diff --git a/.gitignore b/.gitignore
index f22f155..b578bb9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,3 +9,4 @@ coremlsuite-venv/
 experiment_results/
 test_results/
 bench/scripts/*.log
+tests/m2/_latest_generated.png
diff --git a/pyproject.toml b/pyproject.toml
index b1906e8..b35c783 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -37,3 +37,19 @@ dev = [
     "pillow>=12.2.0",
     "psutil>=7.2.2",
 ]
+
+[tool.pytest.ini_options]
+# Phase 2: tier markers gate which environment a test needs.
+# - unit: framework-free pure-logic tests (Tier 0; future Phase 3 will run
+#   these without ComfyUI on Linux). For now they may still transitively
+#   import comfy.
+# - m2:   needs an Apple Silicon Mac with the Neural Engine (Tier 2),
+#   typically the maintainer's self-hosted runner or local M-series box.
+# - smoke: lightweight checks that need Apple Silicon + coremltools but no
+#   ANE/real model (reserved for Phase 4 Tier 1 smoke harness).
+markers = [
+    "unit: framework-free unit test (Tier 0)",
+    "m2: requires Apple Silicon + Neural Engine (Tier 2)",
+    "smoke: macOS-ARM smoke test on a synthetic micro-model (Tier 1)",
+]
+testpaths = ["tests"]
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..0754a0c
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,50 @@
+"""Pytest bootstrap for ComfyUI-CoreMLSuite tests.
+
+- Adds the ComfyUI checkout to sys.path so production modules that
+  transitively import `comfy.*` resolve when pytest is invoked from this
+  package's root. Phase 3 will split pure logic into a comfy-free core and
+  this hack can go.
+- Auto-applies tier markers based on the directory a test lives in, so
+  individual files don't have to repeat @pytest.mark.unit / .m2.
+- Skips the maintainer's in-progress test scaffolds so they don't break
+  collection (they reference modules / venv layouts that aren't part of
+  Phase 2 scope).
+"""
+import sys
+from pathlib import Path
+
+import pytest
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+COMFY_DIR = REPO_ROOT.parents[1]
+
+for p in (str(COMFY_DIR), str(REPO_ROOT)):
+    if p not in sys.path:
+        sys.path.insert(0, p)
+
+
+# Skip WIP test scaffolds left in the tree by the maintainer; they import
+# modules (coreml_suite.experiments, convert_apple) that are not part of
+# Phase 2 scope.
+collect_ignore_glob = [
+    "unit/test_experiments.py",
+    "unit/test_unet_conversion.py",
+    "unit/standalone_test.py",
+]
+
+
+_TIER_BY_DIR = {
+    "tests/unit": "unit",
+    "tests/m2": "m2",
+    "tests/integration": "m2",
+    "tests/smoke": "smoke",
+}
+
+
+def pytest_collection_modifyitems(config, items):
+    for item in items:
+        path = str(item.fspath).replace("\\", "/")
+        for fragment, marker in _TIER_BY_DIR.items():
+            if f"/{fragment}/" in path:
+                item.add_marker(getattr(pytest.mark, marker))
+                break
diff --git a/tests/m2/__init__.py b/tests/m2/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/m2/goldens/sd15_seed42.png b/tests/m2/goldens/sd15_seed42.png
new file mode 100644
index 0000000..a561e16
Binary files /dev/null and b/tests/m2/goldens/sd15_seed42.png differ
diff --git a/tests/m2/goldens/sd15_seed42.sha256 b/tests/m2/goldens/sd15_seed42.sha256
new file mode 100644
index 0000000..6ea161e
--- /dev/null
+++ b/tests/m2/goldens/sd15_seed42.sha256
@@ -0,0 +1 @@
+9e12ba1f98969a99c17e84a87a77c4561fcac3ca2ddd6338a7ae89d324df6994
diff --git a/tests/m2/test_golden_image.py b/tests/m2/test_golden_image.py
new file mode 100644
index 0000000..d9d70e8
--- /dev/null
+++ b/tests/m2/test_golden_image.py
@@ -0,0 +1,162 @@
+"""Phase 2 [M2-ANE] golden-image anchor.
+
+Runs the e2e SD1.5 + CoreML workflow against a local ComfyUI server, fetches
+the generated PNG, and asserts both:
+  - byte-identical SHA256 against the stored golden, OR
+  - PSNR >= GOLDEN_PSNR_MIN_DB against the stored golden PNG.
+
+The hash is the strict gate (a Phase 3 refactor that doesn't touch the math
+should hit it). PSNR is the soft gate that tolerates a sub-bit drift in
+sampler ordering or kernel selection — anything below the threshold is
+treated as a regression.
+
+Skips entirely on non-Apple-Silicon hosts or when the server / converted
+model is missing, so the unit lane on Linux still passes.
+
+The first run with no golden writes one and fails so it's reviewed before
+being committed.
+"""
+import hashlib
+import json
+import os
+import platform
+import shutil
+import time
+import urllib.error
+import urllib.request
+from pathlib import Path
+
+import numpy as np
+import pytest
+from PIL import Image
+
+REPO_ROOT = Path(__file__).resolve().parents[2]
+COMFY_DIR = Path(os.environ.get("COMFY_DIR", REPO_ROOT.parents[1])).resolve()
+COMFY_HOST = os.environ.get("COMFY_HOST", "localhost")
+COMFY_PORT = int(os.environ.get("COMFY_PORT", "8188"))
+COMFY_URL = f"http://{COMFY_HOST}:{COMFY_PORT}"
+
+CKPT_NAME = os.environ.get("CKPT_NAME", "v1-5-pruned-emaonly.safetensors")
+WORKFLOW_PATH = (
+    REPO_ROOT / "tests" / "integration" / "workflows" / "e2e-1.5-basic-conversion.json"
+)
+GOLDEN_DIR = Path(__file__).parent / "goldens"
+GOLDEN_HASH_PATH = GOLDEN_DIR / "sd15_seed42.sha256"
+GOLDEN_PNG_PATH = GOLDEN_DIR / "sd15_seed42.png"
+GOLDEN_PSNR_MIN_DB = float(os.environ.get("GOLDEN_PSNR_MIN_DB", "40"))
+SEED = 42
+
+
+def _server_reachable() -> bool:
+    try:
+        with urllib.request.urlopen(f"{COMFY_URL}/prompt", timeout=3) as r:
+            return r.status == 200
+    except (urllib.error.URLError, urllib.error.HTTPError, ConnectionError):
+        return False
+
+
+@pytest.fixture(scope="module")
+def comfy_server():
+    if platform.machine() != "arm64":
+        pytest.skip("requires Apple Silicon")
+    if not _server_reachable():
+        pytest.skip(f"ComfyUI server not reachable at {COMFY_URL}")
+    return COMFY_URL
+
+
+def _http_post_json(path: str, payload: dict) -> dict:
+    data = json.dumps(payload).encode("utf-8")
+    req = urllib.request.Request(
+        f"{COMFY_URL}{path}", data=data,
+        headers={"Content-Type": "application/json"}, method="POST",
+    )
+    with urllib.request.urlopen(req, timeout=300) as r:
+        return json.loads(r.read().decode())
+
+
+def _http_get_json(path: str, timeout: int = 300) -> dict:
+    """ComfyUI runs UNet inference on its single asyncio loop, so GET /prompt
+    blocks while the queued prompt is executing. Use a generous timeout."""
