test: add comprehensive unit tests for core components

- tests/test_canvas.py: 33 tests for Canvas (2D rendering surface)
- tests/test_firehose.py: 5 tests for FirehoseEffect
- tests/test_pipeline_order.py: 3 tests for execution order verification
- tests/test_renderer.py: 22 tests for ANSI parsing and PIL rendering

These tests provide solid coverage for foundational modules.

tests/test_firehose.py

@@ -0,0 +1,125 @@
+"""Tests for FirehoseEffect plugin."""
+
+import pytest
+
+from engine.effects.plugins.firehose import FirehoseEffect
+from engine.effects.types import EffectContext
+
+
+@pytest.fixture(autouse=True)
+def patch_config(monkeypatch):
+    """Patch config globals for firehose tests."""
+    import engine.config as config
+
+    monkeypatch.setattr(config, "FIREHOSE", False)
+    monkeypatch.setattr(config, "FIREHOSE_H", 12)
+    monkeypatch.setattr(config, "MODE", "news")
+    monkeypatch.setattr(config, "GLITCH", "░▒▓█▌▐╌╍╎╏┃┆┇┊┋")
+    monkeypatch.setattr(config, "KATA", "ﾊﾐﾋｰｳｼﾅﾓﾆｻﾜﾂｵﾘｱﾎﾃﾏｹﾒｴｶｷﾑﾕﾗｾﾈｽﾀﾇﾍ")
+
+
+def test_firehose_disabled_returns_input():
+    """Firehose disabled returns input buffer unchanged."""
+    effect = FirehoseEffect()
+    effect.configure(effect.config)
+    buf = ["line1", "line2"]
+    ctx = EffectContext(
+        terminal_width=80,
+        terminal_height=24,
+        scroll_cam=0,
+        ticker_height=0,
+        items=[("Title", "Source", "2025-01-01T00:00:00")],
+    )
+    import engine.config as config
+
+    config.FIREHOSE = False
+    result = effect.process(buf, ctx)
+    assert result == buf
+
+
+def test_firehose_enabled_adds_lines():
+    """Firehose enabled adds FIREHOSE_H lines to output."""
+    effect = FirehoseEffect()
+    effect.configure(effect.config)
+    buf = ["line1"]
+    ctx = EffectContext(
+        terminal_width=80,
+        terminal_height=24,
+        scroll_cam=0,
+        ticker_height=0,
+        items=[("Title", "Source", "2025-01-01T00:00:00")] * 10,
+    )
+    import engine.config as config
+
+    config.FIREHOSE = True
+    config.FIREHOSE_H = 3
+    result = effect.process(buf, ctx)
+    assert len(result) == 4
+    assert any("\033[" in line for line in result[1:])
+
+
+def test_firehose_respects_terminal_width():
+    """Firehose lines are truncated to terminal width."""
+    effect = FirehoseEffect()
+    effect.configure(effect.config)
+    ctx = EffectContext(
+        terminal_width=40,
+        terminal_height=24,
+        scroll_cam=0,
+        ticker_height=0,
+        items=[("A" * 100, "Source", "2025-01-01T00:00:00")],
+    )
+    import engine.config as config
+
+    config.FIREHOSE = True
+    config.FIREHOSE_H = 2
+    result = effect.process([], ctx)
+    firehose_lines = [line for line in result if "\033[" in line]
+    for line in firehose_lines:
+        # Strip all ANSI escape sequences (CSI sequences ending with letter)
+        import re
+
+        plain = re.sub(r"\x1b\[[^a-zA-Z]*[a-zA-Z]", "", line)
+        # Extract content after position code
+        content = plain.split("H", 1)[1] if "H" in plain else plain
+        assert len(content) <= 40
+
+
+def test_firehose_zero_height_noop():
+    """Firehose with zero height returns buffer unchanged."""
+    effect = FirehoseEffect()
+    effect.configure(effect.config)
+    buf = ["line1"]
+    ctx = EffectContext(
+        terminal_width=80,
+        terminal_height=24,
+        scroll_cam=0,
+        ticker_height=0,
+        items=[("Title", "Source", "2025-01-01T00:00:00")],
+    )
+    import engine.config as config
+
+    config.FIREHOSE = True
+    config.FIREHOSE_H = 0
+    result = effect.process(buf, ctx)
+    assert result == buf
+
+
+def test_firehose_with_no_items():
+    """Firehose with no content items returns buffer unchanged."""
+    effect = FirehoseEffect()
+    effect.configure(effect.config)
+    buf = ["line1"]
+    ctx = EffectContext(
+        terminal_width=80,
+        terminal_height=24,
+        scroll_cam=0,
+        ticker_height=0,
+        items=[],
+    )
+    import engine.config as config
+
+    config.FIREHOSE = True
+    config.FIREHOSE_H = 3
+    result = effect.process(buf, ctx)
+    assert result == buf