fix(env): propagate explicit exec versions to package manager shims

Author: liangmiQwQ

crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/shim_injected_tool_contracts/snapshots.toml

@@ -160,3 +160,12 @@ steps = [
   { argv = ["vp", "env", "on", "npm"], snapshot = false },
   { argv = ["vp", "env", "exec", "--node", "22.18.0", "node", "assert-unix-shim-path.cjs", "partial", "10.5.0"], comment = "A project npm pin still takes priority over bundled npm after a PATH reset" },
 ]
+
+[[case]]
+name = "explicit_npm_after_partial_path_reset"
+vp = "global"
+skip-platforms = ["windows"]
+env = { VP_NPM_VERSION = "10.9.4" }
+steps = [
+  { argv = ["vp", "env", "exec", "--node", "22.18.0", "--npm", "10.5.0", "node", "assert-unix-shim-path.cjs", "partial", "10.5.0"], comment = "An explicit npm version overrides the inherited version and survives a PATH reset" },
+]

crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/shim_injected_tool_contracts/snapshots/explicit_npm_after_partial_path_reset.md

@@ -0,0 +1,9 @@
+# explicit_npm_after_partial_path_reset
+
+## `vp env exec --node 22.18.0 --npm 10.5.0 node assert-unix-shim-path.cjs partial 10.5.0`
+
+An explicit npm version overrides the inherited version and survives a PATH reset
+
+```
+Node and its tools survive partial PATH
+```

crates/vp_global_cli/src/commands/env/exec.rs

@@ -226,6 +226,11 @@ async fn execute_with_version(
     let mut child = tokio::process::Command::new(cmd);
     child.args(args).envs(child_env.into_envs()).env(env_vars::VP_NODE_VERSION, &resolved_node);
     if let Some(package_manager) = resolved_package_manager {
+        if explicit_package_manager {
+            // Preserve explicit versions when a child removes the injected tool directory from PATH.
+            let (kind, version, _) = parse_package_manager_spec_with_hash(&package_manager)?;
+            child.env(package_manager_resolution::version_env_var(kind), version);
+        }
         child.env(env_vars::VP_PACKAGE_MANAGER, package_manager);
     }
     // The child runs in the inherited cwd, which a leading `-C <dir>` changes