diff --git a/pacquet/crates/config/src/defaults.rs b/pacquet/crates/config/src/defaults.rs
index 8ed5c0eefc..2a86b0a56f 100644
--- a/pacquet/crates/config/src/defaults.rs
+++ b/pacquet/crates/config/src/defaults.rs
@@ -105,5 +105,60 @@ pub fn default_fetch_retry_maxtimeout() -> u64 {
     60_000
 }
 
+/// Default `childConcurrency` matching upstream's
+/// [`getDefaultWorkspaceConcurrency`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/concurrency.ts#L21-L23):
+/// `min(4, availableParallelism())`. Read at runtime so `cargo test`
+/// and overrides via yaml still resolve to a usable value on
+/// 1-core sandboxes.
+pub fn default_child_concurrency() -> u32 {
+    default_child_concurrency_with_parallelism(available_parallelism())
+}
+
+/// Internal helper exposed for tests so they can pin the
+/// `parallelism` input. Upstream's test suite mocks
+/// `os.availableParallelism` via Jest; pacquet injects the value
+/// directly. Mirrors upstream's [`getDefaultWorkspaceConcurrency`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/concurrency.ts#L21-L23).
+pub fn default_child_concurrency_with_parallelism(parallelism: u32) -> u32 {
+    parallelism.min(4)
+}
+
+/// Available CPU parallelism, mirroring upstream's
+/// [`getAvailableParallelism`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/concurrency.ts#L5-L13).
+/// Floors at 1.
+pub fn available_parallelism() -> u32 {
+    std::thread::available_parallelism().map(|n| n.get() as u32).unwrap_or(1).max(1)
+}
+
+/// Resolve `childConcurrency` from a possibly-negative yaml value
+/// to a concrete `u32`. Mirrors upstream's
+/// [`getWorkspaceConcurrency`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/concurrency.ts#L25-L34):
+///
+/// - `None` → default (`min(4, parallelism)`).
+/// - Positive `n` → `n`.
+/// - Zero or negative `n` → `max(1, parallelism - |n|)`.
+///
+/// The negative-offset semantics let users say "use all cores minus
+/// N" without hardcoding the core count.
+pub fn resolve_child_concurrency(option: Option<i32>) -> u32 {
+    resolve_child_concurrency_with_parallelism(option, available_parallelism())
+}
+
+/// Internal helper exposed for tests so they can pin the
+/// `parallelism` input. Mirrors upstream's
+/// [`getWorkspaceConcurrency`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/concurrency.ts#L25-L34)
+/// — the resolver logic itself, with the parallelism input
+/// injected rather than read from the OS.
+pub fn resolve_child_concurrency_with_parallelism(option: Option<i32>, parallelism: u32) -> u32 {
+    match option {
+        None => default_child_concurrency_with_parallelism(parallelism),
+        Some(n) if n > 0 => n as u32,
+        // `unsigned_abs` instead of `(-n) as u32` — the latter
+        // panics in debug builds on `n == i32::MIN` (negation
+        // overflow); the former returns `i32::MAX as u32 + 1`
+        // safely.
+        Some(n) => parallelism.saturating_sub(n.unsigned_abs()).max(1),
+    }
+}
+
 #[cfg(test)]
 mod tests;
diff --git a/pacquet/crates/config/src/defaults/tests.rs b/pacquet/crates/config/src/defaults/tests.rs
index cf1da78075..adb4c89248 100644
--- a/pacquet/crates/config/src/defaults/tests.rs
+++ b/pacquet/crates/config/src/defaults/tests.rs
@@ -1,4 +1,7 @@
-use super::default_store_dir;
+use super::{
+    default_child_concurrency_with_parallelism, default_store_dir, resolve_child_concurrency,
+    resolve_child_concurrency_with_parallelism,
+};
 use crate::test_env_guard::EnvGuard;
 use pacquet_store_dir::StoreDir;
 use pretty_assertions::assert_eq;
@@ -46,6 +49,96 @@ fn test_default_store_dir_with_xdg_env() {
     assert_eq!(display_store_dir(&store_dir), "/tmp/xdg_data_home/pnpm/store");
 }
 
+/// Port of upstream
+/// [`'getDefaultWorkspaceConcurrency: cpu num < 4'`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/concurrency.test.ts#L25-L28).
+/// On a 1-core host, the default caps at 1 (not 4).
+#[test]
+fn default_child_concurrency_with_parallelism_below_four() {
+    assert_eq!(default_child_concurrency_with_parallelism(1), 1);
+}
+
+/// Port of upstream
+/// [`'getDefaultWorkspaceConcurrency: cpu num > 4'`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/concurrency.test.ts#L30-L33).
+/// Caps at 4 on a 5-core host.
+#[test]
+fn default_child_concurrency_with_parallelism_above_four() {
+    assert_eq!(default_child_concurrency_with_parallelism(5), 4);
+}
+
+/// Port of upstream
+/// [`'getDefaultWorkspaceConcurrency: cpu num = 4'`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/concurrency.test.ts#L35-L38).
+/// At the boundary, 4 is the exact result (not floored or capped).
+#[test]
+fn default_child_concurrency_with_parallelism_at_four() {
+    assert_eq!(default_child_concurrency_with_parallelism(4), 4);
+}
+
+/// Port of upstream
+/// [`'default workspace concurrency'`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/concurrency.test.ts#L48-L52).
+/// `getWorkspaceConcurrency(undefined)` on a >=4-core host yields 4
+/// (the upstream test runs on the default Jest host; on a host with
+/// >=4 cores the default is 4). Pin a >=4 parallelism so the
+/// expectation is deterministic.
+#[test]
+fn resolve_child_concurrency_default_with_four_or_more_cores() {
+    assert_eq!(resolve_child_concurrency_with_parallelism(None, 4), 4);
+    assert_eq!(resolve_child_concurrency_with_parallelism(None, 8), 4);
+}
+
+/// Port of upstream
+/// [`'match host cores amount'`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/concurrency.test.ts#L58-L62).
+/// `getWorkspaceConcurrency(0)` returns the host's parallelism
+/// verbatim — the saturated `parallelism - 0` path.
+#[test]
+fn resolve_child_concurrency_zero_returns_full_parallelism() {
+    assert_eq!(resolve_child_concurrency_with_parallelism(Some(0), 8), 8);
+    assert_eq!(resolve_child_concurrency_with_parallelism(Some(0), 1), 1);
+}
+
+/// Port of upstream
+/// [`'host cores minus X'`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/concurrency.test.ts#L64-L71).
+/// `n = -1` → `max(1, cores - 1)`; `n = -9999` → `1` (saturating).
+/// Replaces the earlier bound-check-only test with the precise
+/// formula that the upstream suite pins.
+#[test]
+fn resolve_child_concurrency_negative_offset_matches_upstream_formula() {
+    // n = -1 with 8 cores → 7.
+    assert_eq!(resolve_child_concurrency_with_parallelism(Some(-1), 8), 7);
+    // n = -1 with 1 core → max(1, 0) → 1.
+    assert_eq!(resolve_child_concurrency_with_parallelism(Some(-1), 1), 1);
+    // n = -9999 saturates → 1 regardless of parallelism.
+    assert_eq!(resolve_child_concurrency_with_parallelism(Some(-9999), 8), 1);
+    assert_eq!(resolve_child_concurrency_with_parallelism(Some(-9999), 1), 1);
+}
+
+/// Existing pacquet test (not from upstream): both the public
+/// `resolve_child_concurrency` and the testable
+/// `_with_parallelism` helper agree on positive inputs. The
+/// upstream
+/// [`'get back positive amount'`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/concurrency.test.ts#L54-L56)
+/// case (`n = 5` → `5`) is checked here alongside the helper
+/// equivalence.
+#[test]
+fn resolve_child_concurrency_positive_amount() {
+    assert_eq!(resolve_child_concurrency(Some(5)), 5);
+    assert_eq!(resolve_child_concurrency_with_parallelism(Some(5), 1), 5);
+    assert_eq!(resolve_child_concurrency_with_parallelism(Some(5), 100), 5);
+}
+
+/// `resolve_child_concurrency(Some(i32::MIN))` must not panic.
+/// A naive `(-n) as u32` overflows in debug builds when
+/// `n == i32::MIN` because the negation itself overflows;
+/// `unsigned_abs` is the safe path. `i32::MIN.unsigned_abs()`
+/// is `2_147_483_648`, well above any plausible host
+/// parallelism, so `saturating_sub` produces `0` and `.max(1)`
+/// lifts to exactly `1` — assert that precise value so a wrong
+/// result like `2` would still fail the test.
+#[test]
+fn resolve_child_concurrency_handles_i32_min() {
+    let result = resolve_child_concurrency(Some(i32::MIN));
+    assert_eq!(result, 1);
+}
+
 #[cfg(windows)]
 #[test]
 fn test_should_get_the_correct_drive_letter() {
diff --git a/pacquet/crates/config/src/lib.rs b/pacquet/crates/config/src/lib.rs
index a43adc8e63..3ce7a9ef8c 100644
--- a/pacquet/crates/config/src/lib.rs
+++ b/pacquet/crates/config/src/lib.rs
@@ -12,11 +12,12 @@ use serde::Deserialize;
 use smart_default::SmartDefault;
 use std::{collections::HashMap, fs, path::PathBuf};
 
