fix(ci): remove the three sources of flakiness in the weekly example runs

.github/workflows/_run-example.yml

@@ -60,6 +60,17 @@ jobs:
         uses: dfinity/pocketic@a980c334fab1b21b0b8a6bba38e1a10836e7258b # main
         with:
           pocket-ic-server-version: ${{ inputs.pocketic-version }}
+      # Projects with more than one Motoko canister run one `mops build` per canister
+      # concurrently, and those invocations race on the shared moc toolchain download and
+      # extraction: whichever build loses reads a half-extracted moc and fails with no
+      # diagnostics. Warming the cache first makes the download happen exactly once.
+      # Remove once caffeinelabs/mops#818 is fixed and released.
+      - name: Warm the mops toolchain cache
+        working-directory: ${{ inputs.working-directory }}
+        run: |
+          if [ -f mops.toml ] && command -v mops > /dev/null; then
+            mops install
+          fi
       - name: Run
         working-directory: ${{ inputs.working-directory }}
         run: ${{ inputs.run }}

motoko/evm_block_explorer/README.md

@@ -83,6 +83,8 @@ Both give the same interface as long as `icp.yaml` pins the release that is live
 
 The example uses [PublicNode](https://ethereum-rpc.publicnode.com) by default — a free, no-registration provider that works out of the box locally and on mainnet. This is sufficient for getting started and automated testing.
 
+PublicNode routes requests across regional node pools, and not all of them keep the full chain history — some only retain blocks from shortly before the Merge (block ~15500000). Queries for earlier blocks therefore fail with `pruned history unavailable` depending on which pool serves the outcall. `test.sh` queries a post-Merge block for that reason; an archive provider is needed to read early history reliably.
+
 For production deployments requiring premium providers (Alchemy, Ankr, BlockPi), refer to the [EVM RPC canister documentation](https://github.com/dfinity/evm-rpc-canister) for how to configure API keys. Once configured, change `#EthMainnet(?[#PublicNode])` in `backend/EvmRpcApi.mo` to `#EthMainnet(null)` to use all configured providers for better consensus.
 
 ## Security considerations and best practices

motoko/evm_block_explorer/test.sh

@@ -1,9 +1,16 @@
 #!/usr/bin/env bash
 set -e
 
-echo "=== Test 1: get_evm_block returns correct data for Ethereum mainnet block 1 ==="
-result=$(icp canister call backend get_evm_block '(1)')
+# Block 20000000 is post-Merge. PublicNode serves several regional node pools and some of
+# them only retain history from shortly before the Merge (block ~15500000), so querying
+# early blocks such as block 1 fails depending on which pool the outcall lands in.
+BLOCK=20000000
+BLOCK_HASH=0xd24fd73f794058a3807db926d8898c6481e902b7edb91ce0d479d6760f276183
+BLOCK_MINER=0x95222290dd7278aa3ddd389cc1e1d165cc4bafe5
+
+echo "=== Test 1: get_evm_block returns correct data for Ethereum mainnet block $BLOCK ==="
+result=$(icp canister call backend get_evm_block "($BLOCK)")
 echo "$result"
 echo "$result" | grep -q "Ok" && echo "PASS (Ok variant)" || (echo "FAIL (expected Ok)" && exit 1)
-echo "$result" | grep -q "0x88e96d4537bea4d9c05d12549907b32561d3bf31f45aae734cdc119f13406cb6" && echo "PASS (hash)" || (echo "FAIL (wrong hash)" && exit 1)
-echo "$result" | grep -q "0x05a56e2d52c817161883f50c441c3228cfe54d9f" && echo "PASS (miner)" || (echo "FAIL (wrong miner)" && exit 1)
+echo "$result" | grep -q "$BLOCK_HASH" && echo "PASS (hash)" || (echo "FAIL (wrong hash)" && exit 1)
+echo "$result" | grep -q "$BLOCK_MINER" && echo "PASS (miner)" || (echo "FAIL (wrong miner)" && exit 1)

rust/evm_block_explorer/README.md

@@ -64,6 +64,8 @@ icp build backend && candid-extractor target/wasm32-unknown-unknown/release/back
 
 The example uses [PublicNode](https://ethereum-rpc.publicnode.com) by default — a free, no-registration provider that works out of the box locally and on mainnet. This is sufficient for getting started and automated testing.
 
