Cargo.lock handling to be same across examples

.gitignore

@@ -1,4 +1,16 @@
-**/target
-**/target_ci
+**/target/
+/target_ci/
+
+# Ignore lock files, except where we don't.
+#   - examples: ignore, they are just samples
+#   - tests: keep. This provides a common ground of dependencies for CI, for example, without providing too much hassle
+#       for co-developers.
+#
+# Note: 'host/' carries both a library and tests. We have the Cargo.lock and expect it *not to be used* by dependencies
+#       (this should be confirmed).
 Cargo.lock
+!/examples/tests/Cargo.lock
+!/host/Cargo.lock
+
+/tests/
 .idea

CONTRIBUTING.md

@@ -0,0 +1,40 @@
+## 📦 Cargo.lock Policy
+
+This repository contains a mix of libraries, examples, and test binaries. To ensure clarity and reproducibility, we follow a nuanced approach to `Cargo.lock` inclusion:
+
+### ✅ What we commit
+We include `Cargo.lock` files **only** for test binaries that are executed in CI:
+
+- [`examples/tests/Cargo.lock`](examples/tests/Cargo.lock)
+- [`host/Cargo.lock`](host/Cargo.lock) — used by `host/tests`
+
+These lockfiles ensure reproducible CI runs and provide a stable dependency baseline for contributors running tests locally.
+
+### ❌ What we ignore
+We do **not** commit `Cargo.lock` for:
+
+- The root crate (which is a library)
+- Example applications (which are not CI-tested and often target MCU hardware)
+
+This aligns with [Cargo's official guidance](https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html), which recommends:
+
+> *“Cargo.lock is not used for libraries to avoid locking dependencies for downstream users.”*
+
+### 🧠 Why this matters
+- **Libraries** should remain flexible for downstream consumers.
+- **Examples** are illustrative and not CI-tested; locking them would add unnecessary maintenance burden.
+- **Test binaries** benefit from locked dependencies to ensure consistent CI behavior and easier debugging.
+
+### 🛠 `.gitignore` setup
+Our root `.gitignore` reflects this policy:
+
+```gitignore
+# Ignore lock files, except where we don't.
+Cargo.lock
+!/examples/tests/Cargo.lock
+!/host/Cargo.lock
+```
+
+<!--
+Text from Copilot discussion, 16-Oct-25
+-->