diff --git a/client/tests/test_step_canvas_viewer.gd b/client/tests/test_step_canvas_viewer.gd
index da0d3cc5d..63c93bce1 100644
--- a/client/tests/test_step_canvas_viewer.gd
+++ b/client/tests/test_step_canvas_viewer.gd
@@ -810,8 +810,16 @@ func test_request_extent_ignores_a_not_yet_laid_out_viewport() -> void:
 	for degenerate in [Vector2.ZERO, Vector2(4.0, 4.0), Vector2(1920.0, 2.0)]:
 		v.size = degenerate
 		var extent: Vector2i = v._request_extent()
+		# The fallback is sized to the DRAWABLE area, so Global's reserved
+		# legend column comes off the width first — the request must match what
+		# can actually be drawn, or the Global integer fit drops a whole step
+		# and the map renders at half size in a window with room to spare.
+		var drawable := Vector2(
+			StepCanvasViewer.FALLBACK_VIEWPORT_PX.x - StepCanvasTransport.LEGEND_COLUMN_PX,
+			StepCanvasViewer.FALLBACK_VIEWPORT_PX.y
+		)
 		var expected: Vector2i = StepCanvasTransport.viewport_fit_extent(
-			StepCanvasViewer.FALLBACK_VIEWPORT_PX, v.get_held_rung()
+			drawable, v.get_held_rung()
 		)
 		assert_that(extent).override_failure_message(
 			"a %s viewport must fall back, not be taken literally — got %s" % [degenerate, extent]
diff --git a/client/ui/implant/apps/atlas/step_canvas/step_canvas_viewer.gd b/client/ui/implant/apps/atlas/step_canvas/step_canvas_viewer.gd
index 754bc6428..e2eef7faf 100644
--- a/client/ui/implant/apps/atlas/step_canvas/step_canvas_viewer.gd
+++ b/client/ui/implant/apps/atlas/step_canvas/step_canvas_viewer.gd
@@ -501,7 +501,22 @@ func _request_extent() -> Vector2i:
 	# Treat anything below a plausible panel size as "not laid out yet".
 	if viewport.x < MIN_LAID_OUT_VIEWPORT_PX or viewport.y < MIN_LAID_OUT_VIEWPORT_PX:
 		viewport = FALLBACK_VIEWPORT_PX
-	var fit: Vector2i = StepCanvasTransport.viewport_fit_extent(viewport, _held_rung)
+	# Ask for the area we can actually DRAW into, not the whole Control.
+	#
+	# Global reserves LEGEND_COLUMN_PX on the left (_letterbox_scale_for() /
+	# _recompute_canvas_transform() both do). Sizing the request against the
+	# full width while fitting the draw against the reduced width makes the two
+	# disagree, and because the Global fit is an INTEGER px-per-gridunit ratio
+	# the disagreement does not degrade gracefully: at a 1920-wide window we
+	# asked for 960 gridunits but could only fit floor(1628/960) = 1 px each,
+	# so the map drew at HALF SIZE in a window with room to spare (eyeballed on
+	# Lendel 2026-07-27). Reserving the column here makes the request exactly
+	# what fits at the intended ratio, so the fit lands on 2 and the canvas
+	# fills the panel.
+	var drawable: Vector2 = viewport
+	if _held_rung == StepCanvasTransport.RUNG_GLOBAL:
+		drawable.x = maxf(viewport.x - StepCanvasTransport.LEGEND_COLUMN_PX, 1.0)
+	var fit: Vector2i = StepCanvasTransport.viewport_fit_extent(drawable, _held_rung)
 	return StepCanvasTransport.cap_extent_to_body(fit, _held_rung, _global_body_extent)