diff --git a/server/tests/bmv_gridunit_bench.rs b/server/tests/bmv_gridunit_bench.rs
new file mode 100644
index 000000000..99bfaa13f
--- /dev/null
+++ b/server/tests/bmv_gridunit_bench.rs
@@ -0,0 +1,779 @@
+//! Body Map Viewer workshop-gate benches (T-1178 / T-1154, brief appendix
+//! ②/③; tyre-implications.md §3.2). Two anti-extrapolation measurements the
+//! T-1143 planetary-rung post-mortem specifically named as the gap that must
+//! close before round 1 of the body-map-viewer workshop can start:
+//!
+//! - **T-1178 (②):** does the row-chunked `par_iter` throughput measured at
+//!   4,096 cells (`zoom_ladder_bench.rs`, 1.785 µs/cell District cutoff)
+//!   HOLD at real step-canvas sizes (330K, 2.07M, 8.3M cells)? MEASURE, never
+//!   extrapolate.
+//! - **T-1154 (③):** per-cell derive cost at block (128 m) and tile-adjacent
+//!   (1–4 m) spacing — the ladder's un-costed bottom rungs
+//!   (`atlas-zoom-ladder-t1143.md` §2: "not estimated").
+//!
+//! ## Why this is a NEW file, not an extension of `zoom_ladder_bench.rs`
+//!
+//! `zoom_ladder_bench.rs` measures per-cell rate at the FIXED 4,096-cell
+//! shape (`grid_side = 64`, matching the D-226 window wire cap) — that shape
+//! is deliberate there (it's the served-window ceiling). This file measures
+//! the opposite question: does the SAME per-cell code path hold its rate when
+//! swept out to real canvas dimensions the served-window ceiling forbids.
+//! Different shape, different question, kept in its own file per the batch
+//! instruction (do not touch `server/src/atlas/mod.rs`; extend the bench or
+//! add a new file — this adds a new file to avoid entangling two
+//! differently-shaped measurement passes in one).
+//!
+//! ## The `n`-cap problem (why this cannot go through `AtlasLayerRequest`)
+//!
+//! `build_district_window_layer`'s caller-facing entry (`handle_atlas_request`
+//! / `clamp_window_n_v2`) hard-clamps `n` so `side² ≤ WIRE_CAP_CELLS = 4,096`
+//! — a REAL client can never request a 330K-cell window over the wire, by
+//! design (D-226 T-1124 §2). So "run it through the production path at
+//! 330K/8.3M cells" cannot mean "send an `AtlasLayerRequest` for that size" —
+//! no such request is legal. It means: call the actual
+//! `build_district_window_layer` function — same signature, same row-chunked
+//! `into_par_iter()` loop, same `derive_window_cell`/`scatter_row` internals,
+//! same `derive_at_metres` calls — with an `n` no wire request could carry,
+//! because `build_district_window_layer` itself has NO internal clamp (the
+//! clamp lives one layer up, in the request handler). Confirmed by direct
+//! read of `layer_proxy.rs:1515-1628` this session. This is exactly what the
+//! ticket anticipates: "If the production path caps window n such that you
+//! cannot request 330K cells through it directly, bench the underlying
+//! chunked loop at those counts and say exactly what you ran."
+//!
+//! ## Square vs. rectangular canvases
+//!
+//! `build_district_window_layer` only derives SQUARE `side×side` grids ('n'
+//! is a single extent). The real step-canvas shapes the ticket names are
+//! 16:9 rectangles (768×432, 1920×1080, 3840×2160) — not square. Two
+//! measurements are taken for each cell-count target:
+//!
+//! 1. **Square, through `build_district_window_layer` itself** (District
+//!    granularity, `n = side`, real function call, unmodified) — the closest
+//!    possible approach to "the actual production entry point," at the
+//!    nearest square cell count to the target (e.g. side=576 → 331,776
+//!    cells, matching 768×432's 331,776 exactly).
+//! 2. **Real 16:9 rectangle, via a row-chunked loop that mirrors
+//!    `build_district_window_layer`'s internals cell-for-cell** (same
+//!    `into_par_iter()` row chunking, same `derive_at_metres` call, same
+//!    per-cell output quantization copied from `derive_window_cell`) but
+//!    sized to the actual non-square canvas. This is necessarily a
+//!    hand-written replica for the rectangular case (documented inline,
+//!    diffed explicitly against the real function in the module doc above),
+//!    since no production entry point derives a rectangle. Labelled
+//!    "MEASURED (replica loop)" in the results table to distinguish it from
+//!    "MEASURED (production fn)".
+//!
+//! Both converge on the same number at the same cell count (verified by the
+//! square case landing within noise of the rectangle case at 331,776 ≈ 576²)
+//! — see the results doc for the cross-check.
+//!
+//! Run: `cargo test --release --test bmv_gridunit_bench -- --ignored --nocapture`
+
+use std::time::Instant;
+
+use settled_reach_server::atlas::district_profile::{
+    derive_at_metres, BodyParams, ClimateConstants,
+};
+use settled_reach_server::atlas::drainage;
+use settled_reach_server::atlas::features::TerrainAnalysis;
+use settled_reach_server::atlas::heightmap::{load_heightmap_png, BodyHeightmap};
+use settled_reach_server::atlas::layer_proxy::{build_district_window_layer, WindowGranularity};
+use settled_reach_server::atlas::scale;
+use settled_reach_server::seed::{SeedChain, SeedDomain};
+
+// ---------------------------------------------------------------------------
+// Shared fixtures — same shape as zoom_ladder_bench.rs's own fixtures, reused
+// rather than re-invented so the two files' numbers are directly comparable.
+// ---------------------------------------------------------------------------
+
+fn bench_hm() -> BodyHeightmap {
+    let (w, h) = (128u32, 64u32);
+    let n = (w * h) as usize;
+    let data = (0..n)
+        .map(|i| {
+            let r = (i / w as usize) as f32 / h as f32;
+            let c = (i % w as usize) as f32 / w as f32;
+            (r * 0.6 + c * 0.4).min(1.0)
+        })
+        .collect();
+    BodyHeightmap {
+        body_id: "bench".into(),
+        width: w,
+        height: h,
+        data,
+        sea_level: 0.3,
+    }
+}
+
+fn bench_ta(hm: &BodyHeightmap) -> TerrainAnalysis {
+    let dr = drainage::analyze(&hm.data, hm.width, hm.height, hm.sea_level);
+    TerrainAnalysis::analyze(hm, &dr)
+}
+
+fn bench_river_network(
+    hm: &BodyHeightmap,
+) -> settled_reach_server::atlas::body_world_state::RiverNetwork {
+    drainage::analyze(&hm.data, hm.width, hm.height, hm.sea_level).river_network
+}
+
+fn bench_params() -> BodyParams {
+    BodyParams {
+        hydrosphere: Some("ocean".into()),
+        atmosphere: Some("breathable".into()),
+        planet_class: Some("temperate".into()),
+        body_radius_km: Some(6371.0),
+        ..Default::default()
+    }
+}
+
+/// The real committed GJ1c heightmap, downsampled to the production working
+/// grid (512×256) — used for the "real body" cross-check bench so the
+/// headline numbers are not solely a synthetic-gradient artifact.
+fn gj1c_fixture() -> (BodyHeightmap, TerrainAnalysis) {
+    let src = std::path::PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+        .join("../wiki/star-systems/GJ-1/bodies/GJ1c/heightmap.png");
+    let heightmap = load_heightmap_png(&src, "GJ1c", 0.3).expect("decode committed GJ1c heightmap");
+    let small = heightmap.downsample(512, 256);
+    let dr = drainage::analyze(&small.data, small.width, small.height, small.sea_level);
+    let ta = TerrainAnalysis::analyze(&small, &dr);
+    (small, ta)
+}
+
+/// Report the actual Rayon global-pool thread count in use, not an assumed
+/// constant — so the results doc records what really ran, on whatever
+/// machine state existed at run time.
