feat(04-04): add UpdateParamsCommand + BlockInspector module

- UpdateParamsCommand with execute/undo for color/speed/direction/length
- Uses module-level currentShowId (not this._showId) matching existing pattern
- BlockInspector renders compact strip with animation label, color swatch,
  speed input, direction select, length input, and remove button
- Color change committed on 'change' event (not 'input') to avoid command flood
- _onDelete callback wired to remove button for app.js to handle

lightsync/frontend/timeline/commands.js

@@ -88,6 +88,27 @@ export class ResizeBlockCommand {
     }
 }
 
+// ── UpdateParamsCommand ──────────────────────────────────────────────────────
+
+export class UpdateParamsCommand {
+    constructor(tracks, block, oldParams, newParams) {
+        this.tracks = tracks;
+        this.block = block;
+        this.oldParams = { ...oldParams };  // shallow copy
+        this.newParams = { ...newParams };  // shallow copy
+    }
+
+    execute() {
+        Object.assign(this.block.params, this.newParams);
+        syncBlock(currentShowId, this.block.device_id, this.block, 'PATCH');
+    }
+
+    undo() {
+        Object.assign(this.block.params, this.oldParams);
+        syncBlock(currentShowId, this.block.device_id, this.block, 'PATCH');
+    }
+}
+
 // ── DeleteBlockCommand ───────────────────────────────────────────────────────
 
 export class DeleteBlockCommand {

lightsync/frontend/timeline/inspector.js

@@ -0,0 +1,118 @@
+// BlockInspector — compact horizontal strip for editing selected block params
+// Appears between timeline canvas and transport bar when a block is selected.
+// All parameter changes go through UpdateParamsCommand for full undo/redo support.
+
+import { UpdateParamsCommand } from './commands.js';
+
+export class BlockInspector {
+    constructor(containerEl, history) {
+        this.el = containerEl;       // #block-inspector div
+        this.history = history;      // CommandHistory reference
+        this.tracks = null;          // set by app.js from timeline.tracks
+        this.currentBlock = null;
+        this._onDelete = null;       // callback(block) — set by app.js
+    }
+
+    show(block) {
+        this.currentBlock = block;
+        if (!block) {
+            this.el.style.display = 'none';
+            return;
+        }
+        this.el.style.display = 'flex';
+        this._render(block);
+    }
+
+    hide() {
+        this.currentBlock = null;
+        this.el.style.display = 'none';
+    }
+
+    _render(block) {
+        const animName = (block.animation || 'BLOCK').toUpperCase().replace(/_/g, ' ');
+        const color = block.params?.color || '#00ffff';
+        const speed = block.params?.speed ?? 1.0;
+        const direction = block.params?.direction || 'forward';
+        const length = block.params?.length ?? 0.3;
+
+        this.el.innerHTML = `
+            <span class="inspector-label">${animName}</span>
+            <label class="inspector-field">
+                COLOR
+                <div class="inspector-color-swatch" id="color-swatch" style="background:${color};" title="Click to change color"></div>
+                <input type="color" id="inspector-color" value="${color}" style="display:none;">
+            </label>
+            <label class="inspector-field">
+                SPEED
+                <input type="number" id="inspector-speed" step="0.1" min="0.1" max="10" value="${speed}">
+            </label>
+            <label class="inspector-field">
+                DIR
+                <select id="inspector-direction">
+                    <option value="forward" ${direction === 'forward' ? 'selected' : ''}>FWD</option>
+                    <option value="reverse" ${direction === 'reverse' ? 'selected' : ''}>REV</option>
+                </select>
+            </label>
+            <label class="inspector-field">
+                LEN
+                <input type="number" id="inspector-length" step="0.05" min="0.05" max="1" value="${length}">
+            </label>
+            <div style="flex:1"></div>
+            <button class="inspector-remove" title="Remove block">&#10005;</button>
+        `;
+
+        this._wireEvents(block);
+    }
+
+    _wireEvents(block) {
+        // Color swatch → open hidden color input
+        const swatch = this.el.querySelector('#color-swatch');
+        const colorInput = this.el.querySelector('#inspector-color');
+        swatch?.addEventListener('click', () => colorInput?.click());
+
+        // Live preview: update swatch as color drags
+        colorInput?.addEventListener('input', (e) => {
+            swatch.style.background = e.target.value;
+        });
+        // Commit on change (not during drag — avoids command flood)
+        colorInput?.addEventListener('change', (e) => {
+            const oldParams = { ...block.params };
+            const newParams = { ...block.params, color: e.target.value };
+            const cmd = new UpdateParamsCommand(this.tracks, block, oldParams, newParams);
+            this.history.execute(cmd);
+        });
+
+        // Speed
+        this.el.querySelector('#inspector-speed')?.addEventListener('change', (e) => {
+            const val = parseFloat(e.target.value);
+            if (isNaN(val) || val < 0.1 || val > 10) return;
+            const oldParams = { ...block.params };
+            const newParams = { ...block.params, speed: val };
+            const cmd = new UpdateParamsCommand(this.tracks, block, oldParams, newParams);
+            this.history.execute(cmd);
+        });
+
+        // Direction
+        this.el.querySelector('#inspector-direction')?.addEventListener('change', (e) => {
+            const oldParams = { ...block.params };
+            const newParams = { ...block.params, direction: e.target.value };
+            const cmd = new UpdateParamsCommand(this.tracks, block, oldParams, newParams);
+            this.history.execute(cmd);
+        });
+
+        // Length
+        this.el.querySelector('#inspector-length')?.addEventListener('change', (e) => {
+            const val = parseFloat(e.target.value);
+            if (isNaN(val) || val < 0.05 || val > 1) return;
+            const oldParams = { ...block.params };
+            const newParams = { ...block.params, length: val };
+            const cmd = new UpdateParamsCommand(this.tracks, block, oldParams, newParams);
+            this.history.execute(cmd);
+        });
+
+        // Remove button
+        this.el.querySelector('.inspector-remove')?.addEventListener('click', () => {
+            if (this._onDelete) this._onDelete(block);
+        });
+    }
+}