+    with urllib.request.urlopen(f"{COMFY_URL}{path}", timeout=timeout) as r:
+        return json.loads(r.read().decode())
+
+
+def _drain_queue(timeout_s: int = 600) -> None:
+    deadline = time.time() + timeout_s
+    while time.time() < deadline:
+        try:
+            q = _http_get_json("/prompt")
+        except (urllib.error.URLError, TimeoutError):
+            # Transient block while server executes; retry until our overall
+            # deadline expires.
+            continue
+        if q.get("exec_info", {}).get("queue_remaining", -1) == 0:
+            return
+        time.sleep(2)
+    raise TimeoutError(f"queue did not drain within {timeout_s}s")
+
+
+def _post_workflow_and_collect_png() -> bytes:
+    workflow = json.loads(WORKFLOW_PATH.read_text())
+    for nid in ("4", "10"):
+        if nid in workflow:
+            workflow[nid]["inputs"]["ckpt_name"] = CKPT_NAME
+    for nid in ("3", "11"):
+        if nid in workflow and "seed" in workflow[nid].get("inputs", {}):
+            workflow[nid]["inputs"]["seed"] = SEED
+    # Drop the MPS reference branch — torch 2.0.1 MPS path is broken on macOS 26
+    # (see Phase 1 gate report). Only the Core ML pipeline is needed here.
+    for nid in ("3", "8", "9"):
+        workflow.pop(nid, None)
+
+    _http_post_json("/prompt", {"prompt": workflow})
+    _drain_queue()
+
+    comfy_out = COMFY_DIR / "output"
+    matches = sorted(comfy_out.glob("E2E-1.5-CoreML_*.png"), reverse=True)
+    if not matches:
+        raise FileNotFoundError(f"no Core ML image under {comfy_out}")
+    return matches[0].read_bytes()
+
+
+def _psnr(a: np.ndarray, b: np.ndarray) -> float:
+    mse = float(np.mean((a.astype(np.float64) - b.astype(np.float64)) ** 2))
+    if mse == 0:
+        return 100.0
+    return 20.0 * float(np.log10(255.0 / np.sqrt(mse)))
+
+
+def test_sd15_seed42_image_matches_golden(comfy_server):
+    GOLDEN_DIR.mkdir(parents=True, exist_ok=True)
+    png_bytes = _post_workflow_and_collect_png()
+    sha = hashlib.sha256(png_bytes).hexdigest()
+
+    if not GOLDEN_HASH_PATH.exists() or not GOLDEN_PNG_PATH.exists():
+        GOLDEN_HASH_PATH.write_text(sha + "\n")
+        # Persist the PNG too for visual diffing + PSNR.
+        tmp_path = Path(__file__).parent / "_latest_generated.png"
+        tmp_path.write_bytes(png_bytes)
+        shutil.copy2(tmp_path, GOLDEN_PNG_PATH)
+        pytest.fail(
+            f"No golden present; wrote {GOLDEN_HASH_PATH.name} and "
+            f"{GOLDEN_PNG_PATH.name}. Review the image and re-run."
+        )
+
+    expected_hash = GOLDEN_HASH_PATH.read_text().strip()
+    if sha == expected_hash:
+        return
+
+    # Hash drift: fall back to PSNR to distinguish a refactor-safe rounding
+    # change from a real regression.
+    a = np.array(Image.open(GOLDEN_PNG_PATH).convert("RGB"))
+    b_path = Path(__file__).parent / "_latest_generated.png"
+    b_path.write_bytes(png_bytes)
+    b = np.array(Image.open(b_path).convert("RGB"))
+    if a.shape != b.shape:
+        pytest.fail(f"shape mismatch: golden={a.shape} actual={b.shape}")
+    psnr_db = _psnr(a, b)
+    assert psnr_db >= GOLDEN_PSNR_MIN_DB, (
+        f"hash drifted (got {sha[:12]}.., expected {expected_hash[:12]}..) and "
+        f"PSNR {psnr_db:.2f} dB < {GOLDEN_PSNR_MIN_DB} dB threshold; "
+        f"diff PNG at {b_path}"
+    )
diff --git a/tests/unit/test_characterization_controlnet.py b/tests/unit/test_characterization_controlnet.py
new file mode 100644
index 0000000..1c20756
--- /dev/null
+++ b/tests/unit/test_characterization_controlnet.py
@@ -0,0 +1,186 @@
+"""Phase 2 characterization tests for coreml_suite.controlnet.
+
+Locks shapes + dtypes + zero-fill behavior of expand_inputs / no_control /
+extract_residual_kwargs / chunk_control. These pure helpers feed the Core ML
+UNet's additional_residual_N inputs; any drift here silently breaks
+ControlNet-based workflows.
+"""
+import numpy as np
+import pytest
+import torch
+
+from coreml_suite.controlnet import (
+    chunk_control,
+    expand_inputs,
+    extract_residual_kwargs,
+    no_control,
+)
+
+
+@pytest.fixture(autouse=True)
+def _deterministic_seed():
+    torch.manual_seed(0)
+    np.random.seed(0)
+
+
+SD15_RESIDUAL_SPEC = {
+    "additional_residual_0": {"shape": (2, 320, 64, 64)},
+    "additional_residual_1": {"shape": (2, 640, 32, 32)},
+    "additional_residual_2": {"shape": (2, 1280, 8, 8)},
+}
+NON_RESIDUAL_SPEC = {
+    "sample": {"shape": (2, 4, 64, 64)},
+    "encoder_hidden_states": {"shape": (2, 768, 1, 77)},
+}
+
+
+# ---------- expand_inputs ----------------------------------------------------
+
+
+def test_expand_inputs_doubles_singleton_numpy():
+    inputs = {"a": np.ones((1, 4), dtype=np.float32)}
+    out = expand_inputs(inputs)
+    assert out["a"].shape == (2, 4)
+    assert np.array_equal(out["a"], np.ones((2, 4)))
+
+
+def test_expand_inputs_doubles_singleton_torch():
+    inputs = {"a": torch.ones(1, 4)}
+    out = expand_inputs(inputs)
+    assert out["a"].shape == (2, 4)
+    assert torch.equal(out["a"], torch.ones(2, 4))
+
+
+def test_expand_inputs_doubles_singleton_list():
+    inputs = {"a": [42]}
+    out = expand_inputs(inputs)
+    assert out["a"] == [42, 42]
+
+
+def test_expand_inputs_skips_already_batched():
+    """batch > 1 inputs are returned unchanged (same object identity)."""
+    arr = np.ones((2, 4), dtype=np.float32)
+    tensor = torch.ones(3, 4)
+    lst = [1, 2]
+    out = expand_inputs({"a": arr, "b": tensor, "c": lst})
+    assert out["a"] is arr
+    assert out["b"] is tensor
+    assert out["c"] is lst
+
+
+def test_expand_inputs_preserves_unknown_value_types():
+    # Strings/None pass through untouched — locks current permissive contract.
+    inputs = {"s": "hello", "none": None, "int": 7}
+    out = expand_inputs(inputs)
+    assert out == {"s": "hello", "none": None, "int": 7}
+
+
+# ---------- no_control -------------------------------------------------------
+
+
+def test_no_control_returns_zero_fp16_for_residuals():
+    out = no_control({**SD15_RESIDUAL_SPEC, **NON_RESIDUAL_SPEC})
+    # Only additional_residual_* keys are produced.
+    assert set(out.keys()) == set(SD15_RESIDUAL_SPEC.keys())
+    for key, spec in SD15_RESIDUAL_SPEC.items():
+        arr = out[key]
+        assert arr.shape == spec["shape"]
+        assert arr.dtype == np.float16
+        assert np.all(arr == 0)
+
+
+def test_no_control_returns_empty_when_no_residuals():
+    out = no_control(NON_RESIDUAL_SPEC)
+    assert out == {}
+
+
+# ---------- extract_residual_kwargs -----------------------------------------
+
+
+def test_extract_residual_kwargs_empty_when_model_has_no_residual_inputs():
+    out = extract_residual_kwargs(NON_RESIDUAL_SPEC, control={"output": [], "middle": []})
+    assert out == {}
+
+
+def test_extract_residual_kwargs_none_control_returns_no_control_shapes():
+    out = extract_residual_kwargs(SD15_RESIDUAL_SPEC, control=None)
+    assert set(out.keys()) == set(SD15_RESIDUAL_SPEC.keys())
+    for key, spec in SD15_RESIDUAL_SPEC.items():
+        assert out[key].shape == spec["shape"]
+        assert out[key].dtype == np.float16
+        assert np.all(out[key] == 0)
+
+
+def test_extract_residual_kwargs_flattens_output_then_middle_and_casts_fp16():
+    """output residuals come first (indexed 0..N-1), then middle residuals
+    (indexed N..M-1). Values come out of CPU as fp16 numpy arrays."""
+    control = {
+        "output": [torch.ones(2, 320, 64, 64) * 0.5, torch.ones(2, 640, 32, 32) * 2.0],
+        "middle": [torch.ones(2, 1280, 8, 8) * -1.0],
+    }
+    out = extract_residual_kwargs(SD15_RESIDUAL_SPEC, control)
+    assert set(out.keys()) == {"additional_residual_0", "additional_residual_1", "additional_residual_2"}
+    assert out["additional_residual_0"].shape == (2, 320, 64, 64)
+    assert out["additional_residual_1"].shape == (2, 640, 32, 32)
+    assert out["additional_residual_2"].shape == (2, 1280, 8, 8)
+    for arr in out.values():
+        assert arr.dtype == np.float16
+    # Locked order: index 0 == first output residual (0.5), index 2 == middle (-1.0).
+    assert np.allclose(out["additional_residual_0"], 0.5)
+    assert np.allclose(out["additional_residual_1"], 2.0)
+    assert np.allclose(out["additional_residual_2"], -1.0)
+
+
+# ---------- chunk_control ----------------------------------------------------
+
+
+def test_chunk_control_none_returns_list_of_nones_with_length_target():
+    """`no_control` path: when there's no control, you get [None] * target_size
+    (NOT [None, None] regardless of target — this is the contract today)."""
+    assert chunk_control(None, 1) == [None]
+    assert chunk_control(None, 2) == [None, None]
+    assert chunk_control(None, 4) == [None, None, None, None]
+
+
+@pytest.mark.parametrize(
+    "batch,target,expected_chunks",
+    [(1, 2, 1), (2, 2, 1), (3, 2, 2), (4, 2, 2), (5, 3, 2), (9, 4, 3)],
+)
+def test_chunk_control_shapes_after_chunking(batch, target, expected_chunks):
+    cn = {
+        "output": [
+            torch.randn(batch, 320, 64, 64),
+            torch.randn(batch, 640, 32, 32),
+        ],
+        "middle": [torch.randn(batch, 1280, 8, 8)],
+    }
+    chunks = chunk_control(cn, target)
+    assert len(chunks) == expected_chunks
+    for c in chunks:
+        assert c["output"][0].shape == (target, 320, 64, 64)
+        assert c["output"][1].shape == (target, 640, 32, 32)
+        assert c["middle"][0].shape == (target, 1280, 8, 8)
+
+
+def test_chunk_control_preserves_keys_order():
+    """Output dicts contain exactly {"output", "middle"} in that order."""
