docs(agents): require specs and plans to live in this repo

Make explicit that design specs go in docs/superpowers/specs/ and
implementation plans go in docs/superpowers/plans/, both committed
to git, with the YYYY-MM-DD-<topic>[-design].md naming already used
elsewhere in the tree. The plan-mode scratch file under
~/.claude/plans/ is fine while plan mode is open, but the persisted
artifact must end up inside the repo.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -9,3 +9,4 @@ __pycache__/
 l4d2web.db*
 # CocoIndex Code (ccc)
 /.cocoindex_code/
+.superpowers/

AGENTS.md

@@ -23,6 +23,13 @@ Do not invent architecture outside these plans unless explicitly requested.
 - Do not use git worktrees.
 - Local Python venv is direnv-managed via `.envrc` (Python 3.13). After fresh checkout: `direnv allow`, then `pip install -e ./l4d2host -e ./l4d2web pytest`. See README **Local development** for details.
 
+### Planning artifacts
+
+- Design specs live in `docs/superpowers/specs/` as `YYYY-MM-DD-<topic>-design.md`.
+- Implementation plans live in `docs/superpowers/plans/` as `YYYY-MM-DD-<topic>.md` (suffix the topic with `-v1`/`-v2`/etc. if a plan is versioned).
+- Commit both to git as soon as the user approves them.
+- Do not leave specs or plans outside this repo. The `~/.claude/plans/<slug>.md` plan-mode scratch file is acceptable while plan mode is open; the persisted artifact must end up under `docs/superpowers/` and be committed.
+
 ### Naming and boundaries
 
 - Use `l4d2` naming consistently.

deploy/deploy-test-server.sh

@@ -154,17 +154,18 @@ $sudo_cmd install -m 0644 -o root -g root \
     /opt/left4me/deploy/files/etc/left4me/sandbox-resolv.conf \
     /etc/left4me/sandbox-resolv.conf
 
-if [ ! -f /etc/left4me/web.env ]; then
+# Stomp the file every deploy so newly added vars reach existing boxes.
-    secret_key=$(python3 -c 'import secrets; print(secrets.token_hex(32))')
+# SECRET_KEY is derived from /etc/machine-id so it stays stable across
-    tmp_web_env="$remote_tmp/web.env"
+# redeploys (no session invalidation) without persisting state in /etc.
-    {
+secret_key=$(sha256sum < /etc/machine-id | awk '{print $1}')
-        printf 'DATABASE_URL=sqlite:////var/lib/left4me/left4me.db\n'
+tmp_web_env="$remote_tmp/web.env"
-        printf 'SECRET_KEY=%s\n' "$secret_key"
+{
-        printf 'JOB_WORKER_THREADS=4\n'
+    printf 'DATABASE_URL=sqlite:////var/lib/left4me/left4me.db\n'
-        printf 'SESSION_COOKIE_SECURE=false\n'
+    printf 'SECRET_KEY=%s\n' "$secret_key"
-    } > "$tmp_web_env"
+    printf 'JOB_WORKER_THREADS=4\n'
-    $sudo_cmd install -m 0640 -o root -g left4me "$tmp_web_env" /etc/left4me/web.env
+    printf 'SESSION_COOKIE_SECURE=false\n'
-fi
+} > "$tmp_web_env"
+$sudo_cmd install -m 0640 -o root -g left4me "$tmp_web_env" /etc/left4me/web.env
 
 if [ ! -x /opt/left4me/.venv/bin/python ]; then
     run_as_left4me python3 -m venv /opt/left4me/.venv

docs/superpowers/plans/2026-05-08-overlay-file-tree.md

@@ -0,0 +1,161 @@
+# Overlay File Tree Implementation Plan
+
+> **Approval status:** User-approved 2026-05-08; implemented + deployed in the same session. This plan is committed retrospectively to record the work.
+
+**Goal:** Build the overlay-detail "Files" section per `docs/superpowers/specs/2026-05-08-overlay-file-tree-design.md` — a server-rendered collapsible tree of `${LEFT4ME_ROOT}/overlays/{overlay.id}/` with HTMX lazy expansion and click-to-download for individual files. Read-only; same access rule as the rest of the overlay detail page.
+
+**Architecture:** A new `files_bp` blueprint exposes two GETs: `/overlays/<id>/files?path=<rel>` returns the listing as an HTML fragment (used both for first paint at the root level via `page_routes.overlay_detail` context, and for HTMX swaps when a folder expands), and `/overlays/<id>/files/download?path=<rel>` streams a single file. Pure helpers live in `l4d2web/services/overlay_files.py`: `safe_resolve_for_listing` (refuses symlink escape from overlay root), `safe_resolve_for_download` (allows symlink targets anywhere under `LEFT4ME_ROOT` — workshop addons stream from the shared cache; absolute symlinks to `/etc/passwd` are still blocked), and `list_directory` (one-level scan, dirs-first sort, 500-entry cap, symlink + broken-symlink markers, resolved size for files). Two Jinja partials (`_overlay_file_tree.html`, `_overlay_file_node.html`) plus a 12-line event-delegated `static/js/file-tree.js` for collapse/re-expand handle the UI; styles append to `static/css/components.css` against existing tokens.
+
+---
+
+## Locked Decisions
+
+See the design doc for rationale. Implementation-relevant summary:
+
+- New blueprint `files_bp` registered in `l4d2web/app.py` next to `overlay_bp`.
+- Path resolution chains through `l4d2host.paths.overlay_path()` (already validates the overlay ref + resolves under `LEFT4ME_ROOT/overlays/`) and `l4d2web.services.security.validate_overlay_ref` (rejects empty/`.`/`..`/absolute/whitespace/backslash for the sub-path component).
+- Listing rule: target must be a descendant of `overlay_root` after `Path.resolve()`. Download rule: real path must be a descendant of `LEFT4ME_ROOT` after `os.path.realpath()`.
+- Tree shape: single recursive partial. `_overlay_file_tree.html` renders `<ul>`; `_overlay_file_node.html` renders one folder or file `<li>`. Folder buttons carry `data-files-url="/overlays/{id}/files?path=…"`. `static/js/file-tree.js` handles every click — toggles `aria-expanded` + `hidden`, fetches once on first expand, dedupes rapid clicks via `dataset.loaded`.
+- `DEFAULT_MAX_ENTRIES = 500` in the helper module; re-resolved per call so tests can monkeypatch.
+- No changes to `l4d2host`, builders, or workshop/script edit flows.
+
+---
+
+## Task 1: Pure helpers — path safety + directory listing
+
+**Files:**
+
+- Create: `l4d2web/services/overlay_files.py` — `safe_resolve_for_listing`, `safe_resolve_for_download`, `list_directory`, `_format_size`, `DEFAULT_MAX_ENTRIES`.
+- Create: `l4d2web/tests/test_overlay_files.py` — 20 tests (path safety, listing semantics, symlink + broken-symlink handling, sort order, truncation cap, human-size formatting).
+
+Test plan (RED first):
+
+1. Listing returns overlay root for empty sub-path; joins under root for nested sub-path; rejects `..`, absolute path, empty component (`foo//bar`); rejects symlink escaping the overlay root even when target sits in `workshop_cache/`.
+2. Download rejects empty path; returns real path for a regular file; follows a symlink into `workshop_cache/`; rejects a symlink to a path outside `LEFT4ME_ROOT`; rejects `..` and absolute paths.
+3. `list_directory`: empty dir → empty list, truncated 0; dirs-first then files, both case-insensitive alphabetical; `kind ∈ {"dir", "file"}`; `rel` is forward-slash relative to overlay root; symlinks marked with `is_symlink=True` and resolved-target size; broken symlinks marked `broken=True` with `size=None`; truncation at supplied cap returns first N + `truncated_count`; `size_human` formats `5 B` and `3.0 MB` correctly.
+
+**Implementation:**
+
+- `safe_resolve_for_listing` calls `l4d2host.paths.overlay_path(overlay_path_value).resolve()` for the overlay root, short-circuits on empty `sub_path`, validates the sub-path via `validate_overlay_ref`, then `(overlay_root / sub_path).resolve(strict=False)` and asserts the result is the overlay root or a descendant.
+- `safe_resolve_for_download` rejects empty `sub_path`, validates, builds `overlay_root / sub_path`, applies `os.path.realpath()`, asserts the result is under `get_left4me_root().resolve()`.
+- `list_directory(target, overlay_root, *, max_entries=None)` uses `os.scandir` (free `stat` cache, `follow_symlinks` toggle). Per entry: `is_symlink = entry.is_symlink()`; `is_dir = entry.is_dir(follow_symlinks=True)` inside a try (OSError → broken=True, kind=file, size=None); regular files use `entry.stat(follow_symlinks=True).st_size`. `rel` is `"/".join(Path(entry.path).relative_to(overlay_root).parts)`. Sort by `(0 if dir else 1, name.casefold())`. Truncate to `max_entries or DEFAULT_MAX_ENTRIES`.
+- `_format_size`: bytes (`N B`, no decimal) up to 1024, then KB/MB/GB/TB at one decimal place.
+
+**Verification:**
+
+```
+pytest l4d2web/tests/test_overlay_files.py -q
+```
+
+**Commit:** part of Task 4's bundled `feat` commit.
+
+---
+
+## Task 2: HTTP routes — files_bp blueprint
+
+**Files:**
+
+- Create: `l4d2web/routes/files_routes.py` — `files_bp` with `GET /overlays/<id>/files` (fragment) and `GET /overlays/<id>/files/download` (stream).
+- Modify: `l4d2web/app.py` — `from l4d2web.routes.files_routes import bp as files_bp` and `app.register_blueprint(files_bp)` next to `overlay_bp`.
+- Create: `l4d2web/tests/test_overlay_files_routes.py` — 16 HTTP-level tests at this stage (3 more added in Task 4).
+
+Test plan (RED first):
+
+- Fragment: 200 + entries for root listing; 200 + entries for sub-directory; 400 on `..`, absolute path, empty component; 404 on unknown overlay; 404 on missing sub-dir; 403 on foreign user's overlay; 200 for admin viewing foreign overlay; truncation cap exposes "+ N more" footer (monkeypatch `DEFAULT_MAX_ENTRIES`); broken symlink rendered with `broken` badge and no `<a>` link.
+- Download: 200 + `Content-Disposition: attachment` + exact byte match for regular file; 200 + cache content for workshop-cache symlink; 400 for symlink resolving outside `LEFT4ME_ROOT`; 400 for directory target; 404 for missing file; 403 for foreign user's overlay.
+
+**Implementation:**
+
+- Decorator stack: `@files_bp.get(...)` + `@require_login`. Auth gate inside the handler mirrors `page_routes.overlay_detail:194` (`g.user.admin or overlay.user_id is None or overlay.user_id == g.user.id`).
+- Shared `_load_overlay_for_user(overlay_id, user)` does the lookup, the auth gate, and `db.expunge(overlay)` so the route can read scalar attributes after the session closes.
+- `ValueError` from either resolver → `Response("invalid path", status=400)`. `target.is_dir()` failure on the listing route → 404. `real.exists()` / `real.is_dir()` failure on the download route → 404 / 400.
+- `send_file(str(real), as_attachment=True, download_name=os.path.basename(real))`.
+- The fragment renders `_overlay_file_tree.html` only — no `base.html` shell — so HTMX swaps inject just the `<ul>` content.
+
+**Verification:**
+
+```
+pytest l4d2web/tests/test_overlay_files_routes.py -q
+```
+
+**Commit:** part of Task 4's bundled `feat` commit.
+
+---
+
+## Task 3: Templates + page-routes integration
+
+**Files:**
+
+- Create: `l4d2web/templates/_overlay_file_tree.html` — `<ul class="file-tree" role="group">` + per-entry `_overlay_file_node.html` include + optional truncated-footer `<li>`.
+- Create: `l4d2web/templates/_overlay_file_node.html` — folder row (button + HTMX attrs + empty `<div class="file-tree-children" hidden>`) or file row (`<a>` for regular/symlink files; `<span>` for broken symlinks; `link` / `broken link` badges; `size_human`).
+- Modify: `l4d2web/templates/overlay_detail.html` — add `<section class="panel"><h2>Files</h2>…</section>` between the type-specific sections and the existing "Used by" section. Renders empty-state `<p class="muted">No files yet — build this overlay to populate it.</p>` when `file_tree_root_entries is none`, else includes the partial.
+- Modify: `l4d2web/routes/page_routes.py` — import the helpers, add `_root_file_tree(overlay)` (returns `(entries, truncated_count)` or `(None, 0)` on `ValueError` / missing dir / legacy absolute `overlay.path`), pass `file_tree_root_entries` + `file_tree_truncated` + `file_tree_truncated_count` into `render_template("overlay_detail.html", …)`.
+
+Test plan (RED first, added to `test_overlay_files_routes.py`):
+
+- `test_overlay_detail_renders_files_section_with_tree` — page contains "Files" header + entry names.
+- `test_overlay_detail_shows_empty_state_when_overlay_dir_missing` — wipe directory, page shows "No files yet".
+- `test_overlay_detail_files_section_present_for_workshop_overlays` — workshop type also gets the section.
+
+**Implementation:**
+
+- Section placement matters: `<section><h2>Files</h2>…</section>` is inserted before the existing "Used by" `<section>`.
+- The partial uses `{% set entries = file_tree_root_entries %}` etc. so the same partial works whether called from the page (with full context) or from the HTMX route (rendering directly with named kwargs).
+- `_root_file_tree` swallows `ValueError` and missing-dir cases into `(None, 0)`, and the template's `{% if file_tree_root_entries is none %}` renders the empty state.
+- Use `overlay.path` (not `str(overlay.id)`) so legacy/seeded rows whose path differs still work correctly when resolvable.
+
+**Verification:**
+
+```
+pytest l4d2web/tests/test_overlay_files_routes.py -q -k overlay_detail
+pytest l4d2web/tests/ -q              # no regressions across the full suite
+```
+
+**Commit:** part of Task 4's bundled `feat` commit.
+
+---
+
+## Task 4: CSS + JS + base.html script wiring
+
+**Files:**
+
+- Create: `l4d2web/static/js/file-tree.js` — event-delegated `click` handler that toggles `aria-expanded` on `.file-tree-toggle` and `hidden` on the next `.file-tree-children` sibling, and on first expand fires `fetch(button.dataset.filesUrl)` and innerHTMLs the response. `dataset.loaded` flag dedupes rapid clicks; cleared on error to allow retry.
+- Modify: `l4d2web/templates/base.html` — `<script src="{{ url_for('static', filename='js/file-tree.js') }}"></script>` next to the existing `csrf.js` / `sse.js` / `modal.js` lines.
+- Modify: `l4d2web/static/css/components.css` — append `~50` lines: `.file-tree`, `.file-tree-row`, `.file-tree-toggle` (transparent button, inherits color), `.file-tree-toggle .chevron` rotation transform on `aria-expanded="true"`, `.file-tree-children[hidden]`, `.file-tree-badge` + `.file-tree-badge-warn`. All against existing tokens (`--space-xs`, `--space-l`, `--color-surface-muted`, `--color-muted`, `--color-danger`, `--radius-s`).
+
+**Implementation:**
+
+- The JS handler fires on every click. First-expand path: read `button.dataset.filesUrl`, set `dataset.loaded="1"` optimistically, `fetch(url, {credentials: "same-origin"})`, replace `.file-tree-children` innerHTML with the response. Subsequent clicks just toggle `aria-expanded` + `hidden` — no re-fetch since `dataset.loaded` is set. On fetch error: `delete dataset.loaded` so a future click retries.
+- The CSS chevron is a Unicode `›` inside a `<span class="chevron">`; rotated 90° on expanded via `transform: rotate(90deg)` with a 120ms transition.
+
+**Verification:**
+
+```
+pytest l4d2web/tests/ -q            # 293 passed, 1 skipped
+```
+
+Manual smoke (post-deploy on `ckn@10.0.4.128`):
+
+- Navigate to an overlay detail page with a populated runtime directory.
+- Confirm the "Files" section renders the root level.
+- Click a folder: HTMX request fires once, children appear, chevron rotates.
+- Click again: children hide; no second request in DevTools network tab.
+- Click a file: browser downloads it with the correct filename.
+- Visit another user's overlay as a non-admin: 403.
+
+**Commit:** `feat(l4d2-web): overlay detail Files section with HTMX file tree + downloads` — covers all four tasks (services helper + routes + templates + CSS/JS), since the feature is small and the tasks share a single set of integration tests.
+
+---
+
+## End-to-end verification
+
+After all tasks committed:
+
+```
+pytest l4d2web/tests/ -q                 # 293 passed, 1 skipped
+deploy/deploy-test-server.sh ckn@10.0.4.128
+ssh ckn@10.0.4.128 'systemctl status left4me-web --no-pager | head -10'
+curl -s http://10.0.4.128:8000/health    # {"status":"ok"}
+```
+
+Then exercise the manual smoke checklist from Task 4 against the deployed instance.

