fix(ui): calculator polish — smart input steps, unified tech/MAT lock idiom, tech floor, speed-lock ceiling fix

- pkg/calc: DriveForSpeed treats restMass==0 as a valid ceiling-only
  case (every positive drive solves it), so locking the displayed
  speed of a D=1, W=A=S=C=0 ship is no longer a phantom "infeasible".
- ship-design-area: drive/weapons/shields/cargo inputs use a JS-driven
  smart step on ArrowUp/ArrowDown (0↔1 jump, otherwise ±0.1) and hide
  the native spinner so it cannot produce invalid (0, 1) values;
  armament keeps its native step 1.
- Tech and planet MAT cells follow the same lock idiom as goal-seek
  locks: open padlock (🔓) over the inherited value → click to open
  an input with a closed padlock (🔒). The padlock slot is always
  reserved, so the column width is stable.
- Tech overrides (design area and modernization target) are floored
  at the player's current tech on this turn — a lower value is
  flagged as invalid.

pkg/calc/solve.go

@@ -22,12 +22,25 @@ func WeaponsForAttack(targetAttack, weaponsTech float64) (float64, bool) {
 // DriveForSpeed returns the drive block that yields targetSpeed for a
 // ship whose mass excluding the drive block is restMass, at drive tech
 // level driveTech, inverting [Speed] composed with [DriveEffective].
-// Speed approaches but never reaches the stripped-hull ceiling
-// 20*driveTech, so a target at or above the ceiling (or a non-positive
-// target or tech level) is infeasible.
+// With a positive restMass the speed approaches but never reaches the
+// stripped-hull ceiling 20*driveTech, so a target at or above the
+// ceiling is infeasible. With restMass==0 the drive block carries no
+// other mass: every positive drive yields exactly the ceiling speed, so
+// the ceiling target is the only feasible one and any positive drive
+// (canonically 1) solves it. Non-positive targetSpeed or driveTech are
+// always infeasible.
 func DriveForSpeed(targetSpeed, driveTech, restMass float64) (float64, bool) {
+	if driveTech <= 0 || targetSpeed <= 0 {
+		return 0, false
+	}
 	ceiling := 20 * driveTech
-	if driveTech <= 0 || targetSpeed <= 0 || targetSpeed >= ceiling {
+	if restMass <= 0 {
+		if targetSpeed != ceiling {
+			return 0, false
+		}
+		return 1, true
+	}
+	if targetSpeed >= ceiling {
 		return 0, false
 	}
 	return targetSpeed * restMass / (ceiling - targetSpeed), true

pkg/calc/solve_test.go

@@ -24,12 +24,30 @@ func TestDriveForSpeed(t *testing.T) {
 	if !ok || math.Abs(got-drive) > 1e-9 {
 		t.Errorf("DriveForSpeed round-trip = %v (ok=%v), want %v", got, ok, drive)
 	}
-	// Speed can never reach the stripped-hull ceiling 20*driveTech.
+	// With a positive restMass speed can never reach 20*driveTech.
 	if _, ok := calc.DriveForSpeed(20*driveTech, driveTech, restMass); ok {
 		t.Error("DriveForSpeed at the speed ceiling should be infeasible")
 	}
 }
 
+func TestDriveForSpeedZeroRest(t *testing.T) {
+	// With restMass==0 the only achievable speed is the stripped-hull
+	// ceiling 20*driveTech; any positive drive reaches it. Off-ceiling
+	// targets are infeasible.
+	const driveTech = 1.5
+	ceiling := 20 * driveTech
+	got, ok := calc.DriveForSpeed(ceiling, driveTech, 0)
+	if !ok || got <= 0 {
+		t.Errorf("DriveForSpeed(ceiling, _, 0) = %v (ok=%v), want positive", got, ok)
+	}
+	if _, ok := calc.DriveForSpeed(ceiling/2, driveTech, 0); ok {
+		t.Error("DriveForSpeed(below ceiling, _, 0) should be infeasible")
+	}
+	if _, ok := calc.DriveForSpeed(ceiling+1, driveTech, 0); ok {
+		t.Error("DriveForSpeed(above ceiling, _, 0) should be infeasible")
+	}
+}
+
 func TestShieldsForDefence(t *testing.T) {
 	const shields, shieldsTech, restMass = 5.75, 1.0, 40.0
 	defence := calc.EffectiveDefence(shields, shieldsTech, shields+restMass)

ui/docs/calculator-ux.md

@@ -24,8 +24,18 @@ in as a per-ship result rather than a separate mode.
 