+pub use crate::defaults::{available_parallelism, resolve_child_concurrency};
 use crate::defaults::{
-    default_fetch_retries, default_fetch_retry_factor, default_fetch_retry_maxtimeout,
-    default_fetch_retry_mintimeout, default_hoist_pattern, default_modules_cache_max_age,
-    default_modules_dir, default_public_hoist_pattern, default_registry, default_store_dir,
-    default_virtual_store_dir,
+    default_child_concurrency, default_fetch_retries, default_fetch_retry_factor,
+    default_fetch_retry_maxtimeout, default_fetch_retry_mintimeout, default_hoist_pattern,
+    default_modules_cache_max_age, default_modules_dir, default_public_hoist_pattern,
+    default_registry, default_store_dir, default_virtual_store_dir,
 };
 pub use workspace_yaml::{
     LoadWorkspaceYamlError, WORKSPACE_MANIFEST_FILENAME, WorkspaceSettings, workspace_root_or,
@@ -39,6 +40,61 @@ pub enum NodeLinker {
     Pnp,
 }
 
+/// Tri-state mirror of `pacquet_executor::ScriptsPrependNodePath`
+/// with serde wiring. The executor crate keeps its own enum free of
+/// serde so config concerns don't leak into the spawn-path. Converted
+/// at the `BuildModules` call site (see `install_frozen_lockfile.rs`)
+/// via an explicit `match`; no `From` impl exists because neither
+/// crate depends on the other, and adding such a dep just for the
+/// conversion would invert the layering. Both enums share the same
+/// three variants so the match is exhaustive and one-line per arm.
+///
+/// Deserializes the upstream `scriptsPrependNodePath: boolean | 'warn-only'`
+/// yaml shape ([`Config.scriptsPrependNodePath`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/Config.ts#L108)).
+#[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
+pub enum ScriptsPrependNodePath {
+    /// `scriptsPrependNodePath: true` — always prepend.
+    Always,
+    /// `scriptsPrependNodePath: false` (or absent) — never prepend.
+    #[default]
+    Never,
+    /// `scriptsPrependNodePath: 'warn-only'` — emit a warning if the
+    /// node in PATH differs from the running interpreter, do not
+    /// prepend.
+    WarnOnly,
+}
+
+impl<'de> serde::Deserialize<'de> for ScriptsPrependNodePath {
+    fn deserialize<D>(d: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        use serde::de::{self, Visitor};
+        use std::fmt;
+
+        struct V;
+        impl<'de> Visitor<'de> for V {
+            type Value = ScriptsPrependNodePath;
+            fn expecting(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                f.write_str("a boolean or the string \"warn-only\"")
+            }
+            fn visit_bool<E: de::Error>(self, v: bool) -> Result<Self::Value, E> {
+                Ok(if v { ScriptsPrependNodePath::Always } else { ScriptsPrependNodePath::Never })
+            }
+            fn visit_str<E: de::Error>(self, v: &str) -> Result<Self::Value, E> {
+                match v {
+                    "warn-only" => Ok(ScriptsPrependNodePath::WarnOnly),
+                    other => Err(E::invalid_value(
+                        de::Unexpected::Str(other),
+                        &"true, false, or \"warn-only\"",
+                    )),
+                }
+            }
+        }
+        d.deserialize_any(V)
+    }
+}
+
 #[derive(Debug, Default, Clone, Copy, PartialEq, Eq, Deserialize)]
 #[serde(rename_all = "kebab-case")]
 pub enum PackageImportMethod {
@@ -282,6 +338,50 @@ pub struct Config {
     /// `true`, every package may run lifecycle scripts regardless of
     /// `allow_builds`. Default `false` to match pnpm v11.
     pub dangerously_allow_all_builds: bool,
+
+    /// `scriptsPrependNodePath` from `pnpm-workspace.yaml`. Controls
+    /// whether `dirname(node_execpath)` is prepended to `PATH` when
+    /// running lifecycle scripts. Default `Never` to match pnpm's
+    /// [`StrictBuildOptions.scriptsPrependNodePath: false`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/after-install/src/extendBuildOptions.ts#L78).
+    /// Yaml accepts `true` / `false` / `"warn-only"`.
+    pub scripts_prepend_node_path: ScriptsPrependNodePath,
+
+    /// `unsafePerm` from `pnpm-workspace.yaml`. When `false`, pnpm
+    /// runs lifecycle scripts under a TMPDIR isolated to
+    /// `node_modules/.tmp` and (in upstream) drops uid/gid to a
+    /// non-root user. Default `true` here. Pacquet honors the
+    /// TMPDIR side of the upstream behavior (see
+    /// `pacquet_executor::make_env`); the uid/gid drop is a no-op
+    /// in practice because pnpm's npm-lifecycle fork never
+    /// populates `opts.user` / `opts.group`, so even upstream just
+    /// re-applies the current process's uid/gid.
+    ///
+    /// Pacquet's default deviates slightly from upstream's
+    /// [`StrictBuildOptions.unsafePerm`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/after-install/src/extendBuildOptions.ts#L83-L86)
+    /// which auto-detects root-on-POSIX (`getuid() === 0 && setgid`)
+    /// and flips to `false`. Adding the auto-detect requires `libc`
+    /// (not currently in `[workspace.dependencies]`); for now,
+    /// root-run CI must set `unsafePerm: false` in yaml explicitly.
+    /// On Windows, [`WorkspaceSettings::apply_to`] forces this to
+    /// `true` regardless of yaml — matching upstream's
+    /// `process.platform === 'win32'` override at
+    /// [`@pnpm/npm-lifecycle/index.js:204-220`](https://github.com/pnpm/npm-lifecycle/blob/d2d8e790/index.js#L204-L220).
+    #[default = true]
+    pub unsafe_perm: bool,
+
+    /// `childConcurrency` from `pnpm-workspace.yaml` — the maximum
+    /// number of lifecycle-script spawns that may run in parallel
+    /// inside a single `BuildModules` chunk. Resolved through
+    /// [`resolve_child_concurrency`] so the yaml value can be
+    /// negative (interpreted as `parallelism - |value|`).
+    ///
+    /// Default: `min(4, availableParallelism())`, matching upstream's
+    /// [`getDefaultWorkspaceConcurrency`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/concurrency.ts#L21-L23).
+    /// Chunks run sequentially (children before parents); only
+    /// members within a chunk are parallelized — same as upstream's
+    /// [`runGroups(getWorkspaceConcurrency(opts.childConcurrency), groups)`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/during-install/src/index.ts#L124).
+    #[default(_code = "default_child_concurrency()")]
+    pub child_concurrency: u32,
 }
 
 impl Config {
diff --git a/pacquet/crates/config/src/workspace_yaml.rs b/pacquet/crates/config/src/workspace_yaml.rs
index d7c32361b4..c65d50d3fd 100644
--- a/pacquet/crates/config/src/workspace_yaml.rs
+++ b/pacquet/crates/config/src/workspace_yaml.rs
@@ -1,4 +1,6 @@
-use crate::{Config, NodeLinker, PackageImportMethod};
+use crate::{
+    Config, NodeLinker, PackageImportMethod, ScriptsPrependNodePath, resolve_child_concurrency,
+};
 use derive_more::{Display, Error};
 use indexmap::IndexMap;
 use miette::Diagnostic;
@@ -104,6 +106,22 @@ pub struct WorkspaceSettings {
     ///
     /// [`allow_builds`]: Self::allow_builds
     pub dangerously_allow_all_builds: Option<bool>,
+
+    /// `scriptsPrependNodePath` from `pnpm-workspace.yaml`. Tri-state
+    /// — yaml accepts `true` / `false` / `"warn-only"`. Custom serde
+    /// shape, see [`ScriptsPrependNodePath`]'s `Deserialize` impl.
+    pub scripts_prepend_node_path: Option<ScriptsPrependNodePath>,
+
+    /// `unsafePerm` from `pnpm-workspace.yaml`. Forced to `true` on
+    /// Windows in `apply_to` (matches upstream's
+    /// `process.platform === 'win32'` override).
+    pub unsafe_perm: Option<bool>,
+
+    /// `childConcurrency` from `pnpm-workspace.yaml`. Resolved
+    /// through [`crate::resolve_child_concurrency`] in `apply_to`.
+    /// Signed `i32` here so negative values (interpreted as
+    /// `parallelism - |value|`) round-trip cleanly.
+    pub child_concurrency: Option<i32>,
 }
 
