From 25df9f9398b4f8ef90a51e9ee0f9899c36797289 Mon Sep 17 00:00:00 2001
From: Oier Bravo Urtasun <oierbravo@gmail.com>
Date: Tue, 14 Jul 2026 18:08:46 +0200
Subject: [PATCH] feat(files): add Filestash player file share at
 files.${BASE_DOMAIN}
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

One shared login (htpasswd) for all players, writable. Config is rendered
from a template and mounted read-only, so git stays authoritative — the
admin console loads but cannot save, by design.

Filestash's OIDC/SAML middlewares are enterprise-only, so Keycloak SSO is
out; FILES_AUTH keeps htpasswd/passthrough switchable for later. Auth-off
(passthrough) is only valid once the host is off the public internet —
render-config.sh warns loudly when rendering it.

Three traps, all found by testing against the pinned image:
- the `local` backend is admin-gated: without LOCAL_BACKEND_SECRET in the
  connection params every login fails with "backend error - Not Allowed"
- the htpasswd plugin only accepts $2a$ bcrypt, so a $2y$ hash from
  `htpasswd -B` fails every login silently — use `openssl passwd -6`.
  render-config.sh rejects the wrong format rather than shipping it
- APPLICATION_URL/ADMIN_PASSWORD env make filestash rewrite config.json at
  boot, which fails on the :ro mount — both live in the rendered config

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 .env.example                   |  48 ++++++++-
 .gitignore                     |   3 +
 CLAUDE.md                      |  12 +++
 caddy/conf.d/60-files.caddy    |  10 ++
 docker-compose.yml             |  34 +++++++
 filestash/config.json.tmpl     |  30 ++++++
 nginx/ulicraft-caddy.conf.tmpl |  44 +++++++-
 plan/19-routes.md              |  24 +++++
 plan/20-files.md               | 180 +++++++++++++++++++++++++++++++++
 tooling/render-config.sh       |  54 ++++++++++
 10 files changed, 437 insertions(+), 2 deletions(-)
 create mode 100644 caddy/conf.d/60-files.caddy
 create mode 100644 filestash/config.json.tmpl
 create mode 100644 plan/20-files.md

diff --git a/.env.example b/.env.example
index bb91e64..ffec8c0 100644
--- a/.env.example
+++ b/.env.example
@@ -49,6 +49,52 @@ CADDY_HTTP_BIND=127.0.0.1
 # static site — it lives in ANOTHER repo. Bind-mounted read-only into caddy.
 DISTRIBUTION_WEB_ROOT=/home/oier/projects/mc-mods/ulicraft-group/ulicraft-distribution/dist
 
+# ── files.${BASE_DOMAIN} — Filestash player file share ────────────────
+# Screenshots / schematics / maps. ONE shared login for all players, writable.
+# Full design + gotchas: plan/20-files.md.
+
+# Host path holding the shared files. Keep it OUTSIDE the repo — guest-writable
+# data must not live in a git tree we `git pull` into.
+FILES_DATA_DIR=/srv/ulicraft-files
+
+# Literal mount flag for FILES_DATA_DIR: rw | ro. `ro` makes the share
+# read-only at the KERNEL, regardless of what the Filestash UI thinks. It is a
+# mount flag rather than a boolean because compose has no conditionals — the
+# value is substituted straight into the volume string.
+FILES_MOUNT_MODE=rw
+
+# Auth middleware (rendered into config.json by render-config.sh):
+#   htpasswd    one shared user/pass — the only internet-safe value
+#   passthrough NO LOGIN. Anyone reaching the vhost is in.
+#   none        alias of passthrough
+# passthrough/none on a WRITABLE, internet-reachable share is an open upload
+# relay (malware/phishing hosted on your domain, under your cert, with your
+# bandwidth — and a domain blocklisting would take auth. and the apex down
+# with it). Only set it once this host is unreachable from the internet.
+FILES_AUTH=htpasswd
+
+# The shared player credential (FILES_AUTH=htpasswd).
+#   FILES_PASSWORD_HASH:  openssl passwd -6 '<password>'
+# MUST be $6$ (sha512). The htpasswd plugin's bcrypt branch only accepts $2a$,
+# so a $2y$ hash from `htpasswd -B` fails EVERY login, silently.
+# render-config.sh rejects the wrong format rather than shipping it.
+FILES_USER=uli
+FILES_PASSWORD_HASH=
+
+# Filestash /admin console password — bcrypt, and /admin IS publicly exposed, so
+# use a 20+ char generated password. It is the only credential guarding config.
+#   docker run --rm caddy:alpine caddy hash-password --plaintext '<password>'
+FILES_ADMIN_PASSWORD_HASH=
+
+# Session key (openssl rand -hex 16). Must be non-empty: an empty secret_key
+# makes filestash rewrite config.json at boot, which fails on the :ro mount.
+FILES_SECRET_KEY=
+
+# Unlocks the local storage backend, which filestash admin-gates: it refuses to
+# init unless the connection params carry this secret. config.json supplies it
+# server-side; players never see it. openssl rand -hex 24.
+FILES_LOCAL_SECRET=
+
 # Only needed if using CurseForge-exclusive mods:
 # CF_API_KEY=your-curseforge-api-key
 