 1. **Ship Class design area** — five blocks (drive, armament, weapons,
    shields, cargo) and four tech levels (drive, weapons, shields,
-   cargo). Tech defaults to the player's current tech and shows a lock
-   icon once overridden; clicking it resets to the default.
+   cargo). Tech defaults to the player's current tech: the cell renders
+   the inherited number with an open padlock; clicking the open lock
+   activates an input (closed padlock), where the player may type an
+   override at or above their current tech. Clicking the closed
+   padlock resets to the default. The padlock slot is always reserved,
+   so the column width does not shift as the lock state toggles. The
+   four ship-class blocks (drive, weapons, shields, cargo) use a smart
+   keyboard step that respects the engine value rule (`0` or `≥ 1`):
+   ArrowUp from 0 jumps straight to 1, otherwise +0.1; ArrowDown from
+   1 collapses to 0, otherwise −0.1, never producing an invalid value
+   in `(0, 1)`. The native spinner is hidden on these inputs (it would
+   produce invalid intermediates); armament keeps its native step 1.
 2. **Calculator area** — derived results: empty/loaded mass, empty/
    loaded speed, attack, defence, bombing (per ship), cargo capacity.
    A load toggle (empty / full / custom) sets the cargo load (in cargo
@@ -35,17 +45,27 @@ in as a per-ship result rather than a separate mode.
    the load is pinned to empty and the toggle is disabled.
 3. **Planet area** — when an own planet is selected on the map, shows
    its MAT (overridable) and the single-turn build rate (ships per turn,
-   turns per ship). The realistic multi-turn forecast with CAP/COL
+   turns per ship). The MAT follows the same lock idiom as the tech
+   cells: the planet number renders with an open padlock, clicking
+   opens an input with a closed padlock, and the closed padlock resets
+   to the planet value. The realistic multi-turn forecast with CAP/COL
    supply is planned (see ../ROADMAP.md).
 
 ## Locks and goal-seek
 
-Two distinct lock semantics share one icon (a closed padlock; it only
-appears once a value is pinned, click to release):
+Two distinct lock semantics share one padlock affordance. Both follow
+the same idiom — an open padlock (🔓) means *value is inherited /
+derived, click to override*; a closed padlock (🔒) means *value is
+pinned by the player, click to reset*:
 
 - **Override locks** on inputs that have a default — the four techs and
-  the planet MAT. Editing one overrides the default; the lock resets it.
-  Any number may be overridden at once.
+  the planet MAT. By default the cell shows the inherited number plus
+  an open padlock; clicking it switches to an input plus a closed
+  padlock for typing the override. Closing (clicking the closed
+  padlock) resets to the default. Any number may be overridden at once.
+  Tech overrides are floored at the player's current tech on this
+  turn — a lower value is flagged as invalid. The same floor applies
+  to the modernization target tech.
 - **Goal-seek locks** on derived results. Pinning a result back-solves
   the single input it claims, which then renders read-only (computed):
 
@@ -60,12 +80,16 @@ appears once a value is pinned, click to release):
 
   Only **one** result may be locked at a time (the others' lock
   affordances disable with a tooltip). An unreachable target — e.g. a
-  speed at or above the stripped-hull ceiling `20 × driveTech`, or a
+  speed above the stripped-hull ceiling `20 × driveTech`, or a
   solved block that fails the value rules — leaves the locked cell in a
   red error state and does not apply. Inverse solving lives in
   `pkg/calc/solve.go`; the bisection for defence → shields is the only
   non-analytic case. Locking a speed is disabled when the drive block is
-  zero (a deliberately immobile ship has no speed to back-solve).
+  zero (a deliberately immobile ship has no speed to back-solve). With
+  the drive block as the only non-zero mass the displayed speed equals
+  the ceiling exactly (every positive drive gives the same speed), so
+  the solver accepts that ceiling target as a feasible lock and any
+  positive drive solves it.
 