 /// Basename of the file pnpm reads; exported for test use.
@@ -223,6 +241,26 @@ impl WorkspaceSettings {
         if let Some(v) = self.dangerously_allow_all_builds {
             config.dangerously_allow_all_builds = v;
         }
+        if let Some(v) = self.scripts_prepend_node_path {
+            config.scripts_prepend_node_path = v;
+        }
+        if let Some(v) = self.unsafe_perm {
+            config.unsafe_perm = v;
+        }
+        // Windows force-override (matches upstream's
+        // [`process.platform === 'win32'`](https://github.com/pnpm/npm-lifecycle/blob/d2d8e790/index.js#L204-L220)
+        // — running lifecycle scripts under a uid/gid drop is
+        // POSIX-only).
+        if cfg!(windows) {
+            config.unsafe_perm = true;
+        }
+        // `childConcurrency: None` keeps the smart-default
+        // `Config` constructor produced from
+        // [`default_child_concurrency`]; `Some(n)` (including
+        // negative) goes through the upstream resolver.
+        if let Some(v) = self.child_concurrency {
+            config.child_concurrency = resolve_child_concurrency(Some(v));
+        }
     }
 }
 
diff --git a/pacquet/crates/config/src/workspace_yaml/tests.rs b/pacquet/crates/config/src/workspace_yaml/tests.rs
index 56c3bd3ce7..ae1d45bcae 100644
--- a/pacquet/crates/config/src/workspace_yaml/tests.rs
+++ b/pacquet/crates/config/src/workspace_yaml/tests.rs
@@ -1,5 +1,5 @@
 use super::{LoadWorkspaceYamlError, WORKSPACE_MANIFEST_FILENAME, WorkspaceSettings};
-use crate::{Config, NodeLinker};
+use crate::{Config, NodeLinker, ScriptsPrependNodePath};
 use pacquet_store_dir::StoreDir;
 use pipe_trait::Pipe;
 use pretty_assertions::assert_eq;
@@ -276,6 +276,109 @@ fn parses_dangerously_allow_all_builds_from_yaml_and_applies() {
     assert!(config.dangerously_allow_all_builds);
 }
 
+/// `scriptsPrependNodePath` is the tri-state from upstream
+/// [`Config.scriptsPrependNodePath: boolean | 'warn-only'`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/Config.ts#L108).
+/// `true` → Always, `false` → Never, `"warn-only"` → WarnOnly.
+/// Pacquet's default is Never (matches upstream's
+/// [`StrictBuildOptions.scriptsPrependNodePath: false`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/after-install/src/extendBuildOptions.ts#L78)).
+#[test]
+fn parses_scripts_prepend_node_path_true_from_yaml() {
+    let yaml = "scriptsPrependNodePath: true\n";
+    let settings: WorkspaceSettings = serde_saphyr::from_str(yaml).unwrap();
+    assert_eq!(settings.scripts_prepend_node_path, Some(ScriptsPrependNodePath::Always));
+
+    let mut config = Config::new();
+    assert_eq!(config.scripts_prepend_node_path, ScriptsPrependNodePath::Never, "default Never");
+    settings.apply_to(&mut config, Path::new("/irrelevant"));
+    assert_eq!(config.scripts_prepend_node_path, ScriptsPrependNodePath::Always);
+}
+
+#[test]
+fn parses_scripts_prepend_node_path_false_from_yaml() {
+    let yaml = "scriptsPrependNodePath: false\n";
+    let settings: WorkspaceSettings = serde_saphyr::from_str(yaml).unwrap();
+    assert_eq!(settings.scripts_prepend_node_path, Some(ScriptsPrependNodePath::Never));
+}
+
+#[test]
+fn parses_scripts_prepend_node_path_warn_only_from_yaml() {
+    let yaml = "scriptsPrependNodePath: warn-only\n";
+    let settings: WorkspaceSettings = serde_saphyr::from_str(yaml).unwrap();
+    assert_eq!(settings.scripts_prepend_node_path, Some(ScriptsPrependNodePath::WarnOnly));
+}
+
+#[test]
+fn rejects_invalid_scripts_prepend_node_path() {
+    let yaml = "scriptsPrependNodePath: nonsense\n";
+    serde_saphyr::from_str::<WorkspaceSettings>(yaml).expect_err("must reject");
+}
+
+/// `unsafePerm` from yaml flips the default-`true` field. Mirrors
+/// upstream's [`Config.unsafePerm: boolean`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/Config.ts).
+/// Pacquet's auto-root-detect default is a follow-up — for now,
+/// yaml override is the only way to flip the flag on POSIX.
+#[test]
+fn parses_unsafe_perm_from_yaml_and_applies() {
+    // POSIX-only: the Windows force-override below would mask this
+    // test's behavior. See [`WorkspaceSettings::apply_to`].
+    if cfg!(windows) {
+        return;
+    }
+    let yaml = "unsafePerm: false\n";
+    let settings: WorkspaceSettings = serde_saphyr::from_str(yaml).unwrap();
+    assert_eq!(settings.unsafe_perm, Some(false));
+
+    let mut config = Config::new();
+    assert!(config.unsafe_perm, "default is true");
+    settings.apply_to(&mut config, Path::new("/irrelevant"));
+    assert!(!config.unsafe_perm, "yaml override wins on POSIX");
+}
+
+/// On Windows, `apply_to` ignores the yaml value and forces
+/// `unsafe_perm = true`. Mirrors upstream's
+/// [`process.platform === 'win32'` override](https://github.com/pnpm/npm-lifecycle/blob/d2d8e790/index.js#L204-L220)
+/// — running lifecycle scripts under a uid/gid drop is POSIX-only.
+#[cfg(windows)]
+#[test]
+fn unsafe_perm_force_true_on_windows() {
+    let yaml = "unsafePerm: false\n";
+    let settings: WorkspaceSettings = serde_saphyr::from_str(yaml).unwrap();
+    let mut config = Config::new();
+    settings.apply_to(&mut config, Path::new("C:/irrelevant"));
+    assert!(config.unsafe_perm, "Windows forces unsafe_perm true regardless of yaml");
+}
+
+/// A positive `childConcurrency` is taken verbatim — mirrors
+/// upstream's [`getWorkspaceConcurrency`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/config/reader/src/concurrency.ts#L25-L34).
+#[test]
+fn parses_positive_child_concurrency_from_yaml_and_applies() {
+    let yaml = "childConcurrency: 8\n";
+    let settings: WorkspaceSettings = serde_saphyr::from_str(yaml).unwrap();
+    assert_eq!(settings.child_concurrency, Some(8));
+
+    let mut config = Config::new();
+    settings.apply_to(&mut config, Path::new("/irrelevant"));
+    assert_eq!(config.child_concurrency, 8);
+}
+
+/// A non-positive `childConcurrency` is interpreted as
+/// `max(1, parallelism - |value|)`. The exact result depends on
+/// the host's reported parallelism, so we just bound-check it:
+/// negative offsets must produce at least 1 and at most
+/// `parallelism()`.
+#[test]
+fn parses_negative_child_concurrency_from_yaml_and_resolves() {
+    let yaml = "childConcurrency: -1\n";
+    let settings: WorkspaceSettings = serde_saphyr::from_str(yaml).unwrap();
+    assert_eq!(settings.child_concurrency, Some(-1));
+
+    let mut config = Config::new();
+    settings.apply_to(&mut config, Path::new("/irrelevant"));
+    let parallelism = crate::available_parallelism();
+    assert!(config.child_concurrency >= 1, "must floor at 1");
+    assert!(config.child_concurrency <= parallelism, "must not exceed available parallelism");
+}
+
 #[test]
 fn apply_leaves_unset_fields_alone() {
     let yaml = "storeDir: /s\n";
diff --git a/pacquet/crates/executor/src/extend_path.rs b/pacquet/crates/executor/src/extend_path.rs
index 661b376fbb..fbdb4b642a 100644
--- a/pacquet/crates/executor/src/extend_path.rs
+++ b/pacquet/crates/executor/src/extend_path.rs
@@ -7,6 +7,11 @@ use std::{
 /// Controls whether the dir containing the current `node` interpreter
 /// is appended to PATH. Tri-state from
 /// <https://github.com/pnpm/npm-lifecycle/blob/d2d8e790/lib/extendPath.js#L29-L61>.
+///
+/// `pacquet-config` mirrors this enum with its own yaml-deserializable
+/// type (upstream's `scriptsPrependNodePath: boolean | 'warn-only'`
+/// shape) and converts to this one at the call site, so the executor
+/// crate stays free of serde and Config wiring.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
 pub enum ScriptsPrependNodePath {
     /// `scriptsPrependNodePath: true` — always prepend.
diff --git a/pacquet/crates/package-manager/src/build_modules.rs b/pacquet/crates/package-manager/src/build_modules.rs
index 9ca322b465..15e276012f 100644
--- a/pacquet/crates/package-manager/src/build_modules.rs
+++ b/pacquet/crates/package-manager/src/build_modules.rs
@@ -13,9 +13,11 @@ use pacquet_reporter::{
     LogEvent, LogLevel, Reporter, SkippedOptionalDependencyLog, SkippedOptionalPackage,
     SkippedOptionalReason,
 };
+use rayon::prelude::*;
 use std::{
     collections::{BTreeSet, HashMap, HashSet},
     path::{Path, PathBuf},
+    sync::Mutex,
 };
 
 /// Error from the build-modules step.
@@ -40,6 +42,22 @@ pub enum BuildModulesError {
         help("Ensure the package is listed in patchedDependencies configuration")
     )]
     PatchFilePathMissing { dep_path: String },
+
+    /// `ThreadPoolBuilder::build()` failed — most likely the OS
+    /// refused to spawn the requested number of worker threads
+    /// (`EAGAIN` / RLIMIT_NPROC). Surfaced as a structured error
+    /// rather than a panic so the install path can return cleanly.
+    #[display("Failed to build the per-install rayon thread pool: {source}")]
+    #[diagnostic(
+        code(ERR_PACQUET_BUILD_THREAD_POOL),
+        help(
+            "Lower childConcurrency in pnpm-workspace.yaml, or raise the process's RLIMIT_NPROC."
+        )
+    )]
+    ThreadPoolBuild {
+        #[error(source)]
+        source: rayon::ThreadPoolBuildError,
+    },
 }
 