+    cn = {
+        "output": [torch.zeros(2, 4, 4, 4)],
+        "middle": [torch.zeros(2, 4, 4, 4)],
+    }
+    chunks = chunk_control(cn, 2)
+    assert list(chunks[0].keys()) == ["output", "middle"]
+
+
+def test_chunk_control_zero_pads_remainder():
+    """A batch=3, target=2 split puts the third row alongside a zero row."""
+    cn = {
+        "output": [torch.arange(3 * 4).reshape(3, 1, 2, 2).float()],
+        "middle": [torch.arange(3 * 4).reshape(3, 1, 2, 2).float()],
+    }
+    chunks = chunk_control(cn, 2)
+    assert len(chunks) == 2
+    last_out = chunks[-1]["output"][0]
+    # First row is the original third row; second row is padding zeros.
+    assert torch.equal(last_out[0], cn["output"][0][2])
+    assert torch.equal(last_out[1], torch.zeros(1, 2, 2))
diff --git a/tests/unit/test_characterization_inputs.py b/tests/unit/test_characterization_inputs.py
new file mode 100644
index 0000000..c1769ca
--- /dev/null
+++ b/tests/unit/test_characterization_inputs.py
@@ -0,0 +1,228 @@
+"""Phase 2 characterization tests for coreml_suite.models.CoreMLInputs.
+
+Locks the shape transforms applied by chunks() and coreml_kwargs() for the
+four model variants the suite supports: SD1.5, LCM (SD1.5 + timestep_cond),
+SDXL base (time_ids len 6), and SDXL refiner (time_ids len 5).
+
+These contracts feed the Core ML UNet at runtime; if Phase 3 silently
+re-shapes them, generation breaks.
+"""
+import numpy as np
+import pytest
+import torch
+
+from coreml_suite.models import CoreMLInputs
+
+
+@pytest.fixture(autouse=True)
+def _deterministic_seed():
+    torch.manual_seed(0)
+    np.random.seed(0)
+
+
+# ---------- expected_inputs fixtures (mirror real model expectations) -------
+
+SD15_EXPECTED = {
+    "sample": {"shape": (2, 4, 64, 64)},
+    "timestep": {"shape": (2,)},
+    "encoder_hidden_states": {"shape": (2, 768, 1, 77)},
+}
+
+SD15_WITH_CN = {
+    **SD15_EXPECTED,
+    "additional_residual_0": {"shape": (2, 320, 64, 64)},
+    "additional_residual_1": {"shape": (2, 640, 32, 32)},
+}
+
+LCM_EXPECTED = {
+    **SD15_EXPECTED,
+    "timestep_cond": {"shape": (2, 256)},
+}
+
+SDXL_BASE_EXPECTED = {
+    "sample": {"shape": (2, 4, 128, 128)},
+    "timestep": {"shape": (2,)},
+    "encoder_hidden_states": {"shape": (2, 2048, 1, 77)},
+    "time_ids": {"shape": (2, 6)},
+    "text_embeds": {"shape": (2, 1280)},
+}
+
+SDXL_REFINER_EXPECTED = {
+    "sample": {"shape": (2, 4, 128, 128)},
+    "timestep": {"shape": (2,)},
+    "encoder_hidden_states": {"shape": (2, 1280, 1, 77)},
+    "time_ids": {"shape": (2, 5)},
+    "text_embeds": {"shape": (2, 1280)},
+}
+
+
+def _sd15_inputs(batch=1, with_control=False, with_ts_cond=False):
+    x = torch.randn(batch, 4, 64, 64)
+    t = torch.full((batch,), 999.0)
+    context = torch.randn(batch, 77, 768)
+    control = None
+    if with_control:
+        control = {
+            "output": [torch.randn(batch, 320, 64, 64), torch.randn(batch, 640, 32, 32)],
+            "middle": [],
+        }
+    kwargs = {}
+    if with_ts_cond:
+        kwargs["timestep_cond"] = torch.randn(batch, 256)
+    return CoreMLInputs(x, t, context, control, **kwargs)
+
+
+def _sdxl_inputs(batch=1, refiner=False):
+    x = torch.randn(batch, 4, 128, 128)
+    t = torch.full((batch,), 999.0)
+    ctx_dim = 1280 if refiner else 2048
+    context = torch.randn(batch, 77, ctx_dim)
+    time_ids_dim = 5 if refiner else 6
+    time_ids = torch.randn(batch, time_ids_dim)
+    text_embeds = torch.randn(batch, 1280)
+    return CoreMLInputs(
+        x, t, context, control=None, time_ids=time_ids, text_embeds=text_embeds
+    )
+
+
+# ---------- coreml_kwargs ---------------------------------------------------
+
+
+def test_coreml_kwargs_sd15_shapes_and_fp16():
+    out = _sd15_inputs(batch=1).coreml_kwargs(SD15_EXPECTED)
+    assert set(out.keys()) == {"sample", "encoder_hidden_states", "timestep"}
+    assert out["sample"].shape == (1, 4, 64, 64)
+    assert out["sample"].dtype == np.float16
+    # encoder_hidden_states is transposed (b, seq, dim) -> (b, dim, 1, seq).