docs/superpowers/specs/2026-05-08-l4d2-blueprint-overlay-picker-design.md

@@ -0,0 +1,118 @@
+# L4D2 Blueprint Overlay Picker Design
+
+**Goal:** Replace the checkbox + numeric-Order table on the blueprint detail page with a drag-to-reorder list and a single dropdown to add overlays. Drag-and-drop is the primary reorder mechanic; per-row Order text inputs are removed.
+
+**Approval status:** User-approved. No companion implementation plan — small surface, implemented directly.
+
+## Context
+
+`templates/blueprint_detail.html:14-28` currently renders one HTML table for the blueprint's overlays. Each row carries a `Use` checkbox, a numeric `Order` text input, and the overlay name. To enable an overlay you check it; to reorder you type integers into per-row text fields. Adding a new overlay between existing ones means renumbering everything below it by hand.
+
+This spec replaces that table with a single ordered list of *selected* overlays plus a `<select>` dropdown for adding more. Drag-to-reorder is the only reorder interaction. A ✕ button on each row removes it (returning it to the dropdown). Picking an entry from the dropdown appends it to the list (and removes it from the dropdown).
+
+The change is intentionally scoped small: no two-panel layout, no filter widget, no touch / keyboard reorder support, no JS-disabled fallback. The native `<select>` element supplies typeahead-by-letter and keyboard navigation for free, which covers the no-drag path. The page is desktop-primary.
+
+## Locked Decisions
+
+1. **Single ordered list of selected overlays only.** No second pane. The "available" set lives in the `<select>`. Adding via dropdown is one click; removing via ✕ is one click; reordering is one drag.
+2. **Native HTML5 drag-and-drop.** No vendored library, no polyfill. Touch-screen drag is unsupported on Android and rough on iOS — accepted because the page is desktop-primary. Add and remove still work on touch via the `<select>` and the `<button>`.
+3. **JS-required UI.** If JS does not load, the page is unusable. No degradation to the old checkbox table.
+4. **Server contract unchanged.** Each list row owns one `<input type="hidden" name="overlay_ids" value="{id}">`. Form-submission order = DOM order. The existing `ordered_overlay_ids_from_form` handler in `routes/blueprint_routes.py` already falls back to enumerate index when no `overlay_position_<id>` field is present, so it accepts the new shape with no Python edit.
+5. **Dropdown re-sorted alphabetically on remove.** When ✕ removes a row, the corresponding `<option>` is sorted-inserted back into the `<select>` (case-insensitive name compare). The dropdown stays predictable.
+6. **Drop-indicator visual.** A 2px focus-color bar drawn via `box-shadow … inset` on the row under the cursor: top-bar = "drop will land before this row", bottom-bar = "drop will land after this row". The hover side is computed by comparing `event.clientY` to the row's vertical midpoint.
+7. **Drop on empty space inside the list = append.** Drop directly on the dragged row (or with no movement) = no-op. Escape during drag triggers `dragend`, which clears all visual classes.
+8. **Out of scope:** keyboard reorder, ARIA live announcements, touch DnD polyfill, server-side cleanup of the now-unused `overlay_position_<id>` form-field path.
+
+## Architecture
+
+```
+GET /blueprints/<id>
+   page_routes.blueprint_page
+       ├─▶ selected_overlays  (ordered by BlueprintOverlay.position)
+       └─▶ available_overlays = all_overlays \ selected_overlays
+                            (alphabetical)
+
+   templates/blueprint_detail.html
+       <ol data-overlay-list>                    ← drag target, hidden inputs
+         <li data-overlay-id draggable> × ⋮⋮ name </li>
+         …
+       </ol>
+       <select data-overlay-add>                 ← add path
+         <option>Pick a name…</option>
+         <option value=overlay.id>name</option>  ← available_overlays
+         …
+       </select>
+
+   static/js/blueprint-overlay-picker.js
+       ├─ dragstart/over/leave/drop/end → reorder DOM under [data-overlay-list]
+       ├─ click [data-action="remove"]  → remove row + sorted-insert <option>
+       ├─ change [data-overlay-add]     → append <li>, remove <option>
+       └─ refreshEmpty()                → toggle [data-overlay-empty][hidden]
+
+POST /blueprints/<id>
+   form-encoded body: overlay_ids=<id>&overlay_ids=<id>&… (in DOM order)
+   blueprint_routes.update_blueprint_form
+     → ordered_overlay_ids_from_form (existing; fallback_position branch)
+     → replace_blueprint_overlays    (existing)
+```
+
+## Form-contract details
+
+The new template emits one hidden input per selected row, colocated as a child of the `<li>`:
+
+```html
+<li data-overlay-id="3" draggable="true">
+  <span class="overlay-picker-handle">⋮⋮</span>
+  <span class="overlay-picker-name">workshop_maps</span>
+  <button type="button" data-action="remove">×</button>
+  <input type="hidden" name="overlay_ids" value="3">
+</li>
+```
+
+Browser form serialization preserves DOM order across multiple inputs that share a `name`. Werkzeug's `request.form.getlist("overlay_ids")` returns them in submission order. `ordered_overlay_ids_from_form` then assigns each id its enumerate-index position via the `fallback_position` branch (lines 19-31 of `routes/blueprint_routes.py`) and feeds the result to `replace_blueprint_overlays`.
+
+The JSON path (`POST /blueprints` with `application/json`) already takes `overlay_ids` list order at line 64 of the same file — this spec does not affect it.
+
+## UI / UX details
+
+- **Empty state.** When no overlays are selected, a `[data-overlay-empty]` paragraph reads "No overlays selected. Pick one below to add." JS toggles its `hidden` attribute on every list mutation.
+- **Drag handle.** Visual only (`⋮⋮` glyph). The whole row is `draggable="true"`; the user does not have to grab the handle specifically.
+- **Drop indicator math.** During `dragover`, compute `event.clientY < rect.top + rect.height/2`; that boolean picks `drop-before` (bar at top) vs `drop-after` (bar at bottom). On `drop`, read which class is set and `insertBefore` or `insertBefore(…, target.nextSibling)` accordingly.
+- **Sorted insert on remove.** Walk `<select>` children comparing `option.dataset.overlayName` (lowercased) against the removed name; `insertBefore` the new option ahead of the first option whose name sorts later, or append if none.
+- **Reset select after add.** Set `select.value = ""` so the placeholder reappears after each add.
+
+## Files
+
+| Path | Change |
+|---|---|
+| `l4d2web/routes/page_routes.py` | Compute `available_overlays`; pass to template. |
+| `l4d2web/templates/blueprint_detail.html` | Replace overlay table with `<ol>` + `<select>`; add `<script defer>`. |
+| `l4d2web/static/css/components.css` | Append `.overlay-picker-*` rules. Reuse existing tokens. |
+| `l4d2web/static/js/blueprint-overlay-picker.js` | New IIFE. ~150 LOC. |
+| `l4d2web/tests/test_blueprints.py` | Two new GET-page assertions. |
+| `l4d2web/tests/test_pages.py` | Update `test_blueprint_detail_has_ordered_overlay_form` to match new shape. |
+
+## Verification
+
+Manual browser flow (`/blueprints/<id>`):
+
+1. Initial render shows the saved selection in saved order; dropdown holds the rest. No console errors.
+2. Drag a row up/down. Focus-colored bar appears at the top or bottom of the hover-target row (depending on which half is hovered). On drop, the row moves; hidden inputs reflect the new order.
+3. Click ✕ on a row. Row vanishes; the same name appears in the dropdown in alphabetical position.
+4. Pick from the dropdown. New row appears at the end of the list; the option leaves the dropdown; the placeholder is reselected.
+5. Save the blueprint, reload. Order survives the round-trip.
+6. Press Escape mid-drag. Drop indicators clear; source row regains opacity; nothing moved.
+
+Test commands:
+
+```
+pytest l4d2web/tests/test_blueprints.py -q
+pytest l4d2web/tests -q
+```
+
+## Out of scope / future follow-ups
+
+- **Drop the `overlay_position_<id>` server-side path.** Once no client emits those fields, `ordered_overlay_ids_from_form` collapses to `[int(v) for v in request.form.getlist("overlay_ids")]`. Test `test_form_update_preserves_ordered_overlays_and_multiline_fields` (`l4d2web/tests/test_blueprints.py:220`) gets simplified accordingly.
+- **Touch-friendly DnD.** Vendor a polyfill (`drag-drop-touch`) or rewrite the picker on pointer events if mobile editing becomes a real use case.
+- **Keyboard reorder.** Space-to-grab + arrow-keys + ARIA live announcements. Currently only add/remove are keyboard-accessible.
+- **Filter on the selected list.** Not needed at v1's overlay counts; revisit if blueprints commonly carry 20+ overlays.

