Run the live CPUs at the performance governor during install (#89)

archiso boots on whatever governor the kernel defaults to, which on most
laptops ramps conservatively. Package extraction and the UKI build are both
CPU-bound, so pin performance for the whole install and put it back afterwards.

Reduced from #87 by @davydotcom, which also disabled every non-POLL cpuidle
state. That half is left out deliberately: C1 wake latency is 1us on current
hardware, and disabling it leaves POLL as the only idle state, so idle cores
busy-spin instead of halting. Package extraction is single-threaded, so on an
8-core laptop that is 7 cores burning power for no work — on a thermally
limited machine that costs the working core its turbo headroom, which is a
plausible way to make the install slower. #87 measured the two tweaks together
with a page-cache prefetch and an updatedb deferral, so the C-state
contribution was never isolated.

Scoped to the whole install rather than just the pacstrap window, which #87
used: finalize_limine_boot runs mkinitcpio and compresses a UKI, and is the
most purely CPU-bound phase there is.

Restoring only matters when an install fails and the user keeps using the live
environment; a successful one reboots out of it.

Co-authored-by: David Estes <davydotcom@gmail.com>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

configs/airootfs/usr/share/omarchy-iso/orchestrator/main.py

@@ -65,11 +65,15 @@ def main() -> int:
     info(f"Installing Omarchy for {ctx.username} → {ctx.target}")
 
     from .phases_impl import (
+        boost_cpu_governor,
         cleanup_bind_mounts,
         cleanup_protected_state,
         cleanup_target_hook_masks,
+        restore_cpu_governors,
     )
 
+    governors = boost_cpu_governor()
+
     success = False
     try:
         try:
@@ -85,6 +89,7 @@ def main() -> int:
         info("Installation complete.")
         return 0
     finally:
+        restore_cpu_governors(governors)
         cleanup_bind_mounts(ctx)
         cleanup_target_hook_masks(ctx)
         if not success:

configs/airootfs/usr/share/omarchy-iso/orchestrator/phases_impl.py

@@ -1396,6 +1396,40 @@ def _validate_pre_mounted_filesystems(ctx: InstallContext) -> None:
             raise RuntimeError(f"{crypttab} missing LUKS UUID {storage['luks_uuid']}")
 
 
+CPU_SYSFS = Path("/sys/devices/system/cpu")
+
+
+def boost_cpu_governor() -> dict[Path, str]:
+    """Run the live CPUs flat out for the install.
+
+    Package extraction and the UKI build are both CPU-bound, and archiso boots
+    on whatever governor the kernel defaults to. Writing an unsupported
+    governor just fails, so nothing needs probing first, and hosts without
+    cpufreq (most VMs) have no paths at all. Returns the prior governors.
+    """
+    saved: dict[Path, str] = {}
+    for path in sorted(CPU_SYSFS.glob("cpu*/cpufreq/scaling_governor")):
+        try:
+            saved[path] = path.read_text().strip()
+            path.write_text("performance\n")
+        except OSError:
+            saved.pop(path, None)
+
+    if saved:
+        info(f"› CPU governor set to performance ({len(saved)} CPUs)")
+    return saved
+
+
+def restore_cpu_governors(saved: dict[Path, str]) -> None:
+    """Only matters when an install fails and the user keeps using the live
+    environment — a successful one reboots out of it."""
+    for path, governor in saved.items():
+        try:
+            path.write_text(f"{governor}\n")
+        except OSError:
+            continue
+
+
 # ─────────────────────────────────────────────────────────────────────────────
 # cleanup_bind_mounts: invoked from main()'s finally so bind mounts get
 # unwound on success, failure, or interrupt. Idempotent.