diff --git a/tests/test_integration.py b/tests/test_integration.py
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+"""Integration tests — multi-module pipelines without a real browser.
+
+These tests verify that the fingerprint sampler, Profile dataclass, prefs
+translation and proxy translation compose correctly. They do NOT launch
+Firefox. Browser-lifecycle tests live in ``test_e2e.py``.
+
+Scope (per implementation directive): Windows and platform-agnostic only.
+Linux-specific paths (e.g. Xvfb workarounds, GPU spoof on Linux) are
+intentionally covered by their unit tests, not duplicated here.
+"""
+from __future__ import annotations
+
+import random
+import sys
+
+import pytest
+
+from invisible_playwright._fpforge import generate_profile
+from invisible_playwright._proxy import configure_proxy
+from invisible_playwright.prefs import (
+    _WIN_LIGHT_COLORS,
+    translate_profile_to_prefs,
+)
+
+
+# Keys every Profile-derived prefs dict MUST carry. Sourced from
+# ``translate_profile_to_prefs`` direct writes (not from _BASELINE) plus
+# a couple of baseline keys that callers commonly read.
+_REQUIRED_PREFS_KEYS = (
+    "zoom.stealth.screen.width",
+    "zoom.stealth.screen.height",
+    "zoom.stealth.screen.avail_width",
+    "zoom.stealth.screen.avail_height",
+    "zoom.stealth.screen.dpr",
+    "layout.css.devPixelsPerPx",
+    "zoom.stealth.hw_concurrency",
+    "zoom.stealth.storage.quota_mb",
+    "zoom.stealth.audio.sample_rate",
+    "zoom.stealth.audio.output_latency_ms",
+    "zoom.stealth.audio.max_channel_count",
+    "media.av1.enabled",
+    "media.encoder.webm.enabled",
+    "media.mediasource.webm.enabled",
+    "media.mediasource.mp4.enabled",
+    "zoom.stealth.font.whitelist",
+    "zoom.stealth.font.metrics",
+    "ui.systemUsesDarkTheme",
+    "intl.accept_languages",
+    "general.useragent.locale",
+    "intl.locale.requested",
+    "zoom.stealth.seed",
+    "zoom.stealth.fpp.hw_seed",
+    "zoom.stealth.webrtc.host_ip",
+    "zoom.stealth.webgl.renderer",
+    "zoom.stealth.webgl.vendor",
+    "zoom.stealth.webgl.msaa",
+    "zoom.stealth.canvas.noise_skip_mask",
+    # baseline sanity
+    "privacy.resistFingerprinting",
+    "media.peerconnection.enabled",
+    "general.useragent.override",
+)
+
+
+# ──────────────────────────────────────────────────────────────────────
+#  IT1: profile → prefs pipeline yields a complete prefs dict
+# ──────────────────────────────────────────────────────────────────────
+
+
+@pytest.mark.integration
+def test_generate_profile_then_translate_has_all_required_keys():
+    """IT1 — generate_profile → translate_profile_to_prefs succeeds and the
+    returned dict contains every key downstream code (Playwright, the C++
+    patches) needs to find."""
+    profile = generate_profile(seed=42)
+    prefs = translate_profile_to_prefs(profile)
+
+    missing = [k for k in _REQUIRED_PREFS_KEYS if k not in prefs]
+    assert not missing, f"prefs dict missing required keys: {missing}"
+
+
+# ──────────────────────────────────────────────────────────────────────
+#  IT2: SOCKS proxy + prefs — mutates prefs in place, returns None
+# ──────────────────────────────────────────────────────────────────────
+
+
+@pytest.mark.integration
+def test_socks5_proxy_mutates_prefs_then_pipeline_still_valid():
+    """IT2 — configure_proxy writes SOCKS auth keys to the profile-derived
+    prefs dict; the result is still a valid prefs dict (all required keys
+    intact) and the proxy return is ``None`` so Playwright sees no proxy."""
+    profile = generate_profile(seed=42)
+    prefs = translate_profile_to_prefs(profile)
+
+    pw_proxy = configure_proxy(
+        {
+            "server": "socks5://proxy.example.com:1080",
+            "username": "alice",
+            "password": "s3cret",
+        },
+        prefs,
+    )
+
+    assert pw_proxy is None  # Firefox handles SOCKS internally.