 /// Build policy derived from `allowBuilds` and
@@ -148,12 +166,13 @@ impl AllowBuildPolicy {
 /// Run lifecycle scripts for all packages that require a build.
 ///
 /// Ports the core of `buildModules` from
-/// `https://github.com/pnpm/pnpm/blob/80037699fb/building/during-install/src/index.ts`.
+/// <https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/during-install/src/index.ts>.
 ///
 /// Packages are visited in topological order (children before parents) via
-/// [`build_sequence`]. Within a chunk, members are independent and could run
-/// concurrently — pacquet currently runs them sequentially (TODO: honor
-/// `childConcurrency`).
+/// [`build_sequence`]. Chunks run sequentially. Members within a chunk
+/// run in parallel under a per-install rayon thread pool bounded to
+/// [`BuildModules::child_concurrency`] threads — mirrors upstream's
+/// [`runGroups(getWorkspaceConcurrency(opts.childConcurrency), groups)`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/during-install/src/index.ts#L124).
 pub struct BuildModules<'a> {
     pub virtual_store_dir: &'a Path,
     pub modules_dir: &'a Path,
@@ -209,6 +228,25 @@ pub struct BuildModules<'a> {
     /// 3. Patch application — the patch is applied to the extracted
     ///    package dir before postinstall hooks run.
     pub patches: Option<&'a HashMap<PackageKey, pacquet_patching::ExtendedPatchInfo>>,
+    /// Mirrors `config.scripts_prepend_node_path`. Threaded through to
+    /// [`RunPostinstallHooks::scripts_prepend_node_path`] for each
+    /// spawned lifecycle script. Default [`ScriptsPrependNodePath::Never`].
+    pub scripts_prepend_node_path: ScriptsPrependNodePath,
+    /// Mirrors `config.unsafe_perm`. When `false`, [`pacquet_executor`]
+    /// runs each lifecycle script under a per-package TMPDIR set to
+    /// `node_modules/.tmp`; when `true`, TMPDIR is left at the
+    /// inherited value (matches upstream's
+    /// [`@pnpm/npm-lifecycle`](https://github.com/pnpm/npm-lifecycle/blob/d2d8e790/index.js#L204-L220)
+    /// gate). Default `true`.
+    pub unsafe_perm: bool,
+    /// Mirrors `config.child_concurrency`. Per-chunk parallelism
+    /// for build-script spawns. Chunks remain sequential to preserve
+    /// topological ordering; members within a chunk run in parallel
+    /// up to this many at a time. Mirrors upstream's
+    /// [`runGroups(getWorkspaceConcurrency(opts.childConcurrency), groups)`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/during-install/src/index.ts#L124).
+    /// Floored to `1` to guarantee forward progress on
+    /// resource-constrained hosts.
+    pub child_concurrency: u32,
 }
 
 impl<'a> BuildModules<'a> {
@@ -234,6 +272,9 @@ impl<'a> BuildModules<'a> {
             store_dir,
             store_index_writer,
             patches,
+            scripts_prepend_node_path,
+            unsafe_perm,
+            child_concurrency,
         } = self;
 
         let Some(snapshots) = snapshots else { return Ok(Vec::new()) };
@@ -301,281 +342,369 @@ impl<'a> BuildModules<'a> {
                 roots,
             )
         });
-        let mut deps_state_cache: pacquet_graph_hasher::DepsStateCache<PackageKey> =
-            pacquet_graph_hasher::DepsStateCache::new();
+        // `deps_state_cache` memoizes per-snapshot hashes across the
+        // recursive walk in `calc_dep_state`. Shared across all
+        // chunks so diamond-shaped subgraphs hit the memo from
+        // earlier chunks too. Wrapped in `Mutex` because chunks now
+        // dispatch their members concurrently — `calc_dep_state`
+        // mutates the cache through `&mut`, and rayon would
+        // otherwise need each task to own a private cache, defeating
+        // the point of memoization.
+        let deps_state_cache: Mutex<pacquet_graph_hasher::DepsStateCache<PackageKey>> =
+            Mutex::new(pacquet_graph_hasher::DepsStateCache::new());
 
         let chunks = build_sequence(&requires_build_map, patches, snapshots, importers);
 
         // Collect peer-stripped keys so the final list is unique and
         // sorted lexicographically — matches `dedupePackageNamesFromIgnoredBuilds`.
-        let mut ignored_builds: BTreeSet<String> = BTreeSet::new();
+        // `Mutex` for the same parallelism reason as `deps_state_cache` above.
+        let ignored_builds: Mutex<BTreeSet<String>> = Mutex::new(BTreeSet::new());
+
+        // Per-install rayon pool. Bounded to `child_concurrency` so
+        // a chunk with many build-needed members doesn't exhaust the
+        // process's rayon-global threads (which other crates may
+        // depend on). One pool reused across all chunks; chunks
+        // themselves run sequentially.
+        //
+        // Mirrors upstream's
+        // [`runGroups(getWorkspaceConcurrency(opts.childConcurrency), groups)`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/during-install/src/index.ts#L124).
+        // `ThreadPoolBuilder::build()` is fallible — the OS may
+        // refuse the spawn (`EAGAIN` / RLIMIT_NPROC) on a host
+        // already near its process-thread limit. Surface that as
+        // [`BuildModulesError::ThreadPoolBuild`] so the install
+        // returns cleanly with a remediation hint instead of
+        // panicking inside the binary.
+        let pool = rayon::ThreadPoolBuilder::new()
+            .num_threads(child_concurrency.max(1) as usize)
+            .build()
+            .map_err(|source| BuildModulesError::ThreadPoolBuild { source })?;
 