docs/superpowers/specs/2026-05-08-overlay-file-tree-design.md

@@ -0,0 +1,115 @@
+# Overlay File Tree Section Design
+
+**Goal:** Add a "Files" section to the overlay detail page (`/overlays/<id>`) that renders a collapsible tree of the overlay's runtime directory at `${LEFT4ME_ROOT}/overlays/{overlay.id}/`, with lazy expansion of folders (one fetch per first-time expand) and click-to-download for individual files. Same access rule as the rest of the overlay detail page (admin or `overlay.user_id == g.user.id`). Read-only; no rename/delete/upload in v1.
+
+**Approval status:** User-approved 2026-05-08 (visual companion brainstorm + plan-mode review). Implemented + deployed in the same session. The lazy-load originally targeted HTMX (vendored in `base.html`), but the post-deploy smoke uncovered that `static/vendor/htmx.min.js` was a 33-byte placeholder — the real library was never vendored. Rather than vendoring full HTMX for one feature, the lazy-load was switched to plain JS using the same fetch + innerHTML pattern (~30 lines in `static/js/file-tree.js`). The route + partial contracts are unchanged.
+
+## Context
+
+Today, the overlay detail page shows the row's metadata (name, type, scope, path, last build status), a workshop-items table or script editor depending on `overlay.type`, and links to the build-job stream. It never shows what's actually inside the overlay directory on disk. To verify "did my script actually produce what I expected?" or "did the right VPKs land in `addons/`?" the user has to SSH into the host and `ls /var/lib/left4me/overlays/{id}/`.
+
+Click-to-download is a secondary nice-to-have: workshop overlays' `addons/*.vpk` are absolute symlinks into the shared `${LEFT4ME_ROOT}/workshop_cache/`, and pulling a single VPK to a dev box otherwise means scping with the right path translation.
+
+## Locked Decisions
+
+1. **All overlay types show the section.** Script + workshop + system/managed. Consistency over a tighter scope; even workshop's predictable `addons/*.vpk` layout is worth confirming.
+2. **Collapsible tree, lazy load on expand.** Tree can get large; only the root level is rendered server-side at first paint. Each folder click fires `GET /overlays/<id>/files?path=<rel>` and innerHTMLs the response into that folder's `.file-tree-children` div. The no-JS path still shows the root level (the same partial is server-rendered) — folders just won't expand.
+3. **Single delegated JS handler.** `static/js/file-tree.js` listens for `click` on `document`, finds the closest `.file-tree-toggle` button, toggles `aria-expanded` + `hidden`, and on first expand fires a `fetch()` against the URL in the button's `data-files-url`. Subsequent toggles never re-fetch (`button.dataset.loaded` flag, set optimistically before the fetch to dedupe rapid clicks; cleared on error to allow retry).
+4. **Single-file download in v1.** No bulk archive (e.g., "download whole overlay as `.tar.gz`"). Files are streamed via Flask `send_file(..., as_attachment=True)`. No size cap — VPKs are commonly 100–500 MB and that's the whole point.
+5. **No auto-refresh.** The tree reflects what was on disk at page render. After a build, the user reloads the page. Polling/SSE would duplicate the existing live-log mechanism on the build-job page for negligible benefit.
+6. **Same access rule as the rest of the page.** `g.user.admin or overlay.user_id is None or overlay.user_id == g.user.id`. GETs need no CSRF (`l4d2web/app.py:56`).
+7. **`overlay.path` not `overlay.id`.** The runtime directory is reached via `overlay.path` (current creation flow guarantees `path == str(id)`, but legacy/seeded rows may differ). Path resolution happens through the existing `l4d2host.paths.overlay_path()` helper, which already validates the ref string and resolves+verifies it stays under `${LEFT4ME_ROOT}/overlays/`.
+8. **Empty / unresolvable → empty state.** If the overlay's path is unresolvable (legacy absolute-path rows) or the directory doesn't exist (overlay never built), the section renders "No files yet — build this overlay to populate it." rather than crashing.
+9. **500-entry cap per folder.** Folders with more than 500 children render the alphabetical-first 500 plus a `+ M more (truncated)` footer. Tunable at runtime via `l4d2web.services.overlay_files.DEFAULT_MAX_ENTRIES` (re-resolved per call so tests can monkeypatch).
+10. **Hidden files shown.** No filtering of `.git`, `.DS_Store`, etc. Users want ground truth.
+11. **One dedicated blueprint, `files_bp`.** Not folded into `overlay_routes.py` (which is exclusively POST mutations) or `page_routes.py` (top-level pages, not embedded fragments). `files_bp` owns both the tree fragment and the download endpoint.
+
+## Architecture
+
+```text
+GET /overlays/<id>                                 (page_routes.overlay_detail)
+   │
+   ▼  computes (file_tree_root_entries, truncated_count) via
+   │  _root_file_tree(overlay) → safe_resolve_for_listing(overlay.path, "")
+   │                          → list_directory(overlay_root, overlay_root)
+   │
+   ▼  renders overlay_detail.html, which includes _overlay_file_tree.html
+       for the root level (or the empty-state <p>).
+
+GET /overlays/<id>/files?path=<rel>                (files_routes.overlay_files_fragment)
+   │
+   ▼  auth gate (admin or owner)
+   │
+   ▼  safe_resolve_for_listing(overlay.path, rel) → Path under overlay_root
+   │
+   ▼  list_directory(target, overlay_root) → entries[], truncated_count
+   │
+   ▼  renders _overlay_file_tree.html (partial only — no base.html)
+
+GET /overlays/<id>/files/download?path=<rel>       (files_routes.overlay_files_download)
+   │
+   ▼  auth gate
+   │
+   ▼  safe_resolve_for_download(overlay.path, rel) → real Path under LEFT4ME_ROOT
+   │  (follows symlinks; allows targets anywhere in LEFT4ME_ROOT, e.g. workshop_cache)
+   │
+   ▼  Flask send_file(real, as_attachment=True, download_name=basename(real))
+```
+
+### File tree fragment shape
+
+`_overlay_file_tree.html` produces a `<ul class="file-tree">` containing one `_overlay_file_node.html` row per entry plus an optional truncated-footer `<li>`. A folder row is a `<button class="file-tree-toggle" data-files-url="…">` followed by an empty `<div class="file-tree-children" hidden>` that becomes the fetch target. A file row is an `<a href=".../files/download?path=…">` (or a plain `<span>` for broken symlinks) plus optional badges (`link`, `broken link`) and the resolved size.
+
+Nesting after expand:
+
+```html
+<li class="file-tree-row file-tree-row-dir">
+  <button class="file-tree-toggle" aria-expanded="true" data-files-url="…">…</button>
+  <div class="file-tree-children">
+    <ul class="file-tree" role="group">…</ul>   <!-- inserted by file-tree.js -->
+  </div>
+</li>
+```
+
+## Path Safety
+
+Two resolvers in `l4d2web/services/overlay_files.py`:
+
+- `safe_resolve_for_listing(overlay.path, sub_path)` — resolves `overlay_root / sub_path`, applies `Path.resolve(strict=False)`, requires the result to be the overlay root or a descendant. Used by the tree-fragment route. **Refuses to recurse through symlinks that leave the overlay root**, including symlinks pointing into `workshop_cache/` — listing has no need to follow them, since workshop addons are leaf files, not directories we'd descend into.
+- `safe_resolve_for_download(overlay.path, sub_path)` — resolves the candidate path, applies `os.path.realpath()`, requires the result to be under `${LEFT4ME_ROOT}` (anywhere — overlay dir, `workshop_cache/`, future siblings). This is the relaxed gate that lets workshop addons stream from the shared cache while still blocking absolute symlinks to `/etc/passwd` planted by a malicious script overlay.
+
+Both resolvers re-use `l4d2host.paths.overlay_path()` (which itself calls `validate_overlay_ref`) for the overlay-root resolution, and `l4d2web.services.security.validate_overlay_ref` for the sub-path component (rejects empty / `.` / `..` / absolute / whitespace / backslash). Empty `sub_path` is valid for listing (means "the overlay root") and invalid for download.
+
+Listing: `target.is_dir()` check after resolution; non-directory → 404.
+
+Download: `real.exists()` check (404), `real.is_dir()` rejection (400 — "not a file").
+
+## Symlink Behaviour
+
+`list_directory` uses `os.scandir()` with explicit `follow_symlinks` flags:
+
+- `is_symlink = entry.is_symlink()`
+- `kind`: `entry.is_dir(follow_symlinks=True)` inside a try block. Raised `OSError` → broken symlink, treated as `kind="file"` with `broken=True` and no `<a>` download link.
+- `size`: `entry.stat(follow_symlinks=True).st_size` for files (resolved target's size — what users care about for VPKs); `None` for dirs and broken symlinks.
+
+Symlinked directories pointing inside the overlay root are rendered as folders and remain expandable; the listing-time safety check rejects expansion if the symlink resolves outside the overlay root.
+
+Concurrent build vs listing race: a build mid-symlink-rewrite can yield a transient broken-symlink view. Acceptable — page is a snapshot; the visible "broken link" badge tells the user to refresh.
+
+## Test Strategy
+
+Two test modules, both following existing fixture patterns (`tests/test_script_overlay_routes.py` style — `monkeypatch.setenv("LEFT4ME_ROOT", str(tmp_path))`, app fixture with `TESTING=True`).
+
+- `tests/test_overlay_files.py` — pure-helper unit tests (Flask-free): listing-resolver happy/sad paths (root, sub-path, `..`, absolute, empty component, symlink-out-of-overlay), download-resolver happy/sad paths (regular file, workshop-cache symlink, outside-LEFT4ME_ROOT symlink, traversal, absolute, empty), `list_directory` behaviour (empty, dir-first sort, kind detection, rel paths, symlink markers, broken-symlink markers, truncation cap, human-size formatting).
+- `tests/test_overlay_files_routes.py` — HTTP integration tests: tree-fragment 200 / 400 / 403 / 404 across the same axes; download 200 / 400 / 403 / 404 + content-disposition + byte-exact body for both regular files and workshop-cache symlinks; admin-can-view-foreign overlay; truncation-via-route (monkeypatching `DEFAULT_MAX_ENTRIES`); broken-symlink rendering omits the `<a>` download link; the page-level `overlay_detail` integration shows the section with entries when populated and the empty state when the directory is missing.
+
+39 tests total. The full web suite (`pytest l4d2web/tests/ -q`) must remain green.
+
+## Out of Scope
+
+- Bulk download (e.g., "download overlay as tar.gz").
+- Inline file preview (text peek, image thumbnail).
+- File deletion / rename / upload from the UI.
+- Auto-refresh while a build is active.
+- Filtering hidden files or applying a `.gitignore`-style rule.
+- Reusable file-tree component for things outside overlays.

