diff --git a/.changeset/lucky-donuts-tell.md b/.changeset/lucky-donuts-tell.md
new file mode 100644
index 000000000..914e87b59
--- /dev/null
+++ b/.changeset/lucky-donuts-tell.md
@@ -0,0 +1,5 @@
+---
+'@viamrobotics/motion-tools': patch
+---
+
+Add `interpolateTrajectory`, expanding a planned trajectory into preview playback frames budgeted per joint unit (degrees for revolute joints, millimetres for prismatic)
diff --git a/.prettierignore b/.prettierignore
index 96ddae943..5ccb42eec 100644
--- a/.prettierignore
+++ b/.prettierignore
@@ -24,5 +24,9 @@ static/test-fixtures
 # cannot round-trip them.
 src/lib/plugins/MotionPlanReplayer/__tests__/__fixtures__/
 
+# A 225-step capture, stored minified because it is 2,000 lines pretty-printed
+# and nothing reads it by eye. Its sibling fixtures are small and stay formatted.
+src/lib/motion/__tests__/__fixtures__/plan-linear-constrained.json
+
 # IDE
 .cursor
\ No newline at end of file
diff --git a/src/lib/motion/__tests__/__fixtures__/plan-free-space.json b/src/lib/motion/__tests__/__fixtures__/plan-free-space.json
new file mode 100644
index 000000000..8128a875e
--- /dev/null
+++ b/src/lib/motion/__tests__/__fixtures__/plan-free-space.json
@@ -0,0 +1,19 @@
+{
+	"plan": [
+		{
+			"arm": [0, 0, 0, 0, 0, 0],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				1.1050027617288314, -1.8778538694900169, -1.5693986191251539, -4.406731791553699,
+				4.712389313270464, -0.46579159318886737
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		}
+	]
+}
diff --git a/src/lib/motion/__tests__/__fixtures__/plan-gantry.json b/src/lib/motion/__tests__/__fixtures__/plan-gantry.json
new file mode 100644
index 000000000..026cd6724
--- /dev/null
+++ b/src/lib/motion/__tests__/__fixtures__/plan-gantry.json
@@ -0,0 +1,16 @@
+{
+	"plan": [
+		{
+			"arm-1": [0, 0, 0, 0, 0, 0],
+			"arm-1_origin": [],
+			"gantry-1": [50],
+			"gantry-1_origin": []
+		},
+		{
+			"arm-1": [0, 0, 0, 0, 0, 0],
+			"arm-1_origin": [],
+			"gantry-1": [90.00000000000001],
+			"gantry-1_origin": []
+		}
+	]
+}
diff --git a/src/lib/motion/__tests__/__fixtures__/plan-linear-constrained.json b/src/lib/motion/__tests__/__fixtures__/plan-linear-constrained.json
new file mode 100644
index 000000000..6357d52b9
--- /dev/null
+++ b/src/lib/motion/__tests__/__fixtures__/plan-linear-constrained.json
@@ -0,0 +1 @@
+{"plan":[{"arm":[0,0,0,0,0,0],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.002363,-0.065416,0.131886,-0.070124,-0.012278,-0.006263],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.00472,-0.094668,0.188379,-0.101806,-0.024554,-0.011741],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.007073,-0.117096,0.230622,-0.125741,-0.036823,-0.017539],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.009421,-0.135977,0.265438,-0.145418,-0.049085,-0.023724],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.011765,-0.153169,0.296694,-0.163609,-0.061342,-0.029519],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.014103,-0.168814,0.324689,-0.179971,-0.073591,-0.035436],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.016436,-0.183348,0.350331,-0.195069,-0.085834,-0.041381],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.018765,-0.19704,0.374177,-0.209249,-0.098069,-0.047297],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.021088,-0.210026,0.396515,-0.222628,-0.110297,-0.053217],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.023407,-0.222439,0.417619,-0.235371,-0.122513,-0.05912],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.025719,-0.234328,0.437593,-0.247473,-0.134722,-0.065067],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.028027,-0.24582,0.456697,-0.259157,-0.146922,-0.070969],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.030332,-0.256921,0.474946,-0.270354,-0.159114,-0.076897],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.03263,-0.267689,0.492463,-0.281154,-0.171296,-0.082841],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.034923,-0.278178,0.509356,-0.291642,-0.183466,-0.088764],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.037212,-0.288399,0.52565,-0.301792,-0.195625,-0.094704],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.039496,-0.298385,0.541414,-0.311652,-0.207773,-0.10065],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.041775,-0.308158,0.556692,-0.32125,-0.21991,-0.106602],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.044049,-0.317738,0.571527,-0.330607,-0.232036,-0.11256],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.046318,-0.327141,0.585954,-0.339741,-0.244149,-0.118524],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.048583,-0.336383,0.600002,-0.348668,-0.256249,-0.124496],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.050842,-0.345477,0.6137,-0.357402,-0.268337,-0.130475],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.053097,-0.354435,0.627073,-0.365957,-0.280412,-0.136462],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.055348,-0.363266,0.64014,-0.374345,-0.292473,-0.142458],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.057594,-0.371981,0.652923,-0.382575,-0.30452,-0.148463],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.059835,-0.380588,0.665439,-0.390657,-0.316553,-0.154476],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.062072,-0.389095,0.677703,-0.398601,-0.328571,-0.1605],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.064305,-0.397508,0.689731,-0.406413,-0.340575,-0.166534],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.066534,-0.405835,0.701536,-0.414102,-0.352563,-0.172579],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.068758,-0.414081,0.71313,-0.421673,-0.364536,-0.178635],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.070979,-0.422252,0.724524,-0.429134,-0.376493,-0.184703],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.073195,-0.430352,0.735728,-0.436489,-0.388434,-0.190782],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.075408,-0.438386,0.746753,-0.443745,-0.400359,-0.196875],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.077617,-0.446359,0.757607,-0.450905,-0.412267,-0.202981],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.079822,-0.454275,0.768298,-0.457975,-0.424157,-0.2091],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.082024,-0.462137,0.778833,-0.464958,-0.43603,-0.215234],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.084223,-0.469948,0.789221,-0.47186,-0.447886,-0.221382],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.086418,-0.477713,0.799468,-0.478683,-0.459724,-0.227546],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.088611,-0.485434,0.80958,-0.485433,-0.471543,-0.233725],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.0908,-0.493114,0.819563,-0.49211,-0.483344,-0.23992],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.092987,-0.500755,0.829423,-0.49872,-0.495125,-0.246132],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.095171,-0.508362,0.839166,-0.505267,-0.506881,-0.252361],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.097352,-0.515933,0.848792,-0.511749,-0.51863,-0.258608],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.099531,-0.523474,0.858311,-0.518173,-0.530353,-0.264874],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.101708,-0.530986,0.867725,-0.52454,-0.542055,-0.271158],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.103883,-0.538471,0.87704,-0.530853,-0.553738,-0.277462],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.106056,-0.545932,0.886258,-0.537115,-0.565399,-0.283786],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.108228,-0.553368,0.895384,-0.543327,-0.577039,-0.29013],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.110398,-0.560784,0.90442,-0.549492,-0.588658,-0.296495],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.112567,-0.56818,0.913371,-0.555611,-0.600255,-0.302881],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.114734,-0.575557,0.922239,-0.561688,-0.61183,-0.30929],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.116901,-0.582917,0.931028,-0.567724,-0.623383,-0.315722],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.119068,-0.590262,0.93974,-0.57372,-0.634913,-0.322177],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.121233,-0.597594,0.948378,-0.579678,-0.64642,-0.328655],