Split the system level and the command line into a workspace

First step of separating the layers. The library and the binary are now
crates/tsunagi and crates/tsunagi-cli, which means the plugin crate to
come can be told apart from the core by the compiler rather than by
discipline.

Falls out of it immediately: the CLI's dependencies stop being features
of the library. clap, anstream and tracing-subscriber were optional
dependencies behind a `cli` feature that every library user had to
remember to turn off; now they belong to the crate that uses them, and
the library defaults to no features at all.

The one test that drives the binary moved beside it — a library cannot
depend on a binary built from a crate that depends on the library — and
was rewritten against the public API instead of the test harness.

AGENTS.md said to prefer one crate. It now says the system level and its
plugins are separate crates, for the reason above, and that everything
else stays one crate.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Cargo.toml

@@ -1,94 +1,34 @@
-[package]
-name = "tsunagi"
-version = "0.1.0"
+# The system level and its plugins are separate crates, so the boundary
+# between them is checked by the compiler rather than by discipline: a plugin
+# can reach only what the core makes public, and carries its own version.
+[workspace]
+resolver = "3"
+members = ["crates/*"]
+
+[workspace.package]
 edition = "2024"
 rust-version = "1.91"
 license = "MIT OR Apache-2.0"
-description = "Proof-of-concept library for small private mesh networks: persistent agent identity, deterministic network spaces, iroh-based control plane."
 repository = "https://github.com/tsunagi-net/tsunagi"
-readme = "README.md"
-keywords = ["mesh", "p2p", "iroh", "networking"]
-categories = ["network-programming"]
 
-[features]
-default = ["cli"]
-# The `tsunagi` command line binary. Library users can opt out.
-cli = ["dep:clap", "dep:anstream", "dep:anstyle", "dep:tracing-subscriber", "tokio/signal", "tun-device", "dns-publish"]
-# A real TUN device, so the WireGuard plugin can carry actual IP traffic.
-# Needs CAP_NET_ADMIN at run time; without it the plugin still runs and its
-# in-memory device can be used for tests.
-tun-device = ["dep:tun", "dep:rtnetlink", "dep:caps", "dep:futures-util"]
-# Telling the operating system where to send its questions. Linux only for
-# now; the zone and the server work without it.
-dns-publish = ["dep:zbus"]
-
-[[bin]]
-name = "tsunagi"
-path = "src/bin/tsunagi.rs"
-required-features = ["cli"]
-
-[dependencies]
-clap = { version = "4.5", features = ["derive", "env"], optional = true }
-# Already in the tree through clap. `anstream` strips the escapes when stdout
-# is not a terminal and turns on virtual terminal processing on Windows, so
-# colour is never written where it would show up as rubbish.
-anstream = { version = "1.0", optional = true }
-anstyle = { version = "1.0", optional = true }
-tracing-subscriber = { version = "0.3", features = ["env-filter"], optional = true }
-iroh = { version = "1.2", default-features = false, features = ["tls-ring"] }
-tokio = { version = "1.53", features = ["rt", "rt-multi-thread", "sync", "time", "macros"] }
-rusqlite = { version = "0.40", features = ["bundled"] }
-hkdf = "0.13"
-hmac = "0.13"
-sha2 = "0.11"
-subtle = "2.6"
-zeroize = { version = "1.9", features = ["derive"] }
-rand = "0.10"
-serde = { version = "1.0", features = ["derive"] }
-postcard = { version = "1.1", default-features = false, features = ["use-std"] }
-# Already in the tree through iroh. A packet codec, not a DNS server: the
-# zone logic is ours and a full server framework would be a large dependency
-# for answering A records from memory.
-simple-dns = "0.12"
-# The IANA top-level domain list, compiled in: one function, no
-# dependencies, no network. Used only to warn that a zone name shadows a
-# real public domain, never to refuse one.
-tld = "2.40"
-data-encoding = "2.11"
-hex = "0.4"
-thiserror = "2.0"
-tracing = "0.1"
-fs4 = { version = "1.1", features = ["sync"] }
-directories = "6.0"
-# The real system hostname, without a libc call of our own: this crate is
-# forbidden `unsafe` and will not make one.
-gethostname = "1.1"
-netwatch = "0.19.3"
-bytes = "1.12.1"
-boringtun = { version = "0.7.1", default-features = false }
-tun = { version = "0.8", features = ["async"], optional = true }
-
-# Linux-only interface provisioning. `rtnetlink` configures the interface in
-# process, so no `ip` invocation is ever needed; `caps` keeps CAP_NET_ADMIN
-# out of the effective set except during the moments it is used.
-[target.'cfg(target_os = "linux")'.dependencies]
-rtnetlink = { version = "0.23", optional = true }
-# Pure Rust D-Bus, no libdbus to link against. `tokio` rather than the
-# default reactor, because the agent brings its own.
-zbus = { version = "5.19", default-features = false, features = ["tokio"], optional = true }
-caps = { version = "0.5", optional = true }
-futures-util = { version = "0.3", default-features = false, optional = true }
-
-[dev-dependencies]
-tokio = { version = "1.53", features = ["rt", "rt-multi-thread", "sync", "time", "macros", "process"] }
-tempfile = "3.24"
-tracing-subscriber = { version = "0.3", features = ["env-filter"] }
-
-[lints.rust]
+[workspace.lints.rust]
 missing_docs = "warn"
 unsafe_code = "forbid"
 
-[lints.clippy]
+[workspace.lints.clippy]
 unwrap_used = "warn"
 expect_used = "warn"
 panic = "warn"
+
+[workspace.dependencies]
+iroh = { version = "1.2", default-features = false, features = ["tls-ring"] }
+tokio = { version = "1.53", features = ["rt", "rt-multi-thread", "sync", "time", "macros"] }
+serde = { version = "1.0", features = ["derive"] }
+postcard = { version = "1.1", default-features = false, features = ["use-std"] }
+bytes = "1.12.1"
+thiserror = "2.0"
+tracing = "0.1"
+hex = "0.4"
+data-encoding = "2.11"
+tempfile = "3.24"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }