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fix(AGENTS.md): canister env vars are settings, not WASM metadata #1424

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marc0olo merged 1 commit into from
Jun 18, 2026
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fix(AGENTS.md): canister env vars are settings, not WASM metadata #1424

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4 changes: 2 additions & 2 deletions AGENTS.md
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Original file line number Diff line number Diff line change
Expand Up @@ -180,7 +180,7 @@ environments:
ICP_LEDGER_CANISTER_ID: "ryjl3-tyaaa-aaaaa-aaaba-cai"
```

icp-cli injects these as WASM metadata before `cargo build`. Read them at **runtime** via `ic_cdk::api::env_var_value("ICP_LEDGER_CANISTER_ID")` (Rust) or `Runtime.envVar<system>("ICP_LEDGER_CANISTER_ID")` (Motoko) — not via `env!()` or `std::env::var()`.
icp-cli applies these as canister settings at deploy time. Read them at **runtime** via `ic_cdk::api::env_var_value("ICP_LEDGER_CANISTER_ID")` (Rust) or `Runtime.envVar<system>("ICP_LEDGER_CANISTER_ID")` (Motoko) — not via `env!()` or `std::env::var()`.

**When to apply this pattern**: judge whether staging/production environments make sense for the specific example. Apply it when the example hardcodes an external canister principal that has a test counterpart (TESTICP, testnet URLs, staging governance canisters, etc.). Skip it for self-contained examples that don't call external canisters.

Expand Down Expand Up @@ -274,7 +274,7 @@ Always use `ic-cdk = "0.20"` unless a dependency forces a lower version. When us

### Environment variables in Rust canisters

Use `ic_cdk::api::env_var_value("VAR_NAME")` to read icp-cli-injected variables at **runtime** from WASM metadata. This is the Rust equivalent of `Runtime.envVar<system>` in Motoko:
Use `ic_cdk::api::env_var_value("VAR_NAME")` to read canister environment variables at **runtime**. These are canister settings applied by icp-cli at deploy time, not WASM metadata. This is the Rust equivalent of `Runtime.envVar<system>` in Motoko:

```rust
fn ledger_principal() -> Principal {
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