@@ -56,7 +102,7 @@ DISTRIBUTION_WEB_ROOT=/home/oier/projects/mc-mods/ulicraft-group/ulicraft-distri
 # Only needed to issue real TLS certs. DNS-01 needs no inbound ports.
 LE_EMAIL=you@example.com
 # space-separated subdomains; apex ${BASE_DOMAIN} is always included
-LE_SUBDOMAINS=auth distribution www avatar status
+LE_SUBDOMAINS=auth distribution www avatar status files
 # OVH API creds (DNS zone write). Create at https://eu.api.ovh.com/createToken/
 # OVH_CK can be blank on first run — acme.sh prints an auth URL, then paste it.
 OVH_END_POINT=ovh-eu
diff --git a/.gitignore b/.gitignore
index 4a13d41..f1a66d9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,6 +6,9 @@ runtime/authlib-injector.jar
 # rendered configs (from tooling/render-config.sh)
 drasl/config/config.toml
 nmsr/config.toml
+# holds the admin bcrypt hash, the shared player hash, the session key and the
+# local-backend secret — only the .tmpl is tracked
+filestash/config.json
 
 # server mod subset synced from the distribution repo by
 # tooling/sync-server-mods.sh (source of truth is mods-sides.json + $DIST jars)
diff --git a/CLAUDE.md b/CLAUDE.md
index 1518eea..cf91a8d 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -32,6 +32,7 @@ Internet ── host nginx (TLS, LE certs, HSTS) ──► caddy (127.0.0.1:8880
    auth.${BASE_DOMAIN}   ─► drasl        (Yggdrasil API + web UI)
    avatar.${BASE_DOMAIN} ─► nmsr         (skin/avatar renderer, Drasl-backed)
    status.${BASE_DOMAIN} ─► uptime-kuma  (status page + monitors)
+   files.${BASE_DOMAIN}  ─► filestash    (player file share, ONE shared login, writable)
    distribution.${BASE}  ─► static site from ANOTHER repo (DISTRIBUTION_WEB_ROOT)
 
 minecraft :25565 (+ 24454/udp Simple Voice Chat)
@@ -105,6 +106,17 @@ automatically; cosmetic-client mods that declare `BOTH` stay `both` until you
 hand-edit `mods-sides.json` to `client`. No Modrinth/packwiz, no network at
 classify/sync time. See `plan/04-mods.md`.
 