         for chunk in chunks {
-            for snapshot_key in chunk {
-                let metadata_key = snapshot_key.without_peer();
-                // Look up against the peer-stripped key because
-                // patches are configured at the (name, version)
-                // granularity in `pnpm-workspace.yaml`, not per
-                // peer-resolution variant.
-                let patch = patches.and_then(|map| map.get(&metadata_key));
-                let has_patch = patch.is_some();
-                let requires_build =
-                    requires_build_map.get(&snapshot_key).copied().unwrap_or(false);
-
-                // Ancestors of a build/patch candidate are included
-                // in the sequence (so the topo order stays correct)
-                // but only run scripts / apply patches when they
-                // themselves are candidates. Mirrors upstream's
-                // chunk filter at
-                // <https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/during-install/src/index.ts#L73-L77>.
-                if !requires_build && !has_patch {
-                    continue;
-                }
-
-                let (name, version) = parse_name_version_from_key(&metadata_key.to_string());
-
-                // Mirrors upstream's `if (node.requiresBuild) { allowBuild(...) }`
-                // at lines 88-101: the allowBuilds gate only applies
-                // when the node has scripts to run. A patched-only
-                // package skips this check entirely and proceeds to
-                // patch application below.
-                //
-                // `false` / `None` from the policy set
-                // `should_run_scripts = false` (NOT `continue`), so
-                // the patch still gets applied even when scripts
-                // are disallowed. Matches upstream's `ignoreScripts
-                // = true; break` pattern.
-                let mut should_run_scripts = requires_build;
-                if requires_build {
-                    match allow_build_policy.check(&name, &version) {
-                        Some(false) => {
-                            should_run_scripts = false;
-                        }
-                        None => {
-                            // "Not in allowBuilds" — surfaced as
-                            // `pnpm:ignored-scripts`. Explicit
-                            // `false` is silently denied (above),
-                            // matching upstream's switch.
-                            ignored_builds.insert(metadata_key.to_string());
-                            should_run_scripts = false;
-                        }
-                        Some(true) => {}
-                    }
-                }
-
-                // Compute the side-effects cache key once per
-                // snapshot, before the `is_built` gate. The same
-                // value is later consumed by the WRITE-path upload
-                // call after `run_postinstall_hooks` succeeds, so
-                // recomputing it there would just duplicate work —
-                // `deps_state_cache` makes the second call free
-                // anyway, but routing through one `let` keeps the
-                // gate-side and write-side keys provably identical.
-                //
-                // `None` when the cache gate can't fire (no engine,
-                // no graph, etc.); both downstream consumers
-                // short-circuit on `None`.
-                let cache_key = (dep_graph.as_ref().zip(engine_name)).map(|(graph, engine)| {
-                    pacquet_graph_hasher::calc_dep_state(
-                        graph,
-                        &mut deps_state_cache,
-                        &snapshot_key,
-                        &pacquet_graph_hasher::CalcDepStateOptions {
-                            engine_name: engine,
-                            // Mirrors upstream's
-                            // `patchFileHash: depNode.patch?.hash`
-                            // at
-                            // <https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/during-install/src/index.ts#L201>.
-                            // `None` for unpatched snapshots leaves
-                            // the `;patch=...` segment off the cache
-                            // key entirely, matching upstream when
-                            // `depNode.patch == null`.
-                            patch_file_hash: patch.map(|p| p.hash.as_str()),
-                            // Mirrors `includeDepGraphHash: hasSideEffects`
-                            // at upstream line 202. A patched-only
-                            // snapshot (no scripts will run) leaves
-                            // the deps-hash off so the cache key
-                            // stays stable across dep-graph changes
-                            // that don't affect this package's
-                            // patched output.
-                            include_dep_graph_hash: should_run_scripts,
-                        },
+            // The closure runs once per chunk; `try_for_each`
+            // short-circuits on the first error. The only mutable
+            // state shared across tasks is the two `Mutex`-wrapped
+            // collections above and `deps_state_cache`.
+            pool.install(|| -> Result<(), BuildModulesError> {
+                chunk.par_iter().try_for_each(|snapshot_key| {
+                    build_one_snapshot::<R>(
+                        snapshot_key,
+                        snapshots,
+                        packages,
+                        patches,
+                        &requires_build_map,
+                        allow_build_policy,
+                        side_effects_maps_by_snapshot,
+                        engine_name,
+                        side_effects_cache,
+                        side_effects_cache_write,
+                        store_dir,
+                        store_index_writer,
+                        dep_graph.as_ref(),
+                        &deps_state_cache,
+                        &ignored_builds,
+                        virtual_store_dir,
+                        modules_dir,
+                        lockfile_dir,
+                        &extra_bin_paths,
+                        &extra_env,
+                        scripts_prepend_node_path,
+                        unsafe_perm,
                     )
-                });
-
-                // Side-effects-cache `is_built` gate. Mirrors
-                // upstream's `!node.isBuilt` filter at
-                // <https://github.com/pnpm/pnpm/blob/7e3145f9fc/building/during-install/src/index.ts#L73-L77>.
-                // We're already past the policy gate, so this
-                // snapshot would otherwise run its scripts — but if
-                // the prefetch surfaced a matching side-effects-cache
-                // entry, the build is already represented on disk
-                // (pnpm seeded it on a previous install) and we
-                // can skip.
-                if side_effects_cache
-                    && let Some(maps_by_snapshot) = side_effects_maps_by_snapshot
-                    && let Some(maps) = maps_by_snapshot.get(&snapshot_key)
-                    && let Some(key) = cache_key.as_deref()
-                    && maps.contains_key(key)
-                {
-                    tracing::debug!(
-                        target: "pacquet::build",
-                        ?snapshot_key,
-                        cache_key = key,
-                        "side-effects cache hit; skipping build",
-                    );
-                    continue;
-                }
-
-                let pkg_dir = virtual_store_dir_for_key(virtual_store_dir, &snapshot_key);
-                if !pkg_dir.exists() {
-                    continue;
-                }
-
-                let optional = snapshots.get(&snapshot_key).is_some_and(|entry| entry.optional);
-
-                // Apply the patch before running postinstall hooks.
-                // Mirrors upstream at
-                // <https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/during-install/src/index.ts#L171-L178>:
-                // ```
-                // if (depNode.patch) {
-                //   if (!depNode.patch.patchFilePath) throw PATCH_FILE_PATH_MISSING
-                //   isPatched = applyPatchToDir(...)
-                // }
-                // ```
-                // `is_patched` feeds the cache-write gate below
-                // (`is_patched || has_side_effects`), matching
-                // upstream's line 199 condition.
-                let is_patched = if let Some(p) = patch {
-                    let patch_file_path = p.patch_file_path.as_deref().ok_or_else(|| {
-                        BuildModulesError::PatchFilePathMissing {
-                            dep_path: snapshot_key.to_string(),
-                        }
-                    })?;
-                    apply_patch_to_dir(&pkg_dir, patch_file_path)
-                        .map_err(BuildModulesError::PatchApply)?;
-                    true
-                } else {
-                    false
-                };
-
-                let has_side_effects = if should_run_scripts {
-                    let result = run_postinstall_hooks::<R>(RunPostinstallHooks {
-                        dep_path: &snapshot_key.to_string(),
-                        pkg_root: &pkg_dir,
-                        root_modules_dir: modules_dir,
-                        init_cwd: lockfile_dir,
-                        extra_bin_paths: &extra_bin_paths,
-                        extra_env: &extra_env,
-                        node_execpath: None,
-                        npm_execpath: None,
-                        node_gyp_path: None,
-                        user_agent: None,
-                        // Hard-coded until the `unsafe-perm` config knob
-                        // is plumbed through. `true` skips both the
-                        // TMPDIR creation and the uid/gid drop, matching
-                        // pacquet's behavior before any of this landed.
-                        unsafe_perm: true,
-                        node_gyp_bin: None,
-                        scripts_prepend_node_path: ScriptsPrependNodePath::Never,
-                        script_shell: None,
-                        optional,
-                    });
-
-                    match result {
-                        Ok(ran) => ran,
-                        Err(err) => {
-                            if optional {
-                                // Mirrors `building/during-install/src/index.ts:226-238`:
-                                // a build failure on an optional dep is logged
-                                // through the `pnpm:skipped-optional-dependency`
-                                // channel and swallowed so the install can
-                                // continue. The `package.id` field upstream is
-                                // `depNode.dir`; we use the same.
-                                R::emit(&LogEvent::SkippedOptionalDependency(
-                                    SkippedOptionalDependencyLog {
-                                        level: LogLevel::Debug,
-                                        details: Some(err.to_string()),
-                                        package: SkippedOptionalPackage {
-                                            id: pkg_dir.to_string_lossy().into_owned(),
-                                            name: name.clone(),
-                                            version: version.clone(),
-                                        },
-                                        prefix: lockfile_dir.to_string_lossy().into_owned(),
-                                        reason: SkippedOptionalReason::BuildFailure,
-                                    },
-                                ));
-                                continue;
-                            }
-                            return Err(BuildModulesError::LifecycleScript(err));
-                        }
-                    }
-                } else {
-                    false
-                };
-
-                // Side-effects-cache WRITE path. Mirrors
-                // `<https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/during-install/src/index.ts#L198-L216>`:
-                // after a successful `run_postinstall_hooks` (or a
-                // patch application that mutated the dir),
-                // re-hash the package directory and queue a
-                // `PackageFilesIndex.sideEffects[cache_key] = diff`
-                // mutation so a future install can skip the
-                // rebuild.
-                //
-                // Upstream's gate is `(isPatched || hasSideEffects)
-                // && opts.sideEffectsCacheWrite`. Pacquet mirrors
-                // that — a patched-only snapshot still uploads its
-                // post-patch state so subsequent installs hit the
-                // cache.
-                //
-                // The other preconditions: cache_key composable
-                // (engine + graph present), `packages` map
-                // available for the integrity lookup, and the
-                // metadata row carries an integrity (registry /
-                // tarball resolutions — git / directory have no
-                // integrity and pnpm doesn't cache those either).
-                //
-                // All errors are swallowed with a `tracing::warn!`,
-                // matching upstream's `try { upload } catch (err) {
-                // logger.warn(...) }` at lines 208-215. A failed
-                // upload doesn't fail the install: the next install
-                // re-runs the build.
-                if (is_patched || has_side_effects)
-                    && side_effects_cache_write
-                    && let Some(writer) = store_index_writer
-                    && let Some(store) = store_dir
-                    && let Some(cache_key) = cache_key.as_deref()
-                    && let Some(packages) = packages
-                    && let Some(metadata) = packages.get(&metadata_key)
-                    && let Some(integrity) = metadata.resolution.integrity()
-                {
-                    let files_index_file = pacquet_store_dir::store_index_key(
-                        &integrity.to_string(),
-                        &metadata_key.to_string(),
-                    );
-                    if let Err(err) = pacquet_store_dir::upload(
-                        store,
-                        &pkg_dir,
-                        &files_index_file,
-                        cache_key,
-                        writer,
-                    ) {
-                        tracing::warn!(
-                            target: "pacquet::build",
-                            ?err,
-                            dep_path = %snapshot_key,
-                            "side-effects cache upload failed; build proceeds",
-                        );
-                    }
-                }
-            }
+                })
+            })?;
         }
 
+        // If a chunk worker panicked while holding the
+        // `ignored_builds` lock, rayon's `try_for_each` will have
+        // already propagated the panic (or returned an Err) — so a
+        // poisoned mutex here can only mean the protected state is
+        // mid-insertion. A `BTreeSet::insert` is one atomic
+        // operation from the data-structure's POV (no torn writes),
+        // so the canonical poison-recovery pattern is safe.
+        let ignored_builds = ignored_builds.into_inner().unwrap_or_else(|e| e.into_inner());
         Ok(ignored_builds.into_iter().collect())
     }
 }
 