+PublicNode routes requests across regional node pools, and not all of them keep the full chain history — some only retain blocks from shortly before the Merge (block ~15500000). Queries for earlier blocks therefore fail with `pruned history unavailable` depending on which pool serves the outcall. `test.sh` queries a post-Merge block for that reason; an archive provider is needed to read early history reliably.
+
 For production deployments requiring premium providers (Alchemy, Ankr, BlockPi), refer to the [EVM RPC canister documentation](https://github.com/dfinity/evm-rpc-canister) for how to configure API keys. Once configured, change `RpcServices::EthMainnet(Some(vec![EthMainnetService::PublicNode]))` in `backend/src/lib.rs` to `RpcServices::EthMainnet(None)` to use all configured providers for better consensus.
 
 ## Security considerations and best practices

rust/evm_block_explorer/test.sh

@@ -1,9 +1,16 @@
 #!/usr/bin/env bash
 set -e
 
-echo "=== Test 1: get_evm_block returns correct data for Ethereum mainnet block 1 ==="
-result=$(icp canister call backend get_evm_block '(1)')
+# Block 20000000 is post-Merge. PublicNode serves several regional node pools and some of
+# them only retain history from shortly before the Merge (block ~15500000), so querying
+# early blocks such as block 1 fails depending on which pool the outcall lands in.
+BLOCK=20000000
+BLOCK_HASH=0xd24fd73f794058a3807db926d8898c6481e902b7edb91ce0d479d6760f276183
+BLOCK_MINER=0x95222290dd7278aa3ddd389cc1e1d165cc4bafe5
+
+echo "=== Test 1: get_evm_block returns correct data for Ethereum mainnet block $BLOCK ==="
+result=$(icp canister call backend get_evm_block "($BLOCK)")
 echo "$result"
 echo "$result" | grep -q "Ok" && echo "PASS (Ok variant)" || (echo "FAIL (expected Ok)" && exit 1)
-echo "$result" | grep -q "0x88e96d4537bea4d9c05d12549907b32561d3bf31f45aae734cdc119f13406cb6" && echo "PASS (hash)" || (echo "FAIL (wrong hash)" && exit 1)
-echo "$result" | grep -q "0x05a56e2d52c817161883f50c441c3228cfe54d9f" && echo "PASS (miner)" || (echo "FAIL (wrong miner)" && exit 1)
+echo "$result" | grep -q "$BLOCK_HASH" && echo "PASS (hash)" || (echo "FAIL (wrong hash)" && exit 1)
+echo "$result" | grep -q "$BLOCK_MINER" && echo "PASS (miner)" || (echo "FAIL (wrong miner)" && exit 1)

rust/unit_testable_rust_canister/backend/tests/integration_tests.rs

@@ -4,6 +4,7 @@ use serde::Deserialize;
 use std::io;
 use std::path::{Path, PathBuf};
 use std::process::Command;
+use std::sync::LazyLock;
 use std::time::SystemTime;
 use walkdir::WalkDir;
 
@@ -21,11 +22,19 @@ const IC_COMMIT_FOR_PROPOSALS: &str = "4b7cde9a0e3b5ad4725e75cbc36ce635be6fa6a8"
 const NNS_GOVERNANCE_CANISTER_ID: &str = "rrkah-fqaaa-aaaaa-aaaaq-cai";
 const NNS_ROOT_CANISTER_ID: &str = "r7inp-6aaaa-aaaaa-aaabq-cai";
 
-// WASM will be loaded dynamically with smart rebuilding
-fn get_backend_wasm() -> Vec<u8> {
+// Tests run concurrently on separate threads but share the files below, so each artifact is
+// prepared exactly once per test binary. Without this, two tests building or downloading the
+// same path at the same time can read a half-written file.
+static BACKEND_WASM: LazyLock<Vec<u8>> = LazyLock::new(|| {
     let wasm_path = ensure_wasm_built();
     std::fs::read(&wasm_path)
         .unwrap_or_else(|e| panic!("Failed to read WASM file at {:?}: {}", wasm_path, e))
+});
+
+static GOVERNANCE_WASM: LazyLock<Vec<u8>> = LazyLock::new(load_governance_wasm);
+
+fn get_backend_wasm() -> Vec<u8> {
+    BACKEND_WASM.clone()
 }
 
