feat(ip-pool): pre-assign static IPs to build VMs via VMX guestinfo

Eliminates VMware-Tools IP-detect polling (observed: 39–177 s variance on
Linux host B7 benchmark).  When [ip_pool] is configured the orchestrator:

  1. Allocates a slot IP from a JSON-backed pool (fcntl-locked on Linux)
  2. Injects guestinfo.ip-assignment / netmask / gateway into the cloned VMX
     before vmrun start
  3. Skips _wait_for_ip entirely — uses the pre-assigned IP immediately
  4. Releases the slot in _destroy_clone (all paths: success/failure/interrupt)

New modules / changes:
  src/ci_orchestrator/ip_pool.py      IpSlotPool + _file_lock context manager
  src/ci_orchestrator/config.py       IpPoolConfig dataclass; [ip_pool] TOML
  src/ci_orchestrator/commands/job.py _inject_guestinfo_ip helper; pool wiring
  tests/python/test_ip_pool.py        12 unit tests (acquire/release/persist)
  tests/python/test_config.py         ip_pool config parsing tests
  tests/python/test_commands_job.py   pool path + _inject_guestinfo_ip tests
  config.example.toml                 [ip_pool] section (commented example)

Coverage 90.02%; mypy --strict clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/python/test_ip_pool.py

@@ -0,0 +1,117 @@
+"""Tests for ci_orchestrator.ip_pool — IpSlotPool acquire/release."""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+import pytest
+
+from ci_orchestrator.ip_pool import IpSlotPool
+
+
+def make_pool(tmp_path: Path, addresses: list[str] | None = None) -> IpSlotPool:
+    return IpSlotPool(
+        addresses=addresses or ["10.0.0.1", "10.0.0.2"],
+        netmask="255.255.255.0",
+        gateway="10.0.0.254",
+        lease_file=tmp_path / "ip-pool.json",
+    )
+
+
+# ── construction ────────────────────────────────────────────────────────────
+
+
+def test_empty_addresses_raises(tmp_path: Path) -> None:
+    with pytest.raises(ValueError, match="at least one"):
+        IpSlotPool([], "255.255.255.0", "", tmp_path / "pool.json")
+
+
+# ── acquire ─────────────────────────────────────────────────────────────────
+
+
+def test_acquire_returns_first_free_ip(tmp_path: Path) -> None:
+    pool = make_pool(tmp_path)
+    ip = pool.acquire("owner-1")
+    assert ip == "10.0.0.1"
+
+
+def test_acquire_second_slot(tmp_path: Path) -> None:
+    pool = make_pool(tmp_path)
+    pool.acquire("owner-1")
+    ip2 = pool.acquire("owner-2")
+    assert ip2 == "10.0.0.2"
+
+
+def test_acquire_writes_lease_file(tmp_path: Path) -> None:
+    pool = make_pool(tmp_path)
+    pool.acquire("owner-1")
+    leases = json.loads((tmp_path / "ip-pool.json").read_text())
+    assert leases["10.0.0.1"] == "owner-1"
+    assert leases["10.0.0.2"] is None
+
+
+def test_acquire_exhausted_raises(tmp_path: Path) -> None:
+    pool = make_pool(tmp_path, addresses=["10.0.0.1"])
+    pool.acquire("owner-1")
+    with pytest.raises(RuntimeError, match="exhausted"):
+        pool.acquire("owner-2", timeout=0.1)
+
+
+# ── release ──────────────────────────────────────────────────────────────────
+
+
+def test_release_frees_slot(tmp_path: Path) -> None:
+    pool = make_pool(tmp_path)
+    ip = pool.acquire("owner-1")
+    pool.release(ip)
+    leases = json.loads((tmp_path / "ip-pool.json").read_text())
+    assert leases[ip] is None
+
+
+def test_release_unknown_ip_is_noop(tmp_path: Path) -> None:
+    pool = make_pool(tmp_path)
+    pool.release("99.99.99.99")  # should not raise
+
+
+def test_release_and_reacquire(tmp_path: Path) -> None:
+    pool = make_pool(tmp_path, addresses=["10.0.0.1"])
+    ip = pool.acquire("owner-1")
+    pool.release(ip)
+    ip2 = pool.acquire("owner-2")
+    assert ip2 == "10.0.0.1"
+
+
+# ── persistence ──────────────────────────────────────────────────────────────
+
+
+def test_second_pool_instance_sees_leases(tmp_path: Path) -> None:
+    lease = tmp_path / "ip-pool.json"
+    p1 = IpSlotPool(["10.0.0.1", "10.0.0.2"], "255.255.255.0", "", lease)
+    p1.acquire("owner-1")
+
+    p2 = IpSlotPool(["10.0.0.1", "10.0.0.2"], "255.255.255.0", "", lease)
+    ip = p2.acquire("owner-2")
+    assert ip == "10.0.0.2"
+
+
+def test_corrupt_lease_file_treated_as_empty(tmp_path: Path) -> None:
+    lease = tmp_path / "ip-pool.json"
+    lease.write_text("NOT JSON", encoding="utf-8")
+    pool = make_pool(tmp_path)
+    ip = pool.acquire("owner-1")
+    assert ip == "10.0.0.1"
+
+
+def test_missing_lease_file_treated_as_empty(tmp_path: Path) -> None:
+    pool = make_pool(tmp_path)
+    ip = pool.acquire("owner-1")
+    assert ip == "10.0.0.1"
+
+
+def test_non_dict_lease_json_treated_as_empty(tmp_path: Path) -> None:
+    lease = tmp_path / "ip-pool.json"
+    lease.write_text("[1, 2, 3]", encoding="utf-8")  # valid JSON but not a dict
+    pool = make_pool(tmp_path)
+    ip = pool.acquire("owner-1")
+    assert ip == "10.0.0.1"