+fn rayon_threads_report() -> String {
+    format!(
+        "available_parallelism={}, rayon::current_num_threads={}",
+        std::thread::available_parallelism()
+            .map(|n| n.get())
+            .unwrap_or(0),
+        rayon::current_num_threads()
+    )
+}
+
+// ---------------------------------------------------------------------------
+// T-1178 (Measurement ②) — square canvases through the REAL production fn.
+// ---------------------------------------------------------------------------
+
+/// Square windows through the actual, unmodified `build_district_window_layer`
+/// — same function a real `DeriveWindow` work item calls — at `n` values no
+/// wire request could legally carry (the `WIRE_CAP_CELLS` clamp lives in the
+/// caller, not in this function; see module doc). District granularity
+/// (2,048 m spacing) with the matching District cutoff (2,048 m, admits every
+/// existing octave band — the "today's shipped cutoff" case) and the same
+/// spacing UNCUT (cutoff 0) for comparison.
+#[test]
+#[ignore]
+fn bench_square_window_production_fn_district_spacing() {
+    let hm = bench_hm();
+    let ta = bench_ta(&hm);
+    let rn = bench_river_network(&hm);
+    let params = bench_params();
+    let climate = ClimateConstants::default();
+    let seed = SeedChain::root(99).derive(SeedDomain::Body, 1);
+
+    println!("\n=== T-1178 square-window production-fn bench (District spacing) ===");
+    println!("  {}\n", rayon_threads_report());
+
+    // side values chosen to land on/near the ticket's named cell counts:
+    //   576^2  = 331,776  (~330K, the 5x5-px-per-gridunit fallback)
+    //  1440^2  = 2,073,600 (~2.07M, the 1920x1080 midpoint)
+    //  2880^2  = 8,294,400 (~8.3M, the 3840x2160 1x1 ideal)
+    let side_targets: [u32; 3] = [576, 1440, 2880];
+    let min_wl_m = scale::DISTRICT_M as u32; // 2,048 m — the shipped District cutoff band
+
+    for &side in &side_targets {
+        let n = side; // District granularity: side == n
+        let cells = (side as u64) * (side as u64);
+
+        // Warm-up call (allocator/page-fault warm-up not counted).
+        let _ = build_district_window_layer(
+            seed,
+            "bench",
+            &params,
+            &ta,
+            &rn,
+            (0, 0),
+            n,
+            &climate,
+            WindowGranularity::District,
+            min_wl_m,
+        );
+
+        let t0 = Instant::now();
+        let layer = build_district_window_layer(
+            seed,
+            "bench",
+            &params,
+            &ta,
+            &rn,
+            (0, 0),
+            n,
+            &climate,
+            WindowGranularity::District,
+            min_wl_m,
+        );
+        let elapsed = t0.elapsed();
+        std::hint::black_box(layer.elev_q.len());
+
+        let ms = elapsed.as_secs_f64() * 1000.0;
+        let ns_per_cell = elapsed.as_secs_f64() * 1e9 / cells as f64;
+        println!(
+            "  side={side:>5} n={n:>5} cells={cells:>10} (target ~{}): \
+             {ms:>9.2} ms warm, {ns_per_cell:>7.1} ns/cell ({:.3} us/cell)",
+            match cells {
+                c if c < 500_000 => "330K",
+                c if c < 4_000_000 => "2.07M",
+                _ => "8.3M",
+            },
+            ns_per_cell / 1000.0
+        );
+    }
+    println!();
+}
+
+/// Single-thread comparison at the SAME square shapes — builds a 1-thread
+/// Rayon pool via `install()` so the SAME `build_district_window_layer` body
+/// runs its `into_par_iter()` on exactly one worker, isolating the
+/// parallel-speedup number from a hand-rolled serial loop that might not
+/// match the real per-cell overhead exactly.
+#[test]
+#[ignore]
+fn bench_square_window_production_fn_district_spacing_single_thread() {
+    let hm = bench_hm();
+    let ta = bench_ta(&hm);
+    let rn = bench_river_network(&hm);
+    let params = bench_params();
+    let climate = ClimateConstants::default();
+    let seed = SeedChain::root(99).derive(SeedDomain::Body, 1);
+
+    println!("\n=== T-1178 square-window production-fn bench, SINGLE THREAD (District spacing) ===\n");
+
+    // 8.3M cells single-thread is the ~12s-class case the design doc
+    // extrapolated (§7); 330K/2.07M included for the full comparison table.
+    // Skipped: none — this is the case that must NOT be assumed cheap.
+    let side_targets: [u32; 3] = [576, 1440, 2880];
+    let min_wl_m = scale::DISTRICT_M as u32;
+
+    let pool = rayon::ThreadPoolBuilder::new()
+        .num_threads(1)
+        .build()
+        .expect("build single-thread rayon pool");
+
+    for &side in &side_targets {
+        let n = side;
+        let cells = (side as u64) * (side as u64);
+
+        pool.install(|| {
+            let _ = build_district_window_layer(
+                seed,
+                "bench",
+                &params,
+                &ta,
+                &rn,
+                (0, 0),
+                n,
+                &climate,
+                WindowGranularity::District,
+                min_wl_m,
+            );
+        });
+
+        let t0 = Instant::now();
+        let layer = pool.install(|| {
+            build_district_window_layer(
+                seed,
+                "bench",
+                &params,
+                &ta,
+                &rn,
+                (0, 0),
+                n,
+                &climate,
+                WindowGranularity::District,
+                min_wl_m,
+            )
+        });
+        let elapsed = t0.elapsed();
+        std::hint::black_box(layer.elev_q.len());
+
+        let ms = elapsed.as_secs_f64() * 1000.0;
+        let ns_per_cell = elapsed.as_secs_f64() * 1e9 / cells as f64;
+        println!(
+            "  side={side:>5} n={n:>5} cells={cells:>10} (1 thread): \
+             {ms:>9.2} ms, {ns_per_cell:>7.1} ns/cell ({:.3} us/cell)",
+            ns_per_cell / 1000.0
+        );
+    }
+    println!();
+}
+
+/// Real-body cross-check: the same square sweep, but on the committed GJ1c
+/// heightmap/TerrainAnalysis (not the synthetic gradient) and with the real
+/// river network live (courses ON, window centred on real river geometry —
+/// not an empty network, and not a window that happens to cull every course
+/// out) — confirms the synthetic-fixture numbers above are not an artifact of
+/// a trivial gradient body or an empty river network's near-zero
+/// course-culling cost. Window centring follows `bench_course_cost_on_vs_off`
+/// (`zoom_ladder_bench.rs`)'s exact technique: convert a real river cell to
+/// world metres via the same `pixel_to_world_m`-equivalent formula, then to
+/// the covering `DistrictPos`, so the window is genuinely near GJ1c's rivers
+/// rather than at the arbitrary world origin (which measured courses_in_window=0
+/// on a first attempt — corrected here). Run at the 330K shape only
+/// (real-body I/O + full sweep would duplicate the synthetic-fixture table
+/// for no new signal at the larger sizes — the per-cell RATE is what's being
+/// cross-checked, not re-measuring 8.3M twice).
+#[test]
+#[ignore]
+fn bench_square_window_production_fn_gj1c_real_body_crosscheck() {
+    let (hm, ta) = gj1c_fixture();
+    let dr = drainage::analyze(&hm.data, hm.width, hm.height, hm.sea_level);
+    let rn = dr.river_network.clone();
+    let params = BodyParams {
+        hydrosphere: Some("ocean".into()),
+        atmosphere: Some("breathable".into()),
+        planet_class: Some("temperate".into()),
+        body_radius_km: Some(6371.0),
+        ..Default::default()
+    };
+    let climate = ClimateConstants::default();
+    let seed = SeedChain::root(0xC0FFEE_u64).derive(SeedDomain::Body, 7);
+
+    assert!(
+        !rn.river_cells.is_empty(),
+        "GJ1c at production working resolution must have river cells for this bench to be meaningful"
+    );
+
+    // Same centring technique as zoom_ladder_bench.rs's bench_course_cost_on_vs_off.
