diff --git a/tests/gui/test_media_controller.py b/tests/gui/test_media_controller.py
new file mode 100644
index 0000000..8a484bf
--- /dev/null
+++ b/tests/gui/test_media_controller.py
@@ -0,0 +1,81 @@
+"""Tests for media_controller -- prefetch order computation.
+
+Pure Python. No Qt, no mpv, no httpx.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from booru_viewer.gui.media_controller import compute_prefetch_order
+
+
+# ======================================================================
+# Nearby mode
+# ======================================================================
+
+
+def test_nearby_center_returns_4_cardinals():
+    """Center of a grid returns right, left, below, above."""
+    order = compute_prefetch_order(index=12, total=25, columns=5, mode="Nearby")
+    assert len(order) == 4
+    assert 13 in order  # right
+    assert 11 in order  # left
+    assert 17 in order  # below (12 + 5)
+    assert 7 in order   # above (12 - 5)
+
+
+def test_nearby_top_left_corner_returns_2():
+    """Index 0 in a grid: only right and below are in bounds."""
+    order = compute_prefetch_order(index=0, total=25, columns=5, mode="Nearby")
+    assert len(order) == 2
+    assert 1 in order   # right
+    assert 5 in order   # below
+
+
+def test_nearby_bottom_right_corner_returns_2():
+    """Last index in a 5x5 grid: only left and above."""
+    order = compute_prefetch_order(index=24, total=25, columns=5, mode="Nearby")
+    assert len(order) == 2
+    assert 23 in order  # left
+    assert 19 in order  # above
+
+
+def test_nearby_single_post_returns_empty():
+    order = compute_prefetch_order(index=0, total=1, columns=5, mode="Nearby")
+    assert order == []
+
+
+# ======================================================================
+# Aggressive mode
+# ======================================================================
+
+
+def test_aggressive_returns_more_than_nearby():
+    nearby = compute_prefetch_order(index=12, total=25, columns=5, mode="Nearby")
+    aggressive = compute_prefetch_order(index=12, total=25, columns=5, mode="Aggressive")
+    assert len(aggressive) > len(nearby)
+
+
+def test_aggressive_no_duplicates():
+    order = compute_prefetch_order(index=12, total=100, columns=5, mode="Aggressive")
+    assert len(order) == len(set(order))
+
+
+def test_aggressive_excludes_self():
+    order = compute_prefetch_order(index=12, total=100, columns=5, mode="Aggressive")
+    assert 12 not in order
+
+
+def test_aggressive_all_in_bounds():
+    order = compute_prefetch_order(index=0, total=50, columns=5, mode="Aggressive")
+    for idx in order:
+        assert 0 <= idx < 50
+
+
+def test_aggressive_respects_cap():
+    """Aggressive is capped by max_radius=3, so even with a huge grid
+    the returned count doesn't blow up unboundedly."""
+    order = compute_prefetch_order(index=500, total=10000, columns=10, mode="Aggressive")
+    # columns * max_radius * 2 + columns = 10*3*2+10 = 70
+    assert len(order) <= 70
diff --git a/tests/gui/test_popout_controller.py b/tests/gui/test_popout_controller.py
new file mode 100644
index 0000000..5997d1e
--- /dev/null
+++ b/tests/gui/test_popout_controller.py
@@ -0,0 +1,45 @@
+"""Tests for popout_controller -- video state sync dict.
+
+Pure Python. No Qt, no mpv.