 ## Validation and display
 

ui/frontend/src/lib/calculator/ship-design-area.svelte

@@ -1,13 +1,17 @@
 <!--
 Reusable "Ship Class design area": the five design blocks (drive,
 armament, weapons, shields, cargo) plus the four tech levels they are
-built with. Each tech defaults to the player's current level and shows a
-lock icon once overridden; clicking the lock resets it. A block claimed
-by an active goal-seek lock renders read-only with its own lock marker.
-The component is presentational — the parent owns the state and the
+built with. Tech and MAT locks follow the same idiom as goal-seek
+locks below the design area — by default the value renders as plain
+text with an open padlock; clicking it overrides (input + closed
+padlock). Reserved space for the padlock keeps the column width
+stable as the lock state toggles. A block claimed by an active
+goal-seek lock renders read-only with its own lock marker. The
+component is presentational — the parent owns the state and the
 calculator math — so the ship-group upgrade flow can reuse it later.
 -->
 <script lang="ts">
+	import { tick } from "svelte";
 	import { i18n, type TranslationKey } from "$lib/i18n/index.svelte";
 	import {
 		shipClassFieldErrors,
@@ -37,6 +41,10 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 		resolved: DesignBlocksState;
 		techs: TechState;
 		techOverridden: Record<TechKey, boolean>;
+		// Lower bound for the tech inputs: the player's current tech on
+		// this turn. A design cannot be built with tech below the player's
+		// own level, so we surface that as a per-field validation error.
+		techFloor: TechState;
 		computedInput?: ClaimedInput | null;
 		blocksReadonly?: boolean;
 		onTechInput: (key: TechKey) => void;
@@ -47,6 +55,7 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 		resolved,
 		techs = $bindable(),
 		techOverridden,
+		techFloor,
 		computedInput = null,
 		blocksReadonly = false,
 		onTechInput,
@@ -73,7 +82,38 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 		return reason === undefined ? "" : i18n.t(VALUE_REASON_KEY[reason]);
 	}
 	function techError(key: TechKey): string {
-		return techs[key] < 0 ? i18n.t("game.calculator.invalid.tech_value") : "";
+		const value = techs[key];
+		if (value < 0) return i18n.t("game.calculator.invalid.tech_value");
+		if (value < techFloor[key]) {
+			return i18n.t("game.calculator.invalid.tech_below_current");
+		}
+		return "";
+	}
+
+	// Smart step on the four ship-class blocks (drive, weapons, shields,
+	// cargo): values must be 0 or ≥ 1 per `pkg/calc/validator.go`, so the
+	// native 0.01 step would produce invalid intermediates like 0.01.
+	// Up: 0 jumps straight to 1; otherwise +0.1. Down: 1 collapses to 0;
+	// otherwise −0.1 down to 1, clamped at 0. Armament keeps native step 1.
+	function bumpBlock(value: number, dir: 1 | -1): number {
+		if (dir === 1) {
+			if (value < 1) return 1;
+			return Math.round((value + 0.1) * 10) / 10;
+		}
+		if (value <= 1) return 0;
+		return Math.round((value - 0.1) * 10) / 10;
+	}
+	function onBlockKey(
+		event: KeyboardEvent,
+		key: keyof DesignBlocksState,
+	): void {
+		if (event.key === "ArrowUp") {
+			event.preventDefault();
+			blocks[key] = bumpBlock(blocks[key], 1);
+		} else if (event.key === "ArrowDown") {
+			event.preventDefault();
+			blocks[key] = bumpBlock(blocks[key], -1);
+		}
 	}
 
