diff --git a/engine/common/filefunctions.cpp b/engine/common/filefunctions.cpp
index 1c25b79c9..7a12621e9 100644
--- a/engine/common/filefunctions.cpp
+++ b/engine/common/filefunctions.cpp
@@ -55,6 +55,15 @@ QString FileFunctions::get_unique_file_identifier(const QString &filename)
 
 QString FileFunctions::get_configuration_location()
 {
+	// Tests and tooling can redirect the configuration (and, since most
+	// locations derive from it, the cache/data) root. XDG_* vars only work
+	// on Linux; QStandardPaths ignores them on macOS and Windows.
+	const QByteArray override_dir = qgetenv("OAK_CONFIG_DIR");
+	if (!override_dir.isEmpty()) {
+		QDir(override_dir).mkpath(".");
+		return QString::fromUtf8(override_dir);
+	}
+
 	if (is_portable()) {
 		return get_application_path();
 	} else {
diff --git a/engine/node/output/track/track.cpp b/engine/node/output/track/track.cpp
index f4c239c28..ca08e0a29 100644
--- a/engine/node/output/track/track.cpp
+++ b/engine/node/output/track/track.cpp
@@ -511,7 +511,9 @@ void Track::replace_block(Block *old, Block *replace)
 	int cache_index = blocks_.indexOf(old);
 	int index_of_old_block = get_array_index_from_cache_index(cache_index);
 
+	ignore_block_disconnect_++;
 	disconnect_edge(old, NodeInput(this, k_block_input, index_of_old_block));
+	ignore_block_disconnect_--;
 	connect_edge(replace, NodeInput(this, k_block_input, index_of_old_block));
 	blocks_.replace(cache_index, replace);
 	disconnect(old, &Block::length_changed, this, &Track::block_length_changed);
@@ -584,6 +586,37 @@ void Track::InputConnectedEvent(const QString &input, int element, Node *node)
 	}
 }
 
+void Track::InputDisconnectedEvent(const QString &input, int element,
+								   Node *output)
+{
+	Node::InputDisconnectedEvent(input, element, output);
+
+	// Keep the block cache consistent when a block edge is removed outside
+	// the Track's own mutating operations (e.g. the block is being deleted,
+	// or an undo command is detaching the whole track from the graph).
+	// Without this, blocks_ keeps a dangling pointer and later readers such
+	// as track_length() walk into freed memory.
+	//
+	// Only the volatile cache is trimmed here; the persistent array map is
+	// deliberately left alone so that undo can re-attach the blocks from it
+	// (InputConnectedEvent rebuilds the cache while arraymap_invalid_ is
+	// set).
+	if (input == k_block_input && ignore_block_disconnect_ == 0) {
+		const int index = blocks_.indexOf(static_cast<Block *>(output));
+		if (index != -1) {
+			blocks_.removeAt(index);
+			block_array_indexes_.removeAt(index);
+			arraymap_invalid_ = true;
+
+			Block *previous = (index > 0) ? blocks_.at(index - 1) : nullptr;
+			Block *next = (index < blocks_.size()) ? blocks_.at(index) : nullptr;
+			Block::set_previous_next(previous, next);
+
+			update_in_out_from(index);
+		}
+	}
+}
+
 void Track::update_in_out_from(int index)
 {
 	// Find block just before this one to find the last out point
diff --git a/engine/node/output/track/track.h b/engine/node/output/track/track.h
index 7a6e9fd71..d0f2fd514 100644
--- a/engine/node/output/track/track.h
+++ b/engine/node/output/track/track.h
@@ -460,6 +460,8 @@ signals:
 protected:
 	virtual void InputConnectedEvent(const QString &input, int element,
 									 Node *node) override;
+	virtual void InputDisconnectedEvent(const QString &input, int element,
+										Node *output) override;
 	virtual void InputValueChangedEvent(const QString &input,
 										int element) override;
 
@@ -501,6 +503,13 @@ private:
 	bool arraymap_invalid_;
 	bool ignore_arraymap_set_;
 