l4d2web/app.py

@@ -11,6 +11,7 @@ from l4d2web.db import init_db
 from l4d2web.routes.blueprint_routes import bp as blueprint_bp
 from l4d2web.routes.auth_routes import bp as auth_bp
 from l4d2web.routes.auth_routes import reset_login_rate_limits
+from l4d2web.routes.files_routes import bp as files_bp
 from l4d2web.routes.job_routes import bp as job_bp
 from l4d2web.routes.log_routes import bp as log_bp
 from l4d2web.routes.overlay_routes import bp as overlay_bp
@@ -70,6 +71,7 @@ def create_app(test_config: dict[str, object] | None = None) -> Flask:
     app.before_request(load_current_user)
     app.register_blueprint(auth_bp)
     app.register_blueprint(overlay_bp)
+    app.register_blueprint(files_bp)
     app.register_blueprint(workshop_bp)
     app.register_blueprint(blueprint_bp)
     app.register_blueprint(server_bp)

l4d2web/routes/files_routes.py

@@ -0,0 +1,102 @@
+"""Routes for the overlay 'Files' section.
+
+Two GETs, both gated to the overlay's owner or any admin (mirrors the
+overlay detail page rule):
+
+- `GET /overlays/<id>/files?path=<rel>` — HTML fragment listing one
+  directory level. Used both for the initial server-rendered root and
+  for HTMX swaps when a folder expands.
+- `GET /overlays/<id>/files/download?path=<rel>` — streams a single file.
+  Symlinks resolving anywhere under `LEFT4ME_ROOT` are allowed (so
+  workshop addons stream from the shared cache); anything escaping it
+  is refused.
+"""
+from __future__ import annotations
+
+import os
+
+from flask import Blueprint, Response, render_template, request, send_file
+from sqlalchemy import select
+
+from l4d2web.auth import current_user, require_login
+from l4d2web.db import session_scope
+from l4d2web.models import Overlay
+from l4d2web.services.overlay_files import (
+    list_directory,
+    safe_resolve_for_download,
+    safe_resolve_for_listing,
+)
+
+
+bp = Blueprint("files", __name__)
+
+
+def _load_overlay_for_user(overlay_id: int, user) -> Overlay | Response:
+    with session_scope() as db:
+        overlay = db.scalar(select(Overlay).where(Overlay.id == overlay_id))
+        if overlay is None:
+            return Response(status=404)
+        if not user.admin and overlay.user_id is not None and overlay.user_id != user.id:
+            return Response(status=403)
+        # Detach by expunging — caller only reads scalar columns we already
+        # populated, so lazy loads aren't a concern.
+        db.expunge(overlay)
+        return overlay
+
+
+@bp.get("/overlays/<int:overlay_id>/files")
+@require_login
+def overlay_files_fragment(overlay_id: int):
+    user = current_user()
+    assert user is not None
+    sub_path = request.args.get("path", "")
+
+    result = _load_overlay_for_user(overlay_id, user)
+    if isinstance(result, Response):
+        return result
+    overlay = result
+
+    try:
+        target = safe_resolve_for_listing(overlay.path, sub_path)
+        overlay_root = safe_resolve_for_listing(overlay.path, "")
+    except ValueError:
+        return Response("invalid path", status=400)
+
+    if not target.is_dir():
+        return Response(status=404)
+
+    entries, truncated_count = list_directory(target, overlay_root)
+    return render_template(
+        "_overlay_file_tree.html",
+        overlay=overlay,
+        entries=entries,
+        truncated=truncated_count > 0,
+        truncated_count=truncated_count,
+    )
+
+
+@bp.get("/overlays/<int:overlay_id>/files/download")
+@require_login
+def overlay_files_download(overlay_id: int):
+    user = current_user()
+    assert user is not None
+    sub_path = request.args.get("path", "")
+
+    result = _load_overlay_for_user(overlay_id, user)
+    if isinstance(result, Response):
+        return result
+    overlay = result
+
+    try:
+        real = safe_resolve_for_download(overlay.path, sub_path)
+    except ValueError:
+        return Response("invalid path", status=400)
+
+    if not real.exists():
+        return Response(status=404)
+    if real.is_dir():
+        return Response("not a file", status=400)
+
+    return send_file(
+        str(real), as_attachment=True, download_name=os.path.basename(real)
+    )

l4d2web/routes/page_routes.py

@@ -15,6 +15,10 @@ from l4d2web.models import (
     User,
     WorkshopItem,
 )
+from l4d2web.services.overlay_files import (
+    list_directory,
+    safe_resolve_for_listing,
+)
 
 
 bp = Blueprint("pages", __name__)
@@ -219,15 +223,38 @@ def overlay_detail(overlay_id: int):
             .order_by(Job.created_at.desc())
             .limit(1)
         )
+
+    file_tree_root_entries, file_tree_truncated_count = _root_file_tree(overlay)
+
     return render_template(
         "overlay_detail.html",
         overlay=overlay,
         using_blueprints=using_blueprints,
         workshop_items=workshop_items,
         latest_build_job=latest_build_job,
+        file_tree_root_entries=file_tree_root_entries,
+        file_tree_truncated=file_tree_truncated_count > 0
+        if file_tree_root_entries is not None
+        else False,
+        file_tree_truncated_count=file_tree_truncated_count,
     )
 
 
+def _root_file_tree(overlay: Overlay) -> tuple[list[dict] | None, int]:
+    """Return (entries, truncated_count) for the overlay's runtime directory,
+    or (None, 0) if the directory doesn't exist or the path is unresolvable
+    (e.g. legacy absolute `overlay.path` values that pre-date the current
+    `path == str(id)` convention)."""
+    try:
+        overlay_root = safe_resolve_for_listing(overlay.path, "")
+    except ValueError:
+        return None, 0
+    if not overlay_root.is_dir():
+        return None, 0
+    entries, truncated_count = list_directory(overlay_root, overlay_root)
+    return entries, truncated_count
+
+
 @bp.get("/blueprints")
 @require_login
 def blueprints_page() -> str:
@@ -270,12 +297,15 @@ def blueprint_page(blueprint_id: int):
         ).all()
 
     overlay_positions = {overlay_id: position + 1 for overlay_id, position in position_rows}
+    selected_ids = {overlay.id for overlay in selected_overlays}
+    available_overlays = [overlay for overlay in all_overlays if overlay.id not in selected_ids]
     return render_template(
         "blueprint_detail.html",
         blueprint=blueprint,
         selected_overlays=selected_overlays,
+        available_overlays=available_overlays,
         all_overlays=all_overlays,
-        selected_overlay_ids={overlay.id for overlay in selected_overlays},
+        selected_overlay_ids=selected_ids,
         overlay_positions=overlay_positions,
         arguments=json.loads(blueprint.arguments),
         config_lines=json.loads(blueprint.config),

l4d2web/services/overlay_files.py

@@ -0,0 +1,131 @@
+"""Filesystem helpers backing the overlay 'Files' section.
+
+`safe_resolve_for_listing` and `safe_resolve_for_download` translate a
+user-supplied sub-path within an overlay into a real filesystem path,
+rejecting anything that would escape the overlay root (listing) or
+`LEFT4ME_ROOT` (download). `list_directory` walks one level and shapes
+the rows the templates render.
+"""
+from __future__ import annotations
+
+import os
+from pathlib import Path
+
+from l4d2host.paths import get_left4me_root, overlay_path as resolve_overlay_root
+
+from l4d2web.services.security import validate_overlay_ref
+
+
+def _is_under(child: Path, parent: Path) -> bool:
+    return child == parent or parent in child.parents
+
+
+def safe_resolve_for_listing(overlay_path_value: str, sub_path: str) -> Path:
+    """Resolve `overlay_root / sub_path` and refuse anything that escapes the
+    overlay root after symlink resolution. Used to render directory listings."""
+    overlay_root = resolve_overlay_root(overlay_path_value).resolve()
+    if sub_path == "":
+        return overlay_root
+    validate_overlay_ref(sub_path)
+    candidate = (overlay_root / sub_path).resolve(strict=False)
+    if not _is_under(candidate, overlay_root):
+        raise ValueError("path escapes overlay root")
+    return candidate
+
+
+DEFAULT_MAX_ENTRIES = 500
+
+
+def list_directory(
+    target: Path,
+    overlay_root: Path,
+    *,
+    max_entries: int | None = None,
+) -> tuple[list[dict], int]:
+    """List one directory level. Returns (entries, truncated_count) where
+    truncated_count is the number of entries elided after the cap.
+    Directories come first, then files; both case-insensitive alphabetical.
+
+    `max_entries` falls back to module-level `DEFAULT_MAX_ENTRIES` at call
+    time so tests can monkeypatch the cap without re-instantiating routes."""
+    cap = max_entries if max_entries is not None else DEFAULT_MAX_ENTRIES
+
+    rows: list[dict] = []
+    with os.scandir(target) as it:
+        for entry in it:
+            rows.append(_entry_dict(entry, overlay_root))
+
+    rows.sort(key=lambda r: (0 if r["kind"] == "dir" else 1, r["name"].casefold()))
+
+    if len(rows) > cap:
+        truncated = len(rows) - cap
+        rows = rows[:cap]
+    else:
+        truncated = 0
+    return rows, truncated
+
+
+def _entry_dict(entry: "os.DirEntry[str]", overlay_root: Path) -> dict:
+    is_symlink = entry.is_symlink()
+    broken = False
+    try:
+        is_dir = entry.is_dir(follow_symlinks=True)
+    except OSError:
+        is_dir = False
+        broken = True
+
+    if is_dir:
+        kind = "dir"
+        size: int | None = None
+    else:
+        kind = "file"
+        if broken:
+            size = None
+        else:
+            try:
+                size = entry.stat(follow_symlinks=True).st_size
+            except OSError:
+                size = None
+                broken = True
+
+    rel_str = "/".join(Path(entry.path).relative_to(overlay_root).parts)
+
+    return {
+        "name": entry.name,
+        "rel": rel_str,
+        "kind": kind,
+        "is_symlink": is_symlink,
+        "broken": broken,
+        "size": size,
+        "size_human": _format_size(size) if size is not None else "",
+    }
+
+
+def _format_size(num: int) -> str:
+    if num < 1024:
+        return f"{num} B"
+    units = ["KB", "MB", "GB", "TB"]
+    value = float(num)
+    unit = "B"
+    for u in units:
+        value /= 1024.0
+        unit = u
+        if value < 1024:
+            break
+    return f"{value:.1f} {unit}"
+
+
+def safe_resolve_for_download(overlay_path_value: str, sub_path: str) -> Path:
+    """Resolve a file path the user wants to download. Allows symlink targets
+    anywhere inside `LEFT4ME_ROOT` (so workshop addons stream from the shared
+    cache) but blocks any escape outside it."""
+    if sub_path == "":
+        raise ValueError("download requires a file path")
+    validate_overlay_ref(sub_path)
+    overlay_root = resolve_overlay_root(overlay_path_value).resolve()
+    candidate = overlay_root / sub_path
+    real = Path(os.path.realpath(candidate))
+    left4me_root = get_left4me_root().resolve()
+    if not _is_under(real, left4me_root):
+        raise ValueError("path escapes LEFT4ME_ROOT")
+    return real