 	const BLOCK_ROWS: {
@@ -81,13 +121,23 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 		label: () => string;
 		step: string;
 		tech: TechKey | null;
+		smartStep: boolean;
 	}[] = [
-		{ key: "drive", label: () => i18n.t("game.calculator.field.drive"), step: "0.01", tech: "drive" },
-		{ key: "armament", label: () => i18n.t("game.calculator.field.armament"), step: "1", tech: null },
-		{ key: "weapons", label: () => i18n.t("game.calculator.field.weapons"), step: "0.01", tech: "weapons" },
-		{ key: "shields", label: () => i18n.t("game.calculator.field.shields"), step: "0.01", tech: "shields" },
-		{ key: "cargo", label: () => i18n.t("game.calculator.field.cargo"), step: "0.01", tech: "cargo" },
+		{ key: "drive", label: () => i18n.t("game.calculator.field.drive"), step: "0.1", tech: "drive", smartStep: true },
+		{ key: "armament", label: () => i18n.t("game.calculator.field.armament"), step: "1", tech: null, smartStep: false },
+		{ key: "weapons", label: () => i18n.t("game.calculator.field.weapons"), step: "0.1", tech: "weapons", smartStep: true },
+		{ key: "shields", label: () => i18n.t("game.calculator.field.shields"), step: "0.1", tech: "shields", smartStep: true },
+		{ key: "cargo", label: () => i18n.t("game.calculator.field.cargo"), step: "0.1", tech: "cargo", smartStep: true },
 	];
+
+	const techInputEls: Partial<Record<TechKey, HTMLInputElement>> = {};
+
+	async function activateTechOverride(key: TechKey): Promise<void> {
+		onTechInput(key);
+		await tick();
+		techInputEls[key]?.focus();
+		techInputEls[key]?.select();
+	}
 </script>
 
 <div class="design" data-testid="calculator-design-area">
@@ -103,6 +153,7 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 			{#if isComputed}
 				<input
 					class="ship"
+					class:smart-step={row.smartStep}
 					type="number"
 					step={row.step}
 					readonly
@@ -114,6 +165,7 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 			{:else}
 				<input
 					class="ship"
+					class:smart-step={row.smartStep}
 					type="number"
 					step={row.step}
 					min="0"
@@ -122,26 +174,29 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 					aria-invalid={blockError(row.key) !== "" ? "true" : "false"}
 					title={blockError(row.key)}
 					data-testid={`calculator-block-${row.key}`}
+					onkeydown={row.smartStep
+						? (e) => onBlockKey(e, row.key)
+						: null}
 				/>
 			{/if}
 			{#if row.tech !== null}
 				{@const techKey = row.tech}
 				<span class="tech-cell">
-					<input
-						class="tech"
-						type="number"
-						step="0.001"
-						min="0"
-						bind:value={techs[techKey]}
-						oninput={() => onTechInput(techKey)}
-						aria-invalid={techError(techKey) !== "" ? "true" : "false"}
-						title={techError(techKey)}
-						data-testid={`calculator-tech-${techKey}`}
-					/>
 					{#if techOverridden[techKey]}
+						<input
+							bind:this={techInputEls[techKey]}
+							class="tech"
+							type="number"
+							step="0.001"
+							min={techFloor[techKey]}
+							bind:value={techs[techKey]}
+							aria-invalid={techError(techKey) !== "" ? "true" : "false"}
+							title={techError(techKey)}
+							data-testid={`calculator-tech-${techKey}`}
+						/>
 						<button
 							type="button"
-							class="lock"
+							class="lock active"
 							title={i18n.t("game.calculator.tech.reset")}
 							aria-label={i18n.t("game.calculator.tech.reset")}
 							data-testid={`calculator-tech-reset-${techKey}`}
@@ -149,6 +204,23 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 						>
 							🔒
 						</button>
+					{:else}
+						<span
+							class="tech-val"
+							data-testid={`calculator-tech-value-${techKey}`}
+						>
+							{techs[techKey]}
+						</span>
+						<button
+							type="button"
+							class="lock"
+							title={i18n.t("game.calculator.tech.override")}
+							aria-label={i18n.t("game.calculator.tech.override")}
+							data-testid={`calculator-tech-override-${techKey}`}
+							onclick={() => void activateTechOverride(techKey)}
+						>
+							🔓
+						</button>
 					{/if}
 				</span>
 			{:else}
@@ -193,6 +265,18 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 		border-radius: 3px;
 		font-variant-numeric: tabular-nums;
 	}
+	/* Drive/weapons/shields/cargo use the JS-driven smart step (0→1 jump
+	   then 0.1 increments) for keyboard arrows; hide the native spinner
+	   on those inputs so it cannot produce invalid 0.01 intermediates. */
+	input.smart-step::-webkit-inner-spin-button,
+	input.smart-step::-webkit-outer-spin-button {
+		-webkit-appearance: none;
+		margin: 0;
+	}
+	input.smart-step {
+		-moz-appearance: textfield;
+		appearance: textfield;
+	}
 	input[data-computed="true"],
 	input[readonly] {
 		color: var(--color-accent);
@@ -206,6 +290,14 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 		align-items: center;
 		gap: 0.2rem;
 	}
+	.tech-val {
+		flex: 1;
+		min-width: 0;
+		font-size: 0.8rem;
+		font-variant-numeric: tabular-nums;
+		text-align: right;
+		padding: 0.2rem 0.35rem;
+	}
 	.lock {
 		flex: none;
 		padding: 0;
@@ -214,5 +306,10 @@ calculator math — so the ship-group upgrade flow can reuse it later.
 		background: transparent;
 		border: 0;
 		cursor: pointer;
+		opacity: 0.5;
+	}
+	.lock.active,
+	.lock:hover {
+		opacity: 1;
 	}
 </style>