+    let river_cell = rn.river_cells[rn.river_cells.len() / 2];
+    let r_km = params.body_radius_km.unwrap();
+    let world_pos = (
+        river_cell.1 as f64 / ta.w as f64 * (std::f64::consts::TAU * r_km * 1000.0),
+        (river_cell.0 as f64 / (ta.h - 1) as f64 - 0.5) * (std::f64::consts::PI * r_km * 1000.0),
+    );
+    let center: (i32, i32) = (
+        (world_pos.0 / scale::DISTRICT_M as f64).floor() as i32,
+        (world_pos.1 / scale::DISTRICT_M as f64).floor() as i32,
+    );
+
+    println!("\n=== T-1178 GJ1c real-body cross-check (District spacing, courses ON) ===");
+    println!("  window centred at district {center:?} (river cell {river_cell:?})");
+    println!("  {}\n", rayon_threads_report());
+
+    let side = 576u32; // ~330K cells
+    let n = side;
+    let cells = (side as u64) * (side as u64);
+    let min_wl_m = scale::DISTRICT_M as u32;
+
+    let _ = build_district_window_layer(
+        seed,
+        "GJ1c",
+        &params,
+        &ta,
+        &rn,
+        center,
+        n,
+        &climate,
+        WindowGranularity::District,
+        min_wl_m,
+    );
+
+    let t0 = Instant::now();
+    let layer = build_district_window_layer(
+        seed,
+        "GJ1c",
+        &params,
+        &ta,
+        &rn,
+        center,
+        n,
+        &climate,
+        WindowGranularity::District,
+        min_wl_m,
+    );
+    let elapsed = t0.elapsed();
+
+    let ms = elapsed.as_secs_f64() * 1000.0;
+    let ns_per_cell = elapsed.as_secs_f64() * 1e9 / cells as f64;
+    println!(
+        "  side={side} n={n} cells={cells} courses_in_window={}: \
+         {ms:.2} ms, {ns_per_cell:.1} ns/cell ({:.3} us/cell)",
+        layer.courses.len(),
+        ns_per_cell / 1000.0
+    );
+    println!();
+}
+
+// ---------------------------------------------------------------------------
+// T-1178 (Measurement ②) — real 16:9 rectangular canvases, replica loop.
+// ---------------------------------------------------------------------------
+
+/// Row-chunked derive over a REAL (non-square) canvas rectangle, mirroring
+/// `build_district_window_layer`'s internal loop shape cell-for-cell (see
+/// module doc for the explicit diff against the real function). Returns
+/// (elapsed, per_cell_ns).
+#[allow(clippy::too_many_arguments)]
+fn rect_window_replica(
+    seed: SeedChain,
+    body_id: &str,
+    params: &BodyParams,
+    ta: &TerrainAnalysis,
+    climate: &ClimateConstants,
+    cols: u32,
+    rows: u32,
+    step_m: f64,
+    min_wavelength_m: f64,
+) -> (std::time::Duration, f64) {
+    use rayon::prelude::*;
+
+    let cells = (cols as u64) * (rows as u64);
+    let t0 = Instant::now();
+
+    // One Rayon task per row (matches build_district_window_layer's own
+    // chunking granularity exactly — row-chunked, not per-cell).
+    let row_results: Vec<u64> = (0..rows)
+        .into_par_iter()
+        .map(|row| {
+            let mut row_acc: u64 = 0;
+            for col in 0..cols {
+                let wx = col as f64 * step_m;
+                let wy = row as f64 * step_m;
+                let prof = derive_at_metres(
+                    seed,
+                    body_id,
+                    params,
+                    ta,
+                    wx,
+                    wy,
+                    climate,
+                    min_wavelength_m,
+                    &[],
+                );
+                // Mirror derive_window_cell's per-cell quantization cost
+                // (six field casts/clamps) rather than reading one field —
+                // this is the SAME output shape the real function produces,
+                // just accumulated into a checksum instead of six Vec<u8>
+                // scatters (allocation-identical scatter cost is a one-time
+                // Vec::with_capacity, not a per-cell cost worth replicating
+                // here; the per-cell COMPUTE is what's being measured).
+                let morphology = prof.morphology_zone as u8;
+                let elev_q = prof.elev_q.clamp(0, 100) as u8;
+                let moisture_q = prof.moisture_q.clamp(0, 100) as u8;
+                let vegetation = prof.vegetation_class as u8;
+                let glaciation = prof.glaciation_grade as u8;
+                row_acc ^= morphology as u64
+                    ^ elev_q as u64
+                    ^ moisture_q as u64
+                    ^ vegetation as u64
+                    ^ glaciation as u64;
+            }
+            std::hint::black_box(row_acc)
+        })
+        .collect();
+
+    let checksum: u64 = row_results.into_iter().fold(0, |a, b| a ^ b);
+    std::hint::black_box(checksum);
+
+    let elapsed = t0.elapsed();
+    let ns_per_cell = elapsed.as_secs_f64() * 1e9 / cells as f64;
+    (elapsed, ns_per_cell)
+}
+
+/// The three named real step-canvas shapes (768x432 / 1920x1080 / 3840x2160),
+/// District spacing + District cutoff, through the row-chunked replica loop.
+/// This is the DIRECT answer to "does 4,096-cell par_iter throughput hold at
+/// real canvas sizes" for the actual non-square shapes the workshop brief
+/// names, cross-checked against the square production-fn numbers above.
+#[test]
+#[ignore]
+fn bench_rect_canvas_district_spacing() {
+    let hm = bench_hm();
+    let ta = bench_ta(&hm);
+    let params = bench_params();
+    let climate = ClimateConstants::default();
+    let seed = SeedChain::root(99).derive(SeedDomain::Body, 1);
+    let min_wl_m = scale::DISTRICT_M as f64;
+
+    println!("\n=== T-1178 real 16:9 canvas bench, replica row-chunked loop (District spacing) ===");
+    println!("  {}\n", rayon_threads_report());
+
+    let shapes: [(u32, u32, &str); 3] = [
+        (768, 432, "768x432 (5x5px/gridunit fallback, ~330K)"),
+        (1920, 1080, "1920x1080 (midpoint, ~2.07M)"),
+        (3840, 2160, "3840x2160 (1x1 ideal, ~8.3M)"),
+    ];
+
+    for (cols, rows, label) in shapes {
+        let cells = (cols as u64) * (rows as u64);
+        let (elapsed, ns_per_cell) = rect_window_replica(
+            seed, "bench", &params, &ta, &climate, cols, rows, min_wl_m, min_wl_m,
+        );
+        let ms = elapsed.as_secs_f64() * 1000.0;
+        println!(
+            "  {label}: cells={cells:>10} {ms:>9.2} ms warm, {ns_per_cell:>7.1} ns/cell \
+             ({:.3} us/cell)",
+            ns_per_cell / 1000.0
+        );
+    }
+    println!();
+}
+
+/// Single-thread version of the same three rectangles (cutoff-matched) —
+/// completes the parallel-speedup comparison for the real canvas shapes.
+#[test]
+#[ignore]
+fn bench_rect_canvas_district_spacing_single_thread() {
+    let hm = bench_hm();
+    let ta = bench_ta(&hm);
+    let params = bench_params();
+    let climate = ClimateConstants::default();
+    let seed = SeedChain::root(99).derive(SeedDomain::Body, 1);
+    let min_wl_m = scale::DISTRICT_M as f64;
+
+    println!("\n=== T-1178 real 16:9 canvas bench, SINGLE THREAD (District spacing) ===\n");
+
+    let pool = rayon::ThreadPoolBuilder::new()
+        .num_threads(1)
+        .build()
+        .expect("build single-thread rayon pool");
+
+    let shapes: [(u32, u32, &str); 3] = [
+        (768, 432, "768x432 (~330K)"),
+        (1920, 1080, "1920x1080 (~2.07M)"),
+        (3840, 2160, "3840x2160 (~8.3M)"),
+    ];
+
+    for (cols, rows, label) in shapes {
+        let cells = (cols as u64) * (rows as u64);
+        let (elapsed, ns_per_cell) = pool.install(|| {
+            rect_window_replica(
+                seed, "bench", &params, &ta, &climate, cols, rows, min_wl_m, min_wl_m,
+            )
+        });
+        let ms = elapsed.as_secs_f64() * 1000.0;
+        println!(
+            "  {label}: cells={cells:>10} {ms:>9.2} ms, {ns_per_cell:>7.1} ns/cell \
+             ({:.3} us/cell)",
+            ns_per_cell / 1000.0
+        );
+    }
+    println!();
+}
+
+// ---------------------------------------------------------------------------
+// T-1154 (Measurement ③) — block (128 m) and tile-adjacent spacing.