+### Filestash (files.) — three traps
+Full list in `plan/20-files.md`; the ones that cost real time:
+- The `local` backend is **admin-gated**: without `LOCAL_BACKEND_SECRET` in the
+  connection params, every login fails with `backend error - Not Allowed` (looks
+  like bad credentials, isn't).
+- `FILES_PASSWORD_HASH` must be **`$6$`** (`openssl passwd -6`). A `$2y$` bcrypt
+  from `htpasswd -B` fails every login silently — the plugin only matches `$2a$`.
+- `config.json` is rendered + mounted `:ro` (the admin console can't save, on
+  purpose). Single-file bind mount ⇒ **`--force-recreate` after re-rendering**,
+  never `restart`.
+
 ### Memory sizing
 ~50–100 mods, 8 players, 1.21.1: `INIT_MEMORY: 4G`, `MAX_MEMORY: 10G`,
 `USE_AIKAR_FLAGS: TRUE`.
diff --git a/caddy/conf.d/60-files.caddy b/caddy/conf.d/60-files.caddy
new file mode 100644
index 0000000..fb23adb
--- /dev/null
+++ b/caddy/conf.d/60-files.caddy
@@ -0,0 +1,10 @@
+# Files — Filestash player file share (filestash service). Shared login,
+# writable. See plan/20-files.md.
+#
+# Filestash blocks any request whose Host header doesn't match its configured
+# `general.host` (https://files.${BASE_DOMAIN}), with "only traffic from X is
+# allowed". The host nginx forwards the original Host, and caddy passes it
+# through untouched — do NOT rewrite it here or every request 403s.
+http://files.{$BASE_DOMAIN} {
+	reverse_proxy filestash:8334
+}
diff --git a/docker-compose.yml b/docker-compose.yml
index 09dcbfc..c529fb0 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -159,6 +159,7 @@ services:
       - ./caddy/conf.d/30-distribution.caddy:/etc/caddy/conf.d/30-distribution.caddy:ro
       - ./caddy/conf.d/40-avatar.caddy:/etc/caddy/conf.d/40-avatar.caddy:ro
       - ./caddy/conf.d/50-status.caddy:/etc/caddy/conf.d/50-status.caddy:ro
+      - ./caddy/conf.d/60-files.caddy:/etc/caddy/conf.d/60-files.caddy:ro
       - ./www:/srv/www:ro
       - ./launcher:/srv/launcher:ro
       # Static site from ANOTHER repo (absolute host path in .env).
@@ -213,6 +214,38 @@ services:
     networks:
       - mcnet
 
+  # Player file share (screenshots, schematics, maps) at files.${BASE_DOMAIN}.
+  # ONE shared login for everybody (FILES_AUTH=htpasswd), writable. See
+  # plan/20-files.md — it documents every non-obvious bit of this service.
+  #
+  # Config is rendered read-only from filestash/config.json.tmpl: filestash has
+  # no env-var config, and its admin console writes config.json back at runtime,
+  # so pinning it :ro is what keeps git authoritative. The console still loads —
+  # it just cannot save. That is intentional, not a bug.
+  filestash:
+    image: machines/filestash@sha256:8cb09d42470328a02aec6e3861f912addf8a9d54ad63d9c965bcb48df5ad36b1
+    container_name: filestash
+    restart: unless-stopped
+    environment:
+      # The `local` storage backend is admin-gated in filestash: it refuses to
+      # init unless the connection params carry this secret (or the admin
+      # password). config.json's attribute_mapping supplies it server-side, so
+      # players never see it. Without this, every login dies on "Not Allowed".
+      LOCAL_BACKEND_SECRET: ${FILES_LOCAL_SECRET:?FILES_LOCAL_SECRET unset in .env}
+      # Do NOT set APPLICATION_URL / ADMIN_PASSWORD here: either one makes
+      # filestash rewrite config.json at boot, which fails on the :ro mount.
+      # Both live in the rendered config instead (general.host / auth.admin).
+    volumes:
+      # /app/data/state holds config + sqlite + search index + logs, so the
+      # DIRECTORY must stay writable. Only config.json is pinned read-only.
+      - filestash_state:/app/data/state
+      - ./filestash/config.json:/app/data/state/config/config.json:ro
+      # The share itself. FILES_MOUNT_MODE is the literal mount flag (ro|rw) —
+      # `ro` enforces a read-only share at the KERNEL, whatever the UI thinks.
+      - ${FILES_DATA_DIR:?FILES_DATA_DIR unset in .env}:/data/files:${FILES_MOUNT_MODE:-ro}
+    networks:
+      - mcnet
+
   # Status monitoring + public status page. caddy proxies status. -> :3001.
   # Joins mcnet so monitors probe the stack by internal service name.
   uptime-kuma:
@@ -228,6 +261,7 @@ volumes:
   drasl_state:
   mc_data:
   kuma_data:
+  filestash_state:
 
 networks:
   mcnet:
diff --git a/filestash/config.json.tmpl b/filestash/config.json.tmpl
new file mode 100644
index 0000000..fdce85d
--- /dev/null
+++ b/filestash/config.json.tmpl
@@ -0,0 +1,30 @@
+{
+    "general": {
+        "name": "Ulicraft Files",
+        "host": "https://files.${BASE_DOMAIN}",
+        "secret_key": "${FILES_SECRET_KEY}",
+        "editor": "base",
+        "display_hidden": false,
+        "upload_button": true,
+        "fork_button": false
+    },
+    "auth": {
+        "admin": "${FILES_ADMIN_PASSWORD_HASH}"
+    },
+    "middleware": {
+        "identity_provider": {
+            "type": "${FILES_IDP_TYPE}",
+            "params": "${FILES_IDP_PARAMS}"
+        },
+        "attribute_mapping": {
+            "related_backend": "files",
+            "params": "{\"files\":{\"type\":\"local\",\"path\":\"/data/files/\",\"password\":\"${FILES_LOCAL_SECRET}\"}}"
+        }
+    },
+    "connections": [
+        {
+            "label": "files",
+            "type": "local"
+        }
+    ]
+}
diff --git a/nginx/ulicraft-caddy.conf.tmpl b/nginx/ulicraft-caddy.conf.tmpl
index e88949c..21eb94d 100644
--- a/nginx/ulicraft-caddy.conf.tmpl
+++ b/nginx/ulicraft-caddy.conf.tmpl
@@ -26,11 +26,15 @@ upstream ulicraft_caddy {
     server 127.0.0.1:${CADDY_HTTP_PORT};
 }
 
+# Brute-force throttle for the publicly-exposed Filestash /admin console (it is
+# the only credential on files.), applied in its location block below.
+limit_req_zone $binary_remote_addr zone=files_admin:10m rate=6r/m;
+
 # HTTP -> HTTPS for every name.
 server {
     listen 80;
     listen [::]:80;
-    server_name ${BASE_DOMAIN} www.${BASE_DOMAIN} auth.${BASE_DOMAIN} distribution.${BASE_DOMAIN} avatar.${BASE_DOMAIN} status.${BASE_DOMAIN};
+    server_name ${BASE_DOMAIN} www.${BASE_DOMAIN} auth.${BASE_DOMAIN} distribution.${BASE_DOMAIN} avatar.${BASE_DOMAIN} status.${BASE_DOMAIN} files.${BASE_DOMAIN};
     return 301 https://$host$request_uri;
 }
 
@@ -125,6 +129,44 @@ server {
     }
 }
 
+# Filestash player file share. Uploads need a real body limit (nginx defaults to
+# 1m, which rejects almost anything worth sharing) and streaming rather than
+# spooling — a 2g upload buffered to disk would write it twice on a host whose
+# disk is already the shared failure domain for Minecraft + Drasl + backups.
+server {
+    listen 443 ssl http2;
+    listen [::]:443 ssl http2;
+    server_name files.${BASE_DOMAIN};
+
+    ssl_certificate     ${APP_DIR}/certs/files.${BASE_DOMAIN}/cert.pem;
+    ssl_certificate_key ${APP_DIR}/certs/files.${BASE_DOMAIN}/key.pem;
+    add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;
+
+    client_max_body_size 2g;      # uploads; other vhosts stay at 4m
+    proxy_request_buffering off;  # stream uploads, don't spool them to disk
+    proxy_read_timeout 300s;
+    proxy_send_timeout 300s;
+
+    # /admin is reachable on purpose, so throttle it: it is the only password
+    # on this vhost. 6 req/min, small burst.
+    location /admin {
+        limit_req zone=files_admin burst=3 nodelay;
+        proxy_pass http://ulicraft_caddy;
+        proxy_set_header Host              $host;
+        proxy_set_header X-Real-IP         $remote_addr;
+        proxy_set_header X-Forwarded-For   $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+    }
+
+    location / {
+        proxy_pass http://ulicraft_caddy;
+        proxy_set_header Host              $host;
+        proxy_set_header X-Real-IP         $remote_addr;
+        proxy_set_header X-Forwarded-For   $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+    }
+}
+
 server {
     listen 443 ssl http2;
     listen [::]:443 ssl http2;
diff --git a/plan/19-routes.md b/plan/19-routes.md
index 103b6b2..3ad5497 100644
--- a/plan/19-routes.md
+++ b/plan/19-routes.md
@@ -12,6 +12,7 @@
 | `auth.${BASE_DOMAIN}` | `00-core.caddy` | `drasl:25585` |
 | `avatar.${BASE_DOMAIN}` | `40-avatar.caddy` | `nmsr:8080` |
 | `status.${BASE_DOMAIN}` | `50-status.caddy` | `uptime-kuma:3001` |
+| `files.${BASE_DOMAIN}` | `60-files.caddy` | `filestash:8334` |
 | `distribution.${BASE_DOMAIN}` | `30-distribution.caddy` | static `/srv/distribution` (other repo) |
 