+	/**
+   * @brief Nestable guard suppressing the block-cache maintenance in
+   * InputDisconnectedEvent while the Track itself is rewiring block edges
+   * (e.g. replace_block), where the cache update is handled explicitly.
+   */
+	int ignore_block_disconnect_ = 0;
+
 private slots:
 	void block_length_changed();
 
diff --git a/engine/render/renderworkerpool.cpp b/engine/render/renderworkerpool.cpp
index 3bffd2c2d..68c6bd033 100644
--- a/engine/render/renderworkerpool.cpp
+++ b/engine/render/renderworkerpool.cpp
@@ -1141,6 +1141,17 @@ std::unique_ptr<RenderWorkerPool::PooledWorker> RenderWorkerPool::acquire_worker
 	process->setProgram(worker_program_path());
 	process->setArguments({ QStringLiteral("--backend"), gpu_backend_ });
 
+	// The engine defaults QT_QPA_PLATFORM to "offscreen" for headless hosts
+	// (cli/tests), but the worker needs a real platform GL context. Don't let
+	// it inherit the offscreen default from this process.
+	{
+		QProcessEnvironment env = QProcessEnvironment::systemEnvironment();
+		if (qEnvironmentVariable("QT_QPA_PLATFORM") == "offscreen") {
+			env.remove(QStringLiteral("QT_QPA_PLATFORM"));
+			process->setProcessEnvironment(env);
+		}
+	}
+
 	const QString worker_stderr_path =
 		QDir(QDir::tempPath())
 			.filePath(QStringLiteral("oak-render-worker-%1-%2.stderr.log")
diff --git a/engine/tests/oakengine_color_test.cpp b/engine/tests/oakengine_color_test.cpp
index 1e6b065f1..a0c802bb5 100644
--- a/engine/tests/oakengine_color_test.cpp
+++ b/engine/tests/oakengine_color_test.cpp
@@ -396,6 +396,7 @@ TEST(OakEngineColor, Main)
 	EXPECT_TRUE(setenv("XDG_CONFIG_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_CACHE_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_DATA_HOME", g_tmpdir, 1) == 0);
+	EXPECT_TRUE(setenv("OAK_CONFIG_DIR", g_tmpdir, 1) == 0);
 #endif
 
 	EXPECT_TRUE(oakengine_init(OAKENGINE_INIT_HEADLESS) == OAKENGINE_OK);
diff --git a/engine/tests/oakengine_events_test.cpp b/engine/tests/oakengine_events_test.cpp
index 1a3f89092..f9f3e484b 100644
--- a/engine/tests/oakengine_events_test.cpp
+++ b/engine/tests/oakengine_events_test.cpp
@@ -922,6 +922,7 @@ TEST(OakEngineEvents, Main)
 	EXPECT_TRUE(setenv("XDG_CONFIG_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_CACHE_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_DATA_HOME", g_tmpdir, 1) == 0);
+	EXPECT_TRUE(setenv("OAK_CONFIG_DIR", g_tmpdir, 1) == 0);
 #endif
 
 	EXPECT_TRUE(oakengine_init(OAKENGINE_INIT_HEADLESS) == OAKENGINE_OK);
diff --git a/engine/tests/oakengine_export_test.cpp b/engine/tests/oakengine_export_test.cpp
index 17ed5187c..1200c982f 100644
--- a/engine/tests/oakengine_export_test.cpp
+++ b/engine/tests/oakengine_export_test.cpp
@@ -216,6 +216,7 @@ TEST(OakEngineExport, Main)
 	EXPECT_TRUE(setenv("XDG_CONFIG_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_CACHE_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_DATA_HOME", g_tmpdir, 1) == 0);
+	EXPECT_TRUE(setenv("OAK_CONFIG_DIR", g_tmpdir, 1) == 0);
 #endif
 
 	EXPECT_TRUE(oakengine_init(OAKENGINE_INIT_HEADLESS) == OAKENGINE_OK);
diff --git a/engine/tests/oakengine_footage_test.cpp b/engine/tests/oakengine_footage_test.cpp
index 5c90728e2..c16c10883 100644
--- a/engine/tests/oakengine_footage_test.cpp
+++ b/engine/tests/oakengine_footage_test.cpp
@@ -888,6 +888,7 @@ TEST(OakEngineFootage, Main)
 	EXPECT_TRUE(setenv("XDG_CONFIG_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_CACHE_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_DATA_HOME", g_tmpdir, 1) == 0);
+	EXPECT_TRUE(setenv("OAK_CONFIG_DIR", g_tmpdir, 1) == 0);
 #endif
 