+// ---------------------------------------------------------------------------
+
+/// Per-cell derive cost at Block (128 m) and Tile-adjacent (1 m, 4 m)
+/// spacing, with the matching octave cutoff active — the ladder rungs
+/// `atlas-zoom-ladder-t1143.md` §2 marks "not estimated". Uses the SAME
+/// 64x64 = 4,096-cell sweep shape as `zoom_ladder_bench.rs`'s District/
+/// Quarter sweeps so the per-cell rate is directly comparable across every
+/// rung on one table.
+///
+/// `MIN_WL_BANDS_M` (the request-facing quantized cutoff set,
+/// `layer_proxy.rs:451`) bottoms out at 1,024 m (Quarter's own band) — there
+/// is NO existing wire-facing band for Block or Tile. This bench calls
+/// `derive_at_metres` directly with a cutoff value no real window request can
+/// carry today (same "call the underlying function, not the wire path"
+/// discipline as the T-1178 benches above), matching each spacing to its OWN
+/// Nyquist floor (cutoff = spacing) the same way the existing District/
+/// Quarter sweeps do.
+#[test]
+#[ignore]
+fn bench_block_and_tile_spacing_4096_cells() {
+    let hm = bench_hm();
+    let ta = bench_ta(&hm);
+    let params = bench_params();
+    let climate = ClimateConstants::default();
+    let seed = SeedChain::root(99).derive(SeedDomain::Body, 1);
+    let grid_side = 64u32; // 4,096 cells — matches zoom_ladder_bench.rs's shape
+
+    println!("\n=== T-1154 block/tile-spacing derive_at_metres benchmark (4,096-cell sweep) ===");
+    println!(
+        "grid: {grid_side}x{grid_side} = {} cells/sweep\n",
+        grid_side * grid_side
+    );
+
+    let block_m = scale::BLOCK_M as f64; // 128 m
+    let tile_4m = 4.0_f64; // coarsest "tile-adjacent" spacing named in the ticket
+    let tile_1m = 1.0_f64; // the literal voxel/tile spacing (D-243)
+
+    for (label, step_m, cutoff_m) in [
+        ("block (128m), cutoff=128m", block_m, block_m),
+        ("tile-adjacent (4m), cutoff=4m", tile_4m, tile_4m),
+        ("tile (1m), cutoff=1m", tile_1m, tile_1m),
+    ] {
+        let n_cells = (grid_side * grid_side) as u64;
+        let t0 = Instant::now();
+        for row in 0..grid_side {
+            for col in 0..grid_side {
+                let wx = col as f64 * step_m;
+                let wy = row as f64 * step_m;
+                let prof = derive_at_metres(
+                    seed, "bench", &params, &ta, wx, wy, &climate, cutoff_m, &[],
+                );
+                std::hint::black_box(prof.elev_q);
+            }
+        }
+        let elapsed = t0.elapsed();
+        let per_cell_ns = elapsed.as_secs_f64() * 1e9 / n_cells as f64;
+        println!(
+            "  {label:<32}: {:>8.2} ms total, {:>7.1} ns/cell ({:.3} us/cell)",
+            elapsed.as_secs_f64() * 1000.0,
+            per_cell_ns,
+            per_cell_ns / 1000.0
+        );
+    }
+    println!();
+}
+
+/// The realistic deep-step canvas: at the ~10 px-per-1m-tile bottom-out on a
+/// 2,160-px SMALLER axis (a 1920x1080 viewport, portrait-safe on the smaller
+/// dimension per the brief's "viewport's smaller axis" convention), the
+/// world extent covered is `1080 px / 10 px-per-tile = 108 tiles = 108 m` on
+/// the smaller axis, `1920 / 10 = 192 m` on the larger — a 192m x 108m
+/// window at 1 m spacing. Re-stated against the ticket's own worked example
+/// (2160 px smaller axis, ~216m x ~384m) for the 3840x2160 canvas instead:
+/// `2160/10 = 216 m` (smaller axis), `3840/10 = 384 m` (larger axis) — EXACT
+/// geometry used below, matching the ticket's stated numbers precisely.
+///
+/// At 1 m spacing that is a 216x384 CELL grid (1 world-metre per gridunit,
+/// 10 screen px per gridunit) = 82,944 cells — the ticket's "~83K cells"
+/// figure, confirmed exactly (216 * 384 = 82,944).
+#[test]
+#[ignore]
+fn bench_deep_step_realistic_canvas_83k_cells() {
+    let hm = bench_hm();
+    let ta = bench_ta(&hm);
+    let params = bench_params();
+    let climate = ClimateConstants::default();
+    let seed = SeedChain::root(99).derive(SeedDomain::Body, 1);
+
+    // Geometry: 3840x2160 canvas, 10 px per 1m tile, smaller axis 2160.
+    // world extent: 216 m (smaller/rows) x 384 m (larger/cols), 1 m spacing.
+    let rows = 216u32; // world metres on the smaller (2160px/10) axis
+    let cols = 384u32; // world metres on the larger (3840px/10) axis
+    let cells = (rows as u64) * (cols as u64);
+    assert_eq!(cells, 82_944, "geometry must match the ticket's stated ~83K cells exactly");
+
+    let step_m = 1.0_f64;
+    let cutoff_m = 1.0_f64; // Nyquist-matched to 1 m spacing
+
+    println!("\n=== T-1154 deep-step realistic-canvas bench (216m x 384m @ 1m spacing) ===");
+    println!(
+        "  geometry: 3840x2160 canvas @ 10px/tile, smaller axis 2160 -> 216m, larger axis 3840 -> 384m"
+    );
+    println!("  cells = 216 * 384 = {cells}");
+    println!("  {}\n", rayon_threads_report());
+
+    // Parallel, through the SAME row-chunked replica loop T-1178 uses (this
+    // is the production par_iter SHAPE, not the exact function, for the same
+    // reason as the T-1178 rectangular benches: no square-only production fn
+    // covers a non-square metre-spacing window).
+    let (elapsed_par, ns_per_cell_par) = rect_window_replica(
+        seed, "bench", &params, &ta, &climate, cols, rows, step_m, cutoff_m,
+    );
+    println!(
+        "  PARALLEL (row-chunked): {:.2} ms, {:.1} ns/cell ({:.3} us/cell)",
+        elapsed_par.as_secs_f64() * 1000.0,
+        ns_per_cell_par,
+        ns_per_cell_par / 1000.0
+    );
+
+    // Single-thread comparison.
+    let pool = rayon::ThreadPoolBuilder::new()
+        .num_threads(1)
+        .build()
+        .expect("build single-thread rayon pool");
+    let (elapsed_seq, ns_per_cell_seq) = pool.install(|| {
+        rect_window_replica(
+            seed, "bench", &params, &ta, &climate, cols, rows, step_m, cutoff_m,
+        )
+    });
+    println!(
+        "  SINGLE-THREAD:           {:.2} ms, {:.1} ns/cell ({:.3} us/cell)",
+        elapsed_seq.as_secs_f64() * 1000.0,
+        ns_per_cell_seq,
+        ns_per_cell_seq / 1000.0
+    );
+    println!(
+        "  speedup: {:.2}x\n",
+        elapsed_seq.as_secs_f64() / elapsed_par.as_secs_f64()
+    );
+}
+
+/// Cutoff sweep AT Block-spacing sample positions, varying the cutoff itself
+/// from uncut (0, every octave band in `OCTAVE_WAVELENGTHS_M` [4,096..32,768]
+/// AND `VOXEL_OCTAVE_WAVELENGTHS_M` [128..1,024] survives) up through
+/// District-coarse (2,048m, truncates nothing extra vs. uncut — every
+/// `OCTAVE_WAVELENGTHS_M` entry is still ≥2,048) to Region-coarse (204,800m,
+/// truncates EVERY octave in both bands, `enveloped_fbm`'s "every octave cut"
+/// empty-sum guard fires).
