init: ConditionPathExists service gate (systemd-style, with ! negation)

init's Service parser used deny_unknown_fields, so the C0
driver-manager service files (which use ConditionPathExists) were
rejected wholesale — driver-manager stayed dormant by parser accident
instead of by design.

- service.rs: new optional ConditionPathExists field + condition_met()
  gate. A leading '!' negates: the service starts only when the path
  does NOT exist.
- scheduler.rs: skip services whose condition is not met (status_skip,
  same pattern as skip_cmd).
- 00_driver-manager.service: fix inverted polarity — the intent is
  'run unless /etc/driver-manager.d/disabled exists', i.e.
  ConditionPathExists = "!/etc/driver-manager.d/disabled".
- Drop two pre-existing unused imports (Write in service.rs,
  status_fail in main.rs).

init.d/00_driver-manager.service

@@ -23,4 +23,4 @@ args = ["--rootfs"]
 type = "oneshot_async"
 # Operator must explicitly enable this service:
 #   touch /etc/driver-manager.d/disabled  # force fallback to pcid-spawner
-ConditionPathExists = "/etc/driver-manager.d/disabled"
+ConditionPathExists = "!/etc/driver-manager.d/disabled"

init/src/main.rs

@@ -14,7 +14,7 @@ mod script;
 mod service;
 mod unit;
 
-use crate::color::{init_error, init_warn, status_fail, status_ok};
+use crate::color::{init_error, init_warn, status_ok};
 
 fn switch_stdio(stdio: &str) -> io::Result<()> {
     let stdin = libredox::Fd::open(stdio, O_RDONLY, 0)?;

init/src/scheduler.rs

@@ -109,6 +109,13 @@ fn run(unit: &mut Unit, config: &mut InitConfig) {
                 status_skip(&format!("Skipping {} ({})", desc, service.cmd));
                 return;
             }
+            if !service.condition_met() {
+                status_skip(&format!(
+                    "Skipping {} (ConditionPathExists not met)",
+                    desc
+                ));
+                return;
+            }
             if config.log_debug {
                 init_info(&format!("Starting {} ({})", desc, service.cmd));
             } else {

init/src/service.rs

@@ -1,7 +1,7 @@
 use std::collections::{BTreeMap, BTreeSet};
 use std::ffi::OsString;
 use std::fs::File;
-use std::io::{self, Read, Write};
+use std::io::{self, Read};
 use std::os::fd::{AsRawFd, FromRawFd, OwnedFd};
 use std::os::unix::process::CommandExt;
 use std::process::Command;
@@ -24,6 +24,8 @@ pub struct Service {
     pub inherit_envs: BTreeSet<String>,
     #[serde(rename = "type")]
     pub type_: ServiceType,
+    #[serde(default, rename = "ConditionPathExists")]
+    pub condition_path_exists: Option<String>,
 }
 
 #[derive(Clone, Debug, Default, Deserialize)]
@@ -36,6 +38,21 @@ pub enum ServiceType {
     OneshotAsync,
 }
 
+impl Service {
+    /// systemd-style ConditionPathExists gate. A leading `!` negates the
+    /// test: the service starts only when the path does NOT exist.
+    pub fn condition_met(&self) -> bool {
+        let Some(cond) = &self.condition_path_exists else {
+            return true;
+        };
+        let (negated, path) = match cond.strip_prefix('!') {
+            Some(rest) => (true, rest),
+            None => (false, cond.as_str()),
+        };
+        std::path::Path::new(path).exists() != negated
+    }
+}
+
 fn create_pipe() -> io::Result<(File, OwnedFd)> {
     let mut fds = [0i32; 2];
     // Use libc::pipe2() which goes through relibc's FILETABLE-managed path