fix(ci): clippy::double_must_use on #[async_trait] traits + stop toolchain drift (BRO-2814)

.github/dependabot.yml

@@ -7,6 +7,14 @@ updates:
     open-pull-requests-limit: 10
     labels:
       - dependencies
+    # BRO-2814: one grouped PR for routine bumps instead of ten separate
+    # ones hitting the same CI gates in parallel. Major bumps (API breaks)
+    # stay ungrouped so they still get individual review.
+    groups:
+      cargo-patch-and-minor:
+        update-types:
+          - minor
+          - patch
   - package-ecosystem: github-actions
     directory: /
     schedule:

.github/workflows/ci.yml

@@ -20,6 +20,11 @@ on:
       - "docs/**"
       - "research/**"
   workflow_dispatch:
+  # BRO-2814/BRO-2806: main's latest CI run must be under 7 days old even
+  # with no pushes — toolchain drift (e.g. `stable` floating to a new
+  # rustc/clippy) otherwise surfaces only when someone happens to push.
+  schedule:
+    - cron: "0 6 * * 1"
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
@@ -40,8 +45,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v7
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@master
         with:
+          toolchain: "1.99.0"
           components: rustfmt
       - run: cargo fmt --all -- --check
 
@@ -53,8 +59,9 @@ jobs:
       - uses: actions/checkout@v7
       - name: Install protoc
         run: sudo apt-get update && sudo apt-get install -y protobuf-compiler
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@master
         with:
+          toolchain: "1.99.0"
           components: clippy
       - uses: Swatinem/rust-cache@v2
       - run: cargo clippy --workspace -- -D warnings -A clippy::too_many_arguments
@@ -92,7 +99,9 @@ jobs:
           df -h /
       - name: Install protoc
         run: sudo apt-get update && sudo apt-get install -y protobuf-compiler
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: "1.99.0"
       - uses: Swatinem/rust-cache@v2
         with:
           prefix-key: v1-rust
@@ -121,7 +130,9 @@ jobs:
       - uses: actions/checkout@v7
       - name: Install protoc
         run: brew install protobuf
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: "1.99.0"
       - uses: Swatinem/rust-cache@v2
       - run: cargo test --workspace
 
@@ -157,7 +168,9 @@ jobs:
     continue-on-error: true
     steps:
       - uses: actions/checkout@v7
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: "1.99.0"
       - uses: Swatinem/rust-cache@v2
       - run: cargo install cargo-deny --locked
       - run: cargo deny check
@@ -170,7 +183,9 @@ jobs:
       - uses: actions/checkout@v7
       - name: Install protoc
         run: sudo apt-get update && sudo apt-get install -y protobuf-compiler
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: "1.99.0"
       - uses: Swatinem/rust-cache@v2
       - name: Run scripts/verify_dependencies_lifed.sh
         run: bash scripts/verify_dependencies_lifed.sh
@@ -183,7 +198,9 @@ jobs:
       - uses: actions/checkout@v7
       - name: Install protoc
         run: sudo apt-get update && sudo apt-get install -y protobuf-compiler
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: "1.99.0"
       - uses: Swatinem/rust-cache@v2
       - name: Run scripts/verify_dependencies_lifegw.sh
         run: bash scripts/verify_dependencies_lifegw.sh
@@ -196,7 +213,9 @@ jobs:
       - uses: actions/checkout@v7
       - name: Install protoc
         run: sudo apt-get update && sudo apt-get install -y protobuf-compiler
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: "1.99.0"
       - uses: Swatinem/rust-cache@v2
       - name: Run scripts/verify_dependencies_lifegw_anthropic_codec.sh
         run: bash scripts/verify_dependencies_lifegw_anthropic_codec.sh
@@ -217,7 +236,9 @@ jobs:
       - uses: actions/checkout@v7
       - name: Install protoc
         run: sudo apt-get update && sudo apt-get install -y protobuf-compiler
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: "1.99.0"
       - uses: Swatinem/rust-cache@v2
       - name: Self-test (regression guard for FAIL-path detection)
         run: bash scripts/verify_dependencies_ergon.sh --self-test
@@ -246,8 +267,9 @@ jobs:
       - uses: actions/checkout@v7
       - name: Install protoc
         run: sudo apt-get update && sudo apt-get install -y protobuf-compiler
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@master
         with:
+          toolchain: "1.99.0"
           components: rustfmt, clippy
       - uses: Swatinem/rust-cache@v2
       - name: Format check (ergon)
@@ -346,7 +368,9 @@ jobs:
       - uses: actions/checkout@v7
       - name: Install protoc
         run: sudo apt-get update && sudo apt-get install -y protobuf-compiler
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: "1.99.0"
       - uses: oven-sh/setup-bun@v2
         with:
           bun-version: latest