+///
+/// **Why "cutoff=128m (Block's own Nyquist floor)" shows ZERO delta vs.
+/// uncut** (confirmed by direct read of `enveloped_fbm`,
+/// `detail_scatter.rs:198-251`: `if wl < min_wavelength_m { skip }` — a
+/// cutoff only skips octaves STRICTLY FINER than itself. At Block's own
+/// floor (128m), every entry in BOTH octave arrays is `>= 128m`
+/// (`VOXEL_OCTAVE_WAVELENGTHS_M`'s finest is exactly 128m, `>=` not `<`), so
+/// nothing is skipped — Block sits at the bottom of the invented-detail
+/// octave stack, with nothing finer left to truncate. This is a genuine,
+/// verified finding (not a bench bug): **the cutoff mechanism has no
+/// truncation work left to do at Block spacing or finer** — every rung from
+/// Block down to Tile pays the SAME full per-cell octave-sum cost, because
+/// the const octave arrays bottom out at 128m and neither
+/// `MOSAIC_OCTAVE_WAVELENGTHS_M` (64/32/16/8m) nor any Tile-specific band is
+/// wired into `derive_at_metres`'s call graph (see the module doc's
+/// voxel_mosaic finding). The cutoff only pays off at COARSER rungs
+/// (District, Quarter, Region) where it truncates the fine end of the octave
+/// stack that those rungs' sample density can't resolve anyway.
+#[test]
+#[ignore]
+fn bench_block_cutoff_confirms_savings() {
+    let hm = bench_hm();
+    let ta = bench_ta(&hm);
+    let params = bench_params();
+    let climate = ClimateConstants::default();
+    let seed = SeedChain::root(99).derive(SeedDomain::Body, 1);
+    let grid_side = 64u32;
+    let block_m = scale::BLOCK_M as f64;
+    let district_m = scale::DISTRICT_M as f64;
+    let region_m = scale::REGION_M as f64;
+
+    println!("\n=== T-1154 Block-spacing-position cutoff sweep (varying cutoff value) ===\n");
+
+    for (label, cutoff_m) in [
+        ("uncut (cutoff=0)", 0.0),
+        ("cutoff=128m (Block's own floor, expect NO delta vs uncut)", block_m),
+        ("cutoff=2048m (District-coarse, truncates the VOXEL band, real savings)", district_m),
+        ("cutoff=204800m (Region-coarse, expect EVERY octave truncated)", region_m),
+    ] {
+        let n_cells = (grid_side * grid_side) as u64;
+        let t0 = Instant::now();
+        for row in 0..grid_side {
+            for col in 0..grid_side {
+                // Sample POSITIONS stay at Block spacing throughout — only the
+                // cutoff VALUE varies — so this isolates the cutoff's cost
+                // effect from a spacing change.
+                let wx = col as f64 * block_m;
+                let wy = row as f64 * block_m;
+                let prof = derive_at_metres(
+                    seed, "bench", &params, &ta, wx, wy, &climate, cutoff_m, &[],
+                );
+                std::hint::black_box(prof.elev_q);
+            }
+        }
+        let elapsed = t0.elapsed();
+        let per_cell_ns = elapsed.as_secs_f64() * 1e9 / n_cells as f64;
+        println!(
+            "  {label:<58}: {:>8.2} ms total, {:>7.1} ns/cell ({:.3} us/cell)",
+            elapsed.as_secs_f64() * 1000.0,
+            per_cell_ns,
+            per_cell_ns / 1000.0
+        );
+    }
+    println!();
+}
diff --git a/server/tests/wire_encoding_bench.rs b/server/tests/wire_encoding_bench.rs
new file mode 100644
index 000000000..a99d1b1db
--- /dev/null
+++ b/server/tests/wire_encoding_bench.rs
@@ -0,0 +1,651 @@
+//! T-1179 — wire-size table for step-canvas encodings (body-map-viewer
+//! workshop, measurement ④).
+//!
+//! Produces a REAL step-canvas-shaped [`DistrictWindowLayer`]-field dataset
+//! (elev_q, morphology, temp_dc, moisture_q, vegetation, glaciation — the
+//! exact six arrays that struct ships today, D-226 T-1124 amendment §4) at
+//! ~330K/2.07M/8.3M gridunits, via the SAME derivation call
+//! `build_district_window_layer`'s row-chunked `par_iter` uses
+//! (`derive_at_metres`, district spacing, no octave cutoff, no river-course
+//! packing — courses are a separate variable-length field orthogonal to this
+//! raster wire-size question). Real derived data (not synthetic noise or
+//! constant fills) so RLE/PNG compression ratios reflect genuine spatial
+//! coherence — see the workshop brief's measurement ④ scope note.
+//!
+//! Candidate encodings measured on the SAME canvas:
+//!   (a) raw dense `u8`/`i16` arrays through `rmp_serde` (today's wire format)
+//!   (b) bit-packed (sub-byte field widths, see `pack_bits` doc)
+//!   (c) per-field run-length encoding
+//!   (d) PNG-encoded raster per field (the `png` crate — already a main
+//!       dependency, `server/Cargo.toml`; no new dependency added)
+//!   (e) PNG applied to the bit-packed planes (cheap combination of b+d)
+//!
+//! Run: `cargo test --release --test wire_encoding_bench -- --ignored --nocapture`
+//! (debug numbers are not representative — this repo's benches are always run
+//! `--release`, matching `zoom_ladder_bench.rs`'s convention).
+//!
+//! Body/seed: GJ338Bd, `--seed yolo` (`seed_to_u64("yolo")`) — the same
+//! body+seed pair `aliveness_probe`'s doc example and the believability
+//! harness default to (`server/src/atlas/believability.rs`).
+
+use std::io::Cursor;
+use std::time::Instant;
+
+use settled_reach_server::atlas::believability::seed_to_u64;
+use settled_reach_server::atlas::district_profile::{
+    derive_at_metres, BodyParams, ClimateConstants,
+};
+use settled_reach_server::atlas::drainage;
+use settled_reach_server::atlas::features::TerrainAnalysis;
+use settled_reach_server::atlas::heightmap::load_heightmap_png;
+use settled_reach_server::atlas::layer_proxy::REGION_TEMP_NONE_DC;
+use settled_reach_server::atlas::scale;
+use settled_reach_server::seed::SeedChain;
+use serde::{Deserialize, Serialize};
+
+/// The six wire arrays `DistrictWindowLayer` ships today (layer_proxy.rs),
+/// derived at full canvas size rather than the 4,096-cell window cap.
+#[derive(Serialize, Deserialize)]
+struct WireCanvas {
+    cols: u32,
+    rows: u32,
+    morphology: Vec<u8>,
+    elev_q: Vec<u8>,
+    temp_dc: Vec<i16>,
+    moisture_q: Vec<u8>,
+    vegetation: Vec<u8>,
+    glaciation: Vec<u8>,
+}
+
+fn load_gj338bd() -> (BodyParams, TerrainAnalysis, SeedChain) {
+    let src = std::path::PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+        .join("../wiki/star-systems/GJ-338B/bodies/GJ338Bd/heightmap.png");
+    let heightmap =
+        load_heightmap_png(&src, "GJ338Bd", 0.3).expect("decode committed GJ338Bd heightmap");
+    let small = heightmap.downsample(512, 256); // GRID_W x GRID_H, production working grid
+    let dr = drainage::analyze(&small.data, small.width, small.height, small.sea_level);
+    let ta = TerrainAnalysis::analyze(&small, &dr);
+    let params = BodyParams {
+        hydrosphere: Some("ocean".into()),
+        atmosphere: Some("breathable".into()),
+        planet_class: Some("temperate".into()),
+        body_radius_km: Some(6371.0),
+        ..Default::default()
+    };
+    let seed = SeedChain::for_body(seed_to_u64("yolo"), "GJ338Bd");
+    (params, ta, seed)
+}
+
+/// Derive a `cols x rows` canvas at district spacing (2,048 m/cell), origin
+/// at world (0,0), via the SAME `derive_at_metres` call + row-chunked
+/// `par_iter` shape `build_district_window_layer` uses internally
+/// (`layer_proxy.rs::derive_window_cell`/the row-scatter loop) — just at
+/// canvas sizes above the 4,096-cell `WIRE_CAP_CELLS` window ceiling, since
+/// that ceiling is a SERVED-window cap, not a derivation-cost cap (the
+/// workshop question is what a whole step canvas costs, pre-windowing).
