Stop #[contract] injecting alloc use-imports into caller's crate root (#117)

* Stop #[contract] injecting alloc use-imports into caller's crate root

The alloc_setup block emitted at the caller's crate root (sibling of the
contract mod) injected `use alloc::vec;`, `use alloc::vec::Vec;`, and
`use alloc::string::String;` alongside `extern crate alloc;`, gated to
non-abi-gen riscv builds in allocator modes.

These three imports are dead weight:
- They don't reach the contract mod (Rust modules don't inherit a parent
  module's `use`); in-mod user code that needs Vec/String brings its own
  import, which the macro already cfg-gates via use_tree_imports_alloc.
- No generated code consumes them. Every generated allocation uses fully
  qualified paths already (`alloc::vec![..]`, `alloc::vec::Vec<u8>` in the
  dispatch/decode/router codegen), resolved through `extern crate alloc;`.

Their only effect was polluting the caller's crate root, so contract
authors with crate-root helper code that imports Vec/String hit a
confusing E0252/E0259 pointing at the macro invocation line rather than
their own import.

Drop the three imports from both allocator arms; keep `extern crate
alloc;` (load-bearing for the qualified paths). No behavior change for any
contract that compiles today.

Verified: pvm-contract-macros test suite (171 unit + all integration +
trybuild) passes, and all 7 example-mytoken contracts build via the CLI,
including the pico-alloc and bump-alloc variants that exercise this path.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* Document the no-use-injection codegen convention at the emission site

Add a comment explaining why alloc_setup keeps `extern crate alloc;` but
must not inject `use alloc::...` imports, so the deleted imports aren't
reintroduced.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* Retry transient null-response deploy failures in e2e cast harness

CI flaked twice on this branch with 'cast deploy failed: Error: server
returned a null response when a non-null response was expected', hitting
a different test each run (error_call, then dynamic_bytes_length +
dynamic_echo_string). A freshly started anvil-polkadot occasionally
answers a JSON-RPC request with null; retry that specific transient
error up to 3 times before failing the test.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Revert "Retry transient null-response deploy failures in e2e cast harness"

This reverts commit b83acf8.

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: shawntabrizi

crates/pvm-contract-macros/src/codegen/contract.rs

@@ -1223,22 +1223,22 @@ pub fn expand_contract(args: ContractArgs, input: ItemMod) -> syn::Result<TokenS
 
     let mod_content = strip_pvm_attrs(&input, struct_name)?;
 
+    // `alloc_setup` is emitted at the caller's crate root (sibling of the
+    // contract mod). Keep `extern crate alloc;` here, but do NOT add
+    // `use alloc::vec::Vec;` / `use alloc::string::String;` etc.: a `use` at
+    // the crate root pollutes the caller's namespace (colliding with the
+    // author's own crate-root imports, surfacing as E0252/E0259 pointed at the
+    // macro line) and is never consumed — it doesn't reach the contract mod
+    // (modules don't inherit a parent's `use`), and all generated allocations
+    // are fully qualified (`alloc::vec![..]`, `alloc::vec::Vec<u8>`). Codegen
+    // convention: reference external items by absolute path, never inject `use`.
     let alloc_setup = match args.allocator {
         Some(AllocatorKind::Pico) => {
             let allocator_size = args.allocator_size;
             quote! {
                 #[cfg(not(feature = "abi-gen"))]
                 extern crate alloc;
 
-                #[cfg(all(not(feature = "abi-gen"), any(target_arch = "riscv32", target_arch = "riscv64")))]
-                use alloc::vec;
-
-                #[cfg(all(not(feature = "abi-gen"), any(target_arch = "riscv32", target_arch = "riscv64")))]
-                use alloc::vec::Vec;
-
-                #[cfg(all(not(feature = "abi-gen"), any(target_arch = "riscv32", target_arch = "riscv64")))]
-                use alloc::string::String;
-
                 #[cfg(all(not(feature = "abi-gen"), any(target_arch = "riscv32", target_arch = "riscv64")))]
                 #[global_allocator]
                 static mut ALLOC: picoalloc::Mutex<picoalloc::Allocator<picoalloc::ArrayPointer<#allocator_size>>> = {
@@ -1256,15 +1256,6 @@ pub fn expand_contract(args: ContractArgs, input: ItemMod) -> syn::Result<TokenS
                 #[cfg(not(feature = "abi-gen"))]
                 extern crate alloc;
 
-                #[cfg(all(not(feature = "abi-gen"), any(target_arch = "riscv32", target_arch = "riscv64")))]
-                use alloc::vec;
-
-                #[cfg(all(not(feature = "abi-gen"), any(target_arch = "riscv32", target_arch = "riscv64")))]
-                use alloc::vec::Vec;
-
-                #[cfg(all(not(feature = "abi-gen"), any(target_arch = "riscv32", target_arch = "riscv64")))]
-                use alloc::string::String;
-
                 #[cfg(all(not(feature = "abi-gen"), any(target_arch = "riscv32", target_arch = "riscv64")))]
                 #[global_allocator]
                 static ALLOC: pvm_bump_allocator::BumpAllocator<#allocator_size> =