Ponytail build-laziness doctrine (bundled with Fable, 0.19.0) (#313)

* feat(agents): vendor trimmed ponytail doctrine (full + ethos)

* feat(agents): compose ponytail doctrine layer, bundled with fable

* docs: document ponytail doctrine bundled with fable-mode

* style: add trailing newline to ponytail doctrine files test

* docs: changelog + map/rag for ponytail doctrine (0.19.0)

user-facing docs skipped: Fable precedent absent from README/deployment/usage; ponytail is default-off internal.

---------

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

tests/unit/agents/test_ponytail_doctrine_files.py

@@ -0,0 +1,27 @@
+"""The two ponytail doctrine files load with the right content split."""
+
+from __future__ import annotations
+
+from roboco.agents.factories._base import _get_prompts_base_path, _load_layer
+
+_PROMPTS = _get_prompts_base_path()
+
+
+def test_full_doctrine_has_ladder_and_no_frontmatter() -> None:
+    text = _load_layer(_PROMPTS / "doctrine" / "ponytail.md")
+    assert text, "ponytail.md is missing or empty"
+    assert "# Ponytail Doctrine" in text
+    assert "## The ladder" in text
+    assert "## RoboCo preamble" in text
+    assert "## Intensity" in text  # dev doctrine carries the intensity table
+    assert "Forces the laziest solution" not in text  # YAML frontmatter stripped
+
+
+def test_ethos_doctrine_lacks_ladder_and_no_frontmatter() -> None:
+    text = _load_layer(_PROMPTS / "doctrine" / "ponytail-ethos.md")
+    assert text, "ponytail-ethos.md is missing or empty"
+    assert "# Ponytail Doctrine (ethos)" in text
+    assert "## The ladder" not in text
+    assert "## Intensity" not in text  # ethos gets no dial — restrained stance
+    assert "## RoboCo preamble" in text
+    assert "Forces the laziest solution" not in text