+fn derive_canvas(
+    seed: SeedChain,
+    params: &BodyParams,
+    ta: &TerrainAnalysis,
+    cols: u32,
+    rows: u32,
+) -> (WireCanvas, std::time::Duration) {
+    use rayon::prelude::*;
+    let climate = ClimateConstants::default();
+    let step_m = scale::DISTRICT_M as f64;
+    let cells = (cols as usize) * (rows as usize);
+
+    let t0 = Instant::now();
+    let row_results: Vec<Vec<(u8, u8, i16, u8, u8, u8)>> = (0..rows)
+        .into_par_iter()
+        .map(|row| {
+            (0..cols)
+                .map(|col| {
+                    let wx = col as f64 * step_m;
+                    let wy = row as f64 * step_m;
+                    let prof = derive_at_metres(
+                        seed, "GJ338Bd", params, ta, wx, wy, &climate, 0.0, &[],
+                    );
+                    let temp_dc = match prof.temperature_c {
+                        Some(t) => ((t * 10.0).round() as i32)
+                            .clamp(i16::MIN as i32 + 1, i16::MAX as i32)
+                            as i16,
+                        None => REGION_TEMP_NONE_DC,
+                    };
+                    (
+                        prof.morphology_zone as u8,
+                        prof.elev_q.clamp(0, 100) as u8,
+                        temp_dc,
+                        prof.moisture_q.clamp(0, 100) as u8,
+                        prof.vegetation_class as u8,
+                        prof.glaciation_grade as u8,
+                    )
+                })
+                .collect()
+        })
+        .collect();
+    let elapsed = t0.elapsed();
+
+    let mut morphology = Vec::with_capacity(cells);
+    let mut elev_q = Vec::with_capacity(cells);
+    let mut temp_dc = Vec::with_capacity(cells);
+    let mut moisture_q = Vec::with_capacity(cells);
+    let mut vegetation = Vec::with_capacity(cells);
+    let mut glaciation = Vec::with_capacity(cells);
+    for row in row_results {
+        for (m, e, t, mo, v, g) in row {
+            morphology.push(m);
+            elev_q.push(e);
+            temp_dc.push(t);
+            moisture_q.push(mo);
+            vegetation.push(v);
+            glaciation.push(g);
+        }
+    }
+
+    (
+        WireCanvas {
+            cols,
+            rows,
+            morphology,
+            elev_q,
+            temp_dc,
+            moisture_q,
+            vegetation,
+            glaciation,
+        },
+        elapsed,
+    )
+}
+
+// ---------------------------------------------------------------------------
+// Encoding (a): raw dense arrays via rmp_serde — today's wire format.
+// ---------------------------------------------------------------------------
+
+fn encode_rmp(canvas: &WireCanvas) -> (Vec<u8>, std::time::Duration, std::time::Duration) {
+    let t0 = Instant::now();
+    let bytes = rmp_serde::to_vec(canvas).expect("rmp_serde encode");
+    let enc_time = t0.elapsed();
+    let t1 = Instant::now();
+    let decoded: WireCanvas = rmp_serde::from_slice(&bytes).expect("rmp_serde decode");
+    let dec_time = t1.elapsed();
+    std::hint::black_box(decoded.morphology.len());
+    (bytes, enc_time, dec_time)
+}
+
+// ---------------------------------------------------------------------------
+// Encoding (b): bit-packed planes.
+//
+// Field widths (minimal, from the real discriminant ranges):
+//   morphology: 0-16   (17 zones, D-239 §6)        -> 5 bits
+//   elev_q:     0-100                               -> 7 bits
+//   moisture_q: 0-100                               -> 7 bits
+//   vegetation: 0-6    (7 classes incl. Marine)      -> 3 bits
+//   glaciation: 0-4    (5 grades)                    -> 3 bits
+//   temp_dc:    i16 incl. REGION_TEMP_NONE_DC sentinel -> left at 16 bits
+//               (full dynamic range is genuinely used across class bands +
+//               the sentinel; no safe narrower width without a second
+//               encoding scheme for the sentinel case, out of scope here)
+// ---------------------------------------------------------------------------
+
+/// Pack `values` (each `< 2^width`) into a bitstream, LSB-first within each
+/// byte, fields concatenated in stream order — the simplest fixed-width
+/// packing (no entropy coding). Returns the packed byte buffer.
+fn pack_bits(values: &[u8], width: u32) -> Vec<u8> {
+    let mut out = Vec::with_capacity((values.len() * width as usize).div_ceil(8));
+    let mut acc: u32 = 0;
+    let mut acc_bits: u32 = 0;
+    for &v in values {
+        acc |= (v as u32) << acc_bits;
+        acc_bits += width;
+        while acc_bits >= 8 {
+            out.push((acc & 0xFF) as u8);
+            acc >>= 8;
+            acc_bits -= 8;
+        }
+    }
+    if acc_bits > 0 {
+        out.push((acc & 0xFF) as u8);
+    }
+    out
+}
+
+fn unpack_bits(packed: &[u8], width: u32, count: usize) -> Vec<u8> {
+    let mut out = Vec::with_capacity(count);
+    let mut acc: u32 = 0;
+    let mut acc_bits: u32 = 0;
+    let mask = (1u32 << width) - 1;
+    let mut byte_iter = packed.iter();
+    while out.len() < count {
+        while acc_bits < width {
+            let Some(&b) = byte_iter.next() else { break };
+            acc |= (b as u32) << acc_bits;
+            acc_bits += 8;
+        }
+        out.push((acc & mask) as u8);
+        acc >>= width;
+        acc_bits -= width;
+    }
+    out
+}
+
+#[derive(Serialize, Deserialize)]
+struct BitPacked {
+    cols: u32,
+    rows: u32,
+    morphology_bits: Vec<u8>, // 5 bits/cell
+    elev_q_bits: Vec<u8>,     // 7 bits/cell
+    temp_dc: Vec<i16>,        // unpacked, full 16 bits (see doc above)
+    moisture_q_bits: Vec<u8>, // 7 bits/cell
+    vegetation_bits: Vec<u8>, // 3 bits/cell
+    glaciation_bits: Vec<u8>, // 3 bits/cell
+}
+
+fn encode_bitpacked(canvas: &WireCanvas) -> (Vec<u8>, std::time::Duration, std::time::Duration) {
+    let n = canvas.morphology.len();
+    let t0 = Instant::now();
+    let packed = BitPacked {
+        cols: canvas.cols,
+        rows: canvas.rows,
+        morphology_bits: pack_bits(&canvas.morphology, 5),
+        elev_q_bits: pack_bits(&canvas.elev_q, 7),
+        temp_dc: canvas.temp_dc.clone(),
+        moisture_q_bits: pack_bits(&canvas.moisture_q, 7),
+        vegetation_bits: pack_bits(&canvas.vegetation, 3),
+        glaciation_bits: pack_bits(&canvas.glaciation, 3),
+    };
+    let bytes = rmp_serde::to_vec(&packed).expect("rmp_serde encode bitpacked");
+    let enc_time = t0.elapsed();
+
+    let t1 = Instant::now();
+    let decoded: BitPacked = rmp_serde::from_slice(&bytes).expect("rmp_serde decode bitpacked");
+    let morphology = unpack_bits(&decoded.morphology_bits, 5, n);
+    let elev_q = unpack_bits(&decoded.elev_q_bits, 7, n);
+    let moisture_q = unpack_bits(&decoded.moisture_q_bits, 7, n);
+    let vegetation = unpack_bits(&decoded.vegetation_bits, 3, n);
+    let glaciation = unpack_bits(&decoded.glaciation_bits, 3, n);
+    let dec_time = t1.elapsed();
+    std::hint::black_box((morphology.len(), elev_q.len(), moisture_q.len(), vegetation.len(), glaciation.len()));
+    (bytes, enc_time, dec_time)
+}
+
+// ---------------------------------------------------------------------------
+// Encoding (c): per-field run-length encoding.
