workspace: scaffold + three stub crates (sip/tap/spend)

Workspace root, pinned toolchain, and the three stub crates whose only
job in slice 1 is to lock the ADR-0002 boundary shape. Each ships a
lib.rs module doc (what it will hold, why deferred, which spearhead step
fills it) and a crate_compiles test. Spec §2.2.

crates/rutster-signaling-sip/Cargo.toml

@@ -0,0 +1,8 @@
+# crates/rutster-signaling-sip/Cargo.toml
+[package]
+name = "rutster-signaling-sip"
+version = "0.0.0"
+license.workspace = true
+edition.workspace = true
+repository.workspace = true
+description = "Rust-native trunk SIP — stub crate (filled in spearhead step 5)."

crates/rutster-signaling-sip/src/lib.rs

@@ -0,0 +1,23 @@
+//! # rutster-signaling-sip
+//!
+//! **Status:** stub. Fills in at spearhead step 5 (PSTN trunk).
+//!
+//! This crate will hold the Rust-native trunk SIP stack: the SIP parser,
+//! transaction layer, dialog state, and the carrier trunk integration. See
+//! [ADR-0003](../../../docs/adr/0003-sip-rust-native-trunk.md) for the
+//! "own the parser from day one" thesis and [PORT_PLAN §1](../../../docs/PORT_PLAN.md)
+//! for the surface area (`res_pjsip_session`, `chan_sip`, `_sdp_rtp` rows).
+//!
+//! Slice 1's WebRTC-only ingress needs no SIP — this stub exists to lock the
+//! crate boundary without anticipating code (spec §2.2). It depends on
+//! nothing in the workspace in slice 1. Its future dependency direction is
+//! `rutster-signaling-sip` → `rutster-call-model` + `rutster-media` (once
+//! the SDP help lives here, moved out of `rutster-media`'s WebRTC-ICE-coupled
+//! SDP module — see §3.7 of the slice-1 spec for the split rationale).
+
+#[cfg(test)]
+mod tests {
+    /// Stub crates lock boundaries; the compile-test is the lock.
+    #[test]
+    fn crate_compiles() {}
+}

crates/rutster-spend/Cargo.toml

@@ -0,0 +1,8 @@
+# crates/rutster-spend/Cargo.toml
+[package]
+name = "rutster-spend"
+version = "0.0.0"
+license.workspace = true
+edition.workspace = true
+repository.workspace = true
+description = "In-boundary spend / abuse gate — stub crate (filled in spearhead step 6)."

crates/rutster-spend/src/lib.rs

@@ -0,0 +1,21 @@
+//! # rutster-spend
+//!
+//! **Status:** stub. Fills in at spearhead step 6 (spend cap / abuse gate).
+//!
+//! In-boundary spend and abuse control is constitutive of the wedge
+//! ([ADR-0002](../../../docs/adr/0002-north-star-and-fused-core.md)): the
+//! runaway brain structurally cannot exceed spend or pacing because it
+//! doesn't hold the wire — the trunk termination + spend gate do, in one
+//! boundary. Pulling spend out into a service re-introduces the 3-vendor
+//! structural hole the fused vertical was chosen to eliminate.
+//!
+//! This crate will hold: spend caps, pacing caps, deny-by-default routing,
+//! rate-limits, toll-fraud pattern detection — co-located with trunk
+//! termination in `rutster-signaling-sip` (step 5). Depends on nothing in
+//! the workspace in slice 1.
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn crate_compiles() {}
+}

crates/rutster-tap/Cargo.toml

@@ -0,0 +1,8 @@
+# crates/rutster-tap/Cargo.toml
+[package]
+name = "rutster-tap"
+version = "0.0.0"
+license.workspace = true
+edition.workspace = true
+repository.workspace = true
+description = "Agent audio tap — stub crate (filled in spearhead step 2)."

crates/rutster-tap/src/lib.rs

@@ -0,0 +1,21 @@
+//! # rutster-tap
+//!
+//! **Status:** stub. Fills in at spearhead step 2 (the tap itself).
+//!
+//! Slice 1 *pre-paves* the tap by exposing the canonical PCM boundary as
+//! the `AudioSource` / `AudioSink` traits in [`rutster_media`](../rutster-media/index.html),
+//! and wires an `EchoAudioPipe` between sink and source. Step 2 swaps that
+//! pipe for a real WSS tap client (core-as-client, brain-as-server —
+//! [ADR-0006](../../../docs/adr/0006-ingress-posture.md)). No code changes to
+//! `RtcSession` itself in step 2 — that's the test of the seam.
+//!
+//! This crate will, when filled in, re-export `PcmFrame` from
+//! `rutster-media` (one canonical home — spec §3.1) and ship the WSS
+//! tap client + the versioned framing protocol. It depends on nothing in
+//! the workspace in slice 1.
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn crate_compiles() {}
+}