 ---
@@ -58,6 +59,29 @@ base `https://auth.${BASE_DOMAIN}/drasl/api/v2` (`site.draslApiUrl`):
 
 ---
 
+## Files — `files.${BASE_DOMAIN}` (Filestash player share)
+
+`reverse_proxy filestash:8334`. Screenshots / schematics / maps. **One shared
+login** for every player (`FILES_AUTH=htpasswd`), writable. Full design:
+`plan/20-files.md`.
+
+- `/` — SPA. `GET /api/session/auth/?label=files` renders the login form;
+  `POST` the same URL with `user`/`password` authenticates.
+- `/api/*` — JSON API. Requires the header `X-Requested-With: XmlHttpRequest`
+  (the SPA sends it); without it Filestash's intrusion detection 403s the
+  request. Relevant when curling it by hand.
+- `/admin` — admin console, own bcrypt password (`auth.admin`). Deliberately
+  public; nginx throttles it (`limit_req`, 6r/m). It **cannot save** — the
+  config is a read-only mount.
+- **`?label=files` matters.** The attribute mapping is keyed by the connection
+  label; auth without it yields `backend error - Not Allowed`.
+
+Filestash blocks any request whose `Host` doesn't match its `general.host`
+(`https://files.${BASE_DOMAIN}`) — nginx forwards the original Host and caddy
+passes it through, so don't rewrite it anywhere in the chain.
+
+---
+
 ## Auth / Drasl — `auth.${BASE_DOMAIN}`
 
