diff --git a/milestones/README.md b/milestones/README.md
index 95ca73c..bcf8c23 100644
--- a/milestones/README.md
+++ b/milestones/README.md
@@ -5,11 +5,13 @@ repositories that install `docgen` and maintain their own demo bundle. The
 library no longer ships an in-repo dogfood; consumers are the integration test
 of record.
 
-**Active:** **[visual-map-field-strings.md](visual-map-field-strings.md)** —
-`visual_map` type/scene/source and `segment_names` values must be YAML
-strings at config load.
+**Active:** **[path-config-strings.md](path-config-strings.md)** —
+`env_file` / `repo_root` / `dirs.*` must be YAML strings at config load.
 
 **Shipped:**
+- **[visual-map-field-strings.md](visual-map-field-strings.md)** —
+  `visual_map` type/scene/source and `segment_names` values must be YAML
+  strings (#108).
 - **[generation-model-strings.md](generation-model-strings.md)** —
   `narration_from_source` / `manim_scene_generation` model and prompt
   keys must be YAML strings (#107).
diff --git a/milestones/path-config-strings.md b/milestones/path-config-strings.md
new file mode 100644
index 0000000..ed92f3e
--- /dev/null
+++ b/milestones/path-config-strings.md
@@ -0,0 +1,38 @@
+# Milestone: env_file / repo_root / dirs paths must be strings
+
+**Status:** Active  
+**PR:** [#109](https://github.com/jmjava/documentation-generator/pull/109)  
+**Depends on:** `milestones/visual-map-field-strings.md` (PR #108)
+
+## Problem
+
+`manim.manim_path` is already a string at config load. These path keys
+were not:
+
+1. **`env_file` / `repo_root`** — a YAML list loaded successfully, then
+   `Path / list` TypeError’d when CLI applied the env file or the wizard
+   resolved `repo_root`.
+2. **`dirs.narration` / `audio` / `animations` / `recordings` / `hints`**
+   — a list TypeError’d during `Config.__post_init__` Path joins instead
+   of raising `ConfigError`.
+
+## Goal
+
+Fail closed at `Config.from_yaml` with `ConfigError`. Missing keys still
+use defaults (`narration/`, git-discovered repo root, no `env_file`).
+
+## Done when
+
+- [x] Present `env_file` / `repo_root` must be non-empty YAML strings.
+- [x] Present `dirs.narration` / `audio` / `animations` / `recordings` /
+      `hints` must be non-empty YAML strings.
+- [x] Tests for list values of those keys.
+- [x] `ruff check src/ tests/`
+- [x] `pytest tests/`
+- [x] `docgen benchmark` (no clock change)
+
+## Out of scope
+
+- `wizard.default_guidance` type gating is separate.
+- Per-segment generation `system_prompt` / `class_name` are separate.
+- `pages` output directory keys are separate.
diff --git a/milestones/visual-map-field-strings.md b/milestones/visual-map-field-strings.md
index 7715e52..4654810 100644
--- a/milestones/visual-map-field-strings.md
+++ b/milestones/visual-map-field-strings.md
@@ -1,7 +1,7 @@
 # Milestone: visual_map type/scene/source and segment_names values must be strings
 
-**Status:** Active  
-**PR:** [#108](https://github.com/jmjava/documentation-generator/pull/108)  
+**Status:** Shipped  
+**PR:** #108  
 **Depends on:** `milestones/generation-model-strings.md` (PR #107),
 `milestones/visual-map-row-types.md` (PR #86),
 `milestones/segment-id-strings.md` (PR #87)
diff --git a/src/docgen/config.py b/src/docgen/config.py
index 334821a..4a52508 100644
--- a/src/docgen/config.py
+++ b/src/docgen/config.py
@@ -164,7 +164,11 @@ class Config:
     hints_dir: Path = field(init=False)
 
     def __post_init__(self) -> None:
+        src = self._source_label()
         dirs = self._block("dirs")
+        for dkey in ("narration", "audio", "animations", "recordings", "hints"):
+            if dirs.get(dkey) is not None:
+                require_yaml_string(dirs[dkey], label=f"dirs.{dkey}", source=src)
         self.narration_dir = self.base_dir / dirs.get("narration", "narration")
         self.audio_dir = self.base_dir / dirs.get("audio", "audio")
         self.animations_dir = self.base_dir / dirs.get("animations", "animations")
@@ -347,6 +351,10 @@ def __post_init__(self) -> None:
                 f"{src}: manim_scene_generation.scene_spec_system_prompt must be a "
                 f"YAML string, not {type(msg['scene_spec_system_prompt']).__name__}"
             )
+        if self.raw.get("env_file") is not None:
+            require_yaml_string(self.raw["env_file"], label="env_file", source=src)
+        if self.raw.get("repo_root") is not None:
+            require_yaml_string(self.raw["repo_root"], label="repo_root", source=src)
         ocr = self._sub_block(validation, "ocr", label="validation.ocr")
         if ocr.get("error_patterns") is not None:
             string_list_block(
diff --git a/tests/test_config.py b/tests/test_config.py
index eaa301d..2d0f738 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -631,3 +631,24 @@ def test_from_yaml_list_segment_names_value_raises(tmp_path: Path) -> None:
     p.write_text('segment_names:\n  "01":\n    - 01-intro\n', encoding="utf-8")
     with pytest.raises(ConfigError, match="segment_names.01 must be a YAML string"):
         Config.from_yaml(p)
+
+
+def test_from_yaml_list_env_file_raises(tmp_path: Path) -> None:
+    p = tmp_path / "docgen.yaml"
+    p.write_text("env_file:\n  - .env\n", encoding="utf-8")
+    with pytest.raises(ConfigError, match="env_file must be a YAML string"):
+        Config.from_yaml(p)
+
+
+def test_from_yaml_list_repo_root_raises(tmp_path: Path) -> None:
+    p = tmp_path / "docgen.yaml"
+    p.write_text("repo_root:\n  - ..\n", encoding="utf-8")
+    with pytest.raises(ConfigError, match="repo_root must be a YAML string"):
+        Config.from_yaml(p)
+
+
+def test_from_yaml_list_dirs_narration_raises(tmp_path: Path) -> None:
+    p = tmp_path / "docgen.yaml"
+    p.write_text("dirs:\n  narration:\n    - narration\n", encoding="utf-8")
+    with pytest.raises(ConfigError, match="dirs.narration must be a YAML string"):
+        Config.from_yaml(p)