fix(bootstrap): keep the operator's auth sources across re-runs

write_felis_toml regenerates felis.host.toml and felis.pod.toml with a
wholesale `cat >`, and the [[auth_source]] list was a literal LittleSkin
block in that heredoc. Re-running the installer, which is also what
`felis setup` does, threw away any edit to the list: a root the operator
added stopped admitting logins, and a root they removed came back. The
generated comment invited exactly that edit.

Carry the tables forward the way [smtp] already is: read every
[[auth_source]] table from the existing felis.host.toml (falling back to
felis.pod.toml) and emit the LittleSkin default only when there is no
earlier file at all. An earlier file with no tables stays empty, because
that is a Mojang-only server rather than a missing value; felis-api now
treats an empty list that way.

The file header and the comment above the list now say what survives a
re-run, and point at felis.host.toml, which is what the next run reads.

bootstrap_test.sh extracts the new function from bootstrap.sh and checks
the fresh-install default, an operator's own table carried without the
default or the following section, an empty list staying empty, and the
indented form the setup TUI writes. It passes under dash with gawk and
with mawk; forcing the function to always return the default fails five
of the new cases.

deploy/bootstrap.sh

@@ -1935,15 +1935,38 @@ persisted_smtp_block() {
   printf '%s' "$SMTP_BLOCK"
 }
 
+# persisted_auth_source_blocks echoes the [[auth_source]] tables an earlier run left
+# behind, or the LittleSkin default when there is no earlier felis.toml at all. The
+# list is the operator's: it is the only way to add or drop a Yggdrasil root on a full
+# install, and nothing in this script's inputs derives it. Without the carry-forward a
+# re-run would put LittleSkin back after the operator removed it and silently drop any
+# root they added. An earlier file with no tables stays that way — that is a Mojang-only
+# server, not a missing value. Same first-readable-file rule as persisted_smtp_block.
+persisted_auth_source_blocks() {
+  local f
+  for f in "${STATE_DIR}/felis.host.toml" "${STATE_DIR}/felis.pod.toml"; do
+    [ -r "$f" ] || continue
+    # Every [[auth_source]] table, up to (not including) the next other section header.
+    awk '/^[[:space:]]*\[\[auth_source\]\]/ { f=1 }
+         f && /^[[:space:]]*\[/ && !/^[[:space:]]*\[\[auth_source\]\]/ { f=0 }
+         f { print }' "$f"
+    return 0
+  done
+  printf '%s\n' '[[auth_source]]' 'tag = "littleskin"' 'prefix = "LS"' \
+    'url = "https://littleskin.cn/api/yggdrasil/sessionserver/session/minecraft/hasJoined"'
+}
+
 write_felis_toml() {
-  local target="$1" db_host="$2" smtp_block
+  local target="$1" db_host="$2" smtp_block auth_source_blocks
   smtp_block="$(persisted_smtp_block)"
   if [ -n "$smtp_block" ]; then
     log "carrying forward the configured [smtp] relay"
     smtp_block="${smtp_block}"$'\n' # keep a blank line before the next section
   fi
+  auth_source_blocks="$(persisted_auth_source_blocks)"
   cat > "$target" <<EOF
-# Generated by deploy/bootstrap.sh — do not edit by hand; rerun the installer.
+# Generated by deploy/bootstrap.sh; rerun the installer to regenerate. Hand edits are
+# overwritten, except [smtp] and [[auth_source]], which carry forward.
 [server]
 listen = "0.0.0.0:8080"
 root_domain = "${FELIS_ROOT_DOMAIN}"
@@ -1976,12 +1999,10 @@ panel_hostname = "console.${FELIS_ROOT_DOMAIN}"
 ${smtp_block}
 # Third-party Yggdrasil sources federated by the hasJoined multiplexer. Mojang is
 # always the code-owned identity anchor (premium-first), prepended in Go; sources here
-# append as namespace-rewritten guests. Shipping LittleSkin by default lets Mojang and
-# LittleSkin both log in out of the box. Delete this block for a Mojang-only server.
-[[auth_source]]
-tag = "littleskin"
-prefix = "LS"
-url = "https://littleskin.cn/api/yggdrasil/sessionserver/session/minecraft/hasJoined"
+# append as namespace-rewritten guests. A fresh install federates LittleSkin. Edit the
+# list in ${STATE_DIR}/felis.host.toml and rerun the installer; re-runs keep it as it
+# is, and with no [[auth_source]] at all the server is Mojang-only.
+${auth_source_blocks}
 EOF
 }