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.123399,-0.604912,0.956945,-0.585601,-0.657904,-0.335159],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.125565,-0.612219,0.965443,-0.59149,-0.669364,-0.341687],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.12773,-0.619516,0.973875,-0.597346,-0.680801,-0.348241],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.129897,-0.626803,0.982242,-0.603172,-0.692213,-0.354822],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.132064,-0.634082,0.990548,-0.608968,-0.7036,-0.361429],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.134231,-0.641355,0.998793,-0.614736,-0.714963,-0.368064],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.1364,-0.648621,1.006981,-0.620477,-0.7263,-0.374727],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.138571,-0.655882,1.015113,-0.626194,-0.737612,-0.381419],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.140743,-0.663139,1.023191,-0.631886,-0.748898,-0.38814],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.142917,-0.670392,1.031216,-0.637557,-0.760157,-0.394892],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.145094,-0.677644,1.039192,-0.643203,-0.77139,-0.401672],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.147272,-0.684893,1.047116,-0.648836,-0.782596,-0.408487],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.149453,-0.692141,1.054993,-0.654445,-0.793775,-0.415334],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.151638,-0.699389,1.062825,-0.660038,-0.804925,-0.422212],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.153826,-0.706638,1.070612,-0.665614,-0.816048,-0.429125],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.156017,-0.713888,1.078355,-0.671175,-0.827143,-0.436071],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.158212,-0.721139,1.086057,-0.676722,-0.838208,-0.443053],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.160412,-0.728394,1.093717,-0.682256,-0.849244,-0.45007],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.162616,-0.735651,1.101338,-0.687778,-0.860251,-0.457123],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.164825,-0.742912,1.10892,-0.693289,-0.871228,-0.464214],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.167038,-0.750177,1.116465,-0.698789,-0.882174,-0.471343],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.169258,-0.757447,1.123974,-0.70428,-0.893089,-0.47851],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.171483,-0.764722,1.131447,-0.709763,-0.903973,-0.485716],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.173714,-0.772003,1.138886,-0.71524,-0.914825,-0.492964],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.175952,-0.77929,1.146292,-0.720711,-0.925645,-0.500252],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.178196,-0.786583,1.153664,-0.726176,-0.936433,-0.507582],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.180448,-0.793884,1.161005,-0.731637,-0.947188,-0.514955],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.182707,-0.801192,1.168315,-0.737095,-0.957909,-0.52237],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.184974,-0.808508,1.175595,-0.74255,-0.968597,-0.52983],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.187249,-0.815833,1.182845,-0.748004,-0.97925,-0.537336],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.189532,-0.823165,1.190067,-0.753457,-0.989867,-0.544887],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.191825,-0.830507,1.19726,-0.75891,-1.00045,-0.552485],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.194127,-0.837858,1.204426,-0.764364,-1.010996,-0.56013],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.196438,-0.845219,1.211566,-0.76982,-1.021506,-0.567825],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.19876,-0.852589,1.218679,-0.775279,-1.031979,-0.575568],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.201092,-0.85997,1.225766,-0.780741,-1.042415,-0.583362],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.203435,-0.867361,1.232828,-0.786207,-1.052812,-0.591208],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.20579,-0.874762,1.239866,-0.791678,-1.06317,-0.599106],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.208156,-0.882175,1.246879,-0.797155,-1.07349,-0.607058],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.210534,-0.889598,1.253868,-0.802638,-1.083769,-0.615064],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.212924,-0.897032,1.260834,-0.808128,-1.094008,-0.623125],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.215328,-0.904478,1.267777,-0.813627,-1.104205,-0.631242],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.217745,-0.911937,1.274699,-0.819137,-1.11436,-0.639414],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.220176,-0.919407,1.2816,-0.824658,-1.124473,-0.647645],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.222622,-0.926889,1.288478,-0.830188,-1.134542,-0.655934],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.225082,-0.934383,1.295334,-0.83573,-1.144568,-0.664284],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.227558,-0.941894,1.302178,-0.841296,-1.154546,-0.672688],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.230049,-0.949413,1.308994,-0.846864,-1.164481,-0.68116],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.232556,-0.956945,1.31579,-0.852447,-1.174369,-0.689695],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.23508,-0.96449,1.322566,-0.858046,-1.18421,-0.698294],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.237621,-0.972047,1.329321,-0.863659,-1.194004,-0.706959],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.240179,-0.979616,1.336054,-0.869284,-1.203751,-0.715692],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.242756,-0.987197,1.342767,-0.874925,-1.213449,-0.724494],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.245351,-0.994792,1.349462,-0.880587,-1.223095,-0.733361],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.247966,-1.002399,1.356139,-0.886268,-1.23269,-0.742299],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.250601,-1.010019,1.362797,-0.891965,-1.242231,-0.751309],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.253255,-1.017653,1.369436,-0.897687,-1.251721,-0.760388],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.25593,-1.0253,1.376055,-0.903429,-1.261158,-0.769539],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.258626,-1.032957,1.382653,-0.909184,-1.270538,-0.778768],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.261344,-1.04063,1.389236,-0.914972,-1.279864,-0.78807],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.264084,-1.048315,1.395801,-0.920782,-1.289132,-0.797448],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.266848,-1.056012,1.402346,-0.926614,-1.298343,-0.806904],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.269635,-1.063721,1.408871,-0.932469,-1.307494,-0.81644],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.272445,-1.071442,1.415379,-0.938349,-1.316587,-0.826055],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.275281,-1.079176,1.421867,-0.944255,-1.325617,-0.835751],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.278142,-1.086922,1.428338,-0.950188,-1.334584,-0.845531],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.281028,-1.094681,1.434789,-0.956148,-1.343488,-0.855394],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.283942,-1.10245,1.441221,-0.962136,-1.352326,-0.865342],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.286882,-1.110233,1.447635,-0.968154,-1.361099,-0.875377],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.289849,-1.118025,1.45403,-0.9742,-1.369805,-0.885499],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.292845,-1.12583,1.460406,-0.980275,-1.378441,-0.895709],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.295872,-1.133646,1.466764,-0.98638,-1.387,-0.906008],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.298926,-1.141471,1.473101,-0.992518,-1.395497,-0.916399],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.302011,-1.149308,1.479418,-0.998688,-1.403921,-0.926883],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.305126,-1.157154,1.485716,-1.00489,-1.412271,-0.93746],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.308273,-1.165011,1.491994,-1.011125,-1.420545,-0.948131],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.311452,-1.172877,1.498252,-1.017395,-1.428742,-0.958899],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.314664,-1.180752,1.50449,-1.023698,-1.43686,-0.969764],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.317909,-1.188636,1.510708,-1.030037,-1.444898,-0.980727],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.321189,-1.196529,1.516904,-1.03641,-1.452854,-0.99179],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.324504,-1.20443,1.52308,-1.04282,-1.460726,-1.002953],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.327855,-1.212338,1.529234,-1.049265,-1.468513,-1.014219],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.331242,-1.220254,1.535367,-1.055748,-1.476213,-1.025588],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.334666,-1.228177,1.541478,-1.062268,-1.483825,-1.037062],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.338128,-1.236106,1.547566,-1.068826,-1.491346,-1.04864],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.341628,-1.244041,1.553632,-1.075423,-1.498775,-1.060326],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.345168,-1.251982,1.559675,-1.082057,-1.50611,-1.072119],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.348748,-1.259927,1.565694,-1.088731,-1.51335,-1.084021],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.352368,-1.267877,1.571689,-1.095444,-1.520491,-1.096033],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.356031,-1.275831,1.57766,-1.102196,-1.527533,-1.108156],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.359735,-1.283787,1.583606,-1.108988,-1.534473,-1.120391],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.363483,-1.291746,1.589527,-1.115819,-1.54131,-1.13274],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.367275,-1.299707,1.595422,-1.122691,-1.54804,-1.145202],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.371112,-1.30767,1.601291,-1.129601,-1.554663,-1.157779],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.374995,-1.315632,1.607133,-1.136552,-1.561175,-1.170471],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.378923,-1.323595,1.612947,-1.143543,-1.567576,-1.183281],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.382899,-1.331557,1.618734,-1.150573,-1.573866,-1.196206],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.386923,-1.339517,1.624492,-1.157643,-1.580035,-1.209251],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.390996,-1.347474,1.63022,-1.164753,-1.586085,-1.222414],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.395119,-1.355428,1.635918,-1.171901,-1.592013,-1.235698],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.399292,-1.363377,1.641583,-1.179084,-1.597822,-1.249096],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.403517,-1.371323,1.647221,-1.186313,-1.603497,-1.262626],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.407795,-1.379262,1.652825,-1.193574,-1.609048,-1.276272],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.412125,-1.387194,1.658396,-1.200872,-1.614468,-1.29004],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.41651,-1.395118,1.663933,-1.208207,-1.619755,-1.30393],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.420949,-1.403035,1.669438,-1.215582,-1.624908,-1.317947],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.425445,-1.410941,1.674904,-1.222983,-1.629921,-1.332082],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.429997,-1.418835,1.680334,-1.230418,-1.634793,-1.34634],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.434607,-1.426718,1.685727,-1.237886,-1.639522,-1.360722],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.439275,-1.434588,1.691082,-1.245385,-1.644105,-1.375227],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.444003,-1.442445,1.696397,-1.252913,-1.64854,-1.389855],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.448791,-1.450286,1.701673,-1.26047,-1.652824,-1.404607],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.453641,-1.45811,1.706905,-1.268053,-1.656952,-1.419479],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.458553,-1.465919,1.712098,-1.275662,-1.660925,-1.434479],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.463528,-1.473708,1.717247,-1.283294,-1.664738,-1.449599],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.468567,-1.481478,1.722351,-1.290945,-1.668392,-1.464841],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.47367,-1.489227,1.727409,-1.298615,-1.671881,-1.480204],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.47884,-1.496953,1.73242,-1.306302,-1.675204,-1.495688],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.484076,-1.504656,1.737384,-1.314003,-1.678357,-1.511292],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.489379,-1.512335,1.742298,-1.321715,-1.681339,-1.527015],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.494752,-1.519987,1.747161,-1.329437,-1.684146,-1.542857],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.500193,-1.527613,1.751973,-1.337163,-1.68678,-1.558813],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.505704,-1.535211,1.756735,-1.344903,-1.689226,-1.574887],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.511288,-1.542776,1.761436,-1.352627,-1.691494,-1.591083],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.516944,-1.550311,1.766085,-1.360355,-1.693578,-1.607388],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.522672,-1.557814,1.770676,-1.368078,-1.695474,-1.623806],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.528474,-1.565283,1.775209,-1.37579,-1.697181,-1.640336],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.534351,-1.572717,1.779682,-1.383489,-1.698696,-1.656975],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.540303,-1.580113,1.784093,-1.391169,-1.700016,-1.673723],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.546332,-1.587472,1.788442,-1.39883,-1.701143,-1.690576],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.552438,-1.594791,1.792727,-1.406468,-1.702068,-1.707534],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.558621,-1.602069,1.796946,-1.414074,-1.702793,-1.724595],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.564884,-1.609305,1.801098,-1.421646,-1.703315,-1.741757],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.571226,-1.616497,1.80518,-1.42918,-1.703633,-1.759017],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.577647,-1.623644,1.809192,-1.436669,-1.703745,-1.776373],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.584152,-1.630744,1.813133,-1.444115,-1.703645,-1.793828],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.590737,-1.637796,1.817001,-1.451507,-1.703335,-1.811374],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.597404,-1.644799,1.820794,-1.458841,-1.702815,-1.829008],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.604155,-1.65175,1.824509,-1.466113,-1.702081,-1.846731],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.610989,-1.65865,1.828147,-1.473317,-1.701132,-1.86454],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.617907,-1.665496,1.831706,-1.480448,-1.699966,-1.882431],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.62491,-1.672288,1.835182,-1.487503,-1.698582,-1.900405],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.631999,-1.679022,1.838577,-1.494471,-1.69698,-1.918456],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.639173,-1.685697,1.841888,-1.501349,-1.695159,-1.936581],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.646433,-1.692314,1.845112,-1.508132,-1.693117,-1.95478],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.65378,-1.69887,1.848249,-1.514815,-1.690853,-1.97305],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.661214,-1.705364,1.851297,-1.521391,-1.688369,-1.991386],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.668737,-1.711797,1.854259,-1.527867,-1.685653,-2.009802],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.676346,-1.718163,1.857127,-1.534217,-1.68272,-2.028271],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.684043,-1.724464,1.859899,-1.540437,-1.679567,-2.046799],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.691828,-1.730696,1.86258,-1.546537,-1.676186,-2.065387],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.699701,-1.73686,1.865162,-1.552494,-1.672585,-2.084033],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.70766,-1.742952,1.867643,-1.558305,-1.668769,-2.102727],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.715709,-1.748974,1.870031,-1.563978,-1.664721,-2.121478],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.723847,-1.754925,1.87232,-1.569499,-1.660449,-2.140282],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.732072,-1.760799,1.874503,-1.574857,-1.655963,-2.159127],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.740384,-1.766599,1.876585,-1.580051,-1.651252,-2.178021],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.748784,-1.772321,1.878563,-1.585075,-1.646325,-2.196957],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.757271,-1.777965,1.880435,-1.589922,-1.641179,-2.215934],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.765844,-1.78353,1.8822,-1.594587,-1.635818,-2.234951],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.774503,-1.789014,1.883856,-1.599064,-1.630243,-2.254006],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.783247,-1.794414,1.885404,-1.603348,-1.624455,-2.273096],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.792076,-1.799732,1.886842,-1.607435,-1.618455,-2.292223],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.800988,-1.804964,1.888166,-1.611313,-1.612252,-2.311379],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.809983,-1.81011,1.889378,-1.614983,-1.605841,-2.330569],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.819061,-1.815168,1.890476,-1.618439,-1.599226,-2.34979],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.828219,-1.820136,1.891459,-1.621676,-1.592409,-2.369043],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.837456,-1.825015,1.892325,-1.624681,-1.5854,-2.38832],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.846773,-1.8298,1.893072,-1.627458,-1.578198,-2.407623],"arm_origin":[],"table":[],"table_origin":[]},{"arm":[-0.856167,-1.834494,1.893705,-1.630008,-1.570795,-2.426964],"arm_origin":[],"table":[],"table_origin":[]}]}
diff --git a/src/lib/motion/__tests__/__fixtures__/plan-synthetic-obstacle-routed.json b/src/lib/motion/__tests__/__fixtures__/plan-synthetic-obstacle-routed.json
new file mode 100644
index 000000000..073d1dd2e
--- /dev/null
+++ b/src/lib/motion/__tests__/__fixtures__/plan-synthetic-obstacle-routed.json
@@ -0,0 +1,187 @@
+{
+	"plan": [
+		{
+			"arm": [0, 0, 0, 0, 0, 0],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [0, 0, 0, 0, 0, 0],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-0.026296498218373508, -0.15470611393736317, 0.07280992487199799, 0.12735964055862564,
+				0.24431249119848666, -0.08898409746564592
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-0.026855998180466557, -0.15799773338283896, 0.07435907220970006, 0.13006942014497938,
+				0.24951062930909274, -0.09087737613512774
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-0.04028399727069984, -0.2369966000742585, 0.1115386083145501, 0.19510413021746909,
+				0.37426594396363916, -0.13631606420269163
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-0.047557496777909526, -0.279787652865444, 0.1316775237046772, 0.23033126484006763,
+				0.44184173940151833, -0.16092868690595535
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-0.12868499128140226, -0.7570724724594368, 0.35630388767147947, 0.6232493048613595,
+				1.1955717654394027, -0.4354540939808204
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-0.20571028488356596, -0.7822346502344796, 0.3987269923759556, 0.6309936839796001,
+				1.1951027447273148, -0.4255465941728487
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-0.8475877315682634, -0.991919465026503, 0.7522528649132567, 0.6955301766316049,
+				1.1911942387932488, -0.34298409577308436
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-2.216926284495618, -1.4392470699161528, 1.5064413929928322, 0.8332080276225484,
+				1.1828560928005747, -0.16685076585358719
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-2.3239058589430677, -1.4741945390481568, 1.565362371749049, 0.8439641097312159,
+				1.182204675144897, -0.15309034945362646
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-2.3453017738325572, -1.4811840328745576, 1.5771465675002925, 0.8461153261529494,
+				1.1820743916137615, -0.15033826617363433
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-2.3202934038379324, -1.411438640525238, 1.592742600247066, 0.8238222471704858,
+				1.218405987284108, -0.19107643316238532
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-2.317660943838498, -1.404097020277941, 1.594384287904621, 0.8214756072775949,
+				1.2222303657757234, -0.19536466126646437
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-2.236054683856038, -1.17650679261174, 1.645276605288829, 0.7487297705979771,
+				1.3407860990158014, -0.328299732492915
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-2.1873541738665048, -1.0406868180367492, 1.6756478269535984, 0.7053169325794953,
+				1.4115371011106868, -0.4076319524183775
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-2.1807730238679195, -1.0223327674185072, 1.6797520460974862, 0.6994503328472682,
+				1.4210980473397252, -0.4183525226785751
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-2.1794567938682023, -1.0186619572948588, 1.6805728899262637, 0.6982770129008227,
+				1.4230102365855328, -0.42049663673061466
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-2.1583971138727285, -0.9599289953164845, 1.6937063911867045, 0.6795038937576955,
+				1.4536052645184563, -0.45480246156324705
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-2.116277753881781, -0.8424630713597355, 1.719973393707586, 0.6419576554714411,
+				1.514795320384303, -0.5234141112285119
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		},
+		{
+			"arm": [
+				-2.1559561769087057, -0.8733141758332765, 1.738883351746668, 0.7052277081276631,
+				1.5707951402863713, -0.5851599053467483
+			],
+			"arm_origin": [],
+			"table": [],
+			"table_origin": []
+		}
+	]
+}
diff --git a/src/lib/motion/__tests__/interpolateTrajectory.spec.ts b/src/lib/motion/__tests__/interpolateTrajectory.spec.ts
new file mode 100644
index 000000000..10213944c
--- /dev/null
+++ b/src/lib/motion/__tests__/interpolateTrajectory.spec.ts
@@ -0,0 +1,526 @@
+import { describe, expect, it } from 'vitest'
+
+import { Pose } from '$lib/math'
+
+import type { FrameDescriptor } from '../frameDescriptors'
+import type { JointMotion, JointMotions } from '../interpolateTrajectory'
+import type { TrajectoryStep } from '../jointPose'
+
+import {
+	DEFAULT_DEGREES_PER_FRAME,
+	interpolatedFrames,
+	jointMotionsOf,
+	jointTravelRadians,
+	lerpTrajectoryStep,
+	segmentFrameCost,
+	waypointFrames,
+} from '../interpolateTrajectory'
+import freeSpacePlan from './__fixtures__/plan-free-space.json'
+import gantryPlan from './__fixtures__/plan-gantry.json'
+import linearPlan from './__fixtures__/plan-linear-constrained.json'
+import obstaclePlan from './__fixtures__/plan-synthetic-obstacle-routed.json'
+
+const RAD_TO_DEG = 180 / Math.PI
+
+const plans = {
+	freeSpace: freeSpacePlan.plan as TrajectoryStep[],
+	linear: linearPlan.plan as TrajectoryStep[],
+	obstacle: obstaclePlan.plan as TrajectoryStep[],
+	gantry: gantryPlan.plan as TrajectoryStep[],
+}
+
+/** The gantry rig's one prismatic axis; everything else in these fixtures is revolute. */
+const GANTRY_MOTIONS: JointMotions = new Map([['gantry-1', ['translational'] as const]])
+
+const segmentDegrees = (trajectory: TrajectoryStep[]) =>
+	trajectory
+		.slice(1)
+		.map((step, index) => jointTravelRadians(trajectory[index]!, step) * RAD_TO_DEG)
+
+describe('captured plans still have the shape these rules were built for', () => {
+	it.each([
+		['freeSpace', 2, 269, 271],
+		['linear', 225, 7, 8],
+		['obstacle', 21, 78, 79],
+	] as const)('%s: %i steps, worst segment between %i° and %i°', (key, steps, lower, upper) => {
+		const trajectory = plans[key]
+		expect(trajectory).toHaveLength(steps)
+
+		const worst = Math.max(...segmentDegrees(trajectory))
+		expect(worst).toBeGreaterThan(lower)
+		expect(worst).toBeLessThan(upper)
+	})
+
+	// Dividing a segment by its own length would be NaN here. Structural rather than incidental: a
+	// CBiRRT-solved goal returns a path whose first node is the segment's start configuration.
+	it('obstacle plans contain a zero-length segment', () => {
+		expect(segmentDegrees(plans.obstacle).filter((d) => d === 0)).not.toHaveLength(0)
+	})
+
+	it('free-space plans do not', () => {
+		expect(segmentDegrees(plans.freeSpace).filter((d) => d === 0)).toHaveLength(0)
+	})
+
+	it('every step of a plan carries the same columns', () => {
+		for (const trajectory of Object.values(plans)) {
+			const keys = trajectory.map((step) => Object.keys(step).toSorted().join(','))
+			expect(new Set(keys).size).toBe(1)
+		}
+	})
+})
+
+describe('jointTravelRadians', () => {
+	it('reports the largest single-joint change, not the sum', () => {
+		const travel = jointTravelRadians({ arm: [0, 0, 0] }, { arm: [0.1, 0.5, -0.2] })
+		expect(travel).toBeCloseTo(0.5)
+	})
+
+	it('spans every component in the step', () => {
+		const travel = jointTravelRadians({ arm: [0.1], gantry: [2] }, { arm: [0.2], gantry: [0] })
+		expect(travel).toBeCloseTo(2)
+	})
+
+	it('ignores the zero-DoF frames a real trajectory carries', () => {
+		const travel = jointTravelRadians({ arm: [1], table: [] }, { arm: [1.5], table: [] })
+		expect(travel).toBeCloseTo(0.5)
+	})
+})
+
+/**
+ * Neither guard can fire on a real reply, since `ToFrameSystemInputs` serializes every node of a
+ * plan from one schema. They are pinned so a malformed one degrades instead of throwing or costing
+ * `NaN`.
+ */
+describe('a step that does not carry the same columns as its neighbour', () => {
+	it.each([
+		['segmentFrameCost', segmentFrameCost],
+		['jointTravelRadians', jointTravelRadians],
+	])('%s skips a component the next step drops', (_label, cost) => {
+		expect(cost({ arm: [0], gripper: [0] }, { arm: [0] })).toBe(0)
+	})
+
+	it.each([
+		['segmentFrameCost', segmentFrameCost],
+		['jointTravelRadians', jointTravelRadians],
+	])('%s skips a joint the next step drops', (_label, cost) => {
+		expect(cost({ arm: [0, 0] }, { arm: [0] })).toBe(0)
+	})
+
+	it('charges nothing for a component that appears only in the later step', () => {
+		expect(segmentFrameCost({ arm: [0] }, { arm: [0], gripper: [Math.PI] })).toBe(0)
+	})
+})
+
+describe('lerpTrajectoryStep', () => {
+	const from: TrajectoryStep = { arm: [0, 10] }
+	const to: TrajectoryStep = { arm: [1, -10] }
+
+	it.each([
+		[0, [0, 10]],
+		[0.5, [0.5, 0]],
+		[1, [1, -10]],
+	])('blends each joint at t=%s', (t, expected) => {
+		expect(lerpTrajectoryStep(from, to, t).arm).toEqual(expected)
+	})
+
+	it('leaves the endpoints untouched', () => {
+		lerpTrajectoryStep(from, to, 0.5)
+		expect(from.arm).toEqual([0, 10])
+		expect(to.arm).toEqual([1, -10])
+	})
+
+	it.each([
+		['only the start', { arm: [5] }, {}],
+		['only the end', {}, { arm: [5] }],
+	])('holds a component present in %s', (_label, start, end) => {
+		expect(lerpTrajectoryStep(start, end, 0.5).arm).toEqual([5])
+	})
+
+	// Handing back an array the input plan still owns means an in-place edit of a frame rewrites the
+	// plan itself.
+	it.each([
+		['only the start', true],
+		['only the end', false],
+	])('copies a component present in %s rather than aliasing it', (_label, onStart) => {
+		const held = [5]
+		const start: TrajectoryStep = onStart ? { arm: held } : {}
+		const end: TrajectoryStep = onStart ? {} : { arm: held }
+
+		expect(lerpTrajectoryStep(start, end, 0.5).arm).not.toBe(held)
+	})
+
+	it('carries joints a component gained between steps', () => {
+		expect(lerpTrajectoryStep({ arm: [0, 0] }, { arm: [1, 1, 9] }, 0.5).arm).toEqual([0.5, 0.5, 9])
+	})
+
+	it('keeps joints a component lost between steps', () => {
+		expect(lerpTrajectoryStep({ arm: [0, 10, 20] }, { arm: [1] }, 0.5).arm).toEqual([0.5, 10, 20])
+	})
+
+	it('blends straight across ±π rather than taking the short way round', () => {
+		expect(lerpTrajectoryStep({ arm: [3] }, { arm: [3.4] }, 0.5).arm![0]).toBeCloseTo(3.2)
+	})
+})
+
+describe('waypointFrames', () => {
+	it("plays the planner's waypoints and nothing else", () => {
+		const frames = waypointFrames(plans.obstacle)
+		expect(frames.steps).toBe(plans.obstacle)
+		expect(frames.waypoints).toHaveLength(plans.obstacle.length)
+	})
+
+	// Length alone leaves the contents free: every waypoint could point at frame 0 and the assertion
+	// above would still hold.
+	it('indexes every frame as a waypoint, in order', () => {
+		expect(waypointFrames(plans.gantry).waypoints).toEqual([0, 1])
+		expect(waypointFrames(plans.obstacle).waypoints).toEqual(
+			plans.obstacle.map((_, index) => index)
+		)
+	})
+
+	it('reports no coarsening, since it never subdivides', () => {
+		expect(waypointFrames(plans.obstacle).coarsening).toBe(1)
+		expect(waypointFrames([]).coarsening).toBe(1)
+	})
+})
+
+describe('interpolatedFrames', () => {
+	it.each(['freeSpace', 'linear', 'obstacle'] as const)(
+		'keeps every planned waypoint of the %s plan, in order',
+		(key) => {
+			const planned = plans[key]
+			const { steps, waypoints } = interpolatedFrames(planned)
+
+			expect(waypoints).toHaveLength(planned.length)
+			// By reference, not by value: `toEqual` also passes for a blend that lands on the waypoint,
+			// which is what dropping the explicit `steps.push(to)` produces.
+			for (const [index, frame] of waypoints.entries()) {
+				expect(steps[frame]).toBe(planned[index])
+			}
+			expect(waypoints[0]).toBe(0)
+			expect(waypoints.at(-1)).toBe(steps.length - 1)
+		}
+	)
+
+	it.each(['freeSpace', 'linear', 'obstacle'] as const)(
+		'holds the %s plan to the requested resolution',
+		(key) => {
+			const { steps } = interpolatedFrames(plans[key])
+			const worst = Math.max(...segmentDegrees(steps))
+
+			// Allowing a hair over: a segment is split into a whole number of frames, so the last one
+			// lands on or under the target rather than exactly at it.
+			expect(worst).toBeLessThanOrEqual(DEFAULT_DEGREES_PER_FRAME + 0.001)
+		}
+	)
+
+	it('turns the free-space teleport into a sweep', () => {
+		expect(plans.freeSpace).toHaveLength(2)
+		expect(interpolatedFrames(plans.freeSpace).steps.length).toBeGreaterThan(150)
+	})
+
+	it('leaves an already-dense plan essentially alone', () => {
+		// Frames added, not a fraction of the plan's length: 6 of its 224 segments exceed the budget
+		// and contribute all 11, so a `× 1.1` bound would read as slack it does not have.
+		const { steps } = interpolatedFrames(plans.linear)
+		expect(steps.length - plans.linear.length).toBe(11)
+	})
+
+	it('spends frames where the motion is, not where the waypoints are', () => {
+		const planned = plans.obstacle
+		const { waypoints } = interpolatedFrames(planned)
+
+		const segments = segmentDegrees(planned).map((degrees, index) => ({
+			degrees,
+			frames: waypoints[index + 1]! - waypoints[index]!,
+		}))
+
+		const longest = segments.toSorted((a, b) => b.degrees - a.degrees)[0]!
+		const zeroLength = segments.find((segment) => segment.degrees === 0)!
+
+		expect(longest.frames).toBeGreaterThan(40)
+		expect(zeroLength.frames).toBe(1)
+	})
+
+	it('coarsens rather than truncates when the frame cap binds', () => {
+		const { steps, waypoints, coarsening } = interpolatedFrames(plans.linear, { degrees: 0.0001 })
+
+		expect(coarsening).toBeGreaterThan(1)
+		// The cap bounds interpolation; each planned waypoint keeps its own frame regardless, so the
+		// ceiling is the budget plus the plan's own length.
+		expect(steps.length).toBeLessThanOrEqual(2000 + plans.linear.length)
+		expect(steps.at(-1)).toEqual(plans.linear.at(-1))
+		expect(waypoints).toHaveLength(plans.linear.length)
+	})
+
+	// The cap-binding case above asserts how many waypoints there are and never where they point.
+	it('still points each waypoint at its own frame when the cap binds', () => {
+		const { steps, waypoints, coarsening } = interpolatedFrames(plans.linear, { degrees: 0.0001 })
+
+		expect(coarsening).toBeGreaterThan(1)
+		for (const [index, frame] of waypoints.entries()) {
+			expect(steps[frame]).toBe(plans.linear[index])
+		}
+	})
+
+	// Nothing else here pins `coarsening` to a number, only to 1, so a scaled or offset value would
+	// be wrong on every plan with every other assertion green.
+	it('reports a coarsening of exactly 1 when the budget is met', () => {
+		expect(interpolatedFrames(plans.linear).coarsening).toBe(1)
+		expect(interpolatedFrames(plans.freeSpace).coarsening).toBe(1)
+	})
+
+	it('reports coarsening as the factor the cap stretched each frame by', () => {
+		const budget = { degrees: 0.0001 }
+		const total = plans.linear
+			.slice(1)
+			.reduce((sum, step, index) => sum + segmentFrameCost(plans.linear[index]!, step, budget), 0)
+
+		expect(interpolatedFrames(plans.linear, budget).coarsening).toBeCloseTo(total / 2000, 6)
+	})
+
+	it.each([
+		['an empty plan', []],
+		['a single-step plan', [{ arm: [0] }]],
+	])('returns %s unchanged', (_label, planned) => {
+		expect(interpolatedFrames(planned).steps).toBe(planned)
+	})
+})
+
+/**
+ * `plan-gantry.json` is a 40 mm slide with the arm held still. Costed in radians it comes to 1,529
+ * frames, and a longer stroke alongside real arm motion collapses every arm segment to one frame.
+ */
+describe('a plan with a prismatic joint in it', () => {
+	/**
+	 * Exact, not a band: a band wide enough to read as sane accepts a millimetre budget anywhere from
+	 * 2 to 20. Ten and not nine because the stroke is `90.00000000000001 - 50`, which `Math.ceil`
+	 * rounds up.
+	 */
+	it('spends exactly the budgeted frames on a 40 mm slide', () => {
+		const { steps } = interpolatedFrames(plans.gantry, { motions: GANTRY_MOTIONS })
+
+		expect(steps).toHaveLength(10)
+	})
+
+	// The stroke and the arm motion in separate segments, which is where the damage is: read as
+	// radians, 500 mm is 28,648°, enough on its own to blow the frame cap and coarsen what follows.
+	it('lets the arm keep its own resolution when a long stroke shares the plan', () => {
+		const together: TrajectoryStep[] = [
+			{ 'arm-1': [0], 'gantry-1': [0] },
+			{ 'arm-1': [0], 'gantry-1': [500] },
+			{ 'arm-1': [(12 * Math.PI) / 180], 'gantry-1': [500] },
+		]
+
+		const { steps, waypoints } = interpolatedFrames(together, { motions: GANTRY_MOTIONS })
+		// `segmentDegrees` is unit-blind by design, so read the arm's column on its own.
+		const armDegrees = segmentDegrees(steps.map((step) => ({ 'arm-1': step['arm-1']! })))
+
+		expect(waypoints[2]! - waypoints[1]!).toBeGreaterThan(1)
+		expect(Math.max(...armDegrees)).toBeLessThanOrEqual(DEFAULT_DEGREES_PER_FRAME + 0.001)
+	})
+
+	it('reads an unlabelled joint as revolute', () => {
+		const unlabelled = interpolatedFrames(plans.gantry)
+		const labelled = interpolatedFrames(plans.gantry, { motions: GANTRY_MOTIONS })
+
+		expect(unlabelled.steps.length).toBeGreaterThan(labelled.steps.length)
+	})
+})
+
+describe('segmentFrameCost', () => {
+	it('costs a revolute joint by the degree budget', () => {
+		const cost = segmentFrameCost({ arm: [0] }, { arm: [Math.PI / 2] }, { degrees: 1.5 })
+		expect(cost).toBeCloseTo(60)
+	})
+
+	it('costs a prismatic joint by the millimetre budget', () => {
+		const motions: JointMotions = new Map([['gantry', ['translational'] as const]])
+		const cost = segmentFrameCost({ gantry: [0] }, { gantry: [40] }, { millimetres: 5, motions })
+
+		expect(cost).toBeCloseTo(8)
+	})
+
+	it('takes the costliest joint, so the two units never add up', () => {
+		const motions: JointMotions = new Map([['gantry', ['translational'] as const]])
+		const cost = segmentFrameCost(
+			{ arm: [0], gantry: [0] },
+			{ arm: [Math.PI / 2], gantry: [40] },
+			{ degrees: 1.5, millimetres: 5, motions }
+		)
+
+		expect(cost).toBeCloseTo(60)
+	})
+
+	// Every other prismatic assertion here passes `millimetres: 5`, which is the default, so ignoring
+	// the option entirely would look correct.
+	it('reads the millimetre budget rather than always defaulting it', () => {
+		const motions: JointMotions = new Map([['gantry', ['translational'] as const]])
+		const cost = segmentFrameCost({ gantry: [0] }, { gantry: [40] }, { millimetres: 20, motions })
+
+		expect(cost).toBeCloseTo(2)
+	})
+
+	it('costs a segment that moves nothing at zero', () => {
+		expect(segmentFrameCost({ arm: [1, 2] }, { arm: [1, 2] })).toBe(0)
+	})
+
+	it.each([
+		['zero', 0],
+		['negative', -1.5],
+		['NaN', Number.NaN],
+		['Infinity', Number.POSITIVE_INFINITY],
+	])('falls back to the default for a %s degree budget', (_label, degrees) => {
+		const from = { arm: [0] }
+		const to = { arm: [Math.PI / 2] }
+
+		expect(segmentFrameCost(from, to, { degrees })).toBe(segmentFrameCost(from, to))
+	})
+
+	it.each([
+		['zero', 0],
+		['NaN', Number.NaN],
+	])('falls back to the default for a %s millimetre budget', (_label, millimetres) => {
+		const motions: JointMotions = new Map([['gantry', ['translational'] as const]])
+		const from = { gantry: [0] }
+		const to = { gantry: [40] }
+
+		expect(segmentFrameCost(from, to, { millimetres, motions })).toBe(
+			segmentFrameCost(from, to, { motions })
+		)
+	})
+
+	it('still fills in a free-space plan when handed a zero budget', () => {
+		expect(interpolatedFrames(plans.freeSpace, { degrees: 0 }).steps.length).toBeGreaterThan(150)
+	})
+})
+
+// `constructor` and `__proto__` are legal RDK resource names. Only `lerpTrajectoryStep` is hurt; the
+// cost functions' joint guard absorbs a prototype value.
+describe('a component named like an Object.prototype member', () => {
+	const proto = (json: string) => JSON.parse(json) as TrajectoryStep
+
+	it.each(['constructor', 'toString', 'hasOwnProperty', '__proto__'])(
+		'costs a segment that drops %s without reading the prototype',
+		(name) => {
+			const from = proto(`{"arm": [0], ${JSON.stringify(name)}: []}`)
+			const to = proto('{"arm": [1]}')
+
+			expect(segmentFrameCost(from, to)).toBeCloseTo((1 * RAD_TO_DEG) / DEFAULT_DEGREES_PER_FRAME)
+			expect(jointTravelRadians(from, to)).toBeCloseTo(1)
+		}
+	)
+
+	it.each(['constructor', 'toString', 'hasOwnProperty'])('blends a plan containing %s', (name) => {
+		const from = proto(`{"arm": [0], ${JSON.stringify(name)}: []}`)
+		const to = proto('{"arm": [1]}')
+
+		const blended = lerpTrajectoryStep(from, to, 0.5)
+		expect(blended.arm).toEqual([0.5])
+		expect(blended[name]).toEqual([])
+	})
+
+	it('keeps a component named __proto__ as a key rather than a setter', () => {
+		const blended = lerpTrajectoryStep(
+			proto('{"__proto__": [0]}'),
+			proto('{"__proto__": [2]}'),
+			0.5
+		)
+
+		expect(Object.keys(blended)).toEqual(['__proto__'])
+		expect(blended['__proto__']).toEqual([1])
+	})
+
+	it('interpolates a plan containing one end to end', () => {
+		const planned = [proto('{"arm": [0], "constructor": []}'), proto('{"arm": [1]}')]
+		expect(interpolatedFrames(planned).steps.length).toBeGreaterThan(30)
+	})
+})
+
+describe('jointMotionsOf', () => {
+	const joint = (
+		componentName: string,
+		jointIndex: number,
+		motion: JointMotion,
+		mimic?: { multiplier: number; offset: number }
+	): FrameDescriptor => ({
+		kind: 'joint',
+		motion,
+		name: `${componentName}:joint-${jointIndex}`,
+		parent: 'world',
+		axis: { X: 0, Y: 0, Z: 1 },
+		componentName,
+		jointIndex,
+		mimic,
+		uuid: new Uint8Array(16) as Uint8Array<ArrayBuffer>,
+	})
+
+	it('indexes each joint the way a trajectory step does', () => {
+		const motions = jointMotionsOf([
+			joint('gantry', 0, 'translational'),
+			joint('arm', 1, 'rotational'),
+		])
+
+		expect(motions.get('gantry')).toEqual(['translational'])
+		expect(motions.get('arm')?.[1]).toBe('rotational')
+	})
+
+	// The tests around this one use a single joint per component, which leaves the accumulation
+	// untested: rebuilding the array rather than reading it back keeps only the last axis.
+	it('keeps every joint of a component, not just the last', () => {
+		const motions = jointMotionsOf([
+			joint('gantry', 0, 'translational'),
+			joint('gantry', 1, 'translational'),
+			joint('gantry', 2, 'translational'),
+		])
+
+		expect(motions.get('gantry')).toEqual(['translational', 'translational', 'translational'])
+	})
+
+	it('ignores frames that are not joints', () => {
+		const motions = jointMotionsOf([
+			{
+				kind: 'static',
+				name: 'table',
+				parent: 'world',
+				localPose: new Pose(),
+				geometry: null,
+				uuid: new Uint8Array(16) as Uint8Array<ArrayBuffer>,
+			},
+			joint('arm', 0, 'rotational'),
+		])
+
+		expect([...motions.keys()]).toEqual(['arm'])
+	})
+
+	// Both orders, because the winner is decided by frame-system key order: pinning only the order
+	// that happens to fail leaves half of it green.
+	it.each([
+		[
+			'source first',
+			[
+				joint('gantry', 0, 'translational'),
+				joint('gantry', 0, 'rotational', { multiplier: 1, offset: 0 }),
+			],
+		],
+		[
+			'mimic first',
+			[
+				joint('gantry', 0, 'rotational', { multiplier: 1, offset: 0 }),
+				joint('gantry', 0, 'translational'),
+			],
+		],
+	] as const)('lets the column owner win over a mimic of it, %s', (_label, descriptors) => {
+		expect(jointMotionsOf([...descriptors]).get('gantry')).toEqual(['translational'])
+	})
+
+	// 60 anchors the whole-plan consequence: the same slide costed in degrees is 1,529 frames.
+	it('spends a sane number of frames on a slide whose column is mimicked by a revolute joint', () => {
+		const motions = jointMotionsOf([
+			joint('gantry-1', 0, 'translational'),
+			joint('gantry-1', 0, 'rotational', { multiplier: 1, offset: 0 }),
+		])
+
+		expect(interpolatedFrames(plans.gantry, { motions }).steps.length).toBeLessThan(60)
+	})
+})
diff --git a/src/lib/motion/interpolateTrajectory.ts b/src/lib/motion/interpolateTrajectory.ts
new file mode 100644
index 000000000..3e0add129
--- /dev/null
+++ b/src/lib/motion/interpolateTrajectory.ts
@@ -0,0 +1,228 @@
+/**
+ * Turns a planned trajectory into frames to play back, allocating them in proportion to joint
+ * travel so playback reads at a constant speed whether the planner returned 2 waypoints or 225.
+ */
+
+import type { FrameDescriptor } from './frameDescriptors'
+import type { TrajectoryStep } from './jointPose'
+
+const RAD_TO_DEG = 180 / Math.PI
+
+/**
+ * Joint degrees per frame. At the preview's frame interval this works out to a plausible arm speed,
+ * which is the only claim being made — the real duration is unknowable from a trajectory.
+ */
+export const DEFAULT_DEGREES_PER_FRAME = 1.5
+
+/**
+ * Millimetres per frame: the arc {@link DEFAULT_DEGREES_PER_FRAME} sweeps at a 191 mm mid-link
+ * radius. Erring short only over-samples a prismatic axis; erring long under-samples it into a jump.
+ */
+export const DEFAULT_MILLIMETRES_PER_FRAME = 5
+
+/** How a joint's values are measured — the same two kinds a `JointFrameDescriptor` distinguishes. */
+export type JointMotion = 'rotational' | 'translational'
+
+/**
+ * Which joints are prismatic, indexed the way a trajectory step is: `motions.get('gantry')[0]`.
+ * Anything absent reads as rotational, which is what every joint in the captured plans is.
+ */
+export type JointMotions = ReadonlyMap<string, readonly JointMotion[]>
+
+export interface FrameBudget {
+	/** Degrees of revolute travel one frame represents. */
+	degrees?: number
+	/** Millimetres of prismatic travel one frame represents. */
+	millimetres?: number
+	motions?: JointMotions
+}
+
+/**
+ * The joint kinds a plan's descriptors describe, in the shape {@link FrameBudget} wants. Mimics are
+ * skipped: a mimic's `jointIndex` addresses its source's column, so its motion would mislabel it.
+ */
+export const jointMotionsOf = (descriptors: readonly FrameDescriptor[]): JointMotions => {
+	const motions = new Map<string, JointMotion[]>()
+
+	for (const descriptor of descriptors) {
+		if (descriptor.kind !== 'joint' || descriptor.mimic) continue
+
+		const kinds = motions.get(descriptor.componentName) ?? []
+		kinds[descriptor.jointIndex] = descriptor.motion
+		motions.set(descriptor.componentName, kinds)
+	}
+
+	return motions
+}
+
+/**
+ * Backstop for a plan beyond anything observed; the worst real plan came to 236 frames. It bounds
+ * interpolation only, since every planned waypoint keeps its own frame whatever this is set to.
+ */
+const MAX_INTERPOLATED_FRAMES = 2000
+
+export interface PreviewFrames {
+	/** What to render, in order. Contains every planned waypoint, plus any frames added between. */
+	steps: TrajectoryStep[]
+	/**
+	 * Where each planned waypoint landed in `steps`. Always starts at 0 and ends at the last index,
+	 * so a scrubber can mark which frames are real data and which are drawn between them.
+	 */
+	waypoints: number[]
+	/**
+	 * How much the cap stretched each frame: 1 when the requested budget was met, higher when a plan
+	 * long enough to exceed {@link MAX_INTERPOLATED_FRAMES} had to be coarsened to fit.
+	 */
+	coarsening: number
+}
+
+/**
+ * The largest single-joint change between two steps, unit-blind and with no production caller: the
+ * spec measures captured plans against it, while {@link segmentFrameCost} budgets the frames.
+ */
+export const jointTravelRadians = (from: TrajectoryStep, to: TrajectoryStep): number => {
+	let worst = 0
+
+	for (const [component, start] of Object.entries(from)) {
+		const end = to[component]
+		if (!end) continue
+
+		for (const [index, value] of start.entries()) {
+			const target = end[index]
+			if (target === undefined) continue
+			worst = Math.max(worst, Math.abs(target - value))
+		}
+	}
+
+	return worst
+}
+
+/**
+ * `from` and `to` blended at `t`, over the union of both steps' components. Not angle-aware: RDK
+ * collision-checks with this same expression, so wrapping would draw a path it never validated.
+ */
+export const lerpTrajectoryStep = (
+	from: TrajectoryStep,
+	to: TrajectoryStep,
+	t: number
+): TrajectoryStep => {
+	// `constructor` and `__proto__` are legal RDK resource names. On a plain object the first reads a
+	// function off the prototype and the second hits the prototype setter, so neither stays data.
+	const blended = Object.create(null) as TrajectoryStep
+
+	for (const component of new Set([...Object.keys(from), ...Object.keys(to)])) {
+		const start = Object.hasOwn(from, component) ? from[component] : undefined
+		const end = Object.hasOwn(to, component) ? to[component] : undefined
+
+		if (!start) {
+			if (end) blended[component] = [...end]
+			continue
+		}
+		if (!end) {
+			blended[component] = [...start]
+			continue
+		}
+
+		blended[component] = start.map((value, index) => {
+			const target = end[index]
+			return target === undefined ? value : value + (target - value) * t
+		})
+
+		// A component that gained joints between steps would otherwise lose them here.
+		if (end.length > start.length) blended[component].push(...end.slice(start.length))
+	}
+
+	return blended
+}
+
+/**
+ * A budget figure that can be divided by, or the default. `?? fallback` only catches null and
+ * undefined: a zero pins every plan to the frame cap, and a `NaN` collapses every segment to one
+ * frame.
+ */
+const perFrame = (value: number | undefined, fallback: number): number =>
+	value !== undefined && Number.isFinite(value) && value > 0 ? value : fallback
+
+/**
+ * What a segment costs in frames: each joint's change over the budget for its own kind, largest
+ * quotient wins. Normalizing before the max is the point: a raw max lets a millimetre outweigh a
+ * radian 57×.
+ */
+export const segmentFrameCost = (
+	from: TrajectoryStep,
+	to: TrajectoryStep,
+	budget: FrameBudget = {}
+): number => {
+	const degrees = perFrame(budget.degrees, DEFAULT_DEGREES_PER_FRAME)
+	const millimetres = perFrame(budget.millimetres, DEFAULT_MILLIMETRES_PER_FRAME)
+
+	let worst = 0
+
+	for (const [component, start] of Object.entries(from)) {
+		const end = to[component]
+		if (!end) continue
+		const kinds = budget.motions?.get(component)
+
+		for (const [index, value] of start.entries()) {
+			const target = end[index]
+			if (target === undefined) continue
+
+			const delta = Math.abs(target - value)
+			const cost =
+				kinds?.[index] === 'translational' ? delta / millimetres : (delta * RAD_TO_DEG) / degrees
+			worst = Math.max(worst, cost)
+		}
+	}
+
+	return worst
+}
+
+/** One frame per planned waypoint — the trajectory exactly as the planner returned it. */
+export const waypointFrames = (trajectory: TrajectoryStep[]): PreviewFrames => ({
+	steps: trajectory,
+	waypoints: trajectory.map((_, index) => index),
+	coarsening: 1,
+})
+
+/**
+ * Frames spread across `trajectory` at roughly one budget's worth of joint travel each. A segment
+ * shorter than that, a zero-length one included, still gets its frame from `steps.push(to)` below.
+ */
+export const interpolatedFrames = (
+	trajectory: TrajectoryStep[],
+	budget: FrameBudget = {}
+): PreviewFrames => {
+	if (trajectory.length < 2) return waypointFrames(trajectory)
+
+	const travel: number[] = []
+	let total = 0
+	for (let step = 1; step < trajectory.length; step += 1) {
+		const segment = segmentFrameCost(trajectory[step - 1]!, trajectory[step]!, budget)
+		travel.push(segment)
+		total += segment
+	}
+
+	// Coarsen rather than truncate: every segment still gets its frames, just fewer of them.
+	const resolution = Math.max(1, total / MAX_INTERPOLATED_FRAMES)
+
+	const steps: TrajectoryStep[] = [trajectory[0]!]
+	const waypoints: number[] = [0]
+
+	for (const [index, segment] of travel.entries()) {
+		const from = trajectory[index]!
+		const to = trajectory[index + 1]!
+		// `max(1, …)` keeps this a usable divisor below rather than granting the minimum frame, which
+		// `steps.push(to)` already does — a zero-length segment would otherwise `ceil` to 0.
+		const divisions = Math.max(1, Math.ceil(segment / resolution))
+
+		// The segment's own start is already in `steps` as the previous segment's end, so this walks
+		// the interior and finishes on `to` exactly rather than on a blend that rounds to it.
+		for (let division = 1; division < divisions; division += 1) {
+			steps.push(lerpTrajectoryStep(from, to, division / divisions))
+		}
+		steps.push(to)
+		waypoints.push(steps.length - 1)
+	}
+
+	return { steps, waypoints, coarsening: resolution }
+}