ci(host-agent): bootstrap Rust in the runner container; roll to alpha.2

Asgard runner executes jobs in bare node:20-bullseye (no Rust, no sudo)
- install rustup + musl/mingw cross toolchains per-run, same pattern as
setup-go in the Go pipeline. agent-v2.0.0-alpha.1 predates this fix;
forward-only doctrine: version rolls to alpha.2 rather than re-pushing
the tag.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitea/workflows/build-host-agent.yml

@@ -35,11 +35,16 @@ jobs:
             exit 1
           fi
 
-      - name: Install cross toolchains
+      # The Asgard runner executes jobs in a bare node:20-bullseye container
+      # (no Rust, no sudo, runs as root) — bootstrap the toolchain per-run,
+      # same pattern as actions/setup-go in the Go pipeline.
+      - name: Install Rust + cross toolchains
         run: |
-          sudo apt-get update -qq
-          sudo apt-get install -y -qq musl-tools gcc-mingw-w64-x86-64
-          rustup target add x86_64-unknown-linux-musl x86_64-pc-windows-gnu
+          apt-get update -qq
+          apt-get install -y -qq build-essential musl-tools gcc-mingw-w64-x86-64 curl
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain stable --profile minimal
+          echo "$HOME/.cargo/bin" >> $GITHUB_PATH
+          "$HOME/.cargo/bin/rustup" target add x86_64-unknown-linux-musl x86_64-pc-windows-gnu
 
       - name: Build Linux AMD64 (static musl)
         run: |

corrosion-host-agent/Cargo.lock

@@ -258,7 +258,7 @@ checksum = "773648b94d0e5d620f64f280777445740e61fe701025087ec8b57f45c791888b"
 
 [[package]]
 name = "corrosion-host-agent"
-version = "2.0.0-alpha.1"
+version = "2.0.0-alpha.2"
 dependencies = [
  "anyhow",
  "async-nats",

corrosion-host-agent/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "corrosion-host-agent"
-version = "2.0.0-alpha.1"
+version = "2.0.0-alpha.2"
 edition = "2021"
 description = "Corrosion Host Agent — multi-game ops runtime for self-hosted game servers"
 license = "UNLICENSED"