="ec-low"))
+    assert [o for o in out if o.primitive == "motor.error_correction"] == []
+
+
+def test_no_backspaces_no_kill_emits_absent() -> None:
+    events: list[AsciinemaEvent] = [(i * 0.1, "i", c) for i, c in enumerate("hello\r")]
+    out = list(extract_session(events, sid="ec-absent"))
+    obs = _of(out, "motor.error_correction")
+    assert obs.value == "absent"
+    assert obs.confidence == 0.65
+
+
+def test_kill_line_with_no_backspaces_emits_route_around() -> None:
+    events: list[AsciinemaEvent] = [
+        (0.0, "i", "l"),
+        (0.1, "i", "s"),
+        (0.2, "i", "\x15"),  # ^U — kill line
+        (0.3, "i", "p"),
+        (0.4, "i", "s"),
+        (0.5, "i", "\r"),
+    ]
+    out = list(extract_session(events, sid="ec-route"))
+    obs = _of(out, "motor.error_correction")
+    assert obs.value == "route_around"
+
+
+def test_backspace_within_500ms_emits_immediate() -> None:
+    events: list[AsciinemaEvent] = [
+        (0.0, "i", "h"),
+        (0.1, "i", "e"),
+        (0.2, "i", "y"),
+        (0.30, "i", "\x7f"),  # backspace 100ms after 'y' — immediate
+        (0.4, "i", "l"),
+        (0.5, "i", "l"),
+        (0.6, "i", "o"),
+        (0.7, "i", "\r"),
+    ]
+    out = list(extract_session(events, sid="ec-immediate"))
+    obs = _of(out, "motor.error_correction")
+    assert obs.value == "immediate"
+
+
+def test_backspace_after_long_pause_emits_deferred() -> None:
+    events: list[AsciinemaEvent] = [
+        (0.0, "i", "h"),
+        (0.1, "i", "e"),
+        (0.2, "i", "y"),
+        # Backspace 2s after 'y' — deferred
+        (2.2, "i", "\x7f"),
+        (2.3, "i", "l"),
+        (2.4, "i", "l"),
+        (2.5, "i", "o"),
+        (2.6, "i", "\r"),
+    ]
+    out = list(extract_session(events, sid="ec-deferred"))
+    obs = _of(out, "motor.error_correction")
+    assert obs.value == "deferred"
+
+
+def test_pii_no_command_bodies_in_observation() -> None:
+    events: list[AsciinemaEvent] = [(i * 0.1, "i", c) for i, c in enumerate("supersecret\r")]
+    out = list(extract_session(events, sid="ec-pii"))
+    obs = _of(out, "motor.error_correction")
+    assert "supersecret" not in obs.model_dump_json()