+/// Per-snapshot work extracted out of [`BuildModules::run`]'s inner
+/// loop so the bounded-parallelism `par_iter().try_for_each(...)`
+/// dispatch can call it once per chunk member. The body is the same
+/// as the pre-#12 sequential loop — `continue`s become `return Ok(())`
+/// here.
+#[allow(clippy::too_many_arguments)]
+fn build_one_snapshot<R: Reporter>(
+    snapshot_key: &PackageKey,
+    snapshots: &HashMap<PackageKey, SnapshotEntry>,
+    packages: Option<&HashMap<PackageKey, pacquet_lockfile::PackageMetadata>>,
+    patches: Option<&HashMap<PackageKey, pacquet_patching::ExtendedPatchInfo>>,
+    requires_build_map: &HashMap<PackageKey, bool>,
+    allow_build_policy: &AllowBuildPolicy,
+    side_effects_maps_by_snapshot: Option<&crate::SideEffectsMapsBySnapshot>,
+    engine_name: Option<&str>,
+    side_effects_cache: bool,
+    side_effects_cache_write: bool,
+    store_dir: Option<&pacquet_store_dir::StoreDir>,
+    store_index_writer: Option<&std::sync::Arc<pacquet_store_dir::StoreIndexWriter>>,
+    dep_graph: Option<&HashMap<PackageKey, pacquet_graph_hasher::DepsGraphNode<PackageKey>>>,
+    deps_state_cache: &Mutex<pacquet_graph_hasher::DepsStateCache<PackageKey>>,
+    ignored_builds: &Mutex<BTreeSet<String>>,
+    virtual_store_dir: &Path,
+    modules_dir: &Path,
+    lockfile_dir: &Path,
+    extra_bin_paths: &[PathBuf],
+    extra_env: &HashMap<String, String>,
+    scripts_prepend_node_path: ScriptsPrependNodePath,
+    unsafe_perm: bool,
+) -> Result<(), BuildModulesError> {
+    let metadata_key = snapshot_key.without_peer();
+    // Look up against the peer-stripped key because patches are
+    // configured at the (name, version) granularity in
+    // `pnpm-workspace.yaml`, not per peer-resolution variant.
+    let patch = patches.and_then(|map| map.get(&metadata_key));
+    let has_patch = patch.is_some();
+    let requires_build = requires_build_map.get(snapshot_key).copied().unwrap_or(false);
+
+    // Ancestors of a build/patch candidate are included in the
+    // sequence (so the topo order stays correct) but only run
+    // scripts / apply patches when they themselves are candidates.
+    // Mirrors upstream's chunk filter at
+    // <https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/during-install/src/index.ts#L73-L77>.
+    if !requires_build && !has_patch {
+        return Ok(());
+    }
+
+    let (name, version) = parse_name_version_from_key(&metadata_key.to_string());
+
+    // Mirrors upstream's `if (node.requiresBuild) { allowBuild(...) }`
+    // at lines 88-101: the allowBuilds gate only applies when the
+    // node has scripts to run. A patched-only package skips this
+    // check entirely and proceeds to patch application below.
+    //
+    // `false` / `None` from the policy set `should_run_scripts =
+    // false` (NOT early-return), so the patch still gets applied
+    // even when scripts are disallowed. Matches upstream's
+    // `ignoreScripts = true; break` pattern.
+    let mut should_run_scripts = requires_build;
+    if requires_build {
+        match allow_build_policy.check(&name, &version) {
+            Some(false) => {
+                should_run_scripts = false;
+            }
+            None => {
+                // "Not in allowBuilds" — surfaced as
+                // `pnpm:ignored-scripts`. Explicit `false` is
+                // silently denied (above), matching upstream's
+                // switch.
+                // Poison-recover: see the equivalent call site at
+                // the end of `BuildModules::run` for the safety
+                // argument (BTreeSet insertion is atomic from the
+                // data-structure's POV).
+                ignored_builds
+                    .lock()
+                    .unwrap_or_else(|e| e.into_inner())
+                    .insert(metadata_key.to_string());
+                should_run_scripts = false;
+            }
+            Some(true) => {}
+        }
+    }
+
+    // Compute the side-effects cache key once per snapshot, before
+    // the `is_built` gate. The same value is later consumed by the
+    // WRITE-path upload call after `run_postinstall_hooks`
+    // succeeds, so recomputing it there would just duplicate work —
+    // `deps_state_cache` makes the second call free anyway, but
+    // routing through one `let` keeps the gate-side and write-side
+    // keys provably identical.
+    //
+    // `None` when the cache gate can't fire (no engine, no graph,
+    // etc.); both downstream consumers short-circuit on `None`.
+    //
+    // The `deps_state_cache` is shared across all chunk members via
+    // `Mutex` because `calc_dep_state` is recursive and memoizes —
+    // a per-task cache would defeat the memoization for
+    // diamond-shaped subgraphs.
+    let cache_key = (dep_graph.zip(engine_name)).map(|(graph, engine)| {
+        // Poison-recover: `calc_dep_state` mutates the cache by
+        // inserting one entry per recursive walk node, each
+        // insert atomic from `HashMap`'s POV. A panic mid-walk
+        // leaves the map in a usable state — the worst case is
+        // an unfinished sub-walk that the next caller will redo.
+        let mut cache_guard = deps_state_cache.lock().unwrap_or_else(|e| e.into_inner());
+        pacquet_graph_hasher::calc_dep_state(
+            graph,
+            &mut cache_guard,
+            snapshot_key,
+            &pacquet_graph_hasher::CalcDepStateOptions {
+                engine_name: engine,
+                // Mirrors upstream's
+                // `patchFileHash: depNode.patch?.hash` at
+                // <https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/during-install/src/index.ts#L201>.
+                // `None` for unpatched snapshots leaves the
+                // `;patch=...` segment off the cache key entirely,
+                // matching upstream when `depNode.patch == null`.
+                patch_file_hash: patch.map(|p| p.hash.as_str()),
+                // Mirrors `includeDepGraphHash: hasSideEffects` at
+                // upstream line 202. A patched-only snapshot (no
+                // scripts will run) leaves the deps-hash off so the
+                // cache key stays stable across dep-graph changes
+                // that don't affect this package's patched output.
+                include_dep_graph_hash: should_run_scripts,
+            },
+        )
+    });
+
+    // Side-effects-cache `is_built` gate. Mirrors upstream's
+    // `!node.isBuilt` filter at
+    // <https://github.com/pnpm/pnpm/blob/7e3145f9fc/building/during-install/src/index.ts#L73-L77>.
+    // We're already past the policy gate, so this snapshot would
+    // otherwise run its scripts — but if the prefetch surfaced a
+    // matching side-effects-cache entry, the build is already
+    // represented on disk (pnpm seeded it on a previous install)
+    // and we can skip.
+    if side_effects_cache
+        && let Some(maps_by_snapshot) = side_effects_maps_by_snapshot
+        && let Some(maps) = maps_by_snapshot.get(snapshot_key)
+        && let Some(key) = cache_key.as_deref()
+        && maps.contains_key(key)
+    {
+        tracing::debug!(
+            target: "pacquet::build",
+            ?snapshot_key,
+            cache_key = key,
+            "side-effects cache hit; skipping build",
+        );
+        return Ok(());
+    }
+
+    let pkg_dir = virtual_store_dir_for_key(virtual_store_dir, snapshot_key);
+    if !pkg_dir.exists() {
+        return Ok(());
+    }
+
+    let optional = snapshots.get(snapshot_key).is_some_and(|entry| entry.optional);
+
+    // Apply the patch before running postinstall hooks. Mirrors
+    // upstream at
+    // <https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/during-install/src/index.ts#L171-L178>:
+    // ```
+    // if (depNode.patch) {
+    //   if (!depNode.patch.patchFilePath) throw PATCH_FILE_PATH_MISSING
+    //   isPatched = applyPatchToDir(...)
+    // }
+    // ```
+    // `is_patched` feeds the cache-write gate below
+    // (`is_patched || has_side_effects`), matching upstream's
+    // line 199 condition.
+    let is_patched = if let Some(p) = patch {
+        let patch_file_path = p.patch_file_path.as_deref().ok_or_else(|| {
+            BuildModulesError::PatchFilePathMissing { dep_path: snapshot_key.to_string() }
+        })?;
+        apply_patch_to_dir(&pkg_dir, patch_file_path).map_err(BuildModulesError::PatchApply)?;
+        true
+    } else {
+        false
+    };
+
+    let has_side_effects = if should_run_scripts {
+        let result = run_postinstall_hooks::<R>(RunPostinstallHooks {
+            dep_path: &snapshot_key.to_string(),
+            pkg_root: &pkg_dir,
+            root_modules_dir: modules_dir,
+            init_cwd: lockfile_dir,
+            extra_bin_paths,
+            extra_env,
+            node_execpath: None,
+            npm_execpath: None,
+            node_gyp_path: None,
+            user_agent: None,
+            unsafe_perm,
+            node_gyp_bin: None,
+            scripts_prepend_node_path,
+            script_shell: None,
+            optional,
+        });
+
+        match result {
+            Ok(ran) => ran,
+            Err(err) => {
+                if optional {
+                    // Mirrors
+                    // `building/during-install/src/index.ts:226-238`:
+                    // a build failure on an optional dep is logged
+                    // through the `pnpm:skipped-optional-dependency`
+                    // channel and swallowed so the install can
+                    // continue. The `package.id` field upstream is
+                    // `depNode.dir`; we use the same.
+                    R::emit(&LogEvent::SkippedOptionalDependency(SkippedOptionalDependencyLog {
+                        level: LogLevel::Debug,
+                        details: Some(err.to_string()),
+                        package: SkippedOptionalPackage {
+                            id: pkg_dir.to_string_lossy().into_owned(),
+                            name: name.clone(),
+                            version: version.clone(),
+                        },
+                        prefix: lockfile_dir.to_string_lossy().into_owned(),
+                        reason: SkippedOptionalReason::BuildFailure,
+                    }));
+                    return Ok(());
+                }
+                return Err(BuildModulesError::LifecycleScript(err));
+            }
+        }
+    } else {
+        false
+    };
+
+    // Side-effects-cache WRITE path. Mirrors upstream at
+    // <https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/during-install/src/index.ts#L198-L216>:
+    // after a successful `run_postinstall_hooks` (or a patch
+    // application that mutated the dir), re-hash the package
+    // directory and queue a
+    // `PackageFilesIndex.sideEffects[cache_key] = diff` mutation
+    // so a future install can skip the rebuild.
+    //
+    // Upstream's gate is `(isPatched || hasSideEffects) &&
+    // opts.sideEffectsCacheWrite`. Pacquet mirrors that — a
+    // patched-only snapshot still uploads its post-patch state so
+    // subsequent installs hit the cache.
+    //
+    // The other preconditions: cache_key composable (engine + graph
+    // present), `packages` map available for the integrity lookup,
+    // and the metadata row carries an integrity (registry / tarball
+    // resolutions — git / directory have no integrity and pnpm
+    // doesn't cache those either).
+    //
+    // All errors are swallowed with a `tracing::warn!`, matching
+    // upstream's `try { upload } catch (err) { logger.warn(...) }`
+    // at lines 208-215. A failed upload doesn't fail the install:
+    // the next install re-runs the build.
+    if (is_patched || has_side_effects)
+        && side_effects_cache_write
+        && let Some(writer) = store_index_writer
+        && let Some(store) = store_dir
+        && let Some(cache_key) = cache_key.as_deref()
+        && let Some(packages) = packages
+        && let Some(metadata) = packages.get(&metadata_key)
+        && let Some(integrity) = metadata.resolution.integrity()
+    {
+        let files_index_file =
+            pacquet_store_dir::store_index_key(&integrity.to_string(), &metadata_key.to_string());
+        if let Err(err) =
+            pacquet_store_dir::upload(store, &pkg_dir, &files_index_file, cache_key, writer)
+        {
+            tracing::warn!(
+                target: "pacquet::build",
+                ?err,
+                dep_path = %snapshot_key,
+                "side-effects cache upload failed; build proceeds",
+            );
+        }
+    }
+
+    Ok(())
+}
+
 /// Compute the package directory inside the virtual store for a snapshot key.
 ///
 /// Uses `without_peer()` to strip any peer-dependency suffix before
diff --git a/pacquet/crates/package-manager/src/build_modules/tests.rs b/pacquet/crates/package-manager/src/build_modules/tests.rs
index 248d72003f..d751b8115b 100644
--- a/pacquet/crates/package-manager/src/build_modules/tests.rs
+++ b/pacquet/crates/package-manager/src/build_modules/tests.rs
@@ -1,5 +1,6 @@
 use super::{AllowBuildPolicy, BuildModules, parse_name_version_from_key};
 use pacquet_config::Config;
+use pacquet_executor::ScriptsPrependNodePath;
 use pacquet_lockfile::{
     PackageKey, PkgName, PkgVerPeer, ProjectSnapshot, ResolvedDependencyMap,
     ResolvedDependencySpec, SnapshotEntry,
@@ -299,6 +300,10 @@ fn build_modules_collects_ignored_builds() {
         store_dir: None,
         store_index_writer: None,
         patches: None,
+
+        scripts_prepend_node_path: ScriptsPrependNodePath::Never,
+        unsafe_perm: true,
+        child_concurrency: 1,
     }
     .run::<SilentReporter>()
     .expect("run BuildModules");
@@ -311,6 +316,75 @@ fn build_modules_collects_ignored_builds() {
     );
 }
 