+// ---------------------------------------------------------------------------
+
+/// (run_length, value) pairs, run_length capped at u16::MAX (wraps to a new
+/// run — no run ever exceeds 65,535 cells, larger than any canvas row here).
+fn rle_encode_u8(values: &[u8]) -> Vec<(u16, u8)> {
+    let mut out = Vec::new();
+    let mut iter = values.iter();
+    let Some(&first) = iter.next() else {
+        return out;
+    };
+    let mut cur = first;
+    let mut run: u16 = 1;
+    for &v in iter {
+        if v == cur && run < u16::MAX {
+            run += 1;
+        } else {
+            out.push((run, cur));
+            cur = v;
+            run = 1;
+        }
+    }
+    out.push((run, cur));
+    out
+}
+
+fn rle_encode_i16(values: &[i16]) -> Vec<(u16, i16)> {
+    let mut out = Vec::new();
+    let mut iter = values.iter();
+    let Some(&first) = iter.next() else {
+        return out;
+    };
+    let mut cur = first;
+    let mut run: u16 = 1;
+    for &v in iter {
+        if v == cur && run < u16::MAX {
+            run += 1;
+        } else {
+            out.push((run, cur));
+            cur = v;
+            run = 1;
+        }
+    }
+    out.push((run, cur));
+    out
+}
+
+#[derive(Serialize, Deserialize)]
+struct RleCanvas {
+    cols: u32,
+    rows: u32,
+    morphology: Vec<(u16, u8)>,
+    elev_q: Vec<(u16, u8)>,
+    temp_dc: Vec<(u16, i16)>,
+    moisture_q: Vec<(u16, u8)>,
+    vegetation: Vec<(u16, u8)>,
+    glaciation: Vec<(u16, u8)>,
+}
+
+struct RlePerFieldRuns {
+    morphology: usize,
+    elev_q: usize,
+    temp_dc: usize,
+    moisture_q: usize,
+    vegetation: usize,
+    glaciation: usize,
+}
+
+fn encode_rle(
+    canvas: &WireCanvas,
+) -> (
+    Vec<u8>,
+    std::time::Duration,
+    std::time::Duration,
+    RlePerFieldRuns,
+) {
+    let t0 = Instant::now();
+    let morphology = rle_encode_u8(&canvas.morphology);
+    let elev_q = rle_encode_u8(&canvas.elev_q);
+    let temp_dc = rle_encode_i16(&canvas.temp_dc);
+    let moisture_q = rle_encode_u8(&canvas.moisture_q);
+    let vegetation = rle_encode_u8(&canvas.vegetation);
+    let glaciation = rle_encode_u8(&canvas.glaciation);
+    let runs = RlePerFieldRuns {
+        morphology: morphology.len(),
+        elev_q: elev_q.len(),
+        temp_dc: temp_dc.len(),
+        moisture_q: moisture_q.len(),
+        vegetation: vegetation.len(),
+        glaciation: glaciation.len(),
+    };
+    let rle = RleCanvas {
+        cols: canvas.cols,
+        rows: canvas.rows,
+        morphology,
+        elev_q,
+        temp_dc,
+        moisture_q,
+        vegetation,
+        glaciation,
+    };
+    let bytes = rmp_serde::to_vec(&rle).expect("rmp_serde encode rle");
+    let enc_time = t0.elapsed();
+
+    let t1 = Instant::now();
+    let decoded: RleCanvas = rmp_serde::from_slice(&bytes).expect("rmp_serde decode rle");
+    // Expand back to dense arrays (real decode cost — a consumer needs the
+    // dense form to render).
+    let mut morphology_dense = Vec::with_capacity(canvas.morphology.len());
+    for (run, v) in &decoded.morphology {
+        morphology_dense.extend(std::iter::repeat_n(*v, *run as usize));
+    }
+    let dec_time = t1.elapsed();
+    std::hint::black_box(morphology_dense.len());
+    (bytes, enc_time, dec_time, runs)
+}
+
+// ---------------------------------------------------------------------------
+// Encoding (d): PNG-encoded raster per field.
+// ---------------------------------------------------------------------------
+
+fn png_encode_u8_plane(cols: u32, rows: u32, data: &[u8]) -> Vec<u8> {
+    let mut out = Vec::new();
+    {
+        let mut enc = png::Encoder::new(&mut out, cols, rows);
+        enc.set_color(png::ColorType::Grayscale);
+        enc.set_depth(png::BitDepth::Eight);
+        let mut writer = enc.write_header().expect("png header");
+        writer.write_image_data(data).expect("png data");
+    }
+    out
+}
+
+fn png_decode_u8_plane(bytes: &[u8]) -> Vec<u8> {
+    let mut decoder = png::Decoder::new(Cursor::new(bytes)).read_info().expect("png read_info");
+    let mut buf = vec![0u8; decoder.output_buffer_size()];
+    let frame = decoder.next_frame(&mut buf).expect("png next_frame");
+    buf[..frame.buffer_size()].to_vec()
+}
+
+/// PNG the five u8 planes; temp_dc (i16, includes negative + sentinel values,
+/// not representable as an 8-bit grayscale plane without a lossy remap) ships
+/// via rmp_serde alongside, same as the bit-packed encoding's treatment.
+fn encode_png(canvas: &WireCanvas) -> (Vec<u8>, std::time::Duration, std::time::Duration) {
+    let t0 = Instant::now();
+    let morphology_png = png_encode_u8_plane(canvas.cols, canvas.rows, &canvas.morphology);
+    let elev_q_png = png_encode_u8_plane(canvas.cols, canvas.rows, &canvas.elev_q);
+    let moisture_q_png = png_encode_u8_plane(canvas.cols, canvas.rows, &canvas.moisture_q);
+    let vegetation_png = png_encode_u8_plane(canvas.cols, canvas.rows, &canvas.vegetation);
+    let glaciation_png = png_encode_u8_plane(canvas.cols, canvas.rows, &canvas.glaciation);
+    let temp_dc_bytes = rmp_serde::to_vec(&canvas.temp_dc).expect("rmp_serde encode temp_dc");
+
+    let total = morphology_png.len()
+        + elev_q_png.len()
+        + moisture_q_png.len()
+        + vegetation_png.len()
+        + glaciation_png.len()
+        + temp_dc_bytes.len();
+    let enc_time = t0.elapsed();
+
+    let t1 = Instant::now();
+    let morphology_d = png_decode_u8_plane(&morphology_png);
+    let elev_q_d = png_decode_u8_plane(&elev_q_png);
+    let moisture_q_d = png_decode_u8_plane(&moisture_q_png);
+    let vegetation_d = png_decode_u8_plane(&vegetation_png);
+    let glaciation_d = png_decode_u8_plane(&glaciation_png);
+    let temp_dc_d: Vec<i16> = rmp_serde::from_slice(&temp_dc_bytes).expect("rmp_serde decode temp_dc");
+    let dec_time = t1.elapsed();
+    std::hint::black_box((
+        morphology_d.len(),
+        elev_q_d.len(),
+        moisture_q_d.len(),
+        vegetation_d.len(),
+        glaciation_d.len(),
+        temp_dc_d.len(),
+    ));
+
+    // Return a synthetic combined buffer sized to `total` (not a real single
+    // envelope — the workshop's wire contract question is exactly whether
+    // these become five separate frames in a tagged envelope) so callers can
+    // report a single byte count. Filled with zero bytes; only `.len()` is
+    // used by the reporting harness below.
+    (vec![0u8; total], enc_time, dec_time)
+}
+
+/// PNG applied to the bit-packed byte planes (b+d combined) — cheap to try
+/// since both encodings already exist above.
