v0.3: fix Gradio 6 Radio tuple order + indented file-tree with folder rows

Two bugs visible in v0.2 screenshots:

1. ERROR popup ("Value: '__overview__'") + "no <file> in this task" appearing
even when the file is in the tree. Root cause: Gradio 6 expects Radio
choices as `(label, value)` tuples; I had `(value, label)`. So the radio
was returning labels back as the "value" (e.g. "📁 environment/\n └─
Dockerfile" instead of "environment/Dockerfile"), no dispatch branch
matched, and the content lookup returned None.

2. File tree displayed as a flat list with no indentation. Wanted proper
file-explorer feel with folder hierarchy.

Fixes:
- Flip all Radio choice tuples to `(label, value)` order
- New `_build_file_tree(task)` produces folder pseudo-rows ("📂 solution/")
plus indented children (" ├─ patch.diff", " └─ solve.sh") with
unicode tree glyphs
- Folder pseudo-rows route to their first present child via a state-stored
redirect map — click "📂 solution/" → opens patch.diff, radio selection
updates to show which file was actually opened
- Folder rows only appear when ≥1 of their children exists on the task
- Pre-filter top-level files (task.toml, instruction.md) on actual presence

app.py

@@ -40,18 +40,9 @@ logger = logging.getLogger("harbor-visualiser")
 # Virtual entry id for the metadata overview (not a real file).
 _OVERVIEW = "__overview__"
 
-# (file_id, display label, is_markdown) — file_id is either the relative path
-# from the task root OR the special _OVERVIEW sentinel. Display labels use
-# unicode tree glyphs so the radio looks file-explorer-like.
-_FILE_TREE_ENTRIES: list[tuple[str, str]] = [
-    (_OVERVIEW, "ⓘ  Overview"),
-    ("task.toml", "📄  task.toml"),
-    ("instruction.md", "📄  instruction.md"),
-    ("solution/patch.diff", "📁  solution/\n  └─ patch.diff"),
-    ("solution/solve.sh", "  └─ solve.sh"),
-    ("tests/test.sh", "📁  tests/\n  └─ test.sh"),
-    ("environment/Dockerfile", "📁  environment/\n  └─ Dockerfile"),
-]
+# Folder pseudo-ids — selecting one routes to its first present child.
+_FOLDER_PREFIX = "__folder__"
+
 
 # Map suffix → Gradio Code language token. Everything else falls back to "shell".
 _EXTENSION_LANGUAGE: dict[str, str] = {
@@ -71,19 +62,6 @@ def _file_language(filename: str) -> str:
     return _EXTENSION_LANGUAGE.get(suffix, "shell")
 
 
-def _list_present_files(task: HarborTask) -> list[tuple[str, str]]:
-    """Return (file_id, display_label) tuples for every _FILE_TREE_ENTRIES row
-    that exists on this task. Overview is always first."""
-    present: list[tuple[str, str]] = []
-    for file_id, label in _FILE_TREE_ENTRIES:
-        if file_id == _OVERVIEW:
-            present.append((file_id, label))
-            continue
-        if _read_task_file(task, file_id) is not None:
-            present.append((file_id, label))
-    return present
-
-
 def _read_task_file(task: HarborTask, file_id: str) -> str | None:
     """Fetch the content for a file_id; None when the file isn't present."""
     if file_id == "task.toml":
@@ -101,6 +79,56 @@ def _read_task_file(task: HarborTask, file_id: str) -> str | None:
     return None
 
 
+def _build_file_tree(task: HarborTask) -> tuple[list[tuple[str, str]], dict[str, str]]:
+    """Render a file-explorer-style choice list for a task.
+
+    Returns:
+      choices: list of (label, value) tuples for `gr.Radio`. Labels use unicode
+               tree glyphs (📂, ├─, └─) so the radio reads like a file tree.
+      folder_redirects: maps each folder pseudo-id to its first present child
+                        file_id so clicking a folder header opens its first file.
+
+    Order is fixed: Overview first, then top-level files, then folders with
+    their children. Folders only appear when they have ≥1 present child.
+    """
+    choices: list[tuple[str, str]] = [("ⓘ  Overview", _OVERVIEW)]
+    redirects: dict[str, str] = {}
+
+    # Top-level files (always under root)
+    if (task.task_toml_raw or "").strip():
+        choices.append(("📄  task.toml", "task.toml"))
+    if (task.instruction_md or task.instruction_inline):
+        choices.append(("📄  instruction.md", "instruction.md"))
+
+    def _maybe_folder(folder: str, children: list[tuple[str, str]]) -> None:
+        """Append `📂 folder/` + indented children, only if children non-empty.
+
+        `children` is a list of (basename, full_file_id) tuples.
+        """
+        present = [(b, fid) for (b, fid) in children if _read_task_file(task, fid) is not None]
+        if not present:
+            return
+        folder_id = f"{_FOLDER_PREFIX}{folder}"
+        choices.append((f"📂  {folder}/", folder_id))
+        redirects[folder_id] = present[0][1]  # folder header → first child
+        for i, (basename, full_id) in enumerate(present):
+            glyph = "└─" if i == len(present) - 1 else "├─"
+            choices.append((f"     {glyph}  {basename}", full_id))
+
+    _maybe_folder("solution", [
+        ("patch.diff", "solution/patch.diff"),
+        ("solve.sh", "solution/solve.sh"),
+    ])
+    _maybe_folder("tests", [
+        ("test.sh", "tests/test.sh"),
+    ])
+    _maybe_folder("environment", [
+        ("Dockerfile", "environment/Dockerfile"),
+    ])
+
+    return choices, redirects
+
+
 # ---------------------------------------------------------------------------
 # Backend handlers
 # ---------------------------------------------------------------------------
@@ -110,7 +138,7 @@ def load_dataset_action(uri: str):
     """Top-level "Load" button handler.
 