+/// Parallel-path variant of [`build_modules_collects_ignored_builds`]
+/// running under `child_concurrency: 2` so the rayon
+/// `chunk.par_iter().try_for_each(...)` dispatch is actually
+/// exercised. The other `BuildModules` tests all run with
+/// `child_concurrency: 1`, which is the sequential codepath; this
+/// test pins the concurrent codepath against a fixture that places
+/// two policy-denied build candidates in the same chunk (no
+/// dependency edges between them, so the topo sort puts them both
+/// in chunk 0).
+///
+/// The assertion is the same sorted ignored-set as the sequential
+/// test — a regression that dropped the `pool.install` /
+/// `try_for_each` wrapping would still collect both names but in
+/// non-deterministic order on insertion. The
+/// `BTreeSet`-backed `ignored_builds` ordering hides that, so
+/// breakage would more likely show up as a lock contention bug
+/// (e.g. dropping the `Mutex` wrapping) which would manifest as a
+/// rustc / clippy error rather than a runtime failure; this test
+/// at least documents that the codepath is exercised.
+#[test]
+fn build_modules_collects_ignored_builds_under_concurrency() {
+    let snapshots = HashMap::from([
+        (key("zzz", "1.0.0"), SnapshotEntry::default()),
+        (key("aaa", "2.0.0"), SnapshotEntry::default()),
+    ]);
+    let importers = root_importers(&[("zzz", "1.0.0"), ("aaa", "2.0.0")]);
+    let policy = AllowBuildPolicy::default();
+
+    let virtual_store_dir = tempdir().expect("create temp dir");
+    let modules_dir = tempdir().expect("create temp dir");
+    let lockfile_dir = tempdir().expect("create temp dir");
+
+    create_buildable_pkg(virtual_store_dir.path(), &key("zzz", "1.0.0"));
+    create_buildable_pkg(virtual_store_dir.path(), &key("aaa", "2.0.0"));
+
+    let ignored = BuildModules {
+        virtual_store_dir: virtual_store_dir.path(),
+        modules_dir: modules_dir.path(),
+        lockfile_dir: lockfile_dir.path(),
+        snapshots: Some(&snapshots),
+        importers: &importers,
+        packages: None,
+        allow_build_policy: &policy,
+        side_effects_maps_by_snapshot: None,
+        engine_name: None,
+        side_effects_cache: true,
+        side_effects_cache_write: false,
+        store_dir: None,
+        store_index_writer: None,
+        patches: None,
+
+        scripts_prepend_node_path: ScriptsPrependNodePath::Never,
+        unsafe_perm: true,
+        child_concurrency: 2,
+    }
+    .run::<SilentReporter>()
+    .expect("run BuildModules under concurrency");
+    dbg!(&ignored);
+
+    // Same expected output as the sequential test — both members of
+    // the same chunk insert into the `Mutex<BTreeSet>` concurrently
+    // and the BTreeSet's iteration order normalizes the result.
+    assert_eq!(
+        ignored,
+        vec!["aaa@2.0.0".to_string(), "zzz@1.0.0".to_string()],
+        "ignored set must be the same under concurrency 2 as under 1: {ignored:?}",
+    );
+}
+
 /// Explicit `false` in `allowBuilds` is silently skipped — it does NOT
 /// land in the ignored-scripts list. Mirrors upstream
 /// `building/during-install/src/index.ts:91-93`.
@@ -346,6 +420,10 @@ fn build_modules_excludes_explicit_deny_from_ignored() {
         store_dir: None,
         store_index_writer: None,
         patches: None,
+
+        scripts_prepend_node_path: ScriptsPrependNodePath::Never,
+        unsafe_perm: true,
+        child_concurrency: 1,
     }
     .run::<SilentReporter>()
     .expect("run BuildModules");
@@ -420,6 +498,10 @@ fn do_not_fail_on_optional_dep_with_failing_postinstall() {
         store_dir: None,
         store_index_writer: None,
         patches: None,
+
+        scripts_prepend_node_path: ScriptsPrependNodePath::Never,
+        unsafe_perm: true,
+        child_concurrency: 1,
     }
     .run::<RecordingReporter>()
     .expect("optional build failure must NOT abort the install");
@@ -542,6 +624,10 @@ fn using_side_effects_cache_skips_rebuild() {
         store_dir: None,
         store_index_writer: None,
         patches: None,
+
+        scripts_prepend_node_path: ScriptsPrependNodePath::Never,
+        unsafe_perm: true,
+        child_concurrency: 1,
     }
     .run::<RecordingReporter>()
     .expect("install must succeed when the cache hit skips the rebuild");
@@ -599,6 +685,10 @@ fn side_effects_cache_disabled_bypasses_the_gate() {
         store_dir: None,
         store_index_writer: None,
         patches: None,
+
+        scripts_prepend_node_path: ScriptsPrependNodePath::Never,
+        unsafe_perm: true,
+        child_concurrency: 1,
     }
     .run::<SilentReporter>()
     .expect_err("with cache disabled, the failing postinstall must run and the install must fail");
@@ -649,6 +739,10 @@ fn fail_when_failing_postinstall_is_required() {
         store_dir: None,
         store_index_writer: None,
         patches: None,
+
+        scripts_prepend_node_path: ScriptsPrependNodePath::Never,
+        unsafe_perm: true,
+        child_concurrency: 1,
     }
     .run::<SilentReporter>()
     .expect_err("required build failure must propagate");
@@ -876,6 +970,10 @@ async fn write_path_populates_side_effects_row() {
         store_dir: Some(&store_dir),
         store_index_writer: Some(&writer),
         patches: None,
+
+        scripts_prepend_node_path: ScriptsPrependNodePath::Never,
+        unsafe_perm: true,
+        child_concurrency: 1,
     }
     .run::<SilentReporter>()
     .expect("build modules must complete cleanly");
@@ -978,6 +1076,10 @@ async fn write_path_disabled_skips_upload() {
         store_dir: Some(&store_dir),
         store_index_writer: Some(&writer),
         patches: None,
+
+        scripts_prepend_node_path: ScriptsPrependNodePath::Never,
+        unsafe_perm: true,
+        child_concurrency: 1,
     }
     .run::<SilentReporter>()
     .expect("build modules must complete cleanly");
@@ -1089,6 +1191,10 @@ async fn upload_error_does_not_interrupt_install() {
         store_dir: Some(&store_dir),
         store_index_writer: Some(&writer),
         patches: None,
+
+        scripts_prepend_node_path: ScriptsPrependNodePath::Never,
+        unsafe_perm: true,
+        child_concurrency: 1,
     }
     .run::<SilentReporter>()
     .expect("upload failure must not propagate; install continues");
@@ -1310,6 +1416,10 @@ new file mode 100644
         store_dir: Some(&store_dir),
         store_index_writer: Some(&writer),
         patches: Some(&patches),
+
+        scripts_prepend_node_path: ScriptsPrependNodePath::Never,
+        unsafe_perm: true,
+        child_concurrency: 1,
     }
     .run::<SilentReporter>()
     .expect("build modules must complete cleanly");
@@ -1409,6 +1519,10 @@ new file mode 100644
         store_dir: Some(&store_dir),
         store_index_writer: Some(&writer),
         patches: Some(&patches),
+
+        scripts_prepend_node_path: ScriptsPrependNodePath::Never,
+        unsafe_perm: true,
+        child_concurrency: 1,
     }
     .run::<SilentReporter>()
     .expect("build modules must complete cleanly");
@@ -1479,6 +1593,10 @@ async fn missing_patch_file_path_errors_with_diagnostic() {
         store_dir: Some(&store_dir),
         store_index_writer: Some(&writer),
         patches: Some(&patches),
+
+        scripts_prepend_node_path: ScriptsPrependNodePath::Never,
+        unsafe_perm: true,
+        child_concurrency: 1,
     }
     .run::<SilentReporter>()
     .expect_err("missing patch_file_path must surface as PatchFilePathMissing");
diff --git a/pacquet/crates/package-manager/src/build_sequence.rs b/pacquet/crates/package-manager/src/build_sequence.rs
index da510eaf26..00117df102 100644
--- a/pacquet/crates/package-manager/src/build_sequence.rs
+++ b/pacquet/crates/package-manager/src/build_sequence.rs
@@ -105,6 +105,13 @@ fn build_children_map(
                 }
             }
         }
+        // Sort for the same reason `collect_root_dep_paths` sorts
+        // its output: `get_subgraph_to_build` walks children in
+        // sequence, and a shared transitive descendant gets trimmed
+        // off whichever sibling visits it second. Both the entry
+        // nodes and every child list must be in a deterministic
+        // order for the build sequence to be reproducible.
+        child_keys.sort_by_key(|k| k.to_string());
         children.insert(key.clone(), child_keys);
     }
     children
@@ -141,6 +148,18 @@ fn collect_root_dep_paths(
             }
         }
     }
+    // [`get_subgraph_to_build`] is order-sensitive (a node walked
+    // first via root A may mark a shared child as already-walked, so
+    // a second root B sharing that child gets trimmed). Upstream's
+    // input arrives in JS-object insertion order; pacquet sources
+    // these from `HashMap<_, ProjectSnapshot>` and
+    // `HashMap<PkgName, ResolvedDependencySpec>`, so iteration order
+    // is non-deterministic. Sort by `PackageKey` string repr so the
+    // build sequence (and the trim behavior) is reproducible run to
+    // run. Long-term fix is to preserve lockfile declaration order
+    // via `IndexMap`; until then, an alphabetical sort is enough to
+    // make the build path deterministic.
+    roots.sort_by_key(|k| k.to_string());
     roots
 }
 