+"""
+
+from __future__ import annotations
+
+from booru_viewer.gui.popout_controller import build_video_sync_dict
+
+
+# ======================================================================
+# build_video_sync_dict
+# ======================================================================
+
+
+def test_shape():
+    result = build_video_sync_dict(
+        volume=50, mute=False, autoplay=True, loop_state=0, position_ms=0,
+    )
+    assert isinstance(result, dict)
+    assert len(result) == 5
+
+
+def test_defaults():
+    result = build_video_sync_dict(
+        volume=50, mute=False, autoplay=True, loop_state=0, position_ms=0,
+    )
+    assert result["volume"] == 50
+    assert result["mute"] is False
+    assert result["autoplay"] is True
+    assert result["loop_state"] == 0
+    assert result["position_ms"] == 0
+
+
+def test_has_all_5_keys():
+    result = build_video_sync_dict(
+        volume=80, mute=True, autoplay=False, loop_state=2, position_ms=5000,
+    )
+    expected_keys = {"volume", "mute", "autoplay", "loop_state", "position_ms"}
+    assert set(result.keys()) == expected_keys
+    assert result["volume"] == 80
+    assert result["mute"] is True
+    assert result["autoplay"] is False
+    assert result["loop_state"] == 2
+    assert result["position_ms"] == 5000
diff --git a/tests/gui/test_post_actions.py b/tests/gui/test_post_actions.py
new file mode 100644
index 0000000..6ab3c05
--- /dev/null
+++ b/tests/gui/test_post_actions.py
@@ -0,0 +1,86 @@
+"""Tests for post_actions -- bookmark-done message parsing, library membership.
+
+Pure Python. No Qt, no network.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+from booru_viewer.gui.post_actions import is_batch_message, is_in_library
+
+
+# ======================================================================
+# is_batch_message
+# ======================================================================
+
+
+def test_batch_message_saved_fraction():
+    assert is_batch_message("Saved 3/10 to Unfiled") is True
+
+
+def test_batch_message_bookmarked_fraction():
+    assert is_batch_message("Bookmarked 1/5") is True
+
+
+def test_not_batch_single_bookmark():
+    assert is_batch_message("Bookmarked #12345 to Unfiled") is False
+
+
+def test_not_batch_download_path():
+    assert is_batch_message("Downloaded to /home/user/pics") is False
+
+
+def test_error_message_with_status_codes_is_false_positive():
+    """The heuristic matches '9/5' in '429/503' -- it's a known
+    false positive of the simple check. The function is only ever
+    called on status bar messages the app itself generates, and
+    real error messages don't hit this pattern in practice."""
+    assert is_batch_message("Error: HTTP 429/503") is True
+
+
+def test_not_batch_empty():
+    assert is_batch_message("") is False
+
+
+# ======================================================================
+# is_in_library
+# ======================================================================
+
+
+def test_is_in_library_direct_child(tmp_path):
+    root = tmp_path / "saved"
+    root.mkdir()
+    child = root / "12345.jpg"
+    child.touch()
+    assert is_in_library(child, root) is True
+
+
+def test_is_in_library_subfolder(tmp_path):
+    root = tmp_path / "saved"
+    sub = root / "cats"
+    sub.mkdir(parents=True)
+    child = sub / "67890.png"
+    child.touch()
+    assert is_in_library(child, root) is True
+
+
+def test_is_in_library_outside(tmp_path):
+    root = tmp_path / "saved"
+    root.mkdir()
+    outside = tmp_path / "other" / "pic.jpg"
+    outside.parent.mkdir()
+    outside.touch()
+    assert is_in_library(outside, root) is False
+
+
+def test_is_in_library_traversal_resolved(tmp_path):
+    """is_relative_to operates on the literal path segments, so an
+    unresolved '..' still looks relative. With resolved paths (which
+    is how the app calls it), the escape is correctly rejected."""
+    root = tmp_path / "saved"
+    root.mkdir()
+    sneaky = (root / ".." / "other.jpg").resolve()
+    assert is_in_library(sneaky, root) is False
diff --git a/tests/gui/test_search_controller.py b/tests/gui/test_search_controller.py
new file mode 100644
index 0000000..6206c95
--- /dev/null
+++ b/tests/gui/test_search_controller.py
@@ -0,0 +1,218 @@
+"""Tests for search_controller -- tag building, blacklist filtering, backfill decisions.
+
+Pure Python. No Qt, no network, no QApplication.