+    assert out["encoder_hidden_states"].shape == (1, 768, 1, 77)
+    assert out["encoder_hidden_states"].dtype == np.float16
+    assert out["timestep"].shape == (1,)
+    assert out["timestep"].dtype == np.float16
+
+
+def test_coreml_kwargs_sd15_with_controlnet_emits_residuals():
+    inputs = _sd15_inputs(batch=1, with_control=True)
+    out = inputs.coreml_kwargs(SD15_WITH_CN)
+    assert "additional_residual_0" in out
+    assert "additional_residual_1" in out
+    assert out["additional_residual_0"].shape == (1, 320, 64, 64)
+    assert out["additional_residual_1"].shape == (1, 640, 32, 32)
+
+
+def test_coreml_kwargs_sd15_without_controlnet_zero_fills_residuals():
+    inputs = _sd15_inputs(batch=1, with_control=False)
+    out = inputs.coreml_kwargs(SD15_WITH_CN)
+    assert np.all(out["additional_residual_0"] == 0)
+    assert np.all(out["additional_residual_1"] == 0)
+
+
+def test_coreml_kwargs_lcm_adds_timestep_cond():
+    inputs = _sd15_inputs(batch=1, with_ts_cond=True)
+    out = inputs.coreml_kwargs(LCM_EXPECTED)
+    assert "timestep_cond" in out
+    assert out["timestep_cond"].shape == (1, 256)
+    assert out["timestep_cond"].dtype == np.float16
+
+
+def test_coreml_kwargs_lcm_skips_timestep_cond_when_not_provided():
+    """timestep_cond is only forwarded when the input supplied one — even if
+    the model's expected_inputs lists it."""
+    inputs = _sd15_inputs(batch=1, with_ts_cond=False)
+    out = inputs.coreml_kwargs(LCM_EXPECTED)
+    assert "timestep_cond" not in out
+
+
+def test_coreml_kwargs_sdxl_base_emits_time_ids_and_text_embeds():
+    out = _sdxl_inputs(batch=1, refiner=False).coreml_kwargs(SDXL_BASE_EXPECTED)
+    assert out["time_ids"].shape == (1, 6)
+    assert out["text_embeds"].shape == (1, 1280)
+    assert out["time_ids"].dtype == np.float16
+    assert out["text_embeds"].dtype == np.float16
+
+
+def test_coreml_kwargs_sdxl_refiner_uses_len5_time_ids():
+    out = _sdxl_inputs(batch=1, refiner=True).coreml_kwargs(SDXL_REFINER_EXPECTED)
+    assert out["time_ids"].shape == (1, 5)
+
+
+# ---------- chunks ----------------------------------------------------------
+
+
+def test_chunks_sd15_pad_to_batch2_returns_one_chunk():
+    chunked = _sd15_inputs(batch=1).chunks(SD15_EXPECTED)
+    assert len(chunked) == 1
+    c = chunked[0]
+    assert c.x.shape == (2, 4, 64, 64)
+    assert c.t.shape == (2,)
+    # context shape: (b, seq, dim) padded along batch dim.
+    assert c.context.shape == (2, 77, 768)
+    assert c.control is None
+    assert c.ts_cond is None
+    assert c.time_ids is None
+    assert c.text_embeds is None
+
+
+def test_chunks_sd15_with_controlnet_chunks_residuals_too():
+    chunked = _sd15_inputs(batch=1, with_control=True).chunks(SD15_EXPECTED)
+    assert len(chunked) == 1
+    cn = chunked[0].control
+    assert cn is not None
+    assert cn["output"][0].shape == (2, 320, 64, 64)
+    assert cn["output"][1].shape == (2, 640, 32, 32)
+
+
+def test_chunks_lcm_carries_timestep_cond_per_chunk():
+    chunked = _sd15_inputs(batch=1, with_ts_cond=True).chunks(LCM_EXPECTED)
+    assert len(chunked) == 1
+    assert chunked[0].ts_cond is not None
+    assert chunked[0].ts_cond.shape == (2, 256)
+
+
+def test_chunks_sdxl_base_propagates_time_ids_and_text_embeds():
+    chunked = _sdxl_inputs(batch=1, refiner=False).chunks(SDXL_BASE_EXPECTED)
+    assert len(chunked) == 1
+    c = chunked[0]
+    assert c.time_ids is not None and c.time_ids.shape == (2, 6)
+    assert c.text_embeds is not None and c.text_embeds.shape == (2, 1280)
+
+
+def test_chunks_sdxl_refiner_uses_len5_time_ids():
+    chunked = _sdxl_inputs(batch=1, refiner=True).chunks(SDXL_REFINER_EXPECTED)
+    assert chunked[0].time_ids.shape == (2, 5)
+
+
+def test_chunks_sdxl_synthesizes_zero_time_ids_when_caller_omits():
+    """If the model expects time_ids but caller passed nothing, the suite
+    fabricates a zero-filled tensor. Lock that fallback."""
+    x = torch.randn(1, 4, 128, 128)
+    t = torch.full((1,), 999.0)
+    context = torch.randn(1, 77, 2048)
+    inputs = CoreMLInputs(x, t, context, control=None)
+    chunked = inputs.chunks(SDXL_BASE_EXPECTED)
+    assert chunked[0].time_ids.shape == (2, 6)
+    assert torch.equal(chunked[0].time_ids, torch.zeros(2, 6))
+    assert chunked[0].text_embeds.shape == (2, 1280)
+    assert torch.equal(chunked[0].text_embeds, torch.zeros(2, 1280))
+
+
+def test_chunks_splits_batch_into_multiple_target2_chunks():
+    """batch=5 with target_batch=2 -> 3 chunks (last padded)."""
+    chunked = _sd15_inputs(batch=5).chunks(SD15_EXPECTED)
+    assert len(chunked) == 3
+    for c in chunked:
+        assert c.x.shape == (2, 4, 64, 64)
+        assert c.context.shape == (2, 77, 768)
+    # Last chunk's second batch row is the zero-pad.
+    assert torch.equal(chunked[-1].x[1], torch.zeros(4, 64, 64))
+
+
+def test_chunks_timestep_is_broadcast_from_first_value():
+    """t is rebuilt from t[0] across all chunks: locks current behavior that
+    discards any per-row timestep variation."""
+    x = torch.randn(2, 4, 64, 64)
+    t = torch.tensor([42.0, 99.0])  # the second value will be lost
+    context = torch.randn(2, 77, 768)
+    inputs = CoreMLInputs(x, t, context, control=None)
+    chunked = inputs.chunks(SD15_EXPECTED)
+    assert chunked[0].t.shape == (2,)
+    assert torch.equal(chunked[0].t, torch.full((2,), 42.0))
diff --git a/tests/unit/test_characterization_latents.py b/tests/unit/test_characterization_latents.py
new file mode 100644
index 0000000..ff6f136
--- /dev/null
+++ b/tests/unit/test_characterization_latents.py
@@ -0,0 +1,118 @@
+"""Phase 2 characterization tests for coreml_suite.latents.
+
+Locks the *current* behavior of chunk_batch / merge_chunks — including the
+zero-pad regions and the truncation in merge — so the Phase 3 refactor
+cannot silently shift either contract.
+"""
+import pytest
+import torch
+
+from coreml_suite.latents import chunk_batch, merge_chunks
+
+
+@pytest.fixture(autouse=True)
+def _deterministic_seed():
+    torch.manual_seed(0)
+
+
+def _const_tensor(batch, *rest):
+    return torch.arange(batch * 4 * 8 * 8, dtype=torch.float32).reshape(batch, 4, 8, 8)
+
+
+# ---------- chunk_batch ------------------------------------------------------
+
+
+def test_chunk_batch_passthrough_when_shape_matches():
+    x = _const_tensor(2)
+    out = chunk_batch(x, (2, 4, 8, 8))
+    assert len(out) == 1
+    # passthrough: the same object identity is returned (no copy).
+    assert out[0] is x
+
+
+def test_chunk_batch_pads_single_chunk_when_input_smaller():
+    """batch=1, target=2 -> one padded chunk; the second row is exact zero."""
+    x = _const_tensor(1)
+    out = chunk_batch(x, (2, 4, 8, 8))
+    assert len(out) == 1
+    assert out[0].shape == (2, 4, 8, 8)
+    assert torch.equal(out[0][0], x[0])
+    assert torch.equal(out[0][1], torch.zeros(4, 8, 8))
+
+
+def test_chunk_batch_splits_exact_multiple():
+    """batch=4, target=2 -> two chunks, no padding."""
+    x = _const_tensor(4)
+    out = chunk_batch(x, (2, 4, 8, 8))
+    assert len(out) == 2
+    assert out[0].shape == (2, 4, 8, 8)
+    assert out[1].shape == (2, 4, 8, 8)
+    assert torch.equal(out[0], x[:2])
+    assert torch.equal(out[1], x[2:])
+
+
+def test_chunk_batch_pads_remainder_chunk():
+    """batch=5, target=2 -> chunks=[x[0:2], x[2:4]] then [x[4], 0]."""
+    x = _const_tensor(5)
+    out = chunk_batch(x, (2, 4, 8, 8))
+    assert len(out) == 3
+    assert torch.equal(out[0], x[0:2])
+    assert torch.equal(out[1], x[2:4])
+    last = out[-1]
+    assert last.shape == (2, 4, 8, 8)
+    assert torch.equal(last[0], x[4])
+    # The remainder row is zero-padded; lock that exact contract.
+    assert torch.equal(last[1], torch.zeros(4, 8, 8))
+    assert last[1].sum() == 0
+
+
+@pytest.mark.parametrize(
+    "batch_size,target,expected_chunks",
+    [
+        (1, 4, 1),
+        (3, 2, 2),
+        (5, 3, 2),
+        (9, 4, 3),
+    ],
+)
+def test_chunk_batch_pad_region_is_zero(batch_size, target, expected_chunks):
+    x = _const_tensor(batch_size)
+    out = chunk_batch(x, (target, 4, 8, 8))
+    assert len(out) == expected_chunks
+    mod = batch_size % target
+    if mod == 0 and batch_size >= target:
+        return
+    last = out[-1]
+    pad_rows = target - (mod if (mod != 0 and batch_size >= target) else batch_size)
+    pad_region = last[-pad_rows:]
+    assert torch.equal(pad_region, torch.zeros_like(pad_region))
+
+
+# ---------- merge_chunks -----------------------------------------------------
+
+
+def test_merge_chunks_exact_concat():
+    x = _const_tensor(4)
+    chunks = chunk_batch(x, (2, 4, 8, 8))
+    merged = merge_chunks(chunks, x.shape)
+    assert merged.shape == x.shape
+    assert torch.equal(merged, x)
+
+
+def test_merge_chunks_truncates_padding():
+    """Round-trip with a padded last chunk drops the pad rows."""
+    x = _const_tensor(5)
+    chunks = chunk_batch(x, (2, 4, 8, 8))
+    merged = merge_chunks(chunks, x.shape)
+    assert merged.shape == x.shape
+    assert torch.equal(merged, x)
+
+
+def test_merge_chunks_singleton_returns_equal_copy_when_shape_matches():
+    """A singleton chunk list still goes through torch.cat, so we get a new
+    tensor equal to the input — locked here because Phase 3 might be tempted
+    to short-circuit and accidentally return the same object."""
+    x = _const_tensor(2)
+    out = merge_chunks([x], x.shape)
+    assert torch.equal(out, x)
+    assert out is not x
diff --git a/tests/unit/test_characterization_out_name.py b/tests/unit/test_characterization_out_name.py
new file mode 100644
index 0000000..cb2f22d
--- /dev/null
+++ b/tests/unit/test_characterization_out_name.py
@@ -0,0 +1,175 @@
+"""Phase 2 characterization tests for CoreMLConverter.out_name composition.
+
+out_name is encoded into the .mlpackage filename and therefore drives the
+"have we converted this combo already?" cache check. Drift here silently
+invalidates user caches and breaks workflow node references.
+
+Tests intercept converter.get_out_path to capture the composed string,
+and stub out the heavy conversion + Core ML model load.
+"""
+import pytest
+
+import folder_paths
+from coreml_suite import converter
+from coreml_suite import nodes as nodes_mod
+from coreml_suite.nodes import CoreMLConverter
+
+
+@pytest.fixture
+def capture_out_name(monkeypatch):
+    captured = {}
+
+    def fake_get_out_path(submodule, name):
+        captured["submodule"] = submodule
+        captured["out_name"] = name
+        return f"/tmp/fake/{name}.mlpackage"
+
+    monkeypatch.setattr(converter, "get_out_path", fake_get_out_path)
+    monkeypatch.setattr(converter, "convert", lambda **kwargs: None)
+    monkeypatch.setattr(
+        converter,
+        "compile_model",
+        lambda out_path, out_name, submodule_name: f"/tmp/fake/{out_name}_{submodule_name}.mlmodelc",
+    )
+    monkeypatch.setattr(
+        folder_paths,
+        "get_full_path",
+        lambda kind, name: f"/tmp/ckpts/{name}" if kind == "checkpoints" else None,
+    )
+    monkeypatch.setattr(nodes_mod, "CoreMLModel", lambda *a, **kw: object())
+    return captured
+
+
+def _convert(
+    *,
+    ckpt_name="dreamshaper_8.safetensors",
+    model_version="SD15",
+    height=512,
+    width=512,
+    batch_size=1,
+    attention_implementation="SPLIT_EINSUM",
+    compute_unit="CPU_AND_NE",
+    controlnet_support=False,
+    lora_params=None,
+):
+    node = CoreMLConverter()
+    node.convert(
+        ckpt_name=ckpt_name,
+        model_version=model_version,
+        height=height,
+        width=width,
+        batch_size=batch_size,
+        attention_implementation=attention_implementation,
+        compute_unit=compute_unit,
+        controlnet_support=controlnet_support,
+        lora_params=lora_params,
+    )
+
+
+# ---------- basic golden strings --------------------------------------------
+
+
+@pytest.mark.parametrize(
+    "attn_name,suffix",
+    [
+        ("SPLIT_EINSUM", "se"),
+        ("SPLIT_EINSUM_V2", "se2"),
+        ("ORIGINAL", "orig"),
+    ],
+)
+def test_out_name_attention_suffix(capture_out_name, attn_name, suffix):
+    _convert(attention_implementation=attn_name)
+    assert capture_out_name["out_name"] == f"dreamshaper_8_1x512x512_{suffix}"
+
+
+def test_out_name_includes_batch_and_size(capture_out_name):
+    _convert(batch_size=4, width=768, height=1024)
+    assert capture_out_name["out_name"] == "dreamshaper_8_4x768x1024_se"
+
+
+def test_out_name_appends_cn_suffix_when_controlnet_support_true(capture_out_name):
+    _convert(controlnet_support=True)
+    assert capture_out_name["out_name"] == "dreamshaper_8_1x512x512_cn_se"
+
+
+def test_out_name_drops_dot_extension_only_at_first_period(capture_out_name):
+    """`ckpt_name.split('.')[0]` — first '.' wins; locked behaviour."""
+    _convert(ckpt_name="my.checkpoint.v2.safetensors")
+    assert capture_out_name["out_name"] == "my_1x512x512_se"
+
+
+def test_out_name_replaces_spaces_with_underscores(capture_out_name):
+    _convert(ckpt_name="dream shaper 8.safetensors")
+    assert capture_out_name["out_name"] == "dream_shaper_8_1x512x512_se"
+
+
+# ---------- LoRA suffixes ---------------------------------------------------
+
+
+def test_out_name_with_single_lora(capture_out_name, monkeypatch):
+    monkeypatch.setattr(
+        folder_paths,
+        "get_full_path",
+        lambda kind, name: f"/tmp/{kind}/{name}",
+    )
+    _convert(lora_params={"epi_noiseoffset.safetensors": (0.8,)})
+    assert (
+        capture_out_name["out_name"]
+        == "dreamshaper_8_epi_noiseoffset_1x512x512_se"
+    )
+
+
+def test_out_name_with_multiple_loras_sorted(capture_out_name, monkeypatch):
+    """LoRAs are sorted by name then joined with '_' — locks the order."""
+    monkeypatch.setattr(
+        folder_paths,
+        "get_full_path",
+        lambda kind, name: f"/tmp/{kind}/{name}",
+    )
+    _convert(
+        lora_params={
+            "zoom.safetensors": (1.0,),
+            "alpha.safetensors": (0.5,),
+            "moody.safetensors": (0.3,),
+        }
+    )
+    assert (
+        capture_out_name["out_name"]
+        == "dreamshaper_8_alpha_moody_zoom_1x512x512_se"
+    )
+
+
+def test_out_name_lora_plus_controlnet(capture_out_name, monkeypatch):
+    monkeypatch.setattr(
+        folder_paths,
+        "get_full_path",
+        lambda kind, name: f"/tmp/{kind}/{name}",
+    )
+    _convert(
+        lora_params={"a.safetensors": (1.0,)},
+        controlnet_support=True,
+    )
+    assert capture_out_name["out_name"] == "dreamshaper_8_a_1x512x512_cn_se"
+
+
+# ---------- sdxl combinations -----------------------------------------------
+
+
+def test_out_name_sdxl_1024(capture_out_name):
+    _convert(
+        ckpt_name="sd_xl_base_1.0.safetensors",
+        model_version="SDXL",
+        width=1024,
+        height=1024,
+        attention_implementation="ORIGINAL",
+        compute_unit="CPU_AND_GPU",
+    )
+    assert capture_out_name["out_name"] == "sd_xl_base_1_1x1024x1024_orig"
+
+
+# ---------- submodule path --------------------------------------------------
+
+
+def test_get_out_path_invoked_with_unet_submodule(capture_out_name):
+    _convert()
+    assert capture_out_name["submodule"] == "unet"
diff --git a/tests/unit/test_characterization_sdxl_options.py b/tests/unit/test_characterization_sdxl_options.py
new file mode 100644
index 0000000..7b5f9f0
--- /dev/null
+++ b/tests/unit/test_characterization_sdxl_options.py
@@ -0,0 +1,147 @@
+"""Phase 2 characterization tests for add_sdxl_model_options.
+
+Locks the SDXL time_ids / text_embeds assembly: base produces a (2, 6)
+time_ids vector (h, w, crop_h, crop_w, target_h, target_w), refiner
+produces (2, 5) (h, w, crop_h, crop_w, aesthetic_score). Both stack pos
+then neg along the batch dim, and text_embeds is cat(pos_pooled,
+neg_pooled).
+
+Uses a SimpleNamespace-shaped fake ModelPatcher because exercising the
+real comfy.model_patcher.ModelPatcher here is overkill — only three
+attribute paths are read by the SUT.