 	EXPECT_TRUE(oakengine_init(OAKENGINE_INIT_HEADLESS) == OAKENGINE_OK);
diff --git a/engine/tests/oakengine_init_test.cpp b/engine/tests/oakengine_init_test.cpp
index 10fe1abe5..853da1cc2 100644
--- a/engine/tests/oakengine_init_test.cpp
+++ b/engine/tests/oakengine_init_test.cpp
@@ -312,6 +312,14 @@ static void test_footage_fixture(void)
 	EXPECT_TRUE(n > 0 && (size_t)n < sizeof(fixture));
 	EXPECT_TRUE(file_exists(fixture));
 
+	// The fixture stores footage as the relative path "demo.mp4". Run the
+	// load from the fixture directory so the engine does not treat the
+	// project as "moved" and rewrite the stored filename to an absolute
+	// path (see EngineCore footage relocation on load).
+	char fixture_dir[4096];
+	snprintf(fixture_dir, sizeof(fixture_dir), "%s/tests", OAK_TEST_SOURCE_DIR);
+	EXPECT_TRUE(chdir(fixture_dir) == 0);
+
 	OakEngineProject *p = oakengine_project_create();
 	EXPECT_TRUE(p != NULL);
 	char err[512];
@@ -417,6 +425,7 @@ TEST(OakEngineInit, Main)
 	EXPECT_TRUE(setenv("XDG_CONFIG_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_CACHE_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_DATA_HOME", g_tmpdir, 1) == 0);
+	EXPECT_TRUE(setenv("OAK_CONFIG_DIR", g_tmpdir, 1) == 0);
 #endif
 
 	test_init();
diff --git a/engine/tests/oakengine_keyframe_test.cpp b/engine/tests/oakengine_keyframe_test.cpp
index a6482f87c..1c56a5adb 100644
--- a/engine/tests/oakengine_keyframe_test.cpp
+++ b/engine/tests/oakengine_keyframe_test.cpp
@@ -831,6 +831,7 @@ TEST(OakEngineKeyframe, Main)
 	EXPECT_TRUE(setenv("XDG_CONFIG_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_CACHE_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_DATA_HOME", g_tmpdir, 1) == 0);
+	EXPECT_TRUE(setenv("OAK_CONFIG_DIR", g_tmpdir, 1) == 0);
 #endif
 
 	EXPECT_TRUE(oakengine_init(OAKENGINE_INIT_HEADLESS) == OAKENGINE_OK);
diff --git a/engine/tests/oakengine_node_test.cpp b/engine/tests/oakengine_node_test.cpp
index f214f23f1..657063475 100644
--- a/engine/tests/oakengine_node_test.cpp
+++ b/engine/tests/oakengine_node_test.cpp
@@ -1050,6 +1050,7 @@ TEST(OakEngineNode, Main)
 	EXPECT_TRUE(setenv("XDG_CONFIG_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_CACHE_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_DATA_HOME", g_tmpdir, 1) == 0);
+	EXPECT_TRUE(setenv("OAK_CONFIG_DIR", g_tmpdir, 1) == 0);
 #endif
 
 	EXPECT_TRUE(oakengine_init(OAKENGINE_INIT_HEADLESS) == OAKENGINE_OK);
diff --git a/engine/tests/oakengine_playback_test.cpp b/engine/tests/oakengine_playback_test.cpp
index 51e4fbc2d..d74390a48 100644
--- a/engine/tests/oakengine_playback_test.cpp
+++ b/engine/tests/oakengine_playback_test.cpp
@@ -300,6 +300,7 @@ TEST(OakEnginePlayback, Main)
 	EXPECT_TRUE(setenv("XDG_CONFIG_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_CACHE_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_DATA_HOME", g_tmpdir, 1) == 0);
+	EXPECT_TRUE(setenv("OAK_CONFIG_DIR", g_tmpdir, 1) == 0);
 #endif
 
 	// HEADLESS is enough for the validation part and creates the
diff --git a/engine/tests/oakengine_preview_test.cpp b/engine/tests/oakengine_preview_test.cpp
index 1f1b4b0ea..61874d49c 100644
--- a/engine/tests/oakengine_preview_test.cpp
+++ b/engine/tests/oakengine_preview_test.cpp
@@ -244,6 +244,7 @@ TEST(OakEnginePreview, Main)
 	EXPECT_TRUE(setenv("XDG_CONFIG_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_CACHE_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_DATA_HOME", g_tmpdir, 1) == 0);
+	EXPECT_TRUE(setenv("OAK_CONFIG_DIR", g_tmpdir, 1) == 0);
 #endif
 