ui/frontend/src/lib/i18n/locales/en.ts

@@ -393,7 +393,9 @@ const en = {
 	"game.calculator.lock.reset": "locked — click to release to the computed value",
 	"game.calculator.lock.infeasible": "this target cannot be reached with the current design",
 	"game.calculator.lock.max": "release the locked result first — one result at a time",
+	"game.calculator.tech.override": "click to override your current tech",
 	"game.calculator.tech.reset": "overridden — click to reset to your current tech",
+	"game.calculator.mat.override": "click to override the planet value",
 	"game.calculator.mat.reset": "overridden — click to reset to the planet value",
 	"game.calculator.modern.current": "current",
 	"game.calculator.modern.target": "target",
@@ -418,6 +420,7 @@ const en = {
 	"game.calculator.invalid.all_zero": "at least one value must be nonzero",
 	"game.calculator.invalid.negative": "value cannot be negative",
 	"game.calculator.invalid.tech_value": "tech level cannot be negative",
+	"game.calculator.invalid.tech_below_current": "tech level cannot be below your current tech this turn",
 	"game.calculator.invalid.load_over_capacity": "load exceeds the ship's cargo capacity",
 	"game.calculator.lock.no_drive": "set a non-zero drive before locking speed",
 

ui/frontend/src/lib/i18n/locales/ru.ts

@@ -394,7 +394,9 @@ const ru: Record<keyof typeof en, string> = {
 	"game.calculator.lock.reset": "зафиксировано — нажмите, чтобы вернуть вычисляемое значение",
 	"game.calculator.lock.infeasible": "эта цель недостижима при текущих параметрах",
 	"game.calculator.lock.max": "сначала снимите фиксацию с другого результата — по одному за раз",
+	"game.calculator.tech.override": "нажмите, чтобы задать свой технологический уровень",
 	"game.calculator.tech.reset": "переопределено — нажмите, чтобы вернуть ваши текущие технологии",
+	"game.calculator.mat.override": "нажмите, чтобы задать своё значение MAT",
 	"game.calculator.mat.reset": "переопределено — нажмите, чтобы вернуть значение планеты",
 	"game.calculator.modern.current": "текущий",
 	"game.calculator.modern.target": "целевой",
@@ -419,6 +421,7 @@ const ru: Record<keyof typeof en, string> = {
 	"game.calculator.invalid.all_zero": "хотя бы одно значение должно быть ненулевым",
 	"game.calculator.invalid.negative": "значение не может быть отрицательным",
 	"game.calculator.invalid.tech_value": "технологический уровень не может быть отрицательным",
+	"game.calculator.invalid.tech_below_current": "технологический уровень не может быть ниже ваших текущих технологий на этом ходу",
 	"game.calculator.invalid.load_over_capacity": "загрузка превышает грузоподъёмность корабля",
 	"game.calculator.lock.no_drive": "задайте ненулевой двигатель, прежде чем фиксировать скорость",
 

ui/frontend/src/lib/sidebar/calculator-tab.svelte

@@ -14,7 +14,7 @@ switch (the inspector auto-opens on a planet click) — the calculator is a
 long-lived planning tool. `ensureGame` resets it when the game changes.
 -->
 <script lang="ts">
-	import { getContext } from "svelte";
+	import { getContext, tick } from "svelte";
 	import { appScreen } from "$lib/app-nav.svelte";
 
 	import { i18n, type TranslationKey } from "$lib/i18n/index.svelte";
@@ -273,6 +273,18 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 		cs.matValue < 0 ? i18n.t("game.calculator.invalid.negative") : "",
 	);
 