l4d2web/static/css/components.css

@@ -50,6 +50,14 @@ textarea {
   padding: var(--space-s) var(--space-m);
 }
 
+textarea {
+  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
+  font-size: 0.875rem;
+  line-height: 1.5;
+  resize: vertical;
+  tab-size: 4;
+}
+
 input:focus,
 select:focus,
 textarea:focus,
@@ -188,3 +196,160 @@ dialog.modal::backdrop {
   display: grid;
   gap: var(--space-s);
 }
+
+.file-tree {
+  list-style: none;
+  padding: 0;
+  margin: 0;
+  display: grid;
+  gap: var(--space-xs);
+  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
+  font-size: 0.875rem;
+}
+
+.file-tree .file-tree {
+  padding-left: var(--space-l);
+  margin-top: var(--space-xs);
+}
+
+.file-tree-row {
+  display: flex;
+  /* Row-gap 0 so the wrapped .file-tree-children div sits directly under
+     the toggle button; vertical spacing is owned exclusively by the
+     outer grid's gap and the nested ul's margin-top. */
+  gap: 0 var(--space-s);
+  align-items: baseline;
+  flex-wrap: wrap;
+}
+
+.file-tree-toggle {
+  background: none;
+  border: 0;
+  color: inherit;
+  cursor: pointer;
+  padding: 0;
+  font: inherit;
+  text-align: left;
+}
+
+.file-tree-toggle .chevron {
+  display: inline-block;
+  width: 1ch;
+  text-align: center;
+  transition: transform 120ms ease;
+  margin-right: var(--space-xs);
+}
+
+.file-tree-row-file {
+  padding-left: calc(1ch + var(--space-xs));
+}
+
+.file-tree-toggle[aria-expanded="true"] .chevron {
+  transform: rotate(90deg);
+}
+
+.file-tree-children {
+  flex-basis: 100%;
+}
+
+.file-tree-children[hidden] {
+  display: none;
+}
+
+.file-tree-badge {
+  font-size: 0.75rem;
+  padding: 0 0.4em;
+  border-radius: var(--radius-s);
+  background: var(--color-surface-muted);
+  color: var(--color-muted);
+  border: var(--line);
+}
+
+.file-tree-badge-warn {
+  background: transparent;
+  color: var(--color-danger);
+  border-color: var(--color-danger);
+}
+
+.file-tree-row-truncated {
+  font-style: italic;
+}
+
+.overlay-picker {
+  display: grid;
+  gap: var(--space-m);
+}
+
+.overlay-picker-list {
+  list-style: none;
+  padding: 0;
+  margin: 0;
+  display: flex;
+  flex-direction: column;
+  gap: var(--space-xs);
+  min-height: 3rem;
+}
+
+.overlay-picker-row {
+  display: flex;
+  align-items: center;
+  gap: var(--space-s);
+  padding: var(--space-s) var(--space-m);
+  background: var(--color-surface-muted);
+  border: var(--line);
+  border-radius: var(--radius-s);
+  cursor: grab;
+  user-select: none;
+}
+
+.overlay-picker-row:active {
+  cursor: grabbing;
+}
+
+.overlay-picker-row.is-dragging {
+  opacity: 0.4;
+}
+
+.overlay-picker-row.drop-before {
+  box-shadow: 0 2px 0 0 var(--color-focus) inset;
+}
+
+.overlay-picker-row.drop-after {
+  box-shadow: 0 -2px 0 0 var(--color-focus) inset;
+}
+
+.overlay-picker-handle {
+  color: var(--color-muted);
+  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
+  letter-spacing: -0.1em;
+}
+
+.overlay-picker-name {
+  flex: 1;
+}
+
+.overlay-picker-remove {
+  background: none;
+  color: var(--color-muted);
+  padding: 0 var(--space-s);
+  font-size: 1.1rem;
+  line-height: 1;
+}
+
+.overlay-picker-remove:hover {
+  color: var(--color-danger);
+}
+
+.overlay-picker-empty {
+  margin: 0;
+}
+
+.overlay-picker-add {
+  display: flex;
+  align-items: center;
+  gap: var(--space-s);
+}
+
+.overlay-picker-add select {
+  flex: 1;
+}

l4d2web/static/js/blueprint-overlay-picker.js

@@ -0,0 +1,159 @@
+(() => {
+  const root = document.querySelector("[data-overlay-list]");
+  if (!root) return;
+  const select = document.querySelector("[data-overlay-add]");
+  const empty = document.querySelector("[data-overlay-empty]");
+
+  let dragRow = null;
+
+  const clearDropMarkers = () => {
+    root
+      .querySelectorAll(".drop-before, .drop-after")
+      .forEach((el) => el.classList.remove("drop-before", "drop-after"));
+  };
+
+  const refreshEmpty = () => {
+    if (!empty) return;
+    empty.hidden = root.children.length > 0;
+  };
+
+  const buildHiddenInput = (overlayId) => {
+    const input = document.createElement("input");
+    input.type = "hidden";
+    input.name = "overlay_ids";
+    input.value = overlayId;
+    return input;
+  };
+
+  const buildRow = (overlayId, overlayName) => {
+    const li = document.createElement("li");
+    li.className = "overlay-picker-row";
+    li.draggable = true;
+    li.dataset.overlayId = overlayId;
+    li.dataset.overlayName = overlayName;
+
+    const handle = document.createElement("span");
+    handle.className = "overlay-picker-handle";
+    handle.setAttribute("aria-hidden", "true");
+    handle.textContent = "⋮⋮";
+
+    const name = document.createElement("span");
+    name.className = "overlay-picker-name";
+    name.textContent = overlayName;
+
+    const remove = document.createElement("button");
+    remove.type = "button";
+    remove.className = "overlay-picker-remove";
+    remove.dataset.action = "remove";
+    remove.setAttribute("aria-label", `Remove ${overlayName}`);
+    remove.textContent = "×";
+
+    li.append(handle, name, remove, buildHiddenInput(overlayId));
+    return li;
+  };
+
+  const insertOptionSorted = (overlayId, overlayName) => {
+    if (!select) return;
+    const option = document.createElement("option");
+    option.value = overlayId;
+    option.dataset.overlayName = overlayName;
+    option.textContent = overlayName;
+
+    const lower = overlayName.toLowerCase();
+    const existing = Array.from(select.querySelectorAll("option[value]:not([value=''])"));
+    const next = existing.find(
+      (opt) => (opt.dataset.overlayName || opt.textContent).toLowerCase() > lower,
+    );
+    if (next) {
+      select.insertBefore(option, next);
+    } else {
+      select.appendChild(option);
+    }
+  };
+
+  root.addEventListener("dragstart", (event) => {
+    const row = event.target.closest(".overlay-picker-row");
+    if (!row) return;
+    dragRow = row;
+    row.classList.add("is-dragging");
+    if (event.dataTransfer) {
+      event.dataTransfer.effectAllowed = "move";
+      event.dataTransfer.setData("text/plain", row.dataset.overlayId || "");
+    }
+  });
+
+  root.addEventListener("dragend", () => {
+    if (dragRow) {
+      dragRow.classList.remove("is-dragging");
+    }
+    clearDropMarkers();
+    dragRow = null;
+  });
+
+  root.addEventListener("dragover", (event) => {
+    if (!dragRow) return;
+    const row = event.target.closest(".overlay-picker-row");
+    event.preventDefault();
+    if (event.dataTransfer) {
+      event.dataTransfer.dropEffect = "move";
+    }
+    clearDropMarkers();
+    if (row && row !== dragRow) {
+      const rect = row.getBoundingClientRect();
+      const before = event.clientY < rect.top + rect.height / 2;
+      row.classList.add(before ? "drop-before" : "drop-after");
+    }
+  });
+
+  root.addEventListener("dragleave", (event) => {
+    const row = event.target.closest(".overlay-picker-row");
+    if (row) {
+      row.classList.remove("drop-before", "drop-after");
+    }
+  });
+
+  root.addEventListener("drop", (event) => {
+    if (!dragRow) return;
+    event.preventDefault();
+    const row = event.target.closest(".overlay-picker-row");
+    if (row && row !== dragRow) {
+      const before = row.classList.contains("drop-before");
+      row.classList.remove("drop-before", "drop-after");
+      if (before) {
+        root.insertBefore(dragRow, row);
+      } else {
+        root.insertBefore(dragRow, row.nextSibling);
+      }
+    } else if (!row) {
+      root.appendChild(dragRow);
+    }
+    clearDropMarkers();
+  });
+
+  root.addEventListener("click", (event) => {
+    const trigger = event.target.closest("[data-action='remove']");
+    if (!trigger) return;
+    const row = trigger.closest(".overlay-picker-row");
+    if (!row) return;
+    const overlayId = row.dataset.overlayId;
+    const overlayName = row.dataset.overlayName || "";
+    row.remove();
+    if (overlayId) insertOptionSorted(overlayId, overlayName);
+    refreshEmpty();
+  });
+
+  if (select) {
+    select.addEventListener("change", () => {
+      const value = select.value;
+      if (!value) return;
+      const option = select.querySelector(`option[value="${CSS.escape(value)}"]`);
+      const overlayName = option ? option.dataset.overlayName || option.textContent : "";
+      root.appendChild(buildRow(value, overlayName));
+      if (option) option.remove();
+      select.value = "";
+      refreshEmpty();
+    });
+  }
+
+  refreshEmpty();
+})();

