feat(build): add FreeBSD x86_64 cross-compile support

方案 A（clang + lld + 本地 sysroot）。rustc 为 freebsd target 链接的系统库
（libc/libexecinfo/libgcc_s/libthr）及 sysinfo 依赖的 freebsd 专有库
（libkvm/libmemstat/libprocstat/libdevstat）需 FreeBSD 运行时，无法纯靠
clang+lld 无 sysroot 完成；故从 FreeBSD 15.1 base.txz 解出 crt 对象 + 系统库
到 .freebsd-sysroot/（gitignored，machine-local）。

- .cargo/config.toml: freebsd target 配置作为注释模板（sysroot 路径机器相关，
  不硬编码进仓库）；linker 经 rustflags 的 -C linker=clang 设置，使 Makefile
  能用 CARGO_TARGET_*_RUSTFLAGS 环境变量整体注入。
- Makefile: 新增 freebsd-sysroot（幂等下载+解压 base.txz）与 build-freebsd
  （release server 二进制交叉编译）target。server 用 cargo 直出而非 dx CLI，
  因 dx 对该 target 的支持未经验证。
- .gitignore: 忽略 .freebsd-sysroot/。
- AGENTS.md: 补充构建命令说明。

实测 release 二进制 16MB，stripped ELF for FreeBSD 15.1，动态依赖均为
FreeBSD base 自带库（libc.so.7 libthr.so.3 libkvm.so.7 等）。

.cargo/config.toml

@@ -7,3 +7,30 @@ rustflags = ["--cfg", "getrandom_backend=\"wasm_js\""]
 # Uncomment and adjust after installing a musl C toolchain:
 [target.x86_64-unknown-linux-musl]
 linker = "x86_64-linux-musl-gcc"
+
+# FreeBSD x86_64 交叉编译（方案 A：clang + lld + 本地 sysroot）。
+#
+# rustc 为 freebsd target 链接的系统库（libc/libexecinfo/libgcc_s/libthr 等）及 sysinfo
+# 依赖的 freebsd 专有库（libkvm/libmemstat/libprocstat/libdevstat）需 FreeBSD 运行时，
+# 因此除 clang + lld 外还需一个本地 sysroot（由 base.txz 解出，见 .freebsd-sysroot/）。
+# ring（C + 预生成 ELF 汇编，freebsd 归入 LINUX_ABI）与 zstd-sys（bundled C）用 clang 编译。
+#
+# sysroot 路径与机器绑定，故此 target 配置默认注释；`make build-freebsd` 会用环境变量
+# CARGO_TARGET_X86_64_UNKNOWN_FREEBSD_RUSTFLAGS 注入当前机器的 sysroot 路径。
+#
+# 准备步骤：
+#   1. pacman -S clang lld              # 或 apt install clang lld
+#   2. rustup target add x86_64-unknown-freebsd
+#   3. make freebsd-sysroot             # 下载 base.txz 并解压到 .freebsd-sysroot/
+#   4. make build-freebsd               # 交叉编译 release server 二进制
+#
+# 手动调用（Makefile 之外）时取消注释并把 <SYSROOT> 改成实际路径：
+# [target.x86_64-unknown-freebsd]
+# linker = "clang"
+# rustflags = [
+#     "-C", "link-arg=--target=x86_64-unknown-freebsd",
+#     "-C", "link-arg=-fuse-ld=lld",
+#     "-C", "link-arg=--sysroot=<SYSROOT>",
+#     "-C", "link-arg=-L<SYSROOT>/usr/lib",
+#     "-C", "link-arg=-L<SYSROOT>/lib",
+# ]

.gitignore

@@ -29,3 +29,6 @@ profile.json.gz
 
 # Git worktrees
 .worktrees/
+
+# FreeBSD cross-compile sysroot (extracted from base.txz, machine-local)
+.freebsd-sysroot/

AGENTS.md

@@ -13,6 +13,8 @@
 make dev           # tailwindcss watch + dx serve (needs PostgreSQL)
 make build         # build-editor → highlight-css → tailwindcss → doc → dx build --release
 make build-linux   # same as build but targets x86_64-unknown-linux-musl
+make build-freebsd # cross-compile FreeBSD x86_64 server binary (clang + lld + sysroot)
+make freebsd-sysroot # download/extract FreeBSD base.txz → .freebsd-sysroot/ (idempotent)
 make css           # one-shot CSS
 make css-watch     # watch mode
 make test          # cargo test + vitest (tiptap-editor + lightbox + yggdrasil-core libs)