+"""
+import inspect
+from types import SimpleNamespace
+
+import pytest
+import torch
+
+from coreml_suite.models import add_sdxl_model_options
+
+
+@pytest.fixture(autouse=True)
+def _deterministic_seed():
+    torch.manual_seed(0)
+
+
+def _fake_patcher(is_base: bool, is_refiner: bool):
+    diffusion = SimpleNamespace(is_sdxl_base=is_base, is_sdxl_refiner=is_refiner)
+    model = SimpleNamespace(diffusion_model=diffusion)
+    patcher = SimpleNamespace(model=model, model_options={})
+    patcher.clone = lambda: patcher  # in-place: simplest mock that matches contract
+    return patcher
+
+
+def _cond(pooled, **overrides):
+    base = {"pooled_output": pooled}
+    base.update(overrides)
+    return [(None, base)]
+
+
+def _closure_vars(wrapper):
+    return inspect.getclosurevars(wrapper).nonlocals
+
+
+# ---------- base (len 6) -----------------------------------------------------
+
+
+def test_add_sdxl_model_options_base_produces_len6_time_ids_with_defaults():
+    pos_pooled = torch.randn(1, 1280)
+    neg_pooled = torch.randn(1, 1280)
+    patcher = _fake_patcher(is_base=True, is_refiner=False)
+    out = add_sdxl_model_options(patcher, _cond(pos_pooled), _cond(neg_pooled))
+    wrapper = out.model_options["model_function_wrapper"]
+    closure = _closure_vars(wrapper)
+    assert closure["time_ids"].shape == (2, 6)
+    # Defaults: 768 height/width, 0 crop, 768 target.
+    expected = torch.tensor([[768, 768, 0, 0, 768, 768], [768, 768, 0, 0, 768, 768]])
+    assert torch.equal(closure["time_ids"], expected)
+    assert closure["refiner"] is False
+
+
+def test_add_sdxl_model_options_base_respects_overrides():
+    pos_pooled = torch.randn(1, 1280)
+    neg_pooled = torch.randn(1, 1280)
+    patcher = _fake_patcher(is_base=True, is_refiner=False)
+    out = add_sdxl_model_options(
+        patcher,
+        _cond(pos_pooled, height=1024, width=512, crop_h=8, crop_w=4, target_height=1024, target_width=1024),
+        _cond(neg_pooled, height=256, width=256, crop_h=0, crop_w=0, target_height=256, target_width=256),
+    )
+    closure = _closure_vars(out.model_options["model_function_wrapper"])
+    expected = torch.tensor([[1024, 512, 8, 4, 1024, 1024], [256, 256, 0, 0, 256, 256]])
+    assert torch.equal(closure["time_ids"], expected)
+
+
+# ---------- refiner (len 5) -------------------------------------------------
+
+
+def test_add_sdxl_model_options_refiner_produces_len5_time_ids():
+    pos_pooled = torch.randn(1, 1280)
+    neg_pooled = torch.randn(1, 1280)
+    patcher = _fake_patcher(is_base=False, is_refiner=True)
+    out = add_sdxl_model_options(patcher, _cond(pos_pooled), _cond(neg_pooled))
+    closure = _closure_vars(out.model_options["model_function_wrapper"])
+    assert closure["time_ids"].shape == (2, 5)
+    # Defaults: pos aesthetic_score=6, neg aesthetic_score=2.5.
+    expected = torch.tensor(
+        [[768, 768, 0, 0, 6.0], [768, 768, 0, 0, 2.5]],
+    )
+    assert torch.equal(closure["time_ids"], expected)
+    assert closure["refiner"] is True
+
+
+def test_add_sdxl_model_options_refiner_respects_aesthetic_score_overrides():
+    pos_pooled = torch.randn(1, 1280)
+    neg_pooled = torch.randn(1, 1280)
+    patcher = _fake_patcher(is_base=False, is_refiner=True)
+    out = add_sdxl_model_options(
+        patcher,
+        _cond(pos_pooled, aesthetic_score=8.5),
+        _cond(neg_pooled, aesthetic_score=1.5),
+    )
+    closure = _closure_vars(out.model_options["model_function_wrapper"])
+    expected = torch.tensor([[768, 768, 0, 0, 8.5], [768, 768, 0, 0, 1.5]])
+    assert torch.equal(closure["time_ids"], expected)
+
+
+# ---------- text_embeds ----------------------------------------------------
+
+
+def test_text_embeds_is_concat_pos_then_neg_along_batch():
+    pos_pooled = torch.full((1, 1280), 1.0)
+    neg_pooled = torch.full((1, 1280), -1.0)
+    patcher = _fake_patcher(is_base=True, is_refiner=False)
+    out = add_sdxl_model_options(patcher, _cond(pos_pooled), _cond(neg_pooled))
+    closure = _closure_vars(out.model_options["model_function_wrapper"])
+    embeds = closure["text_embeds"]
+    assert embeds.shape == (2, 1280)
+    assert torch.equal(embeds[0], pos_pooled[0])
+    assert torch.equal(embeds[1], neg_pooled[0])
+
+
+def test_neither_base_nor_refiner_yields_len4_time_ids():
+    """Locked edge case: if both is_sdxl_base and is_sdxl_refiner are False,
+    no extra entries are appended -> time_ids is only the 4 shared fields."""
+    pos_pooled = torch.randn(1, 1280)
+    neg_pooled = torch.randn(1, 1280)
+    patcher = _fake_patcher(is_base=False, is_refiner=False)
+    out = add_sdxl_model_options(patcher, _cond(pos_pooled), _cond(neg_pooled))
+    closure = _closure_vars(out.model_options["model_function_wrapper"])
+    assert closure["time_ids"].shape == (2, 4)
+
+
+# ---------- patcher contract ------------------------------------------------
+
+
+def test_model_options_dict_is_merged_into_clone_not_original():
+    """Verify SUT writes to the clone's model_options. Our fake reuses the
+    same instance, so the merge should still leave the model_function_wrapper
+    key present after the call."""
+    pos_pooled = torch.randn(1, 1280)
+    neg_pooled = torch.randn(1, 1280)
+    patcher = _fake_patcher(is_base=True, is_refiner=False)
+    patcher.model_options["pre_existing"] = "kept"
+    out = add_sdxl_model_options(patcher, _cond(pos_pooled), _cond(neg_pooled))
+    assert "model_function_wrapper" in out.model_options
+    assert out.model_options["pre_existing"] == "kept"