 `reverse_proxy drasl:25585`. One service exposes three surfaces:
diff --git a/plan/20-files.md b/plan/20-files.md
new file mode 100644
index 0000000..bc0c303
--- /dev/null
+++ b/plan/20-files.md
@@ -0,0 +1,180 @@
+# 20 — Filestash (`files.${BASE_DOMAIN}`)
+
+> Web file share for player media (screenshots, schematics, maps, guides).
+> One [Filestash](https://github.com/mickael-kerjean/filestash) container behind
+> caddy, **one shared username/password for everybody**, **writable**.
+> Config is rendered read-only from a template, like drasl/nmsr.
+>
+> **Not** a backup browser, **not** a mod mirror. See "What goes in it".
+>
+> Everything below was verified against the real image (digest pinned in
+> compose) and against the upstream source, not inferred from the docs — the
+> docs omit most of it.
+
+## Shape
+
+```
+Internet ── host nginx (TLS, LE cert for files.) ──► caddy ──► filestash:8334
+                                                                  │
+                                              ${FILES_DATA_DIR} ──┘ (bind mount)
+```
+
+| Thing | Value |
+|---|---|
+| Vhost | `files.${BASE_DOMAIN}` |
+| Image | `machines/filestash` **pinned by digest** (upstream ships only `latest`) |
+| Container port | `8334`, runs as **uid/gid 1000** (`filestash`) |
+| Auth | htpasswd, **one shared account**, `FILES_USER` / `FILES_PASSWORD_HASH` |
+| Access | read **+ write** for anyone with the password |
+| Data | `${FILES_DATA_DIR}` on the host, **outside the repo** |
+| State | named volume `filestash_state` → `/app/data/state` |
+| Config | `filestash/config.json` rendered from `.tmpl`, mounted `:ro` |
+| Backups | **none** — outside mc-backup's scope. Treat as disposable. |
+| Quota | none — eyeballed |
+
+## Decisions (settled — don't relitigate)
+
+**Auth is htpasswd with one shared credential, not SSO.** Filestash's OIDC and
+SAML middlewares are **enterprise-only**; the community build compiles in
+`htpasswd`, `ldap`, `passthrough`, `wordpress`, `local` only (verified in
+`server/plugin/index.go`). Keycloak was considered and dropped — it would need an
+oauth2-proxy sidecar in front + `passthrough`. That path stays open but is not
+built.
+
+**One instance, everything behind the password.** No anonymous read tier.
+Filestash's auth middleware is **global to the instance**, so "anonymous read +
+authenticated write" is impossible in one container (that's the enterprise
+RBAC). A two-instance split was designed and rejected as not worth it.
+
+**`FILES_AUTH=none` is gated on the host being internal-only.** The off-switch
+exists for when this server moves behind a LAN/VPN. **Do not set it while
+`files.` is internet-reachable** — auth-off on a *writable* public share is an
+open upload relay: someone parks malware or a phishing kit on your domain, under
+your LE cert, and the abuse mail, the bandwidth, and a possible domain
+blocklisting (which would take `auth.` and the apex down with it, breaking logins
+and the launcher for every player) all land on you. `render-config.sh` prints a
+loud warning when it renders this mode.
+
+**Shared credential ⇒ no audit trail, no per-person revocation.** You will never
+know who deleted a folder; rotating means re-telling everyone. Fine for a
+friends' media share — but nothing here is backed up, so treat the share as
+disposable and keep anything you'd miss elsewhere.
+
+## What goes in it
+
+| Content | Verdict |
+|---|---|
+| Screenshots, schematics, maps, guides | ✅ the point |
+| World downloads / `./backups/*.tgz` | ❌ contains `playerdata/`, `stats/`, the full map — every player's inventory and coords, handed to anyone with the shared password |
+| Mods / jars | ❌ redistribution; `distribution.${BASE_DOMAIN}` already serves the modset to launchers |
+
+## `.env`
+
+See `.env.example` for the annotated block. Summary:
+
+| Var | What |
+|---|---|
+| `FILES_DATA_DIR` | host path of the share, outside the repo |
+| `FILES_MOUNT_MODE` | literal mount flag, `rw` \| `ro` |
+| `FILES_AUTH` | `htpasswd` \| `passthrough` \| `none` |
+| `FILES_USER` | shared login name |
+| `FILES_PASSWORD_HASH` | **`$6$`**, from `openssl passwd -6 '<pw>'` |
+| `FILES_ADMIN_PASSWORD_HASH` | bcrypt, from `docker run --rm caddy:alpine caddy hash-password --plaintext '<pw>'` |
+| `FILES_SECRET_KEY` | `openssl rand -hex 16`, must be non-empty |
+| `FILES_LOCAL_SECRET` | `openssl rand -hex 24`, unlocks the local backend |
+| `LE_SUBDOMAINS` | must include `files` |
+
+`filestash/config.json` is **rendered and gitignored** — it holds every hash and
+both secrets. Only the `.tmpl` is tracked.
+
+## Deploy
+
+```sh
+tooling/render-config.sh                       # -> filestash/config.json (validates the JSON)
+tooling/issue-letsencrypt.sh                   # picks up `files` from LE_SUBDOMAINS
+tooling/render-nginx.sh --install              # adds the files. vhost + reloads nginx
+mkdir -p "$FILES_DATA_DIR"                     # uid 1000 must be able to write it
