diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
new file mode 100644
index 00000000..c2b1b94b
--- /dev/null
+++ b/.github/copilot-instructions.md
@@ -0,0 +1,161 @@
+# Copilot Instructions for embedded-services
+
+## Overview
+
+This is an embedded controller (EC) services workspace — a collection of `no_std` Rust crates implementing hardware-agnostic business logic for embedded controllers. Services glue together MCU HALs (via `embedded-hal` traits), peripheral drivers, and EC subsystem abstractions (sensors, batteries, fans, USB-PD, etc.) using the Embassy async runtime.
+
+## Build, Test, and Lint
+
+Toolchain: Rust 1.88 (`rust-toolchain.toml`), edition 2024. Targets: `x86_64-unknown-linux-gnu` (std/testing) and `thumbv8m.main-none-eabihf` (ARM Cortex-M33).
+
+```shell
+# Format
+cargo fmt --check
+
+# Lint (all feature combos, both targets)
+cargo hack --feature-powerset --mutually-exclusive-features=log,defmt,defmt-timestamp-uptime clippy --locked --target x86_64-unknown-linux-gnu
+cargo hack --feature-powerset --mutually-exclusive-features=log,defmt,defmt-timestamp-uptime clippy --locked --target thumbv8m.main-none-eabihf
+
+# Test (workspace, host target only)
+cargo test --locked
+
+# Test a single crate
+cargo test --locked -p partition-manager
+
+# Test a single test function
+cargo test --locked -p partition-manager test_name
+
+# Lint test code
+cargo clippy --locked --tests
+
+# Check docs
+cargo doc --no-deps -F log --locked
+cargo doc --no-deps -F defmt --locked
+
+# Unused dependency check
+cargo machete
+
+# Dependency license/advisory/audit checks
+cargo deny check --all-features --locked
+cargo vet --locked
+```
+
+The `examples/` directory contains separate workspaces (excluded from the root workspace). Build/lint them independently:
+
+```shell
+# ARM board examples
+cd examples/rt685s-evk && cargo clippy --target thumbv8m.main-none-eabihf --locked
+# Std examples
+cd examples/std && cargo clippy --locked
+```
+
+## Architecture
+
+### Service Pattern
+
+Each service crate follows a consistent structure:
+
+1. **Service struct** with a `comms::Endpoint` and domain-specific context/state
+2. **`MailboxDelegate` impl** — the `receive()` method handles incoming messages using type-safe downcasting via `message.data.get::<T>()`
+3. **Global singleton** — services are stored in `OnceLock<Service>` statics
+4. **Async task function** — registers the endpoint, then loops calling a `process()` or `process_next()` method
+5. **Spawned via Embassy** — `#[embassy_executor::task]` functions are spawned from main
+
+```rust
+// Typical service skeleton
+pub struct MyService {
+    endpoint: comms::Endpoint,
+    // ... domain state
+}
+
+impl comms::MailboxDelegate for MyService {
+    fn receive(&self, message: &comms::Message) -> Result<(), comms::MailboxDelegateError> {
+        if let Some(event) = message.data.get::<MyEvent>() {
+            // handle event
+        }
+        Ok(())
+    }
+}
+
+static SERVICE: OnceLock<MyService> = OnceLock::new();
+
+pub async fn task() {
+    let service = SERVICE.get_or_init(MyService::new);
+    comms::register_endpoint(service, &service.endpoint).await.unwrap();
+    loop {
+        service.process_next().await;
+    }
+}
+```
+
+### Communication (IPC)
+
+Services communicate through `embedded_services::comms` — a type-erased message routing system built on intrusive linked lists (zero allocation):
+
+- **EndpointID**: `Internal(Battery | Thermal | ...)` or `External(Host | Debug | ...)`
+- **Messages**: use `&dyn Any` for payload, receivers downcast with `message.data.get::<T>()`
+- Services call `embedded_services::init()` before registering endpoints
+- Each `EndpointID` has its own static intrusive list of registered endpoints
+
+### Composition
+
+At the top level, an EC is composed by spawning service tasks on an Embassy executor:
+
+```rust
+embedded_services::init().await;
+spawner.must_spawn(battery_service_task());
+spawner.must_spawn(thermal_service_task());
+spawner.must_spawn(power_policy_task(config));
+```
+
+### Core Utilities (embedded-service crate)
+
+- **`GlobalRawMutex`**: `ThreadModeRawMutex` on ARM bare-metal, `CriticalSectionRawMutex` in tests/std
+- **`SyncCell<T>`**: `ThreadModeCell` on ARM, `CriticalSectionCell` elsewhere — interior mutability for embedded
+- **`define_static_buffer!`**: macro for creating static buffers with borrow-checked `OwnedRef`/`SharedRef` access
+- **`intrusive_list`**: no-alloc linked list using embedded `Node` fields for endpoint routing
+- **`Never`**: type alias for `core::convert::Infallible` used in `Result<Never, Error>` for tasks that shouldn't return
+
+## Key Conventions
+
+### `no_std` and Feature Flags
+
+All service crates are `#![no_std]`. Logging is feature-gated with **mutually exclusive** features:
+
+- `defmt` — embedded debug formatting (used on bare-metal targets)
+- `log` — standard Rust logging (used on std targets / tests)
+
+These must never be enabled simultaneously in production. Use the unified macros from `embedded_services::fmt` (`trace!`, `debug!`, `info!`, `warn!`, `error!`) which dispatch to the correct backend.
+
+### Error Handling
+
+- Custom `enum` error types per module — no `thiserror` (it requires std)
+- All error enums derive `Debug, Clone, Copy, PartialEq, Eq`
+- Conditional defmt support: `#[cfg_attr(feature = "defmt", derive(defmt::Format))]`
+- Result type aliases per module (e.g., `pub type BatteryResponse = Result<ContextResponse, ContextError>`)
+
+### Clippy Configuration
+
+The workspace enforces strict clippy lints (in root `Cargo.toml`). Key denials:
+
+- `unwrap_used`, `expect_used`, `panic`, `unreachable`, `unimplemented`, `todo` — no panicking in production code
+- `indexing_slicing` — use `.get()` instead of `[]`
+- Tests can relax these with `#[allow(clippy::panic)]`, `#[allow(clippy::unwrap_used)]`
+
+### Dependencies
+
+- Workspace dependencies are centralized in root `Cargo.toml` under `[workspace.dependencies]`; member crates use `dep.workspace = true`
+- Git dependencies from the OpenDevicePartnership GitHub org (embassy-imxrt, embedded-usb-pd, tps6699x, etc.)
+- Feature-gated optional deps (`log`, `defmt`) should be listed in `[package.metadata.cargo-machete] ignored` to avoid false positives
+- Supply chain security enforced via `cargo-vet` (config in `supply-chain/`) and `cargo-deny` (config in `deny.toml`)
+
+### Testing
+
+- Async tests use `embassy_futures::block_on(async { ... })`
+- Dev-dependencies enable `std` features: `embassy-sync/std`, `embassy-time/std`, `critical-section/std`
+- `tokio` with `rt`, `macros`, `time` features for integration tests
+- Tests are organized in `#[cfg(test)]` modules or dedicated `test/` subdirectories
+
+### Formatting
+
+Max line width is 120 characters (`rustfmt.toml`).