l4d2web/static/js/file-tree.js

@@ -0,0 +1,40 @@
+// Lazy-loaded collapsible file tree on overlay detail pages.
+//
+// One delegated click handler on document. Each `.file-tree-toggle` button
+// carries `data-files-url`. First expand fires a fetch and innerHTMLs the
+// returned partial into the next `.file-tree-children`; subsequent clicks
+// just toggle visibility — no re-fetch.
+(function () {
+  document.addEventListener("click", function (event) {
+    const button = event.target.closest(".file-tree-toggle");
+    if (!button) return;
+
+    const children = button.nextElementSibling;
+    if (!children || !children.classList.contains("file-tree-children")) return;
+
+    const wasExpanded = button.getAttribute("aria-expanded") === "true";
+    button.setAttribute("aria-expanded", wasExpanded ? "false" : "true");
+    children.hidden = wasExpanded;
+
+    if (wasExpanded) return; // collapsing — nothing to fetch
+    if (button.dataset.loaded === "1") return; // already populated
+    const url = button.dataset.filesUrl;
+    if (!url) return;
+
+    button.dataset.loaded = "1"; // optimistic — prevents duplicate fetches on rapid clicks
+    fetch(url, { headers: { Accept: "text/html" }, credentials: "same-origin" })
+      .then(function (response) {
+        if (!response.ok) throw new Error("HTTP " + response.status);
+        return response.text();
+      })
+      .then(function (html) {
+        children.innerHTML = html;
+      })
+      .catch(function (err) {
+        delete button.dataset.loaded; // allow retry
+        children.innerHTML =
+          '<p class="muted">Failed to load directory contents.</p>';
+        console.error("file-tree:", err);
+      });
+  });
+})();

l4d2web/templates/_overlay_file_node.html

@@ -0,0 +1,22 @@
+{% if entry.kind == 'dir' %}
+<li class="file-tree-row file-tree-row-dir">
+  <button type="button"
+          class="file-tree-toggle"
+          aria-expanded="false"
+          data-files-url="/overlays/{{ overlay.id }}/files?path={{ entry.rel|urlencode }}">
+    <span class="chevron" aria-hidden="true">›</span>{{ entry.name }}/
+  </button>
+  <div class="file-tree-children" hidden></div>
+</li>
+{% else %}
+<li class="file-tree-row file-tree-row-file">
+  {% if entry.broken %}
+    <span>{{ entry.name }}</span>
+    <span class="file-tree-badge file-tree-badge-warn">broken link</span>
+  {% else %}
+    <a href="/overlays/{{ overlay.id }}/files/download?path={{ entry.rel|urlencode }}">{{ entry.name }}</a>
+    {% if entry.is_symlink %}<span class="file-tree-badge">link</span>{% endif %}
+    <span class="muted">{{ entry.size_human }}</span>
+  {% endif %}
+</li>
+{% endif %}

l4d2web/templates/_overlay_file_tree.html

@@ -0,0 +1,8 @@
+<ul class="file-tree" role="group">
+  {% for entry in entries %}{% include "_overlay_file_node.html" %}{% endfor %}
+  {% if truncated %}
+  <li class="file-tree-row file-tree-row-truncated muted">
+    + {{ truncated_count }} more (truncated)
+  </li>
+  {% endif %}
+</ul>

l4d2web/templates/base.html

@@ -40,5 +40,6 @@
     <script src="{{ url_for('static', filename='js/csrf.js') }}"></script>
     <script src="{{ url_for('static', filename='js/sse.js') }}"></script>
     <script src="{{ url_for('static', filename='js/modal.js') }}"></script>
+    <script src="{{ url_for('static', filename='js/file-tree.js') }}"></script>
   </body>
 </html>

l4d2web/templates/blueprint_detail.html

@@ -12,22 +12,30 @@
     <input type="hidden" name="csrf_token" value="{{ session.get('csrf_token', '') }}">
     <label>Name <input name="name" value="{{ blueprint.name }}" required></label>
     <p class="muted">Overlay order matters: the first overlay has highest precedence.</p>
-    <table class="table">
+    <div class="overlay-picker">
-      <thead><tr><th>Use</th><th>Order</th><th>Overlay</th></tr></thead>
+      <ol class="overlay-picker-list" data-overlay-list>
-      <tbody>
+        {% for overlay in selected_overlays %}
-        {% for overlay in all_overlays %}
+        <li class="overlay-picker-row" draggable="true" data-overlay-id="{{ overlay.id }}" data-overlay-name="{{ overlay.name }}">
-        <tr>
+          <span class="overlay-picker-handle" aria-hidden="true">⋮⋮</span>
-          <td><input type="checkbox" name="overlay_ids" value="{{ overlay.id }}" {% if overlay.id in selected_overlay_ids %}checked{% endif %}></td>
+          <span class="overlay-picker-name">{{ overlay.name }}</span>
-          <td><input class="position-input" name="overlay_position_{{ overlay.id }}" value="{{ overlay_positions.get(overlay.id, '') }}" inputmode="numeric"></td>
+          <button type="button" class="overlay-picker-remove" data-action="remove" aria-label="Remove {{ overlay.name }}">×</button>
-          <td>{{ overlay.name }}</td>
+          <input type="hidden" name="overlay_ids" value="{{ overlay.id }}">
-        </tr>
+        </li>
-        {% else %}
-        <tr><td colspan="3" class="muted">No overlays available.</td></tr>
         {% endfor %}
-      </tbody>
+      </ol>
-    </table>
+      <p class="overlay-picker-empty muted" data-overlay-empty {% if selected_overlays %}hidden{% endif %}>No overlays selected. Pick one below to add.</p>
-    <label>Arguments <textarea name="arguments">{{ arguments | join('\n') }}</textarea></label>
+      <label class="overlay-picker-add">
-    <label>Config <textarea name="config">{{ config_lines | join('\n') }}</textarea></label>
+        <span>Add overlay</span>
+        <select data-overlay-add>
+          <option value="">Pick a name…</option>
+          {% for overlay in available_overlays %}
+          <option value="{{ overlay.id }}" data-overlay-name="{{ overlay.name }}">{{ overlay.name }}</option>
+          {% endfor %}
+        </select>
+      </label>
+    </div>
+    <label>Arguments <textarea name="arguments" rows="8" spellcheck="false">{{ arguments | join('\n') }}</textarea></label>
+    <label>Config <textarea name="config" rows="8" spellcheck="false">{{ config_lines | join('\n') }}</textarea></label>
     <button type="submit">Save blueprint</button>
   </form>
 </section>
@@ -48,4 +56,5 @@
     </form>
   </div>
 </dialog>
+<script src="{{ url_for('static', filename='js/blueprint-overlay-picker.js') }}" defer></script>
 {% endblock %}

l4d2web/templates/blueprints.html

@@ -34,8 +34,8 @@
     <div class="modal-body">
       <input type="hidden" name="csrf_token" value="{{ session.get('csrf_token', '') }}">
       <label>Name <input name="name" required></label>
-      <label>Arguments <textarea name="arguments"></textarea></label>
+      <label>Arguments <textarea name="arguments" rows="8" spellcheck="false"></textarea></label>
-      <label>Config <textarea name="config"></textarea></label>
+      <label>Config <textarea name="config" rows="8" spellcheck="false"></textarea></label>
     </div>
     <div class="modal-footer">
       <button type="button" class="button-secondary" data-modal-close>Cancel</button>

l4d2web/templates/overlay_detail.html

@@ -129,6 +129,18 @@
 </section>
 {% endif %}
 
+<section class="panel">
+  <h2>Files</h2>
+  {% if not file_tree_root_entries %}
+    <p class="muted">No files yet — build this overlay to populate it.</p>
+  {% else %}
+    {% set entries = file_tree_root_entries %}
+    {% set truncated = file_tree_truncated %}
+    {% set truncated_count = file_tree_truncated_count %}
+    {% include "_overlay_file_tree.html" %}
+  {% endif %}
+</section>
+
 <section class="panel">
   <h2>Used by</h2>
   {% if using_blueprints %}

l4d2web/tests/test_blueprints.py

@@ -1,6 +1,7 @@
 import json
 
 import pytest
+from sqlalchemy import select
 
 from l4d2web.app import create_app
 from l4d2web.auth import hash_password
@@ -247,3 +248,48 @@ def test_form_update_preserves_ordered_overlays_and_multiline_fields(user_client
 
     assert update.status_code == 302
     assert update.headers["Location"] == "/blueprints/1"
+
+
+def test_blueprint_detail_renders_picker_list_and_select(user_client) -> None:
+    with session_scope() as session:
+        session.add(Overlay(name="o3", path="/opt/l4d2/overlays/o3"))
+        user = session.scalar(select(User).where(User.username == "alice"))
+        blueprint = Blueprint(user_id=user.id, name="bp", arguments="[]", config="[]")
+        session.add(blueprint)
+        session.flush()
+        session.add(BlueprintOverlay(blueprint_id=blueprint.id, overlay_id=1, position=0))
+        blueprint_id = blueprint.id
+
+    response = user_client.get(f"/blueprints/{blueprint_id}")
+    assert response.status_code == 200
+    body = response.get_data(as_text=True)
+    assert "data-overlay-list" in body
+    assert "data-overlay-add" in body
+    assert body.count('data-overlay-id="1"') == 1
+    assert 'data-overlay-id="2"' not in body
+    assert '<option value="2"' in body
+    assert '<option value="3"' in body
+    assert '<option value="1"' not in body
+
+
+def test_blueprint_detail_picker_emits_hidden_overlay_ids_in_order(user_client) -> None:
+    with session_scope() as session:
+        user = session.scalar(select(User).where(User.username == "alice"))
+        blueprint = Blueprint(user_id=user.id, name="bp", arguments="[]", config="[]")
+        session.add(blueprint)
+        session.flush()
+        session.add_all(
+            [
+                BlueprintOverlay(blueprint_id=blueprint.id, overlay_id=2, position=0),
+                BlueprintOverlay(blueprint_id=blueprint.id, overlay_id=1, position=1),
+            ]
+        )
+        blueprint_id = blueprint.id
+
+    response = user_client.get(f"/blueprints/{blueprint_id}")
+    assert response.status_code == 200
+    body = response.get_data(as_text=True)
+    first = body.find('name="overlay_ids" value="2"')
+    second = body.find('name="overlay_ids" value="1"')
+    assert first != -1 and second != -1
+    assert first < second