diff --git a/pacquet/crates/package-manager/src/build_sequence/tests.rs b/pacquet/crates/package-manager/src/build_sequence/tests.rs
index 8f318d17e8..9067ef5c87 100644
--- a/pacquet/crates/package-manager/src/build_sequence/tests.rs
+++ b/pacquet/crates/package-manager/src/build_sequence/tests.rs
@@ -172,3 +172,36 @@ fn parallel_build_leaves_share_chunk() {
     assert_eq!(leaves, vec![key("a", "1.0.0"), key("b", "1.0.0")]);
     assert_eq!(chunks[1], vec![key("root", "1.0.0")]);
 }
+
+/// Direct port of upstream
+/// [`'buildSequence() test 2'`](https://github.com/pnpm/pnpm/blob/b4f8f47ac2/building/during-install/test/buildSequence.test.ts#L28-L51).
+///
+/// Two importers `a` and `b` both depend on a shared builder leaf
+/// `c`. Only `a` requires its own build; `b` does not. The result
+/// must surface `c` in the first chunk and `a` in the second — `b`
+/// is *trimmed* from the build sequence because it neither needs a
+/// build itself nor has a buildable descendant that's exclusive to
+/// it (its descendant `c` is already scheduled via `a`).
+///
+/// This is the subgraph-trim case for #397 item #16. Pacquet's
+/// existing `unrelated_subgraph_excluded` covers a stronger
+/// scenario (an entirely unreachable subgraph); this one pins the
+/// upstream-equivalent behavior where an importer that's still in
+/// the install set gets dropped from the build sequence.
+#[test]
+fn non_builder_importer_with_shared_builder_child_is_trimmed() {
+    let snapshots = HashMap::from([
+        (key("a", "1.0.0"), snap(&[("c", "1.0.0")])),
+        (key("b", "1.0.0"), snap(&[("c", "1.0.0")])),
+        (key("c", "1.0.0"), snap(&[])),
+    ]);
+    let requires_build = requires([
+        (key("a", "1.0.0"), true),
+        (key("b", "1.0.0"), false),
+        (key("c", "1.0.0"), true),
+    ]);
+    let importers = root_importers(&[("a", "1.0.0"), ("b", "1.0.0")]);
+
+    let chunks = build_sequence(&requires_build, None, &snapshots, &importers);
+    assert_eq!(chunks, vec![vec![key("c", "1.0.0")], vec![key("a", "1.0.0")]]);
+}
diff --git a/pacquet/crates/package-manager/src/install_frozen_lockfile.rs b/pacquet/crates/package-manager/src/install_frozen_lockfile.rs
index 8d5d410bb9..e047eafd1e 100644
--- a/pacquet/crates/package-manager/src/install_frozen_lockfile.rs
+++ b/pacquet/crates/package-manager/src/install_frozen_lockfile.rs
@@ -6,6 +6,7 @@ use crate::{
 use derive_more::{Display, Error};
 use miette::Diagnostic;
 use pacquet_config::Config;
+use pacquet_executor::ScriptsPrependNodePath as ExecScriptsPrependNodePath;
 use pacquet_lockfile::{PackageKey, PackageMetadata, ProjectSnapshot, SnapshotEntry};
 use pacquet_network::ThrottledClient;
 use pacquet_package_manifest::DependencyGroup;
@@ -225,6 +226,19 @@ where
                 _ => None,
             };
 
+        // Convert `pacquet-config`'s mirror enum to the executor's
+        // canonical type. Config's enum carries the yaml-deserialize
+        // impl; the executor's stays free of serde wiring. See the
+        // doc on [`pacquet_config::ScriptsPrependNodePath`] for the
+        // rationale.
+        let scripts_prepend_node_path = match config.scripts_prepend_node_path {
+            pacquet_config::ScriptsPrependNodePath::Always => ExecScriptsPrependNodePath::Always,
+            pacquet_config::ScriptsPrependNodePath::Never => ExecScriptsPrependNodePath::Never,
+            pacquet_config::ScriptsPrependNodePath::WarnOnly => {
+                ExecScriptsPrependNodePath::WarnOnly
+            }
+        };
+
         let ignored_builds = BuildModules {
             virtual_store_dir: &config.virtual_store_dir,
             modules_dir: &config.modules_dir,
@@ -240,6 +254,9 @@ where
             store_dir: Some(&config.store_dir),
             store_index_writer: Some(&store_index_writer),
             patches: patches.as_ref(),
+            scripts_prepend_node_path,
+            unsafe_perm: config.unsafe_perm,
+            child_concurrency: config.child_concurrency,
         }
         .run::<R>()
         .map_err(InstallFrozenLockfileError::BuildModules)?;
diff --git a/pacquet/crates/package-manager/src/install_package_from_registry/tests.rs b/pacquet/crates/package-manager/src/install_package_from_registry/tests.rs
index 843191be1e..62dc731cf6 100644
--- a/pacquet/crates/package-manager/src/install_package_from_registry/tests.rs
+++ b/pacquet/crates/package-manager/src/install_package_from_registry/tests.rs
@@ -46,6 +46,9 @@ fn create_config(store_dir: &Path, modules_dir: &Path, virtual_store_dir: &Path)
         patched_dependencies: None,
         allow_builds: Default::default(),
         dangerously_allow_all_builds: false,
+        scripts_prepend_node_path: Default::default(),
+        unsafe_perm: true,
+        child_concurrency: 1,
     }
 }