 	EXPECT_TRUE(oakengine_init(OAKENGINE_INIT_HEADLESS) == OAKENGINE_OK);
diff --git a/engine/tests/oakengine_renderer_test.cpp b/engine/tests/oakengine_renderer_test.cpp
index fe7e1449d..c812e4433 100644
--- a/engine/tests/oakengine_renderer_test.cpp
+++ b/engine/tests/oakengine_renderer_test.cpp
@@ -240,6 +240,7 @@ TEST(OakEngineRenderer, Main)
 	EXPECT_TRUE(setenv("XDG_CONFIG_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_CACHE_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_DATA_HOME", g_tmpdir, 1) == 0);
+	EXPECT_TRUE(setenv("OAK_CONFIG_DIR", g_tmpdir, 1) == 0);
 #endif
 
 	// HEADLESS is enough for the validation part and creates the offscreen
diff --git a/engine/tests/oakengine_sync_test.cpp b/engine/tests/oakengine_sync_test.cpp
index c54d0d5fb..00f67ff47 100644
--- a/engine/tests/oakengine_sync_test.cpp
+++ b/engine/tests/oakengine_sync_test.cpp
@@ -212,6 +212,7 @@ TEST(OakEngineSync, Main)
 	EXPECT_TRUE(setenv("XDG_CONFIG_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_CACHE_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_DATA_HOME", g_tmpdir, 1) == 0);
+	EXPECT_TRUE(setenv("OAK_CONFIG_DIR", g_tmpdir, 1) == 0);
 #endif
 
 	// HEADLESS is enough for the validation part.
diff --git a/engine/tests/oakengine_timeline_edit_test.cpp b/engine/tests/oakengine_timeline_edit_test.cpp
index 295470b3e..04a73e140 100644
--- a/engine/tests/oakengine_timeline_edit_test.cpp
+++ b/engine/tests/oakengine_timeline_edit_test.cpp
@@ -1806,6 +1806,7 @@ TEST(OakEngineTimelineEdit, Main)
 	EXPECT_TRUE(setenv("XDG_CONFIG_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_CACHE_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_DATA_HOME", g_tmpdir, 1) == 0);
+	EXPECT_TRUE(setenv("OAK_CONFIG_DIR", g_tmpdir, 1) == 0);
 #endif
 
 	EXPECT_TRUE(oakengine_init(OAKENGINE_INIT_HEADLESS) == OAKENGINE_OK);
diff --git a/engine/tests/oakengine_traverse_test.cpp b/engine/tests/oakengine_traverse_test.cpp
index 78c0b26d1..5ed15b19e 100644
--- a/engine/tests/oakengine_traverse_test.cpp
+++ b/engine/tests/oakengine_traverse_test.cpp
@@ -250,6 +250,7 @@ TEST(OakEngineTraverse, Main)
 	EXPECT_TRUE(setenv("XDG_CONFIG_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_CACHE_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_DATA_HOME", g_tmpdir, 1) == 0);
+	EXPECT_TRUE(setenv("OAK_CONFIG_DIR", g_tmpdir, 1) == 0);
 #endif
 
 	EXPECT_TRUE(oakengine_init(OAKENGINE_INIT_HEADLESS) == OAKENGINE_OK);
diff --git a/engine/tests/oakengine_viewer_test.cpp b/engine/tests/oakengine_viewer_test.cpp
index ec47fc7db..fe7df4bd5 100644
--- a/engine/tests/oakengine_viewer_test.cpp
+++ b/engine/tests/oakengine_viewer_test.cpp
@@ -552,6 +552,7 @@ TEST(OakEngineViewer, Main)
 	EXPECT_TRUE(setenv("XDG_CONFIG_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_CACHE_HOME", g_tmpdir, 1) == 0);
 	EXPECT_TRUE(setenv("XDG_DATA_HOME", g_tmpdir, 1) == 0);
+	EXPECT_TRUE(setenv("OAK_CONFIG_DIR", g_tmpdir, 1) == 0);
 #endif
 
 	EXPECT_TRUE(oakengine_init(OAKENGINE_INIT_HEADLESS) == OAKENGINE_OK);