l4d2web/tests/test_overlay_files.py

@@ -0,0 +1,267 @@
+"""Pure-helper tests for l4d2web.services.overlay_files.
+
+Covers path safety (listing vs download), directory listing semantics,
+symlink handling, and the children cap. Flask-free; only exercises the
+filesystem.
+"""
+from __future__ import annotations
+
+import os
+from pathlib import Path
+
+import pytest
+
+
+@pytest.fixture
+def overlay_root(monkeypatch, tmp_path: Path) -> Path:
+    """LEFT4ME_ROOT/overlays/7/ ready for tests to populate. Returns the overlay root."""
+    monkeypatch.setenv("LEFT4ME_ROOT", str(tmp_path))
+    root = tmp_path / "overlays" / "7"
+    root.mkdir(parents=True)
+    return root
+
+
+def test_safe_resolve_for_listing_returns_overlay_root_when_sub_path_empty(
+    overlay_root: Path,
+) -> None:
+    from l4d2web.services.overlay_files import safe_resolve_for_listing
+
+    resolved = safe_resolve_for_listing("7", "")
+
+    assert resolved == overlay_root.resolve()
+
+
+def test_safe_resolve_for_listing_joins_sub_path_under_overlay_root(
+    overlay_root: Path,
+) -> None:
+    from l4d2web.services.overlay_files import safe_resolve_for_listing
+
+    (overlay_root / "left4dead2" / "addons").mkdir(parents=True)
+
+    resolved = safe_resolve_for_listing("7", "left4dead2/addons")
+
+    assert resolved == (overlay_root / "left4dead2" / "addons").resolve()
+
+
+def test_safe_resolve_for_listing_rejects_dotdot(overlay_root: Path) -> None:
+    from l4d2web.services.overlay_files import safe_resolve_for_listing
+
+    with pytest.raises(ValueError):
+        safe_resolve_for_listing("7", "../../etc")
+
+
+def test_safe_resolve_for_listing_rejects_absolute_path(overlay_root: Path) -> None:
+    from l4d2web.services.overlay_files import safe_resolve_for_listing
+
+    with pytest.raises(ValueError):
+        safe_resolve_for_listing("7", "/etc/passwd")
+
+
+def test_safe_resolve_for_listing_rejects_empty_component(overlay_root: Path) -> None:
+    from l4d2web.services.overlay_files import safe_resolve_for_listing
+
+    with pytest.raises(ValueError):
+        safe_resolve_for_listing("7", "foo//bar")
+
+
+def test_safe_resolve_for_listing_rejects_symlink_escaping_overlay_root(
+    overlay_root: Path, tmp_path: Path
+) -> None:
+    """A directory inside the overlay that is itself a symlink to somewhere
+    outside the overlay must be refused — even if the target sits within
+    LEFT4ME_ROOT/workshop_cache."""
+    from l4d2web.services.overlay_files import safe_resolve_for_listing
+
+    cache = tmp_path / "workshop_cache" / "shared"
+    cache.mkdir(parents=True)
+    (overlay_root / "shared").symlink_to(cache)
+
+    with pytest.raises(ValueError):
+        safe_resolve_for_listing("7", "shared")
+
+
+def test_safe_resolve_for_download_rejects_empty_path(overlay_root: Path) -> None:
+    from l4d2web.services.overlay_files import safe_resolve_for_download
+
+    with pytest.raises(ValueError):
+        safe_resolve_for_download("7", "")
+
+
+def test_safe_resolve_for_download_returns_real_path_for_regular_file(
+    overlay_root: Path,
+) -> None:
+    from l4d2web.services.overlay_files import safe_resolve_for_download
+
+    target = overlay_root / "cfg" / "server.cfg"
+    target.parent.mkdir()
+    target.write_text("hostname test\n")
+
+    resolved = safe_resolve_for_download("7", "cfg/server.cfg")
+
+    assert resolved == target.resolve()
+
+
+def test_safe_resolve_for_download_follows_symlink_into_workshop_cache(
+    overlay_root: Path, tmp_path: Path
+) -> None:
+    """Workshop overlays populate addons/*.vpk as symlinks into
+    LEFT4ME_ROOT/workshop_cache/. Download must follow the symlink and
+    return the cache target."""
+    from l4d2web.services.overlay_files import safe_resolve_for_download
+
+    cache_file = tmp_path / "workshop_cache" / "12345.vpk"
+    cache_file.parent.mkdir(parents=True)
+    cache_file.write_bytes(b"vpk-bytes")
+
+    addons = overlay_root / "left4dead2" / "addons"
+    addons.mkdir(parents=True)
+    (addons / "deathcraft.vpk").symlink_to(cache_file)
+
+    resolved = safe_resolve_for_download("7", "left4dead2/addons/deathcraft.vpk")
+
+    assert resolved == cache_file.resolve()
+
+
+def test_safe_resolve_for_download_rejects_symlink_outside_left4me_root(
+    overlay_root: Path, tmp_path: Path
+) -> None:
+    """A malicious script overlay that plants a symlink at evil → /etc/passwd
+    must be refused."""
+    from l4d2web.services.overlay_files import safe_resolve_for_download
+
+    outside = tmp_path.parent / "outside-left4me-root.txt"
+    outside.write_text("nope")
+    (overlay_root / "evil").symlink_to(outside)
+
+    with pytest.raises(ValueError):
+        safe_resolve_for_download("7", "evil")
+
+
+def test_safe_resolve_for_download_rejects_dotdot(overlay_root: Path) -> None:
+    from l4d2web.services.overlay_files import safe_resolve_for_download
+
+    with pytest.raises(ValueError):
+        safe_resolve_for_download("7", "../../etc/passwd")
+
+
+def test_safe_resolve_for_download_rejects_absolute_path(overlay_root: Path) -> None:
+    from l4d2web.services.overlay_files import safe_resolve_for_download
+
+    with pytest.raises(ValueError):
+        safe_resolve_for_download("7", "/etc/passwd")
+
+
+def test_list_directory_returns_empty_for_empty_dir(overlay_root: Path) -> None:
+    from l4d2web.services.overlay_files import list_directory
+
+    entries, truncated = list_directory(overlay_root, overlay_root)
+
+    assert entries == []
+    assert truncated == 0
+
+
+def test_list_directory_returns_dirs_before_files_alphabetically(
+    overlay_root: Path,
+) -> None:
+    from l4d2web.services.overlay_files import list_directory
+
+    (overlay_root / "Zeta").mkdir()
+    (overlay_root / "alpha").mkdir()
+    (overlay_root / "Beta-file.txt").write_text("b")
+    (overlay_root / "alpha-file.txt").write_text("a")
+
+    entries, _ = list_directory(overlay_root, overlay_root)
+    names = [e["name"] for e in entries]
+
+    # Dirs first (case-insensitive alpha), then files (case-insensitive alpha).
+    assert names == ["alpha", "Zeta", "alpha-file.txt", "Beta-file.txt"]
+
+
+def test_list_directory_marks_kind_dir_or_file(overlay_root: Path) -> None:
+    from l4d2web.services.overlay_files import list_directory
+
+    (overlay_root / "subdir").mkdir()
+    (overlay_root / "leaf.txt").write_text("hi")
+
+    entries, _ = list_directory(overlay_root, overlay_root)
+    by_name = {e["name"]: e for e in entries}
+
+    assert by_name["subdir"]["kind"] == "dir"
+    assert by_name["leaf.txt"]["kind"] == "file"
+
+
+def test_list_directory_includes_relative_path_under_overlay_root(
+    overlay_root: Path,
+) -> None:
+    from l4d2web.services.overlay_files import list_directory
+
+    addons = overlay_root / "left4dead2" / "addons"
+    addons.mkdir(parents=True)
+    (addons / "foo.vpk").write_text("v")
+
+    entries, _ = list_directory(addons, overlay_root)
+
+    assert entries[0]["rel"] == "left4dead2/addons/foo.vpk"
+
+
+def test_list_directory_marks_symlinks_with_resolved_size(
+    overlay_root: Path, tmp_path: Path
+) -> None:
+    from l4d2web.services.overlay_files import list_directory
+
+    cache_file = tmp_path / "workshop_cache" / "12345.vpk"
+    cache_file.parent.mkdir(parents=True)
+    cache_file.write_bytes(b"x" * 4096)
+
+    addons = overlay_root / "left4dead2" / "addons"
+    addons.mkdir(parents=True)
+    (addons / "deathcraft.vpk").symlink_to(cache_file)
+
+    entries, _ = list_directory(addons, overlay_root)
+    entry = entries[0]
+
+    assert entry["is_symlink"] is True
+    assert entry["broken"] is False
+    assert entry["size"] == 4096
+    assert entry["kind"] == "file"
+
+
+def test_list_directory_marks_broken_symlinks(overlay_root: Path) -> None:
+    from l4d2web.services.overlay_files import list_directory
+
+    (overlay_root / "missing.vpk").symlink_to(overlay_root / "does-not-exist.vpk")
+
+    entries, _ = list_directory(overlay_root, overlay_root)
+    entry = entries[0]
+
+    assert entry["is_symlink"] is True
+    assert entry["broken"] is True
+    assert entry["size"] is None
+    assert entry["kind"] == "file"
+
+
+def test_list_directory_truncates_at_cap(overlay_root: Path) -> None:
+    from l4d2web.services.overlay_files import list_directory
+
+    for i in range(7):
+        (overlay_root / f"f{i:02d}.txt").write_text("x")
+
+    entries, truncated = list_directory(overlay_root, overlay_root, max_entries=5)
+
+    assert len(entries) == 5
+    assert truncated == 2
+    assert [e["name"] for e in entries] == [f"f{i:02d}.txt" for i in range(5)]
+
+
+def test_list_directory_includes_size_human_for_files(overlay_root: Path) -> None:
+    from l4d2web.services.overlay_files import list_directory
+
+    (overlay_root / "tiny.txt").write_text("hello")
+    (overlay_root / "big.bin").write_bytes(b"x" * (3 * 1024 * 1024))
+
+    entries, _ = list_directory(overlay_root, overlay_root)
+    by_name = {e["name"]: e for e in entries}
+
+    # Files only — directories don't have size_human.
+    assert by_name["tiny.txt"]["size_human"] == "5 B"
+    assert by_name["big.bin"]["size_human"] == "3.0 MB"