+    assert prefs["network.proxy.type"] == 1
+    assert prefs["network.proxy.socks"] == "proxy.example.com"
+    assert prefs["network.proxy.socks_port"] == 1080
+    assert prefs["network.proxy.socks_version"] == 5
+    assert prefs["network.proxy.socks_username"] == "alice"
+    assert prefs["network.proxy.socks_password"] == "s3cret"
+    assert prefs["network.proxy.socks_remote_dns"] is True
+
+    # Profile-derived keys must still be present after proxy mutation.
+    for k in _REQUIRED_PREFS_KEYS:
+        assert k in prefs, f"proxy mutation dropped required key {k!r}"
+
+
+# ──────────────────────────────────────────────────────────────────────
+#  IT3: pin overrides propagate end-to-end into the prefs dict
+# ──────────────────────────────────────────────────────────────────────
+
+
+@pytest.mark.integration
+def test_pin_screen_width_propagates_through_pipeline():
+    """IT3 — a pinned ``screen.width`` shows up in the final prefs dict
+    under ``zoom.stealth.screen.width``."""
+    profile = generate_profile(seed=42, pin={"screen.width": 2560})
+    prefs = translate_profile_to_prefs(profile)
+
+    assert profile.screen.width == 2560
+    assert prefs["zoom.stealth.screen.width"] == 2560
+
+
+@pytest.mark.integration
+def test_multiple_pins_all_visible_in_prefs():
+    """IT3.b — pinning several unrelated fields at once still routes every
+    one through to the prefs dict."""
+    pin = {
+        "screen.width": 3840,
+        "screen.height": 2160,
+        "hardware.concurrency": 16,
+        "audio.sample_rate": 48000,
+    }
+    profile = generate_profile(seed=42, pin=pin)
+    prefs = translate_profile_to_prefs(profile)
+
+    assert prefs["zoom.stealth.screen.width"] == 3840
+    assert prefs["zoom.stealth.screen.height"] == 2160
+    assert prefs["zoom.stealth.hw_concurrency"] == 16
+    assert prefs["zoom.stealth.audio.sample_rate"] == 48000
+
+
+# ──────────────────────────────────────────────────────────────────────
+#  IT4 / IT5: end-to-end determinism + variation
+# ──────────────────────────────────────────────────────────────────────
+
+
+@pytest.mark.integration
+def test_pipeline_deterministic_for_same_seed():
+    """IT4 — running the full pipeline twice with the same seed produces
+    identical prefs dicts."""
+    a = translate_profile_to_prefs(generate_profile(seed=1234))
+    b = translate_profile_to_prefs(generate_profile(seed=1234))
+    assert a == b
+
+
+@pytest.mark.integration
+def test_pipeline_varies_across_seeds():
+    """IT5 — different seeds produce different prefs dicts. Compare the
+    full dict, not just a sampled field, to catch regressions where a
+    single hot field accidentally becomes seed-invariant."""
+    a = translate_profile_to_prefs(generate_profile(seed=1))
+    b = translate_profile_to_prefs(generate_profile(seed=2))
+    assert a != b
+
+
+# ──────────────────────────────────────────────────────────────────────
+#  IT6: HTTP proxy passthrough does NOT mutate SOCKS prefs
+# ──────────────────────────────────────────────────────────────────────
+
+
+@pytest.mark.integration
+def test_http_proxy_returned_unchanged_no_socks_mutations():
+    """IT6 — an HTTP proxy is returned to Playwright unchanged and the
+    SOCKS prefs are never written. Verifies the two proxy paths don't
+    cross-pollute the prefs dict."""
+    profile = generate_profile(seed=42)
+    prefs = translate_profile_to_prefs(profile)
+    proxy_in = {"server": "http://proxy.example.com:8080", "username": "bob"}
+
+    pw_proxy = configure_proxy(proxy_in, prefs)
+
+    assert pw_proxy is proxy_in  # returned unchanged (same object)
+    # No SOCKS prefs should have been written.