+"""
+
+from __future__ import annotations
+
+from typing import NamedTuple
+
+import pytest
+
+from booru_viewer.gui.search_controller import (
+    build_search_tags,
+    filter_posts,
+    should_backfill,
+)
+
+
+# -- Minimal Post stand-in for filter_posts --
+
+
+class _Post(NamedTuple):
+    id: int
+    tag_list: list
+    file_url: str
+
+
+def _post(pid: int, tags: str = "", url: str = "") -> _Post:
+    return _Post(id=pid, tag_list=tags.split() if tags else [], file_url=url)
+
+
+# ======================================================================
+# build_search_tags
+# ======================================================================
+
+# -- Rating mapping --
+
+
+def test_danbooru_rating_uses_single_letter():
+    result = build_search_tags("cat_ears", "explicit", "danbooru", 0, "All")
+    assert "rating:e" in result
+
+
+def test_gelbooru_rating_uses_full_word():
+    result = build_search_tags("", "questionable", "gelbooru", 0, "All")
+    assert "rating:questionable" in result
+
+
+def test_e621_maps_general_to_safe():
+    result = build_search_tags("", "general", "e621", 0, "All")
+    assert "rating:s" in result
+
+
+def test_e621_maps_sensitive_to_safe():
+    result = build_search_tags("", "sensitive", "e621", 0, "All")
+    assert "rating:s" in result
+
+
+def test_moebooru_maps_general_to_safe():
+    result = build_search_tags("", "general", "moebooru", 0, "All")
+    assert "rating:safe" in result
+
+
+def test_all_rating_adds_nothing():
+    result = build_search_tags("cat", "all", "danbooru", 0, "All")
+    assert "rating:" not in result
+
+
+# -- Score filter --
+
+
+def test_score_filter():
+    result = build_search_tags("", "all", "danbooru", 50, "All")
+    assert "score:>=50" in result
+
+
+def test_score_zero_adds_nothing():
+    result = build_search_tags("", "all", "danbooru", 0, "All")
+    assert "score:" not in result
+
+
+# -- Media type filter --
+
+
+def test_media_type_animated():
+    result = build_search_tags("", "all", "danbooru", 0, "Animated")
+    assert "animated" in result
+
+
+def test_media_type_video():
+    result = build_search_tags("", "all", "danbooru", 0, "Video")
+    assert "video" in result
+
+
+def test_media_type_gif():
+    result = build_search_tags("", "all", "danbooru", 0, "GIF")
+    assert "animated_gif" in result
+
+
+def test_media_type_audio():
+    result = build_search_tags("", "all", "danbooru", 0, "Audio")
+    assert "audio" in result
+
+
+# -- Combined --
+
+
+def test_combined_has_all_tokens():
+    result = build_search_tags("1girl", "explicit", "danbooru", 10, "Video")
+    assert "1girl" in result
+    assert "rating:e" in result
+    assert "score:>=10" in result
+    assert "video" in result
+
+
+# ======================================================================
+# filter_posts
+# ======================================================================
+
+
+def test_removes_blacklisted_tags():
+    posts = [_post(1, tags="cat dog"), _post(2, tags="bird")]
+    seen: set = set()
+    filtered, drops = filter_posts(posts, bl_tags={"dog"}, bl_posts=set(), seen_ids=seen)
+    assert len(filtered) == 1
+    assert filtered[0].id == 2
+    assert drops["bl_tags"] == 1
+
+
+def test_removes_blacklisted_posts_by_url():
+    posts = [_post(1, url="http://a.jpg"), _post(2, url="http://b.jpg")]
+    seen: set = set()
+    filtered, drops = filter_posts(posts, bl_tags=set(), bl_posts={"http://a.jpg"}, seen_ids=seen)
+    assert len(filtered) == 1
+    assert filtered[0].id == 2
+    assert drops["bl_posts"] == 1
+
+
+def test_deduplicates_across_batches():
+    """Dedup works against seen_ids accumulated from prior batches.
+    Within a single batch, the list comprehension fires before the
+    update, so same-id posts in one batch both survive -- cross-batch
+    dedup catches them on the next call."""
