merge the Godot port's history into the monorepo

Brought in with a subtree merge rather than a copy, so the port's 31 commits
survive as history rather than arriving as one anonymous import. Landed under
godot-import/ and moved into the final layout in the next commit, which keeps
git's rename detection able to follow each file across the move.

godot-import/docker/bin/build-reference-cli

@@ -0,0 +1,80 @@
+#!/usr/bin/env bash
+# Build `sylpheed-cli` from the SAME revision of sylpheed-formats the exporter
+# is pinned to, and put it on the persistent target volume.
+#
+#   build-reference-cli       -> $CARGO_TARGET_DIR/release/sylpheed-cli
+#
+# Why not just use /reborn/target/release/sylpheed-cli: that binary is built
+# from whatever /reborn's working tree is at, which is a LIVE mount of the other
+# agent's checkout and moves under you mid-iteration. `sylpheed-cli screen
+# render` is the reference the Godot port is diffed against, so if it runs
+# different decoders than the exporter, a pixel disagreement has a free variable
+# in it and proves nothing about the port.
+#
+# The pinned source lives in CARGO_HOME, which is on the container overlay and
+# does not survive a fresh container -- cargo re-fetches it. The BINARY goes to
+# CARGO_TARGET_DIR, which is a volume, so this is a one-off per image.
+#
+# Jobs are capped for the same reason as build-export.
+set -euo pipefail
+cd "${PROJECT_DIR:-/work}"
+export CARGO_BUILD_JOBS="${CARGO_BUILD_JOBS:-3}"
+
+rev=$(sed -n 's/.*Syplheed-Reborn\.git", rev = "\([0-9a-f]*\)".*/\1/p' \
+      crates/sylpheed-export/Cargo.toml | head -1)
+[ -n "$rev" ] || { echo "build-reference-cli: no rev pin found in Cargo.toml" >&2; exit 1; }
+
+# The checkout only exists once cargo has fetched it; a fresh container has not.
+find_checkout() {
+  find "${CARGO_HOME:?}/git/checkouts" -maxdepth 2 -type d -name "${rev}*" 2>/dev/null | head -1
+}
+src=$(find_checkout)
+if [ -z "$src" ]; then
+  echo "build-reference-cli: fetching the pinned decoders ($rev)"
+  cargo fetch
+  src=$(find_checkout)
+fi
+[ -n "$src" ] || { echo "build-reference-cli: no checkout for rev $rev" >&2; exit 1; }
+
+# Build into a target directory KEYED BY THE REVISION.
+#
+# This is not tidiness. Sharing one target dir across pins silently served a
+# stale binary: after the pin moved 8b6dbcf -> 5414db3, cargo reported
+# "Finished in 0.13s" and left in place a `sylpheed-cli` built from the OLD
+# decoders. `screen list` still worked, so the old check passed, and the
+# reference renderer this whole project verifies against was a revision behind
+# for three consecutive diff runs. A per-rev tree cannot do that: a new pin has
+# no artifacts to reuse.
+echo "build-reference-cli: building sylpheed-cli from $rev"
+tree="$CARGO_TARGET_DIR/reference-cli/$rev"
+CARGO_TARGET_DIR="$tree" cargo build --release --manifest-path "$src/Cargo.toml" -p sylpheed-cli
+
+stable="$CARGO_TARGET_DIR/reference-cli/sylpheed-cli"
+mkdir -p "$(dirname "$stable")"
+cp -f "$tree/release/sylpheed-cli" "$stable"
+
+"$stable" screen list "${SYLPHEED_DISC:-/disc}/dat/GP_TITLE.pak" >/dev/null \
+  || { echo "build-reference-cli: built, but 'screen list' failed" >&2; exit 1; }
+
+# And check the binary is actually the pinned code, not merely a working one.
+# `screen info` prints each element's resting placement, which is decoder
+# output; if this disagrees with what the exporter wrote from the same pin, the
+# two halves of the verification are not the same revision and every diff below
+# is meaningless. Compare rather than assert a value, so this stays true when
+# the pin moves again.
+if [ -f "${PROJECT_DIR:-/work}/export/screens/title/main_menu.json" ]; then
+  cli_rest=$("$stable" screen info "${SYLPHEED_DISC:-/disc}/dat/GP_TITLE.pak" --build 5 \
+             | sed -n 's/.*ptframe1\.t32.*rest (\([0-9]*\),\([0-9]*\)).*/\1,\2/p')
+  exp_rest=$(python3 -c '
+import json,sys
+d=json.load(open(sys.argv[1]))
+e=next(e for e in d["elements"] if e["id"]=="ptframe1")
+print("%d,%d" % tuple(e["rest"]["pos"]))' "${PROJECT_DIR:-/work}/export/screens/title/main_menu.json")
+  if [ "$cli_rest" != "$exp_rest" ]; then
+    echo "build-reference-cli: STALE OR MISMATCHED BINARY" >&2
+    echo "  the CLI resolves ptframe1 rest to ($cli_rest) but export/ says ($exp_rest)." >&2
+    echo "  Both should come from rev $rev. Delete $tree and rebuild." >&2
+    exit 1
+  fi
+fi
+echo "build-reference-cli: $stable  (rev $rev, agrees with export/ on ptframe1)"