l4d2web/tests/test_overlay_files_routes.py

@@ -0,0 +1,385 @@
+"""HTTP-level tests for the overlay 'Files' tree-fragment + download routes."""
+from __future__ import annotations
+
+import os
+from pathlib import Path
+
+import pytest
+
+from l4d2web.app import create_app
+from l4d2web.auth import hash_password
+from l4d2web.db import init_db, session_scope
+from l4d2web.models import Overlay, User
+
+
+@pytest.fixture
+def app(tmp_path, monkeypatch):
+    db_url = f"sqlite:///{tmp_path/'files-routes.db'}"
+    monkeypatch.setenv("DATABASE_URL", db_url)
+    monkeypatch.setenv("LEFT4ME_ROOT", str(tmp_path))
+    flask_app = create_app(
+        {"TESTING": True, "DATABASE_URL": db_url, "SECRET_KEY": "test"}
+    )
+    init_db()
+    return flask_app
+
+
+@pytest.fixture
+def left4me_root(tmp_path) -> Path:
+    return tmp_path
+
+
+def _client_for(app, user_id: int):
+    client = app.test_client()
+    with client.session_transaction() as sess:
+        sess["user_id"] = user_id
+        sess["csrf_token"] = "test-token"
+    return client
+
+
+def _make_user(*, username: str = "alice", admin: bool = False) -> int:
+    with session_scope() as s:
+        user = User(
+            username=username, password_digest=hash_password("x"), admin=admin
+        )
+        s.add(user)
+        s.flush()
+        return user.id
+
+
+def _make_overlay(left4me_root: Path, *, user_id: int | None, name: str) -> int:
+    """Create an Overlay row + the matching `LEFT4ME_ROOT/overlays/{id}/`
+    directory, mirroring what `overlay_creation.create_overlay_directory`
+    would do in production."""
+    with session_scope() as s:
+        overlay = Overlay(name=name, path="", type="script", user_id=user_id)
+        s.add(overlay)
+        s.flush()
+        overlay.path = str(overlay.id)
+        overlay_id = overlay.id
+    (left4me_root / "overlays" / str(overlay_id)).mkdir(parents=True)
+    return overlay_id
+
+
+def test_files_fragment_lists_root_directory(app, left4me_root: Path) -> None:
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+    overlay_dir = left4me_root / "overlays" / str(overlay_id)
+    (overlay_dir / "left4dead2").mkdir()
+    (overlay_dir / "readme.txt").write_text("hi")
+
+    client = _client_for(app, user_id)
+    response = client.get(f"/overlays/{overlay_id}/files")
+
+    assert response.status_code == 200
+    text = response.get_data(as_text=True)
+    assert "left4dead2" in text
+    assert "readme.txt" in text
+
+
+def test_files_fragment_lists_subdirectory(app, left4me_root: Path) -> None:
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+    overlay_dir = left4me_root / "overlays" / str(overlay_id)
+    addons = overlay_dir / "left4dead2" / "addons"
+    addons.mkdir(parents=True)
+    (addons / "deathcraft.vpk").write_text("vpk")
+
+    client = _client_for(app, user_id)
+    response = client.get(
+        f"/overlays/{overlay_id}/files?path=left4dead2/addons"
+    )
+
+    assert response.status_code == 200
+    text = response.get_data(as_text=True)
+    assert "deathcraft.vpk" in text
+    # Fragment, no full document.
+    assert "<html" not in text
+
+
+def test_files_fragment_returns_400_on_dotdot(app, left4me_root: Path) -> None:
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+
+    client = _client_for(app, user_id)
+    response = client.get(f"/overlays/{overlay_id}/files?path=../../etc")
+
+    assert response.status_code == 400
+
+
+def test_files_fragment_returns_400_on_absolute_path(app, left4me_root: Path) -> None:
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+
+    client = _client_for(app, user_id)
+    response = client.get(f"/overlays/{overlay_id}/files?path=/etc/passwd")
+
+    assert response.status_code == 400
+
+
+def test_files_fragment_returns_404_for_unknown_overlay(app) -> None:
+    user_id = _make_user()
+    client = _client_for(app, user_id)
+    response = client.get("/overlays/9999/files")
+
+    assert response.status_code == 404
+
+
+def test_files_fragment_returns_404_for_missing_subdir(app, left4me_root: Path) -> None:
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+
+    client = _client_for(app, user_id)
+    response = client.get(f"/overlays/{overlay_id}/files?path=ghost")
+
+    assert response.status_code == 404
+
+
+def test_files_fragment_returns_403_for_other_users_overlay(
+    app, left4me_root: Path
+) -> None:
+    owner_id = _make_user(username="owner")
+    other_id = _make_user(username="other")
+    overlay_id = _make_overlay(left4me_root, user_id=owner_id, name="private")
+
+    client = _client_for(app, other_id)
+    response = client.get(f"/overlays/{overlay_id}/files")
+
+    assert response.status_code == 403
+
+
+def test_admin_can_view_files_for_other_users_overlay(
+    app, left4me_root: Path
+) -> None:
+    owner_id = _make_user(username="owner")
+    admin_id = _make_user(username="admin", admin=True)
+    overlay_id = _make_overlay(left4me_root, user_id=owner_id, name="private")
+    overlay_dir = left4me_root / "overlays" / str(overlay_id)
+    (overlay_dir / "secret.cfg").write_text("k=v")
+
+    client = _client_for(app, admin_id)
+    response = client.get(f"/overlays/{overlay_id}/files")
+
+    assert response.status_code == 200
+    assert "secret.cfg" in response.get_data(as_text=True)
+
+
+def test_download_streams_regular_file(app, left4me_root: Path) -> None:
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+    overlay_dir = left4me_root / "overlays" / str(overlay_id)
+    cfg = overlay_dir / "cfg" / "server.cfg"
+    cfg.parent.mkdir()
+    cfg.write_bytes(b"hostname test")
+
+    client = _client_for(app, user_id)
+    response = client.get(
+        f"/overlays/{overlay_id}/files/download?path=cfg/server.cfg"
+    )
+
+    assert response.status_code == 200
+    assert response.headers["Content-Disposition"].startswith("attachment")
+    assert "filename=server.cfg" in response.headers["Content-Disposition"]
+    assert response.get_data() == b"hostname test"
+
+
+def test_download_follows_workshop_cache_symlink(
+    app, left4me_root: Path
+) -> None:
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+    overlay_dir = left4me_root / "overlays" / str(overlay_id)
+
+    cache_file = left4me_root / "workshop_cache" / "12345.vpk"
+    cache_file.parent.mkdir(parents=True)
+    cache_file.write_bytes(b"vpk-content")
+
+    addons = overlay_dir / "left4dead2" / "addons"
+    addons.mkdir(parents=True)
+    (addons / "deathcraft.vpk").symlink_to(cache_file)
+
+    client = _client_for(app, user_id)
+    response = client.get(
+        f"/overlays/{overlay_id}/files/download?path=left4dead2/addons/deathcraft.vpk"
+    )
+
+    assert response.status_code == 200
+    assert response.get_data() == b"vpk-content"
+
+
+def test_download_rejects_symlink_outside_left4me_root(
+    app, left4me_root: Path, tmp_path_factory
+) -> None:
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+    overlay_dir = left4me_root / "overlays" / str(overlay_id)
+
+    outside = tmp_path_factory.mktemp("outside") / "secret.txt"
+    outside.write_text("nope")
+    (overlay_dir / "evil").symlink_to(outside)
+
+    client = _client_for(app, user_id)
+    response = client.get(f"/overlays/{overlay_id}/files/download?path=evil")
+
+    assert response.status_code == 400
+
+
+def test_download_rejects_directory_target(app, left4me_root: Path) -> None:
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+    overlay_dir = left4me_root / "overlays" / str(overlay_id)
+    (overlay_dir / "left4dead2").mkdir()
+
+    client = _client_for(app, user_id)
+    response = client.get(
+        f"/overlays/{overlay_id}/files/download?path=left4dead2"
+    )
+
+    assert response.status_code == 400
+
+
+def test_download_returns_404_for_missing_file(app, left4me_root: Path) -> None:
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+
+    client = _client_for(app, user_id)
+    response = client.get(
+        f"/overlays/{overlay_id}/files/download?path=ghost.txt"
+    )
+
+    assert response.status_code == 404
+
+
+def test_download_returns_403_for_other_users_overlay(
+    app, left4me_root: Path
+) -> None:
+    owner_id = _make_user(username="owner")
+    other_id = _make_user(username="other")
+    overlay_id = _make_overlay(left4me_root, user_id=owner_id, name="private")
+    overlay_dir = left4me_root / "overlays" / str(overlay_id)
+    (overlay_dir / "secret.cfg").write_text("nope")
+
+    client = _client_for(app, other_id)
+    response = client.get(
+        f"/overlays/{overlay_id}/files/download?path=secret.cfg"
+    )
+
+    assert response.status_code == 403
+
+
+def test_files_fragment_truncates_at_cap(app, left4me_root: Path, monkeypatch) -> None:
+    """The cap default is 500 — exercise it via the public route by lowering
+    it for this test through the helper module."""
+    from l4d2web.services import overlay_files as overlay_files_module
+
+    monkeypatch.setattr(overlay_files_module, "DEFAULT_MAX_ENTRIES", 5)
+
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+    overlay_dir = left4me_root / "overlays" / str(overlay_id)
+    for i in range(8):
+        (overlay_dir / f"f{i}.txt").write_text("x")
+
+    client = _client_for(app, user_id)
+    response = client.get(f"/overlays/{overlay_id}/files")
+    text = response.get_data(as_text=True)
+
+    assert response.status_code == 200
+    assert "+ 3 more" in text
+
+
+def test_overlay_detail_renders_files_section_with_tree(
+    app, left4me_root: Path
+) -> None:
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+    overlay_dir = left4me_root / "overlays" / str(overlay_id)
+    (overlay_dir / "left4dead2").mkdir()
+    (overlay_dir / "readme.txt").write_text("hi")
+
+    client = _client_for(app, user_id)
+    response = client.get(f"/overlays/{overlay_id}")
+    text = response.get_data(as_text=True)
+
+    assert response.status_code == 200
+    assert "Files" in text
+    assert "left4dead2" in text
+    assert "readme.txt" in text
+
+
+def test_overlay_detail_shows_empty_state_when_overlay_dir_missing(
+    app, left4me_root: Path
+) -> None:
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+    # Wipe the directory created by _make_overlay so the on-disk dir is gone.
+    overlay_dir = left4me_root / "overlays" / str(overlay_id)
+    overlay_dir.rmdir()
+
+    client = _client_for(app, user_id)
+    response = client.get(f"/overlays/{overlay_id}")
+    text = response.get_data(as_text=True)
+
+    assert response.status_code == 200
+    assert "No files yet" in text
+
+
+def test_overlay_detail_shows_empty_state_when_overlay_dir_is_empty(
+    app, left4me_root: Path
+) -> None:
+    """A built overlay whose directory has been wiped (or seeded but never
+    built) should also fall back to the empty-state message — not render an
+    invisible empty <ul>."""
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+    # _make_overlay leaves the directory in place but empty.
+
+    client = _client_for(app, user_id)
+    response = client.get(f"/overlays/{overlay_id}")
+    text = response.get_data(as_text=True)
+
+    assert response.status_code == 200
+    assert "No files yet" in text
+
+
+def test_overlay_detail_files_section_present_for_workshop_overlays(
+    app, left4me_root: Path
+) -> None:
+    user_id = _make_user()
+    # Create a workshop overlay manually since _make_overlay defaults to script.
+    with session_scope() as s:
+        overlay = Overlay(name="ws", path="", type="workshop", user_id=user_id)
+        s.add(overlay)
+        s.flush()
+        overlay.path = str(overlay.id)
+        overlay_id = overlay.id
+    (left4me_root / "overlays" / str(overlay_id)).mkdir(parents=True)
+
+    client = _client_for(app, user_id)
+    response = client.get(f"/overlays/{overlay_id}")
+    text = response.get_data(as_text=True)
+
+    assert response.status_code == 200
+    # Section heading present even when the overlay dir is empty.
+    assert "Files" in text
+
+
+def test_files_fragment_renders_broken_symlink_without_download_link(
+    app, left4me_root: Path
+) -> None:
+    user_id = _make_user()
+    overlay_id = _make_overlay(left4me_root, user_id=user_id, name="my")
+    overlay_dir = left4me_root / "overlays" / str(overlay_id)
+    (overlay_dir / "missing.vpk").symlink_to(overlay_dir / "does-not-exist.vpk")
+
+    client = _client_for(app, user_id)
+    response = client.get(f"/overlays/{overlay_id}/files")
+    text = response.get_data(as_text=True)
+
+    assert response.status_code == 200
+    assert "missing.vpk" in text
+    assert "broken" in text
+    # No download link for broken symlinks.
+    assert (
+        f'href="/overlays/{overlay_id}/files/download?path=missing.vpk"' not in text
+    )

l4d2web/tests/test_pages.py

@@ -459,7 +459,8 @@ def test_blueprint_detail_has_ordered_overlay_form(auth_client_with_server) -> N
     assert 'name="arguments"' in text
     assert 'name="config"' in text
     assert 'name="overlay_ids"' in text
-    assert 'name="overlay_position_1"' in text
+    assert "data-overlay-list" in text
+    assert "data-overlay-add" in text
 
 
 def test_admin_jobs_page_renders_system_job(tmp_path, monkeypatch) -> None: