fix(client): the deep rungs were flat because relief_q fell off the wire (T-1213)

`relief_q` is the one field with signal below District — elev_q's 80 m steps
quantise sub-district detail away, which is precisely why relief_q was invented.
The server has encoded it since 5eb394b36 and the terrain layer has asked for it
by name ever since. step_canvas_protocol.gd's decode dictionary never listed the
key, so `canvas.get("relief_q")` was always null and the plane arrived nowhere.
The server half of that change landed; the protocol half did not.

That is the whole reason Region and below rendered as a flat wash. Measured plane
variety at District before the fix:

    {morphology: 1, elev_q: 11, relief_q: 0, moisture_q: 25, vegetation: 3}

A 0 there means ABSENT, not constant — a distinction the capture could not make
until this commit adds it, and the reason two earlier sessions read the flatness
as a missing generator rather than a missing key.

Also spends the field properly. It drove a stipple PROBABILITY only, so a ridge
and a plain differed in dot density, which at one pixel per cell reads as noise;
and `_ruggedness()` took absf(relief_q - 50), discarding the sign the server
deliberately preserved ("a hollow and a rise are different ground... the reverse
is not recoverable"). Relief now shades continuously and signed — rises lighten,
hollows darken — UNDER the stipple rather than instead of it. Ruggedness
(unsigned) and elevation (signed) are different questions and both are worth
asking.

Ladder, before -> after (tooling/atlas-flatness, lum p1-p99):

    Global    145.69 -> 145.69   unchanged, correct: relief_q is flat 50 at
                                 orbital rungs by construction
    Region     33.59 ->  71.01   2.1x
    District   13.72 ->  77.01   5.6x
    Quarter    11.01 ->  42.56   3.9x

Structure retention Global->Quarter: 7.6% -> 29%.

NOT finished, and the ticket says so: Region now reads as heavy speckle, because
ruggedness is real data instead of an elev_q-gradient fallback and far more cells
earn a mark than the T-1194 tuning assumed; District reads as soft blobby relief,
form without directionality. Both are grammar/tuning follow-ups on a channel that
finally carries signal.

0.4.9 is a REQUIRED bump. The disk cache stores the DECODED canvas, so every
earlier entry physically lacks the field and would keep rendering flat against a
build that reads it — the first bump in this series where a warm cache is wrong
about CONTENT, not merely stale. tooling/canvas_sources.py gains
step_canvas_protocol.gd for the same reason: it decides which planes exist, the
cache stores its output, and the T-1242 gate would not have flagged this fix
while the registry stopped at ui/.../step_canvas/.

Regression cover: every protocol test passed throughout the weeks the plane was
missing, because each asserted a field it already knew about and none asserted
the SET. There is now a test walking all eight dense planes of EncodedStepCanvas,
verified by disabling the fix and watching it fail by name.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

client/tests/test_step_canvas_protocol.gd

@@ -176,6 +176,55 @@ func test_decode_encoded_canvas_passes_through_temp_dc_and_settlement_id_as_arra
 	assert_that(canvas["settlement_id"]).is_equal([0, 7])
 
 
+## T-1213 REGRESSION. `relief_q` shipped server-side, the terrain layer asked for
+## it by name, and this decode never listed the key — so the plane the deep rungs
+## exist to draw arrived nowhere for weeks, and District rendered as a flat wash.
+## Every test here passed throughout, because each asserted a field it already
+## knew about; none asserted the SET.
+##
+## So this one is written against the wire contract rather than against a list of
+## fields someone remembered: every dense plane the server encodes must survive
+## the decode. Adding a plane to EncodedStepCanvas without adding it here now
+## fails loudly instead of rendering as "that rung is just flat".
+func test_decode_encoded_canvas_carries_every_dense_plane() -> void:
+	# The eight PNG-per-field planes of EncodedStepCanvas (step_canvas.rs).
+	var planes := [
+		"morphology",
+		"elev_q",
+		"moisture_q",
+		"vegetation",
+		"lake_margin_q",
+		"relief_q",
+		"glaciation",
+		"flooded_q",
+	]
+	var canvas_in := {"width": 1, "height": 1, "temp_dc": {"values": [0]}}
+	for plane: String in planes:
+		# A one-pixel L8 PNG payload in the array-of-ints shape the wire uses.
+		canvas_in[plane] = {"png_bytes": [137, 80, 78, 71]}
+	var raw := {
+		"body_id": "GJ380c",
+		"rung": "District",
+		"status": "Ready",
+		"canvas": canvas_in,
+	}
+
+	var decoded = Protocol.step_canvas_response_from_raw(raw)
+	var canvas: Dictionary = decoded["canvas"]
+	for plane: String in planes:
+		assert_bool(canvas.has(plane)).override_failure_message(
+			(
+				"decoded canvas is missing the '%s' plane — the server encodes it and "
+				+ "the renderer reads it, so a missing key here renders as a flat rung "
+				+ "rather than as an error (T-1213)"
+			)
+			% plane
+		).is_true()
+		assert_that(canvas[plane]).override_failure_message(
+			"plane '%s' decoded to null rather than bytes" % plane
+		).is_not_null()
+
+
 func test_decode_encoded_canvas_passes_through_courses_and_cliffs_unshaped() -> void:
 	var courses := [{"edge_id": 1, "class": 2, "points": [[0, 0], [100, 100]], "terminus": "Mouth"}]
 	var cliffs := [{"point": [5, 5], "channel_depth_dm": 10, "cliff_edge": true}]

client/tests/visual_capture.gd

@@ -335,7 +335,7 @@ func _log_atlas_view_transform(tree_root: Node, scenario_name: String) -> void:
 		(
 			"visual_capture: view-transform[%s] rung=%s world_center=%s held_extent=%s "
 			+ "canvas_position=%s canvas_scale=%s footprint_px=%s canvas_cells=%dx%d "
-			+ "courses=%d runs=%d longest=%.1fpx drawn=%d settlements=%d"
+			+ "courses=%d runs=%d longest=%.1fpx drawn=%d settlements=%d planes=%s"
 		)
 		% [
 			scenario_name,
@@ -352,6 +352,7 @@ func _log_atlas_view_transform(tree_root: Node, scenario_name: String) -> void:
 			float(summary.get("longest_run_px", 0.0)),
 			int(summary.get("drawn_course_count", 0)),
 			int(summary.get("settlement_count", 0)),
+			str(summary.get("plane_variety", {})),
 		]
 	)