+	// Modernization target tech mirrors the design-area floor: a target
+	// below the player's current tech on this turn is meaningless (no
+	// upgrade), so flag it the same way.
+	function targetTechError(key: TechKey): string {
+		const value = cs.targetTech[key];
+		if (value < 0) return i18n.t("game.calculator.invalid.negative");
+		if (value < playerTech[key]) {
+			return i18n.t("game.calculator.invalid.tech_below_current");
+		}
+		return "";
+	}
+
 	// Locking a speed back-solves the drive block; with a zero drive the
 	// ship is deliberately immobile, so disallow it.
 	function lockDisabledReason(output: LockableOutputId): string {
@@ -291,8 +303,12 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 	function onResetTech(key: TechKey): void {
 		cs.techOverridden[key] = false;
 	}
-	function onMatInput(): void {
+	const matInputRef: { el?: HTMLInputElement } = {};
+	async function activateMatOverride(): Promise<void> {
 		cs.matOverridden = true;
+		await tick();
+		matInputRef.el?.focus();
+		matInputRef.el?.select();
 	}
 	function resetMat(): void {
 		cs.matOverridden = false;
@@ -485,6 +501,7 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 		resolved={resolvedCeil}
 		bind:techs={cs.techValues}
 		techOverridden={cs.techOverridden}
+		techFloor={playerTech}
 		computedInput={result.computedInput}
 		{onTechInput}
 		{onResetTech}
@@ -589,17 +606,17 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 				<div class="rrow">
 					<span class="label">{i18n.t("game.calculator.planet.mat")}</span>
 					<span class="cell">
-						<input
-							type="number"
-							step="0.01"
-							min="0"
-							bind:value={cs.matValue}
-							oninput={onMatInput}
-							aria-invalid={matError !== "" ? "true" : "false"}
-							title={matError}
-							data-testid="calculator-planet-mat"
-						/>
 						{#if cs.matOverridden}
+							<input
+								bind:this={matInputRef.el}
+								type="number"
+								step="0.01"
+								min="0"
+								bind:value={cs.matValue}
+								aria-invalid={matError !== "" ? "true" : "false"}
+								title={matError}
+								data-testid="calculator-planet-mat"
+							/>
 							<button
 								type="button"
 								class="lock active"
@@ -610,6 +627,23 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 							>
 								🔒
 							</button>
+						{:else}
+							<span
+								class="mat-val"
+								data-testid="calculator-planet-mat-value"
+							>
+								{cs.matValue}
+							</span>
+							<button
+								type="button"
+								class="lock"
+								title={i18n.t("game.calculator.mat.override")}
+								aria-label={i18n.t("game.calculator.mat.override")}
+								data-testid="calculator-mat-override"
+								onclick={() => void activateMatOverride()}
+							>
+								🔓
+							</button>
 						{/if}
 					</span>
 					<span></span>
@@ -638,18 +672,17 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 				<span class="col-head">{i18n.t("game.calculator.modern.cost")}</span>
 			</div>
 			{#each modernCosts?.perBlock ?? [] as row (row.key)}
+				{@const targetError = targetTechError(row.key)}
 				<div class="rrow">
 					<span class="label">{i18n.t(`game.calculator.field.${row.key}` as TranslationKey)}</span>
 					<span class="cell">
 						<input
 							type="number"
 							step="0.001"
-							min="0"
+							min={playerTech[row.key]}
 							bind:value={cs.targetTech[row.key]}
-							aria-invalid={cs.targetTech[row.key] < 0 ? "true" : "false"}
-							title={cs.targetTech[row.key] < 0
-								? i18n.t("game.calculator.invalid.negative")
-								: ""}
+							aria-invalid={targetError !== "" ? "true" : "false"}
+							title={targetError}
 							data-testid={`calculator-target-${row.key}`}
 						/>
 					</span>
@@ -899,4 +932,15 @@ long-lived planning tool. `ensureGame` resets it when the game changes.
 		font-size: 0.8rem;
 		color: var(--color-accent);
 	}
+	/* Plain-text view of the planet MAT (mirrors `.tech-val` in the
+	   design area) so the cell width stays the same whether the value is
+	   the inherited planet number or the player's override. */
+	.mat-val {
+		flex: 1;
+		min-width: 0;
+		font-size: 0.85rem;
+		font-variant-numeric: tabular-nums;
+		text-align: right;
+		padding: 0.15rem 0.3rem;
+	}
 </style>