+docker compose up -d filestash caddy
+```
+
+Then add an Uptime Kuma HTTP monitor for `https://files.${BASE_DOMAIN}` (expect
+`200` — the login page is a 200) and put it on the status page with the others.
+
+## Gotchas (all of these were hit for real)
+
+### The `local` backend is admin-gated — this is the one that wastes an evening
+`plg_backend_local.Init()` **refuses to start** unless the connection params
+carry `$LOCAL_BACKEND_SECRET` or the bcrypt admin password. Miss it and every
+login dies at `backend error - Not Allowed`, which reads like a credentials
+problem and isn't. `config.json`'s `attribute_mapping` injects the secret
+server-side (Filestash calls this the "facade pattern"), so players never see it.
+`FILES_LOCAL_SECRET` must be **identical** in the compose env and the rendered
+config — `render-config.sh` renders both from the same var.
+
+### `$2y$` bcrypt silently fails every login
+The htpasswd plugin's bcrypt branch matches on the literal prefix **`$2a$`**.
+`htpasswd -B` emits `$2y$`, which falls through to `return false` — so every
+login fails with correct credentials and no useful log line. Use
+**`openssl passwd -6`** (`$6$`, sha512) for `FILES_PASSWORD_HASH`.
+`render-config.sh` hard-fails on a `$2y$`/`$2b$` hash rather than shipping a
+config nobody can log into. (The *admin* password is checked by Go's bcrypt
+directly, which does accept `$2y$` — but `caddy hash-password` gives `$2a$`
+anyway, so just use that for both.)
+
+### `general.host` must match the incoming `Host` header
+Filestash blocks every non-`/admin/` request whose `Host` differs from its
+configured `general.host`, with *"only traffic from X is allowed"*. It's a 403
+that looks like an auth failure. nginx forwards the original Host and caddy
+passes it through — don't rewrite it anywhere. If `files.` starts 403ing after a
+domain change, this is why.
+
+### `config.json` is a single-file bind mount → stale inode
+Same shape as the caddy `conf.d` gotcha. The mount pins the **inode**, so
+re-rendering (or a `git pull`) writes a *new* file while the container keeps
+reading the *old* one.
+
+**After re-rendering: `docker compose up -d --force-recreate filestash`.**
+`restart` is not enough. Rotating the shared password needs a recreate too.
+
+### Don't set `APPLICATION_URL` or `ADMIN_PASSWORD` env
+Either one makes Filestash **rewrite `config.json` at boot**, which fails against
+the `:ro` mount. Both live in the rendered config instead (`general.host` /
+`auth.admin`). `general.secret_key` must likewise be non-empty, or Filestash
+generates one and tries to save that. With all three set in the file, Filestash
+never attempts a boot write and the `:ro` mount is clean — you get one harmless
+`cannot chmod config file` WARN in the log, and nothing else.
+
+### The admin console cannot save
+`/admin` loads and its login works, but `config.json` is `:ro`, so every save
+silently fails. That's the deliberate trade for keeping git authoritative
+(drasl/nmsr never write their configs; Filestash does, which is exactly why it
+needs pinning). To change config: edit the `.tmpl`, re-render, recreate. To
+re-derive the schema after an upstream upgrade: run the image locally against a
+*writable* state volume, click it into shape, `docker cp` the result out.
+
+### The API needs `X-Requested-With: XmlHttpRequest`
+The SPA sends it; anything else (curl, a naive monitor) trips intrusion
+detection and gets a 403 that looks like an auth bug. Only matters when probing
+by hand — the Kuma monitor hits `/`, which is fine.
+
+### Disk is the shared failure domain
+`FILES_DATA_DIR` grows without a quota, driven by whoever has the password. A
+full disk on `cochi` does not just break `files.` — it takes **Minecraft, Drasl,
+and mc-backup** down with it. Eyeballing is the accepted plan. Revisit (quota,
+separate partition, or a Kuma disk monitor) if the share sees real use.
+
+### Pinned digest, not `latest`
+`machines/filestash` publishes essentially only `latest`. Unpinned, any
+`docker compose pull` silently ships a new upstream build of an internet-facing,
+writable file manager. Pin the digest; upgrade deliberately — same discipline as
+`NEOFORGE_VERSION`.
+
+## Deferred
+
+- **Keycloak SSO** — needs oauth2-proxy + `FILES_AUTH=passthrough`. Not built.
+- **Anonymous access** (`FILES_AUTH=none`) — only once the host is internal-only.
+- **Landing page link** — deliberately none on day one; `plan/18-landing-rework.md`
+  is mid-rework, so revisit with WS5 (footer) rather than merging into a moving
+  design.
+- **Per-user accounts / roles** — htpasswd RBAC is enterprise-only.
+- **Backups / quota** — none.
diff --git a/tooling/render-config.sh b/tooling/render-config.sh
index c913321..de784a2 100755
--- a/tooling/render-config.sh
+++ b/tooling/render-config.sh
@@ -29,6 +29,60 @@ render() {  # $1=template  $2=output
 render drasl/config/config.toml.tmpl drasl/config/config.toml
 render nmsr/config.toml.tmpl          nmsr/config.toml
 