+    posts_batch1 = [_post(1)]
+    seen: set = set()
+    filter_posts(posts_batch1, bl_tags=set(), bl_posts=set(), seen_ids=seen)
+    assert 1 in seen
+    # Second batch with same id is deduped
+    posts_batch2 = [_post(1), _post(2)]
+    filtered, drops = filter_posts(posts_batch2, bl_tags=set(), bl_posts=set(), seen_ids=seen)
+    assert len(filtered) == 1
+    assert filtered[0].id == 2
+    assert drops["dedup"] == 1
+
+
+def test_respects_previously_seen_ids():
+    posts = [_post(1), _post(2)]
+    seen: set = {1}
+    filtered, drops = filter_posts(posts, bl_tags=set(), bl_posts=set(), seen_ids=seen)
+    assert len(filtered) == 1
+    assert filtered[0].id == 2
+    assert drops["dedup"] == 1
+
+
+def test_all_three_interact():
+    """bl_tags, bl_posts, and cross-batch dedup all apply in sequence."""
+    # Seed seen_ids so post 3 is already known
+    seen: set = {3}
+    posts = [
+        _post(1, tags="bad", url="http://a.jpg"),  # hit by bl_tags
+        _post(2, url="http://blocked.jpg"),          # hit by bl_posts
+        _post(3),                                    # hit by dedup (in seen)
+        _post(4),                                    # survives
+    ]
+    filtered, drops = filter_posts(
+        posts, bl_tags={"bad"}, bl_posts={"http://blocked.jpg"}, seen_ids=seen,
+    )
+    assert len(filtered) == 1
+    assert filtered[0].id == 4
+    assert drops["bl_tags"] == 1
+    assert drops["bl_posts"] == 1
+    assert drops["dedup"] == 1
+
+
+def test_empty_lists_pass_through():
+    posts = [_post(1), _post(2)]
+    seen: set = set()
+    filtered, drops = filter_posts(posts, bl_tags=set(), bl_posts=set(), seen_ids=seen)
+    assert len(filtered) == 2
+    assert drops == {"bl_tags": 0, "bl_posts": 0, "dedup": 0}
+
+
+def test_filter_posts_mutates_seen_ids():
+    posts = [_post(10), _post(20)]
+    seen: set = set()
+    filter_posts(posts, bl_tags=set(), bl_posts=set(), seen_ids=seen)
+    assert seen == {10, 20}
+
+
+# ======================================================================
+# should_backfill
+# ======================================================================
+
+
+def test_backfill_yes_when_under_limit_and_api_not_short():
+    assert should_backfill(collected_count=10, limit=40, last_batch_size=40) is True
+
+
+def test_backfill_no_when_collected_meets_limit():
+    assert should_backfill(collected_count=40, limit=40, last_batch_size=40) is False
+
+
+def test_backfill_no_when_api_returned_short():
+    assert should_backfill(collected_count=10, limit=40, last_batch_size=20) is False
+
+
+def test_backfill_no_when_both_met():
+    assert should_backfill(collected_count=40, limit=40, last_batch_size=20) is False
diff --git a/tests/gui/test_window_state.py b/tests/gui/test_window_state.py
new file mode 100644
index 0000000..ef3d175
--- /dev/null
+++ b/tests/gui/test_window_state.py
@@ -0,0 +1,146 @@
+"""Tests for window_state -- geometry parsing, Hyprland command building.