ui/frontend/tests/calc-model.test.ts

@@ -135,6 +135,25 @@ describe("computeCalculator goal-seek", () => {
 		expect(result.blocks.drive).toBe(10);
 	});
 
+	test("speed lock is feasible at the ceiling when rest mass is zero", () => {
+		// Regression for the D=1, W=A=S=C=0 case: every block except
+		// drive is zero, so speed equals 20*driveTech (the ceiling); the
+		// solver must accept that exact target instead of flagging it
+		// as unreachable.
+		const core = makeFakeCore();
+		const result = computeCalculator(
+			input({
+				blocks: { drive: 1, armament: 0, weapons: 0, shields: 0, cargo: 0 },
+				driveTech: 1,
+				lock: { output: "speedEmpty", value: 20 },
+			}),
+			core,
+		);
+		expect(result.lockFeasible).toBe(true);
+		expect(result.computedInput).toBe("drive");
+		expect(result.outputs?.speedEmpty).toBeCloseTo(20, 9);
+	});
+
 	test("calls the matching solver with the right context", () => {
 		const weaponsForAttack = vi.fn(() => 7);
 		const core = makeFakeCore({ weaponsForAttack });

ui/frontend/tests/calculator-tab.test.ts

@@ -278,4 +278,106 @@ describe("calculator-tab", () => {
 			"15.273",
 		);
 	});
+
+	test("tech defaults render as a number with an open-lock affordance", () => {
+		const ui = mount();
+		// Default state: no override → number + open lock, no input.
+		expect(ui.getByTestId("calculator-tech-value-drive")).toHaveTextContent(
+			"1.2",
+		);
+		expect(
+			ui.getByTestId("calculator-tech-override-drive"),
+		).toBeInTheDocument();
+		expect(ui.queryByTestId("calculator-tech-drive")).toBeNull();
+	});
+
+	test("clicking the open tech lock reveals the input + closed lock", async () => {
+		const ui = mount();
+		await fireEvent.click(ui.getByTestId("calculator-tech-override-drive"));
+		// Now an input is rendered and the lock turned closed (reset).
+		expect(ui.getByTestId("calculator-tech-drive")).toHaveValue(1.2);
+		expect(ui.getByTestId("calculator-tech-reset-drive")).toBeInTheDocument();
+		expect(ui.queryByTestId("calculator-tech-value-drive")).toBeNull();
+	});
+
+	test("flags a tech override below the player's current tech", async () => {
+		const ui = mount();
+		await fireEvent.click(ui.getByTestId("calculator-tech-override-drive"));
+		// Player drive is 1.2; setting 0.5 is below the floor.
+		await fireEvent.input(ui.getByTestId("calculator-tech-drive"), {
+			target: { value: "0.5" },
+		});
+		expect(ui.getByTestId("calculator-tech-drive")).toHaveAttribute(
+			"aria-invalid",
+			"true",
+		);
+	});
+
+	test("smart step jumps from 0 to 1 on ArrowUp for ship blocks", async () => {
+		const ui = mount();
+		const drive = ui.getByTestId("calculator-block-drive") as HTMLInputElement;
+		drive.focus();
+		await fireEvent.keyDown(drive, { key: "ArrowUp" });
+		expect(drive).toHaveValue(1);
+		await fireEvent.keyDown(drive, { key: "ArrowUp" });
+		expect(drive).toHaveValue(1.1);
+		await fireEvent.keyDown(drive, { key: "ArrowDown" });
+		expect(drive).toHaveValue(1);
+		await fireEvent.keyDown(drive, { key: "ArrowDown" });
+		expect(drive).toHaveValue(0);
+	});
+
+	test("regression: speed lock works at the ceiling with all-zero non-drive blocks", async () => {
+		const ui = mount();
+		await setBlock(ui, "drive", 1);
+		// Override drive tech to 1 so the ceiling math is plain.
+		await fireEvent.click(ui.getByTestId("calculator-tech-override-drive"));
