feat(profiler/behave_shell): emit environmental.shell_type

Per-prompt classification mode over ctx.prompt_lines. $/# → bash;
% → zsh; > with 'PS ' prefix → powershell; > with 'C:\' substring →
cmd.exe; > otherwise → fish. New _features/environmental.py module
opens Phase F.

decnet/profiler/behave_shell/_features/__init__.py

@@ -24,6 +24,9 @@ from decnet.profiler.behave_shell._features.cognitive import (
     inter_command_consistency,
     inter_command_latency_class,
 )
+from decnet.profiler.behave_shell._features.environmental import (
+    shell_type,
+)
 from decnet.profiler.behave_shell._features.temporal import (
     escalation_pattern,
     landing_ritual,
@@ -67,4 +70,5 @@ FEATURES: tuple[FeatureFn, ...] = (
     session_duration,
     escalation_pattern,
     landing_ritual,
+    shell_type,
 )

decnet/profiler/behave_shell/_features/environmental.py

@@ -0,0 +1,75 @@
+"""``environmental.*`` feature functions.
+
+Phase F ships the five environmental primitives plus F.0's shared
+prompt-line detector. F.0 itself emits no primitive — it populates
+``SessionContext.prompt_lines`` and ``Command.followed_by_prompt``
+which F.1 / F.3 / E.4 read.
+
+Step F.1: ``environmental.shell_type``.
+"""
+from __future__ import annotations
+
+import collections
+from typing import Iterator
+
+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._parse import PromptLine
+from decnet.profiler.behave_shell._thresholds import (
+    SHELL_TYPE_MIN_PROMPTS,
+)
+
+
+def _classify_shell_from_prompt(p: PromptLine) -> str:
+    """Map one prompt line to a shell-type label."""
+    suffix = p.suffix_char
+    line = p.raw_line
+    if suffix in ("$", "#"):
+        # bash / sh / dash all share these — collapsed to "bash" per
+        # registry's bash-family stance. zsh CAN be configured to use
+        # $/# but that's the user's PS1 override; default zsh is %.
+        return "bash"
+    if suffix == "%":
+        return "zsh"
+    if suffix == ">":
+        # Disambiguate by line content. powershell's PS1 starts with
+        # "PS "; cmd.exe's prompt typically contains a Windows path
+        # like "C:\". Everything else is fish.
+        if line.lstrip().startswith("PS "):
+            return "powershell"
+        if "C:\\" in line or "c:\\" in line:
+            return "cmd.exe"
+        return "fish"
+    return "bash"  # defensive — _detect_prompt_suffix only emits one of $#%>
+
+
+def shell_type(ctx: SessionContext) -> Iterator[Observation]:
+    """Emit ``environmental.shell_type``.
+
+    Mode of per-prompt-line classification across
+    ``ctx.prompt_lines``. Skip emission when no prompts detected —
+    the registry's enum doesn't admit ``unknown`` and emitting
+    ``bash`` from no observation at all would be dishonest.
+
+    Confidence drops below ``SHELL_TYPE_MIN_PROMPTS`` (3 prompts);
+    above that threshold the vote is solid.
+    """
+    if not ctx.prompt_lines:
+        return
+    votes = collections.Counter(
+        _classify_shell_from_prompt(p) for p in ctx.prompt_lines
+    )
+    value, _ = votes.most_common(1)[0]
+
+    if len(ctx.prompt_lines) < SHELL_TYPE_MIN_PROMPTS:
+        confidence = 0.40
+    else:
+        confidence = 0.75
+    yield make_observation(
+        ctx,
+        primitive="environmental.shell_type",
+        value=value,
+        confidence=confidence,
+    )

decnet/profiler/behave_shell/_thresholds.py

@@ -228,6 +228,11 @@ LANDING_RITUAL_MIN_COMMANDS: int = 3
 PROMPT_SUFFIX_CHARS: frozenset[str] = frozenset({"$", "#", "%", ">"})
 PROMPT_LINE_MAX_CHARS: int = 256
 
+# ── environmental.shell_type (Step F.1) ────────────────────────────────────
+# Below this many detected prompt-lines, drop confidence (sample-size
+# honesty). Above, the shell-type vote is robust.
+SHELL_TYPE_MIN_PROMPTS: int = 3
+
 # ── 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