+    assert "network.proxy.type" not in prefs
+    assert "network.proxy.socks" not in prefs
+    assert "network.proxy.socks_port" not in prefs
+
+
+# ──────────────────────────────────────────────────────────────────────
+#  IT7: profile.fonts reaches prefs as a comma-joined whitelist
+# ──────────────────────────────────────────────────────────────────────
+
+
+@pytest.mark.integration
+def test_profile_fonts_propagate_to_prefs_whitelist():
+    """IT7 — every font in ``profile.fonts`` appears in the comma-joined
+    ``zoom.stealth.font.whitelist`` pref, in order."""
+    profile = generate_profile(seed=42)
+    prefs = translate_profile_to_prefs(profile)
+
+    assert profile.fonts, "fixture seed=42 produced empty fonts list"
+    whitelist = prefs["zoom.stealth.font.whitelist"]
+    assert isinstance(whitelist, str)
+    assert whitelist == ",".join(profile.fonts)
+    for font in profile.fonts:
+        assert font in whitelist
+
+
+# ──────────────────────────────────────────────────────────────────────
+#  IT8: dark_theme controls the Win10 light-palette overlay
+# ──────────────────────────────────────────────────────────────────────
+
+
+@pytest.mark.integration
+def test_dark_theme_pipeline_omits_light_palette():
+    """IT8.a — dark_theme=True profile → no light-palette colors in prefs."""
+    profile = generate_profile(seed=42, pin={"dark_theme": True})
+    prefs = translate_profile_to_prefs(profile)
+
+    assert prefs["ui.systemUsesDarkTheme"] == 1
+    for key in _WIN_LIGHT_COLORS:
+        assert key not in prefs, f"dark theme leaked light color: {key}"
+
+
+@pytest.mark.integration
+def test_light_theme_pipeline_includes_light_palette():
+    """IT8.b — dark_theme=False profile → full Win10 light palette is
+    overlaid onto the prefs dict."""
+    profile = generate_profile(seed=42, pin={"dark_theme": False})
+    prefs = translate_profile_to_prefs(profile)
+
+    assert prefs["ui.systemUsesDarkTheme"] == 0
+    for key, value in _WIN_LIGHT_COLORS.items():
+        assert prefs[key] == value
+
+
+# ──────────────────────────────────────────────────────────────────────
+#  IT9: many seeds all produce valid prefs dicts
+# ──────────────────────────────────────────────────────────────────────
+
+
+@pytest.mark.integration
+def test_many_seeds_all_produce_valid_prefs():
+    """IT9 — sweep 10 distinct seeds through the full pipeline. Every run
+    must succeed and yield a prefs dict containing every required key.
+    Catches regressions where a rare CPT branch produces a prefs key
+    missing/wrong-typed."""
+    rng = random.Random(2026)
+    seeds = [rng.randint(1, 2**31 - 1) for _ in range(10)]
+
+    for seed in seeds:
+        profile = generate_profile(seed=seed)
+        prefs = translate_profile_to_prefs(profile)
+        missing = [k for k in _REQUIRED_PREFS_KEYS if k not in prefs]
+        assert not missing, f"seed={seed} missing keys: {missing}"
+
+
+# ──────────────────────────────────────────────────────────────────────
+#  IT10 (extra): Windows-specific pipeline — virtual display + SOCKS
+#
+#  Combines two Windows-specific branches that real callers stack:
+#  headless mode (virtual_display=True) and a SOCKS5 proxy. Catches
+#  ordering bugs where one branch silently overwrites the other.
+# ──────────────────────────────────────────────────────────────────────
+
+
+@pytest.mark.integration
+def test_windows_virtual_display_with_socks_proxy(monkeypatch):
+    """IT10 — Windows + virtual_display=True + SOCKS5 proxy: both branches
+    land their keys in the prefs dict and don't clobber each other."""
+    monkeypatch.setattr(sys, "platform", "win32")
+    profile = generate_profile(seed=42)
+    prefs = translate_profile_to_prefs(profile, virtual_display=True)
+    pw_proxy = configure_proxy(
+        {"server": "socks5://127.0.0.1:1080"}, prefs
+    )
+
+    assert pw_proxy is None
+    assert prefs["security.sandbox.gpu.level"] == 0  # virtual_display branch
+    assert prefs["network.proxy.type"] == 1          # SOCKS branch
+    assert prefs["network.proxy.socks"] == "127.0.0.1"
+    # Windows still has the renderer cleared.
+    assert prefs["zoom.stealth.webgl.renderer"] == ""