+		await fireEvent.input(ui.getByTestId("calculator-tech-drive"), {
+			target: { value: "1" },
+		});
+		// With D=1, W=A=S=C=0 the only achievable speed is 20*driveTech=20.
+		expect(ui.getByTestId("calculator-out-speedEmpty")).toHaveTextContent("20");
+		await fireEvent.click(ui.getByTestId("calculator-lock-speedEmpty"));
+		const locked = ui.getByTestId("calculator-locked-speedEmpty");
+		expect(locked).toHaveValue(20);
+		// The lock is feasible — no infeasible title and no red error class.
+		expect(locked).not.toHaveAttribute(
+			"title",
+			expect.stringMatching(/cannot be reached/i),
+		);
+	});
+
+	test("planet MAT defaults to a value + open lock and opens an input on click", async () => {
+		const selection = new SelectionStore();
+		selection.selectPlanet(17);
+		const ui = mount({
+			report: makeReport({ planets: [LOCAL_PLANET] }),
+			selection,
+		});
+		// Initial state: the MAT shows the planet's value via the number cell
+		// and an open lock; no input until the override is activated.
+		expect(
+			ui.getByTestId("calculator-planet-mat-value"),
+		).toHaveTextContent("100");
+		expect(
+			ui.getByTestId("calculator-mat-override"),
+		).toBeInTheDocument();
+		expect(ui.queryByTestId("calculator-planet-mat")).toBeNull();
+		await fireEvent.click(ui.getByTestId("calculator-mat-override"));
+		expect(ui.getByTestId("calculator-planet-mat")).toHaveValue(100);
+		expect(ui.getByTestId("calculator-mat-reset")).toBeInTheDocument();
+	});
+
+	test("flags a modernization target below the player's current tech", async () => {
+		const ui = mount();
+		await fireEvent.click(ui.getByTestId("calculator-mode-modernization"));
+		// Player drive is 1.2; the target is seeded with the same value.
+		await fireEvent.input(ui.getByTestId("calculator-target-drive"), {
+			target: { value: "0.5" },
+		});
+		expect(ui.getByTestId("calculator-target-drive")).toHaveAttribute(
+			"aria-invalid",
+			"true",
+		);
+	});
 });

ui/frontend/tests/e2e/game-shell-inspector.spec.ts

@@ -275,6 +275,9 @@ test("calculator draws reach circles for the selected planet", async ({
 	await calc.getByTestId("calculator-block-drive").fill("10");
 	await calc.getByTestId("calculator-block-shields").fill("5");
 	await calc.getByTestId("calculator-block-cargo").fill("5");
+	// Tech defaults render as a number + open lock; click to reveal the
+	// input before typing an override (the F8-06 unified lock idiom).
+	await calc.getByTestId("calculator-tech-override-drive").click();
 	await calc.getByTestId("calculator-tech-drive").fill("1.2");
 
 	await expect.poll(() => countReachCircles(page)).toBeGreaterThan(0);

ui/frontend/tests/fake-core.ts

@@ -94,10 +94,13 @@ export function makeFakeCore(overrides: Partial<Core> = {}): Core {
 		weaponsForAttack: ({ targetAttack, weaponsTech }) =>
 			weaponsTech <= 0 || targetAttack < 0 ? null : targetAttack / weaponsTech,
 		driveForSpeed: ({ targetSpeed, driveTech, restMass }) => {
+			if (driveTech <= 0 || targetSpeed <= 0) return null;
 			const ceiling = 20 * driveTech;
-			if (driveTech <= 0 || targetSpeed <= 0 || targetSpeed >= ceiling) {
-				return null;
+			if (restMass <= 0) {
+				if (targetSpeed !== ceiling) return null;
+				return 1;
 			}
+			if (targetSpeed >= ceiling) return null;
 			return (targetSpeed * restMass) / (ceiling - targetSpeed);
 		},
 		shieldsForDefence: ({ targetDefence, shieldsTech, restMass }) => {