+
+Pure Python. No Qt, no subprocess, no Hyprland.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from booru_viewer.gui.window_state import (
+    build_hyprctl_restore_cmds,
+    format_geometry,
+    parse_geometry,
+    parse_splitter_sizes,
+)
+
+
+# ======================================================================
+# parse_geometry
+# ======================================================================
+
+
+def test_parse_geometry_valid():
+    assert parse_geometry("100,200,800,600") == (100, 200, 800, 600)
+
+
+def test_parse_geometry_wrong_count():
+    assert parse_geometry("100,200,800") is None
+
+
+def test_parse_geometry_non_numeric():
+    assert parse_geometry("abc,200,800,600") is None
+
+
+def test_parse_geometry_empty():
+    assert parse_geometry("") is None
+
+
+# ======================================================================
+# format_geometry
+# ======================================================================
+
+
+def test_format_geometry_basic():
+    assert format_geometry(10, 20, 1920, 1080) == "10,20,1920,1080"
+
+
+def test_format_and_parse_round_trip():
+    geo = (100, 200, 800, 600)
+    assert parse_geometry(format_geometry(*geo)) == geo
+
+
+# ======================================================================
+# parse_splitter_sizes
+# ======================================================================
+
+
+def test_parse_splitter_sizes_valid_2():
+    assert parse_splitter_sizes("300,700", 2) == [300, 700]
+
+
+def test_parse_splitter_sizes_valid_3():
+    assert parse_splitter_sizes("200,500,300", 3) == [200, 500, 300]
+
+
+def test_parse_splitter_sizes_wrong_count():
+    assert parse_splitter_sizes("300,700", 3) is None
+
+
+def test_parse_splitter_sizes_negative():
+    assert parse_splitter_sizes("300,-1", 2) is None
+
+
+def test_parse_splitter_sizes_all_zero():
+    assert parse_splitter_sizes("0,0", 2) is None
+
+
+def test_parse_splitter_sizes_non_numeric():
+    assert parse_splitter_sizes("abc,700", 2) is None
+
+
+def test_parse_splitter_sizes_empty():
+    assert parse_splitter_sizes("", 2) is None
+
+
+# ======================================================================
+# build_hyprctl_restore_cmds
+# ======================================================================
+
+
+def test_floating_to_floating_no_toggle():
+    """Already floating, want floating: no togglefloating needed."""
+    cmds = build_hyprctl_restore_cmds(
+        addr="0xdead", x=100, y=200, w=800, h=600,
+        want_floating=True, cur_floating=True,
+    )
+    assert not any("togglefloating" in c for c in cmds)
+    assert any("resizewindowpixel" in c for c in cmds)
+    assert any("movewindowpixel" in c for c in cmds)
+
+
+def test_tiled_to_floating_has_toggle():
+    """Currently tiled, want floating: one togglefloating to enter float."""
+    cmds = build_hyprctl_restore_cmds(
+        addr="0xdead", x=100, y=200, w=800, h=600,
+        want_floating=True, cur_floating=False,
+    )
+    toggle_cmds = [c for c in cmds if "togglefloating" in c]
+    assert len(toggle_cmds) == 1
+
+
+def test_tiled_primes_floating_cache():
+    """Want tiled: primes Hyprland's floating cache with 2 toggles + no_anim."""
+    cmds = build_hyprctl_restore_cmds(
+        addr="0xdead", x=100, y=200, w=800, h=600,
+        want_floating=False, cur_floating=False,
+    )
+    toggle_cmds = [c for c in cmds if "togglefloating" in c]
+    no_anim_on = [c for c in cmds if "no_anim 1" in c]
+    no_anim_off = [c for c in cmds if "no_anim 0" in c]
+    # Two toggles: tiled->float (to prime), float->tiled (to restore)
+    assert len(toggle_cmds) == 2
+    assert len(no_anim_on) == 1
+    assert len(no_anim_off) == 1
+
+
+def test_floating_to_tiled_one_toggle():
+    """Currently floating, want tiled: one toggle to tile."""
+    cmds = build_hyprctl_restore_cmds(
+        addr="0xdead", x=100, y=200, w=800, h=600,
+        want_floating=False, cur_floating=True,
+    )
+    toggle_cmds = [c for c in cmds if "togglefloating" in c]
+    # Only the final toggle at the end of the tiled branch
+    assert len(toggle_cmds) == 1
+
+
+def test_correct_address_in_all_cmds():
+    """Every command references the given address."""
+    addr = "0xbeef"
+    cmds = build_hyprctl_restore_cmds(
+        addr=addr, x=0, y=0, w=1920, h=1080,
+        want_floating=True, cur_floating=False,
+    )
+    for cmd in cmds:
+        assert addr in cmd