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.

tests/profiler/behave_shell/test_environmental_shell_type.py

@@ -0,0 +1,87 @@
+"""Step F.1: ``environmental.shell_type``."""
+from __future__ import annotations
+
+from decnet.profiler.behave_shell import extract_session
+from decnet.profiler.behave_shell._parse import AsciinemaEvent
+
+
+PRIMITIVE = "environmental.shell_type"
+
+
+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 _typed(text: str, t0: float = 0.0, dt: float = 0.05) -> list[AsciinemaEvent]:
+    return [(t0 + i * dt, "i", c) for i, c in enumerate(text)]
+
+
+def _session(prompt_lines: list[str]) -> list[AsciinemaEvent]:
+    """Build a synthetic session: one ``ls`` per prompt, prompt printed
+    as the post-execution output of that command."""
+    events: list[AsciinemaEvent] = []
+    for i, prompt in enumerate(prompt_lines):
+        events.extend(_typed("ls\r", t0=i * 1.0))
+        events.append((i * 1.0 + 0.5, "o", f"out\n{prompt}"))
+    return events
+
+
+def test_no_prompts_no_emission() -> None:
+    events = _typed("ls\r", t0=0.0) + [(0.5, "o", "file1\n")]
+    out = list(extract_session(events, sid="sht-noprompt"))
+    assert [o for o in out if o.primitive == PRIMITIVE] == []
+
+
+def test_bash_prompt_emits_bash() -> None:
+    out = list(extract_session(_session(["anti@host:~$ "] * 5), sid="sht-bash"))
+    assert _of(out, PRIMITIVE).value == "bash"
+
+
+def test_root_prompt_still_bash() -> None:
+    """# is bash root, not a separate shell."""
+    out = list(extract_session(_session(["root@host:/etc# "] * 5), sid="sht-root"))
+    assert _of(out, PRIMITIVE).value == "bash"
+
+
+def test_zsh_prompt_emits_zsh() -> None:
+    out = list(extract_session(_session(["host% "] * 5), sid="sht-zsh"))
+    assert _of(out, PRIMITIVE).value == "zsh"
+
+
+def test_fish_prompt_emits_fish() -> None:
+    out = list(extract_session(_session(["anti@host ~> "] * 5), sid="sht-fish"))
+    assert _of(out, PRIMITIVE).value == "fish"
+
+
+def test_powershell_prompt_emits_powershell() -> None:
+    out = list(extract_session(
+        _session(["PS C:\\Users\\anti> "] * 5), sid="sht-ps",
+    ))
+    assert _of(out, PRIMITIVE).value == "powershell"
+
+
+def test_cmd_exe_prompt_emits_cmd_exe() -> None:
+    out = list(extract_session(_session(["C:\\Users\\anti>"] * 5), sid="sht-cmd"))
+    assert _of(out, PRIMITIVE).value == "cmd.exe"
+
+
+def test_majority_wins() -> None:
+    """Mixed prompts, bash majority → bash."""
+    out = list(extract_session(_session([
+        "anti@host:~$ ",
+        "anti@host:~$ ",
+        "anti@host:~$ ",
+        "host% ",  # one zsh outlier
+        "anti@host:~$ ",
+    ]), sid="sht-mix"))
+    assert _of(out, PRIMITIVE).value == "bash"
+
+
+def test_few_prompts_low_confidence() -> None:
+    short = list(extract_session(_session(["anti@host:~$ "] * 2), sid="sht-short"))
+    full = list(extract_session(_session(["anti@host:~$ "] * 6), sid="sht-full"))
+    s = _of(short, PRIMITIVE)
+    f = _of(full, PRIMITIVE)
+    assert s.confidence < f.confidence