     Outputs (in order):
-      status_md, source_state, root_state, all_tasks_state,
+      status_md, source_state, root_state, all_tasks_state, folder_redirects_state,
       task_search_value, task_radio_update,
       file_radio_update, markdown_update, code_update
     """
@@ -137,7 +165,7 @@ def load_dataset_action(uri: str):
 
     first = tasks[0]
     task = load_task(root, first)
-    file_choices = _list_present_files(task)
+    file_choices, redirects = _build_file_tree(task)
     md_html, code_update = _render_file(task, _OVERVIEW)
     status = (
         f"✅ Loaded **{source.display}** — {len(tasks)} task"
@@ -147,7 +175,8 @@ def load_dataset_action(uri: str):
         status,
         source.display,
         str(root),
-        tasks,  # cached "all tasks" — used by the search filter
+        tasks,
+        redirects,
         "",  # clear search box
         gr.update(choices=tasks, value=first, label=f"Tasks ({len(tasks)})"),
         gr.update(choices=file_choices, value=_OVERVIEW, label="Files"),
@@ -159,30 +188,57 @@ def load_dataset_action(uri: str):
 def select_task_action(task_id: str, root: str):
     """Switch task → repopulate file tree, render the Overview."""
     if not task_id or not root:
-        return _render_no_task()
+        return (
+            {},
+            gr.update(choices=[], value=None, label="Files"),
+            "Pick a task from the list.",
+            gr.update(value="", visible=False),
+        )
     try:
         task = load_task(Path(root), task_id)
     except Exception as exc:
         logger.exception("load_task failed")
-        return _render_no_task(error=str(exc))
-    file_choices = _list_present_files(task)
+        return (
+            {},
+            gr.update(choices=[], value=None, label="Files"),
+            f"❌ {exc}",
+            gr.update(value="", visible=False),
+        )
+    file_choices, redirects = _build_file_tree(task)
     md_html, code_update = _render_file(task, _OVERVIEW)
     return (
+        redirects,
         gr.update(choices=file_choices, value=_OVERVIEW, label="Files"),
         md_html,
         code_update,
     )
 
 
-def select_file_action(file_id: str, root: str, task_id: str):
-    """Switch file inside a task → render its content."""
+def select_file_action(file_id: str, root: str, task_id: str, folder_redirects: dict):
+    """Switch file inside a task → render its content.
+
+    Folder pseudo-ids are routed to their first child via `folder_redirects`.
+    The file_tree radio's value is also updated so the user sees which file
+    was opened.
+    """
     if not file_id or not root or not task_id:
-        return ("Pick a task first.", gr.update(value="", visible=False))
+        return ("Pick a task first.", gr.update(value="", visible=False), gr.update())
+
+    # Folder header click → redirect to first child + update radio selection
+    redirect = (folder_redirects or {}).get(file_id)
+    if redirect is not None:
+        file_id = redirect
+        radio_update = gr.update(value=file_id)
+    else:
+        radio_update = gr.update()  # no-op for normal file clicks
+
     try:
         task = load_task(Path(root), task_id)
     except Exception as exc:
-        return (f"❌ {exc}", gr.update(value="", visible=False))
-    return _render_file(task, file_id)
+        return (f"❌ {exc}", gr.update(value="", visible=False), gr.update())
+
+    md_html, code_update = _render_file(task, file_id)
+    return (md_html, code_update, radio_update)
 
 
 def filter_tasks_action(query: str, all_tasks: list[str], current_root: str):
@@ -221,6 +277,7 @@ def _empty_state(status: str):
         "",  # source_state
         "",  # root_state
         [],  # all_tasks_state
+        {},  # folder_redirects_state
         "",  # task search clear
         gr.update(choices=[], value=None, label="Tasks"),
         gr.update(choices=[], value=None, label="Files"),
@@ -229,16 +286,6 @@ def _empty_state(status: str):
     )
 
 
-def _render_no_task(error: str | None = None):
-    """Used by select_task_action when no task is selected."""
-    msg = error or "Pick a task from the list."
-    return (
-        gr.update(choices=[], value=None, label="Files"),
-        msg,
-        gr.update(value="", visible=False),
-    )
-
-
 def _render_file(task: HarborTask, file_id: str):
     """Return (markdown_html, code_update) for the right-panel content area.
 
@@ -400,6 +447,7 @@ def build_ui() -> gr.Blocks:
         source_state = gr.State("")
         root_state = gr.State("")
         all_tasks_state = gr.State([])  # full unfiltered list for the search box
+        folder_redirects_state = gr.State({})  # folder pseudo-id → first child file_id
 
         # ─── 3-column file-explorer layout ────────────────────────────────
         with gr.Row():
@@ -447,6 +495,7 @@ def build_ui() -> gr.Blocks:
             source_state,
             root_state,
             all_tasks_state,
+            folder_redirects_state,
             task_search,
             task_list,
             file_tree,
@@ -468,13 +517,13 @@ def build_ui() -> gr.Blocks:
         task_list.change(
             fn=select_task_action,
             inputs=[task_list, root_state],
-            outputs=[file_tree, content_md, content_code],
+            outputs=[folder_redirects_state, file_tree, content_md, content_code],
         )
 
         file_tree.change(
             fn=select_file_action,
-            inputs=[file_tree, root_state, task_list],
-            outputs=[content_md, content_code],
+            inputs=[file_tree, root_state, task_list, folder_redirects_state],
+            outputs=[content_md, content_code, file_tree],
         )
 
         task_search.change(