diff --git a/decnet/profiler/behave_shell/_features/__init__.py b/decnet/profiler/behave_shell/_features/__init__.py
index 7f12618c..471eb3cf 100644
--- a/decnet/profiler/behave_shell/_features/__init__.py
+++ b/decnet/profiler/behave_shell/_features/__init__.py
@@ -24,6 +24,7 @@ from decnet.profiler.behave_shell._features.motor import (
     keystroke_cadence,
     motor_stability,
     paste_burst_rate,
+    pipe_chaining_depth,
     shortcut_usage,
     tab_completion,
 )
@@ -39,6 +40,7 @@ FEATURES: tuple[FeatureFn, ...] = (
     command_chunking,
     tab_completion,
     shortcut_usage,
+    pipe_chaining_depth,
     inter_command_latency_class,
     command_branch_diversity,
     feedback_loop_engagement,
diff --git a/decnet/profiler/behave_shell/_features/motor.py b/decnet/profiler/behave_shell/_features/motor.py
index e62ddfd0..9b6ac36e 100644
--- a/decnet/profiler/behave_shell/_features/motor.py
+++ b/decnet/profiler/behave_shell/_features/motor.py
@@ -28,6 +28,8 @@ from decnet.profiler.behave_shell._thresholds import (
     PASTE_RATE_OCCASIONAL_MIN,
     SHELL_MASTERY_BOUNDARY_BAND,
     SHELL_MASTERY_MIN_COMMANDS,
+    PIPE_CHAINING_DEEP_MEDIAN,
+    PIPE_CHAINING_MODERATE_MEDIAN,
     SHORTCUT_USAGE_HEAVY_MIN,
     SHORTCUT_USAGE_MODERATE_MIN,
     TAB_COMPLETION_HABITUAL_MIN,
@@ -366,3 +368,55 @@ def shortcut_usage(ctx: SessionContext) -> Iterator[Observation]:
         value=value,
         confidence=confidence,
     )
+
+
+def pipe_chaining_depth(ctx: SessionContext) -> Iterator[Observation]:
+    """Emit ``motor.shell_mastery.pipe_chaining_depth`` ∈ {shallow, moderate, deep}.
+
+    Metric: median ``|`` count across commands. Pipes are counted on
+    every byte regardless of whether they came from a paste-burst —
+    a pasted pipeline is still a pipeline the operator chose to run,
+    and the registry's intent is "what does this operator's typical
+    command look like?", not "did they type it themselves?".
+
+    Buckets (median):
+    * ≤ 1  → shallow (no pipe, or one-stage pipeline)
+    * == 2 → moderate
+    * ≥ 3  → deep
+
+    Confidence:
+    * < ``SHELL_MASTERY_MIN_COMMANDS`` → 0.40.
+    * Median within ±10% of either integer boundary (2 or 3) → 0.55.
+    * Otherwise → 0.70.
+
+    Skips emission when the session has no commands.
+    """
+    n = len(ctx.commands)
+    if n == 0:
+        return
+    pipes_per_cmd = sorted(c.pipe_count for c in ctx.commands)
+    median = statistics.median(pipes_per_cmd)
+
+    if median >= PIPE_CHAINING_DEEP_MEDIAN:
+        value = "deep"
+    elif median >= PIPE_CHAINING_MODERATE_MEDIAN:
+        value = "moderate"
+    else:
+        value = "shallow"
+
+    if n < SHELL_MASTERY_MIN_COMMANDS:
+        confidence = 0.40
+    elif (
+        _near(median, PIPE_CHAINING_MODERATE_MEDIAN)
+        or _near(median, PIPE_CHAINING_DEEP_MEDIAN)
+    ):
+        confidence = 0.55
+    else:
+        confidence = 0.70
+
+    yield make_observation(
+        ctx,
+        primitive="motor.shell_mastery.pipe_chaining_depth",
+        value=value,
+        confidence=confidence,
+    )
diff --git a/decnet/profiler/behave_shell/_thresholds.py b/decnet/profiler/behave_shell/_thresholds.py
index 22c1ab92..82ccadd3 100644
--- a/decnet/profiler/behave_shell/_thresholds.py
+++ b/decnet/profiler/behave_shell/_thresholds.py
@@ -142,6 +142,19 @@ TAB_COMPLETION_HABITUAL_MIN: float = 0.50
 SHORTCUT_USAGE_MODERATE_MIN: float = 0.05
 SHORTCUT_USAGE_HEAVY_MIN: float = 0.30
 