.github/workflows/harness.yml

@@ -64,8 +64,9 @@ jobs:
           df -h /
       - name: Install protoc
         run: sudo apt-get update && sudo apt-get install -y protobuf-compiler
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@master
         with:
+          toolchain: "1.99.0"
           components: rustfmt, clippy
       - uses: Swatinem/rust-cache@v2
         with:

Cargo.toml

@@ -417,6 +417,14 @@ gray_matter = { version = "0.2", default-features = false, features = ["yaml"] }
 
 [workspace.lints.clippy]
 too_many_arguments = "allow"
+# BRO-2814: async_trait's generated methods return a boxed `dyn Future`,
+# which clippy (since the stable->1.99.0 bump) treats as already
+# #[must_use]; the #[must_use] async_trait also stamps on top then reads
+# as redundant. Not a bug in any of the ~60 `#[async_trait]` port traits
+# this flags across the workspace — a known async-trait/clippy
+# interaction. Two crates that predate `[lints] workspace = true`
+# (arcan-tui, life-cli) carry a local #[allow(...)] instead.
+double_must_use = "allow"
 
 [profile.release]
 lto = "thin"

crates/arcan/arcan-tui/src/client.rs

@@ -102,6 +102,10 @@ pub struct ProviderInfo {
 ///
 /// Implementations may use HTTP/SSE (daemon mode) or direct function calls
 /// (in-process mode). The TUI's `App` only sees this trait.
+#[allow(
+    clippy::double_must_use,
+    reason = "async_trait boxes the return in a Pin<Box<dyn Future>>, which clippy now treats as already #[must_use]; the attribute it generates on top is therefore redundant, not a real bug"
+)]
 #[async_trait]
 pub trait AgentClientPort: Send + Sync + 'static {
     /// Submit a user message to start or continue a run.

crates/cli/life-cli/src/deploy/backend.rs

@@ -34,6 +34,10 @@ pub struct DeploymentResult {
 ///
 /// Implementations handle the specifics of provisioning, monitoring, and
 /// tearing down agent stacks on different cloud providers.
+#[allow(
+    clippy::double_must_use,
+    reason = "async_trait boxes the return in a Pin<Box<dyn Future>>, which clippy now treats as already #[must_use]; the attribute it generates on top is therefore redundant, not a real bug"
+)]
 #[async_trait]
 pub trait DeployBackend: Send + Sync {
     /// Deploy an agent template to the cloud target.

crates/lago/lago-ingest/src/lib.rs

@@ -3,6 +3,7 @@ pub mod codec;
 pub mod server;
 
 /// Generated protobuf types.
+#[allow(unused_qualifications, clippy::all)]
 pub mod proto {
     tonic::include_proto!("lago.v1");
 }

crates/spaces-a2a/spaces-a2a/src/grpc.rs

@@ -8,6 +8,7 @@ use crate::types::{MessagePart, TaskMessage};
 use std::sync::Arc;
 use tonic::{Request, Response, Status};
 
+#[allow(unused_qualifications, clippy::all)]
 pub mod pb {
     tonic::include_proto!("a2a.v1");
 }

rust-toolchain.toml

@@ -0,0 +1,18 @@
+# BRO-2814: pin the toolchain CI and local dev both resolve to.
+#
+# Before this file existed, every CI job used `dtolnay/rust-toolchain@stable`,
+# which floats to whatever is current `stable` on the day the job runs. main
+# went red with no code change in between: `stable` moved from rustc 1.93.0
+# to 1.99.0 and a new clippy lint pass started flagging every
+# `#[async_trait]`-annotated trait as `clippy::double_must_use`. Pinning here
+# makes that kind of drift a deliberate, reviewed bump (edit this file, see
+# what breaks, fix it in the same PR) instead of a silent one that only shows
+# up when Dependabot or a push happens to land that week.
+#
+# Bump deliberately: update `channel`, run `cargo fmt && cargo clippy
+# --workspace -- -D warnings -A clippy::too_many_arguments && cargo test
+# --workspace` locally, fix whatever the new toolchain flags, then commit
+# both together.
+[toolchain]
+channel = "1.99.0"
+components = ["rustfmt", "clippy"]