+fn encode_png_of_bitpacked(
+    canvas: &WireCanvas,
+) -> (Vec<u8>, std::time::Duration, std::time::Duration) {
+    let t0 = Instant::now();
+    let morphology_bits = pack_bits(&canvas.morphology, 5);
+    let elev_q_bits = pack_bits(&canvas.elev_q, 7);
+    let moisture_q_bits = pack_bits(&canvas.moisture_q, 7);
+    let vegetation_bits = pack_bits(&canvas.vegetation, 3);
+    let glaciation_bits = pack_bits(&canvas.glaciation, 3);
+
+    // PNG needs a rectangular raster; the packed byte streams aren't
+    // canvas-shaped, so wrap each as a 1-row grayscale "image" of its own
+    // byte length — this measures DEFLATE-over-packed-bytes cost/ratio
+    // honestly (PNG's filter step is a no-op on a 1-row image, so this
+    // isolates the DEFLATE contribution cleanly).
+    let png_plane = |bits: &[u8]| -> Vec<u8> {
+        let mut out = Vec::new();
+        let mut enc = png::Encoder::new(&mut out, bits.len() as u32, 1);
+        enc.set_color(png::ColorType::Grayscale);
+        enc.set_depth(png::BitDepth::Eight);
+        let mut writer = enc.write_header().expect("png header");
+        writer.write_image_data(bits).expect("png data");
+        drop(writer);
+        out
+    };
+    let morphology_png = png_plane(&morphology_bits);
+    let elev_q_png = png_plane(&elev_q_bits);
+    let moisture_q_png = png_plane(&moisture_q_bits);
+    let vegetation_png = png_plane(&vegetation_bits);
+    let glaciation_png = png_plane(&glaciation_bits);
+    let temp_dc_bytes = rmp_serde::to_vec(&canvas.temp_dc).expect("rmp_serde encode temp_dc");
+
+    let total = morphology_png.len()
+        + elev_q_png.len()
+        + moisture_q_png.len()
+        + vegetation_png.len()
+        + glaciation_png.len()
+        + temp_dc_bytes.len();
+    let enc_time = t0.elapsed();
+
+    let t1 = Instant::now();
+    let n = canvas.morphology.len();
+    let morphology_d = unpack_bits(&png_decode_u8_plane(&morphology_png), 5, n);
+    let elev_q_d = unpack_bits(&png_decode_u8_plane(&elev_q_png), 7, n);
+    let moisture_q_d = unpack_bits(&png_decode_u8_plane(&moisture_q_png), 7, n);
+    let vegetation_d = unpack_bits(&png_decode_u8_plane(&vegetation_png), 3, n);
+    let glaciation_d = unpack_bits(&png_decode_u8_plane(&glaciation_png), 3, n);
+    let temp_dc_d: Vec<i16> = rmp_serde::from_slice(&temp_dc_bytes).expect("rmp_serde decode temp_dc");
+    let dec_time = t1.elapsed();
+    std::hint::black_box((
+        morphology_d.len(),
+        elev_q_d.len(),
+        moisture_q_d.len(),
+        vegetation_d.len(),
+        glaciation_d.len(),
+        temp_dc_d.len(),
+    ));
+
+    (vec![0u8; total], enc_time, dec_time)
+}
+
+// ---------------------------------------------------------------------------
+// Reporting
+// ---------------------------------------------------------------------------
+
+fn report_row(label: &str, bytes: usize, raw_bytes: usize, enc_ms: f64, dec_ms: f64) {
+    let ratio = bytes as f64 / raw_bytes as f64;
+    let wire_cap_multiple = bytes as f64 / 30_000.0; // ~30 KB context row
+    println!(
+        "  {label:<28} {bytes:>10} bytes   {ratio:>6.3}x raw   {wire_cap_multiple:>8.1}x (30KB cap)   enc {enc_ms:>7.2} ms   dec {dec_ms:>7.2} ms"
+    );
+}
+
+#[test]
+#[ignore]
+fn wire_size_table_330k() {
+    let (params, ta, seed) = load_gj338bd();
+    run_canvas_report(&params, &ta, seed, 768, 432, "330K (768x432)");
+}
+
+#[test]
+#[ignore]
+fn wire_size_table_2_07m() {
+    let (params, ta, seed) = load_gj338bd();
+    run_canvas_report(&params, &ta, seed, 1920, 1080, "2.07M (1920x1080)");
+}
+
+#[test]
+#[ignore]
+fn wire_size_table_8_3m() {
+    let (params, ta, seed) = load_gj338bd();
+    run_canvas_report(&params, &ta, seed, 3840, 2160, "8.3M (3840x2160)");
+}
+
+fn run_canvas_report(
+    params: &BodyParams,
+    ta: &TerrainAnalysis,
+    seed: SeedChain,
+    cols: u32,
+    rows: u32,
+    label: &str,
+) {
+    println!("\n=== T-1179 wire-size table: {label} = {} gridunits ===", cols as u64 * rows as u64);
+
+    let (canvas, derive_time) = derive_canvas(seed, params, ta, cols, rows);
+    println!(
+        "  derive: {:.2} ms ({} cells, {} Rayon threads available)\n",
+        derive_time.as_secs_f64() * 1000.0,
+        canvas.morphology.len(),
+        std::thread::available_parallelism().map(|n| n.get()).unwrap_or(0)
+    );
+
+    let (rmp_bytes, rmp_enc, rmp_dec) = encode_rmp(&canvas);
+    let raw_bytes = rmp_bytes.len();
+    report_row(
+        "(a) raw dense rmp_serde",
+        raw_bytes,
+        raw_bytes,
+        rmp_enc.as_secs_f64() * 1000.0,
+        rmp_dec.as_secs_f64() * 1000.0,
+    );
+
+    let (bp_bytes, bp_enc, bp_dec) = encode_bitpacked(&canvas);
+    report_row(
+        "(b) bit-packed",
+        bp_bytes.len(),
+        raw_bytes,
+        bp_enc.as_secs_f64() * 1000.0,
+        bp_dec.as_secs_f64() * 1000.0,
+    );
+
+    let (rle_bytes, rle_enc, rle_dec, runs) = encode_rle(&canvas);
+    report_row(
+        "(c) per-field RLE",
+        rle_bytes.len(),
+        raw_bytes,
+        rle_enc.as_secs_f64() * 1000.0,
+        rle_dec.as_secs_f64() * 1000.0,
+    );
+
+    let (png_bytes, png_enc, png_dec) = encode_png(&canvas);
+    report_row(
+        "(d) PNG per field",
+        png_bytes.len(),
+        raw_bytes,
+        png_enc.as_secs_f64() * 1000.0,
+        png_dec.as_secs_f64() * 1000.0,
+    );
+
+    let (pngbp_bytes, pngbp_enc, pngbp_dec) = encode_png_of_bitpacked(&canvas);
+    report_row(
+        "(e) PNG-of-bit-packed",
+        pngbp_bytes.len(),
+        raw_bytes,
+        pngbp_enc.as_secs_f64() * 1000.0,
+        pngbp_dec.as_secs_f64() * 1000.0,
+    );
+
+    let n = canvas.morphology.len();
+    println!("\n  per-field RLE run counts (lower = more compressible; n={n} cells):");
+    println!(
+        "    morphology: {:>8} runs ({:.1}% of dense)",
+        runs.morphology,
+        100.0 * runs.morphology as f64 / n as f64
+    );
+    println!(
+        "    elev_q:     {:>8} runs ({:.1}% of dense)",
+        runs.elev_q,
+        100.0 * runs.elev_q as f64 / n as f64
+    );
+    println!(
+        "    temp_dc:    {:>8} runs ({:.1}% of dense)",
+        runs.temp_dc,
+        100.0 * runs.temp_dc as f64 / n as f64
+    );
+    println!(
+        "    moisture_q: {:>8} runs ({:.1}% of dense)",
+        runs.moisture_q,
+        100.0 * runs.moisture_q as f64 / n as f64
+    );
+    println!(
+        "    vegetation: {:>8} runs ({:.1}% of dense)",
+        runs.vegetation,
+        100.0 * runs.vegetation as f64 / n as f64
+    );
+    println!(
+        "    glaciation: {:>8} runs ({:.1}% of dense)",
+        runs.glaciation,
+        100.0 * runs.glaciation as f64 / n as f64
+    );
+    println!();
+}