Makefile

@@ -1,4 +1,4 @@
-.PHONY: dev build build-linux docker css css-watch clean build-editor build-editor-incremental build-lightbox build-lightbox-incremental build-core build-core-incremental build-codemirror build-codemirror-incremental highlight-css test doc doc-open start clippy fix
+.PHONY: dev build build-linux build-freebsd freebsd-sysroot docker css css-watch clean build-editor build-editor-incremental build-lightbox build-lightbox-incremental build-core build-core-incremental build-codemirror build-codemirror-incremental highlight-css test doc doc-open start clippy fix
 
 build:
 	@$(MAKE) build-editor
@@ -24,6 +24,43 @@ build-linux:
 	@echo "Remember to deploy it alongside the target/dx/yggdrasil/release/web/public directory."
 	@echo "When running the server, ensure DIOXUS_ASSET_DIR is set or the public directory is in CWD."
 
+# FreeBSD 15.1 base.txz 版本与下载源。sysroot 仅需 ./lib 与 ./usr/lib（crt 对象 + 系统库）。
+FREEBSD_VERSION ?= 15.1-RELEASE
+FREEBSD_BASE_URL ?= https://download.freebsd.org/ftp/releases/amd64/amd64/$(FREEBSD_VERSION)/base.txz
+FREEBSD_SYSROOT := $(CURDIR)/.freebsd-sysroot
+
+# 下载并解压 FreeBSD base.txz 到 .freebsd-sysroot/，供交叉链接（crt 对象 + 系统库）。
+# 幂等：若 sysroot 已存在则跳过下载。
+freebsd-sysroot:
+	@if [ -d "$(FREEBSD_SYSROOT)/usr/lib" ] && [ -d "$(FREEBSD_SYSROOT)/lib" ]; then \
+		echo "FreeBSD sysroot already present at $(FREEBSD_SYSROOT)"; \
+	else \
+		echo "Downloading FreeBSD $(FREEBSD_VERSION) base.txz..."; \
+		curl -fL --retry 3 -o /tmp/freebsd-base.txz "$(FREEBSD_BASE_URL)"; \
+		mkdir -p "$(FREEBSD_SYSROOT)"; \
+		echo "Extracting crt objects and system libs..."; \
+		tar -xf /tmp/freebsd-base.txz -C "$(FREEBSD_SYSROOT)" ./lib ./usr/lib; \
+		rm -f /tmp/freebsd-base.txz; \
+		echo "FreeBSD sysroot ready at $(FREEBSD_SYSROOT)"; \
+	fi
+
+# 交叉编译 FreeBSD x86_64 release server 二进制。
+# 前置：clang + lld 已装（pacman -S clang lld）、rustup target add x86_64-unknown-freebsd、
+# `make freebsd-sysroot`。sysroot 路径经 CARGO_TARGET_*_RUSTFLAGS 注入，避免在
+# .cargo/config.toml 里硬编码机器相关路径。server 二进制用 cargo 直出（dx CLI 对该
+# target 未经验证）；前端 wasm 与静态资源与 build-linux 相同，不在此重复构建。
+build-freebsd:
+	@$(MAKE) freebsd-sysroot
+	@SYSROOT="$(FREEBSD_SYSROOT)"; \
+	RUSTFLAGS_FREEBSD="-C linker=clang -C link-arg=--target=x86_64-unknown-freebsd -C link-arg=-fuse-ld=lld -C link-arg=--sysroot=$$SYSROOT -C link-arg=-L$$SYSROOT/usr/lib -C link-arg=-L$$SYSROOT/lib"; \
+	echo "Cross-compiling yggdrasil server for FreeBSD x86_64..."; \
+	CARGO_TARGET_X86_64_UNKNOWN_FREEBSD_RUSTFLAGS="$$RUSTFLAGS_FREEBSD" \
+		cargo build --release --target x86_64-unknown-freebsd --features server --bin yggdrasil
+	@echo ""
+	@echo "FreeBSD build complete! Server binary: target/x86_64-unknown-freebsd/release/yggdrasil"
+	@echo "Deploy it to FreeBSD 15+ alongside the static public/ directory."
+	@echo "Runtime needs (bundled in FreeBSD base): libc.so.7 libthr.so.3 libkvm.so.7 etc."
+
 highlight-css:
 	@cargo run --bin generate_highlight_css