+# ── filestash (files.${BASE_DOMAIN}) ────────────────────────────────────
+# Filestash has NO env-var config: config.json is the source of truth and the
+# admin console writes it back at runtime. We render it and mount it read-only,
+# so git stays authoritative (the console renders but cannot save — by design).
+#
+# FILES_AUTH picks the identity_provider block. The params fields are JSON
+# *strings* holding escaped JSON (that's Filestash's schema, not a typo) —
+# built here rather than in the template because the shape differs per mode.
+: "${FILES_AUTH:=htpasswd}"
+: "${FILES_SECRET_KEY:?FILES_SECRET_KEY unset (openssl rand -hex 16)}"
+: "${FILES_ADMIN_PASSWORD_HASH:?FILES_ADMIN_PASSWORD_HASH unset (docker run --rm caddy:alpine caddy hash-password --plaintext '<pw>')}"
+: "${FILES_LOCAL_SECRET:?FILES_LOCAL_SECRET unset (openssl rand -hex 24) — unlocks the admin-gated local backend}"
+
+case "$FILES_AUTH" in
+  htpasswd)
+    : "${FILES_USER:?FILES_USER unset (shared login for players)}"
+    : "${FILES_PASSWORD_HASH:?FILES_PASSWORD_HASH unset (openssl passwd -6 '<pw>')}"
+    # The htpasswd plugin's bcrypt branch only accepts $2a$ — a $2y$ hash (what
+    # `htpasswd -B` emits) silently fails every login. $6$ (openssl passwd -6)
+    # is the safe, explicitly-supported format. Halt rather than ship a config
+    # nobody can log into.
+    case "$FILES_PASSWORD_HASH" in
+      '$6$'*|'$5$'*|'$2a$'*|'$apr1$'*|'$1$'*) ;;
+      '$2y$'*|'$2b$'*)
+        echo "FILES_PASSWORD_HASH is bcrypt '${FILES_PASSWORD_HASH:0:4}' — the htpasswd plugin only accepts \$2a\$." >&2
+        echo "Use: openssl passwd -6 '<password>'" >&2
+        exit 1 ;;
+      *) echo "FILES_PASSWORD_HASH is not a recognised hash (want \$6\$… from: openssl passwd -6 '<password>')" >&2; exit 1 ;;
+    esac
+    FILES_IDP_TYPE="htpasswd"
+    FILES_IDP_PARAMS="{\\\"type\\\":\\\"htpasswd\\\",\\\"users\\\":\\\"${FILES_USER}:${FILES_PASSWORD_HASH}\\\"}"
+    ;;
+  passthrough|none)
+    # NO LOGIN — anyone who reaches the vhost gets in. Only safe once this host
+    # is NOT reachable from the internet (see plan/20-files.md).
+    echo "!! FILES_AUTH=$FILES_AUTH — filestash will have NO authentication." >&2
+    echo "!! Only valid if files.${BASE_DOMAIN} is unreachable from the internet." >&2
+    FILES_IDP_TYPE="passthrough"
+    FILES_IDP_PARAMS="{\\\"type\\\":\\\"passthrough\\\",\\\"strategy\\\":\\\"direct\\\"}"
+    ;;
+  *)
+    echo "FILES_AUTH must be 'htpasswd', 'passthrough' or 'none' (got '$FILES_AUTH')" >&2; exit 1 ;;
+esac
+export FILES_IDP_TYPE FILES_IDP_PARAMS
+
+envsubst '${BASE_DOMAIN} ${FILES_IDP_TYPE} ${FILES_IDP_PARAMS} ${FILES_ADMIN_PASSWORD_HASH} ${FILES_SECRET_KEY} ${FILES_LOCAL_SECRET}' \
+  < filestash/config.json.tmpl > filestash/config.json
+
+# The hashes contain '$' and the params fields are nested JSON — one bad escape
+# yields a config filestash silently ignores. Fail loudly instead.
+python3 -c 'import json,sys; json.load(open("filestash/config.json"))' \
+  || { echo "filestash/config.json is not valid JSON — refusing to ship it" >&2; exit 1; }
+echo "rendered filestash/config.json (auth=$FILES_AUTH)"
+
 # Server mods are no longer rendered here — they come from the distribution repo
 # via tooling/sync-server-mods.sh (run separately in the deploy flow). See
 # plan/04-mods.md.