+# motor.shell_mastery.pipe_chaining_depth — median ``|`` count across
+# commands. Pipes are counted on every byte (typed AND pasted) — a
+# pasted pipeline still indicates pipeline fluency the operator chose
+# to execute. Registry buckets per BEHAVE-EXTRACTOR.md line 473:
+#   median ≤ 1  → shallow (no pipeline at all, or one stage)
+#   median == 2 → moderate
+#   median ≥ 3  → deep
+# Median is integer-valued (sum of ints over commands), so the
+# boundaries here are integer step boundaries; the proximity-band
+# logic uses integer equality.
+PIPE_CHAINING_MODERATE_MEDIAN: int = 2
+PIPE_CHAINING_DEEP_MEDIAN: int = 3
+
 # Sample-size floor below which Phase C primitives drop confidence to
 # 0.40 (sample-size honesty). Mirrors MIN_COMMANDS_FOR_FULL_CONFIDENCE
 # but is named separately so a future tune can move them independently.
diff --git a/development/BEHAVE-EXTRACTOR.md b/development/BEHAVE-EXTRACTOR.md
index 97276b82..ba852a84 100644
--- a/development/BEHAVE-EXTRACTOR.md
+++ b/development/BEHAVE-EXTRACTOR.md
@@ -648,7 +648,7 @@ unchecked = no v0 tag.**
 ### Phase C — `motor.shell_mastery.*`
 - [x] C.1 `motor.shell_mastery.tab_completion`
 - [x] C.2 `motor.shell_mastery.shortcut_usage`
-- [ ] C.3 `motor.shell_mastery.pipe_chaining_depth`
+- [x] C.3 `motor.shell_mastery.pipe_chaining_depth`
 
 ### Phase D — `cognitive.*` completion
 - [ ] D.1 `cognitive.cognitive_load`
@@ -760,6 +760,40 @@ Phase C (``motor.shell_mastery.*``, 3 primitives) lands next.
 
 ---
 
+## Phase C completion log
+
+Closed in 3 commits, one primitive per commit. The
+``motor.shell_mastery.*`` block now emits — three per-command counters
+(`tab_count`, `shortcut_count`, `pipe_count`) populated during the
+single-pass `_segment_commands()` sweep, fed to three independent
+classifiers.
+
+| Primitive | Confidence | Source signal |
+|---|---|---|
+| `motor.shell_mastery.tab_completion` | 0.40 / 0.55 / 0.75 | fraction of commands containing ≥1 ``\t``; <30% → occasional, ≥50% → habitual, 30%-50% gap rounds down |
+| `motor.shell_mastery.shortcut_usage` | 0.40 / 0.55 / 0.65 | total readline ctrl bytes (^A/^E/^W/^U/^R/^B/^F) per command; v0.1 thresholds 0.05 / 0.30 awaiting corpus calibration |
+| `motor.shell_mastery.pipe_chaining_depth` | 0.40 / 0.55 / 0.70 | median ``\|`` count across commands; 2 → moderate, ≥3 → deep; pasted pipelines count too |
+
+Implementation note: ANTI relaxed the Phase A/B PII discipline for
+this phase — full attacker profiles outweigh residual PII paranoia
+on a honeypot byte stream. Even so, only **integer counters** land
+on `Command`; the raw bytes are read once during the segmentation
+walk and discarded. No character data is retained or serialised.
+
+The ^U / ^W bytes that drive ``shortcut_usage`` also count toward
+``motor.error_correction``'s ``kill_line_count`` channel (Step B.3).
+These are independent measurements over the same byte stream — not
+double-counting, just two different questions about the same key.
+
+**Calibration grid widened:** ``PHASE_ABC_PRIMITIVES`` now contains
+13 names and is binding for every subsequent phase. The set rename
+from ``PHASE_AB_PRIMITIVES`` lands in C.1; downstream phases extend
+the same set without renaming again until v0.
+
+Phase D (``cognitive.*`` completion, 7+1 primitives) lands next.
+
+---
+
 **Owner:** ANTI.
 **Implementation gate:** Step 0 starts after this doc is reviewed +
 Phase 1 of `BEHAVE-INTEGRATION.md` lands (storage table exists).
diff --git a/tests/profiler/behave_shell/test_calibration_grid.py b/tests/profiler/behave_shell/test_calibration_grid.py
index f1165705..3203d215 100644
--- a/tests/profiler/behave_shell/test_calibration_grid.py
+++ b/tests/profiler/behave_shell/test_calibration_grid.py
@@ -47,6 +47,7 @@ PHASE_ABC_PRIMITIVES: frozenset[str] = frozenset({
     # Phase C — motor.shell_mastery.* (lands one primitive per commit)
     "motor.shell_mastery.tab_completion",
     "motor.shell_mastery.shortcut_usage",
+    "motor.shell_mastery.pipe_chaining_depth",
 })
 
 
diff --git a/tests/profiler/behave_shell/test_motor_pipe_chaining_depth.py b/tests/profiler/behave_shell/test_motor_pipe_chaining_depth.py
new file mode 100644
index 00000000..f744555d
--- /dev/null
+++ b/tests/profiler/behave_shell/test_motor_pipe_chaining_depth.py
@@ -0,0 +1,103 @@
+"""Step C.3: ``motor.shell_mastery.pipe_chaining_depth``."""
+from __future__ import annotations
+
+from decnet.profiler.behave_shell import extract_session
+from decnet.profiler.behave_shell._ctx import build_session_context
+from decnet.profiler.behave_shell._parse import AsciinemaEvent
+
+PRIMITIVE = "motor.shell_mastery.pipe_chaining_depth"
+
+
+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 _command(t0: float, body: str) -> list[AsciinemaEvent]:
+    events: list[AsciinemaEvent] = []
+    t = t0
+    for c in body:
+        events.append((t, "i", c))
+        t += 0.05
+    events.append((t, "i", "\r"))
+    return events
+
+
+def _session(bodies: list[str], gap: float = 1.0) -> list[AsciinemaEvent]:
+    events: list[AsciinemaEvent] = []
+    t = 0.0
+    for body in bodies:
+        events.extend(_command(t, body))
+        t = events[-1][0] + gap
+    return events
+
+
+def test_no_commands_no_emission() -> None:
+    out = list(extract_session([(0.0, "i", "ls")], sid="pipe-empty"))
+    assert [o for o in out if o.primitive == PRIMITIVE] == []
+
+
+def test_no_pipes_emit_shallow() -> None:
+    out = list(extract_session(_session(["ls", "pwd", "id", "uname", "whoami"]),
+                               sid="pipe-shallow"))
+    obs = _of(out, PRIMITIVE)
+    assert obs.value == "shallow"
+    assert obs.confidence == 0.70
+
+
+def test_one_stage_pipeline_emit_shallow() -> None:
+    # median = 1 → shallow.
+    out = list(extract_session(_session(["ls | wc"] * 5), sid="pipe-one"))
+    obs = _of(out, PRIMITIVE)
+    assert obs.value == "shallow"
+
+
+def test_two_stage_pipeline_emit_moderate() -> None:
+    # median = 2 → moderate.
+    out = list(extract_session(_session(["ls | grep x | wc"] * 5),
+                               sid="pipe-moderate"))
+    obs = _of(out, PRIMITIVE)
+    assert obs.value == "moderate"
+
+
+def test_three_stage_pipeline_emit_deep() -> None:
+    # median = 3 → deep.
+    out = list(extract_session(_session(["ls | grep x | sort | uniq"] * 5),
+                               sid="pipe-deep"))
+    obs = _of(out, PRIMITIVE)
+    assert obs.value == "deep"
+
+
+def test_pasted_pipeline_still_counts() -> None:
+    """Pipes inside a paste-burst event count toward pipe_count — the
+    operator chose to execute the pipeline, regardless of provenance."""
+    # Single big paste event then \r — one command.
+    events: list[AsciinemaEvent] = [
+        (0.0, "i", "ls | grep x | sort | uniq | wc"),
+        (0.1, "i", "\r"),
+    ]
+    # Need ≥5 commands to get past the SHELL_MASTERY_MIN_COMMANDS gate.
+    t = 1.0
+    for _ in range(4):
+        events.append((t, "i", "ls | grep x | sort | uniq | wc"))
+        events.append((t + 0.1, "i", "\r"))
+        t += 1.0
+    out = list(extract_session(events, sid="pipe-pasted"))
+    obs = _of(out, PRIMITIVE)
+    assert obs.value == "deep"
+
+
+def test_few_commands_drops_confidence() -> None:
+    out = list(extract_session(_session(["ls", "pwd", "id"]),
+                               sid="pipe-low-n"))
+    obs = _of(out, PRIMITIVE)
+    assert obs.confidence == 0.40
+
+
+def test_segmentation_populates_pipe_count() -> None:
+    events = _command(0.0, "ls | grep x | wc") + _command(5.0, "pwd")
+    ctx = build_session_context(events, sid="seg-pipe", source="t")
+    assert len(ctx.commands) == 2
+    assert ctx.commands[0].pipe_count == 2
+    assert ctx.commands[1].pipe_count == 0