 /// Ensures the WASM is built and up-to-date, returns path to the WASM file
@@ -123,45 +132,80 @@ fn rebuild_wasm() {
     }
 }
 
+/// Download to a temporary file and rename into place, so an interrupted or failed transfer
+/// never leaves a truncated file behind for the next run to pick up from the cache. The
+/// temporary name carries the process id so that concurrent runs of the test binary cannot
+/// clobber each other's transfer either.
 fn download_wasm_to(url: String, wasm_path: &Path) {
-    // Ensure the target directory exists
     if let Some(parent) = wasm_path.parent() {
         std::fs::create_dir_all(parent)
             .unwrap_or_else(|e| panic!("Failed to create directory {:?}: {}", parent, e));
     }
-
-    let wasm = std::process::Command::new("curl")
-        .args(["-L", "-f", &url])
+    let download_path = wasm_path.with_extension(format!("gz.{}.partial", std::process::id()));
+
+    let output = Command::new("curl")
+        .args([
+            "--location",
+            "--fail",
+            "--silent",
+            "--show-error",
+            "--retry",
+            "5",
+            "--retry-all-errors",
+            "--retry-delay",
+            "2",
+            "--output",
+            &download_path.to_string_lossy(),
+            &url,
+        ])
         .output()
-        .expect("Failed to download NNS Governance WASM")
-        .stdout;
+        .expect("Failed to run curl");
+
+    if !output.status.success() {
+        let _ = std::fs::remove_file(&download_path);
+        panic!(
+            "Failed to download {url}: curl exited with {:?}: {}",
+            output.status.code(),
+            String::from_utf8_lossy(&output.stderr)
+        );
+    }
 
-    std::fs::write(wasm_path, wasm).expect("Failed to write compressed WASM");
+    std::fs::rename(&download_path, wasm_path).expect("Failed to move downloaded WASM into place");
 }
 
-/// Get the NNS Governance WASM binary, downloading if necessary
-fn get_governance_wasm() -> Vec<u8> {
+/// Reads the file only if it is a gzip archive. A missing prefix means a partial or failed
+/// download, which would otherwise surface as an opaque `CanisterInvalidWasm` rejection.
+fn read_gzip(wasm_path: &Path) -> Option<Vec<u8>> {
+    std::fs::read(wasm_path)
+        .ok()
+        .filter(|bytes| bytes.starts_with(&[0x1f, 0x8b]))
+}
+
+/// Get the NNS Governance WASM binary, downloading if necessary.
+/// Call [`get_governance_wasm`] instead — this runs once, behind `GOVERNANCE_WASM`.
+fn load_governance_wasm() -> Vec<u8> {
     let wasm_path = PathBuf::from("../../target/ic/governance-canister.wasm.gz");
 
-    // Check if we need to download
-    if !wasm_path.exists() {
-        let url = format!(
-            "https://download.dfinity.systems/ic/{}/canisters/governance-canister.wasm.gz",
-            IC_COMMIT_FOR_PROPOSALS
-        );
-        download_wasm_to(url, &wasm_path);
-    } else {
+    if let Some(wasm) = read_gzip(&wasm_path) {
         println!("NNS Governance WASM already exists, skipping download");
+        return wasm;
     }
 
-    std::fs::read(&wasm_path).unwrap_or_else(|e| {
-        panic!(
-            "Failed to read governance WASM file at {:?}: {}",
-            wasm_path, e
-        )
+    let url = format!(
+        "https://download.dfinity.systems/ic/{}/canisters/governance-canister.wasm.gz",
+        IC_COMMIT_FOR_PROPOSALS
+    );
+    download_wasm_to(url, &wasm_path);
+
+    read_gzip(&wasm_path).unwrap_or_else(|| {
+        panic!("Downloaded governance WASM at {wasm_path:?} is not a readable gzip archive")
     })
 }
 
+fn get_governance_wasm() -> Vec<u8> {
+    GOVERNANCE_WASM.clone()
+}
+
 /// Sets up a minimal NNS Governance canister for testing.
 ///
 /// **Expected errors in test output (non-fatal):**