diff --git a/packages/web/src/components/InteractiveGraphVisualization.tsx b/packages/web/src/components/InteractiveGraphVisualization.tsx
index 27b7376f..512cd728 100644
--- a/packages/web/src/components/InteractiveGraphVisualization.tsx
+++ b/packages/web/src/components/InteractiveGraphVisualization.tsx
@@ -52,6 +52,7 @@ import { computeNodeLayerY, isHierarchicalLayout, parseLayoutMode, LAYOUT_MODE_S
 import { edgeBorderEndpoints, minEdgeLength, clampToMinNeighbors } from '../lib/edgeGeometry';
 import { directionStrategy, arrowVisibility, labelVisibility, perpendicularOffset } from '../lib/edgeLOD';
 import { assignParallelEdgeIndices } from '../lib/parallelEdges';
+import { isTap, touchHitSize, isCoarsePointer } from '../lib/touchInteraction';
 import { spawnCelebration } from '../lib/celebration';
 import { buildNeighborhood } from '../lib/graphAdjacency';
 import { UndoStack } from '../lib/undoStack';
@@ -2826,6 +2827,24 @@ export function InteractiveGraphVisualization({ onResetLayout, onNodeSelected, i
         if (d.subgraphId) descendIntoRef.current(d.subgraphId);
       });
 
+    // 44px touch targets (#29): the header icon buttons draw at iconSize (16-24px),
+    // far below the 44px minimum, so they're hard to hit on a phone. On a coarse
+    // pointer, prepend a transparent hit-rect of touchHitSize() to each icon group
+    // (pointer-events bubble to the group's handlers) — bigger tap area, identical
+    // look. The rect lives in the group's counter-zoomed local space, so it tracks.
+    if (isCoarsePointer()) {
+      const hit = touchHitSize(iconSize, true);
+      nodeElements.selectAll('.node-edit-icon, .node-relationship-icon, .node-expand-icon, .node-descend-icon')
+        .insert('rect', ':first-child')
+        .attr('class', 'touch-hit-area')
+        .attr('x', -hit / 2)
+        .attr('y', -hit / 2)
+        .attr('width', hit)
+        .attr('height', hit)
+        .attr('fill', 'transparent')
+        .style('pointer-events', 'all');
+    }
+
     // Child-graph count line (LOD-gated like the description text).
     sheetNodes.append('text')
       .attr('class', 'node-subgraph-count')
@@ -3568,7 +3587,7 @@ export function InteractiveGraphVisualization({ onResetLayout, onNodeSelected, i
         }
       }
     })
-    .on('touchend', function() {
+    .on('touchend', function(event: TouchEvent, d: any) {
       // Clean up long-press detection
       const element = d3.select(this);
       const touchData = (element.node() as any).__touchData;
@@ -3577,6 +3596,16 @@ export function InteractiveGraphVisualization({ onResetLayout, onNodeSelected, i
         if (touchData.timeout) {
           clearTimeout(touchData.timeout);
         }
+        // TAP-TO-OPEN (#29): a quick touch that didn't move = a tap → select/open
+        // the node, deterministically. preventDefault suppresses the flaky
+        // synthetic mouse-click so the tap doesn't double-fire (open then toggle
+        // shut). Long-press (handled by the touchstart timeout) and drag/pan
+        // (moved past the slop) are excluded by isTap.
+        const duration = Date.now() - touchData.startTime;
+        if (isTap(duration, touchData.moved ? 999 : 0)) {
+          event.preventDefault();
+          handleNodeClick(event as unknown as MouseEvent, d);
+        }
         delete (element.node() as any).__touchData;
       }
 
diff --git a/packages/web/src/lib/__tests__/touchInteraction.test.ts b/packages/web/src/lib/__tests__/touchInteraction.test.ts
new file mode 100644
index 00000000..3b1d054d
--- /dev/null
+++ b/packages/web/src/lib/__tests__/touchInteraction.test.ts
@@ -0,0 +1,59 @@
+import { describe, it, expect } from 'vitest';
+import {
+  MIN_TOUCH_TARGET, isTap, isLongPress, touchHitSize, distance, isCoarsePointer,
+} from '../touchInteraction';
+
+describe('isTap', () => {
+  it('quick + still = tap', () => {
+    expect(isTap(120, 3)).toBe(true);
+    expect(isTap(0, 0)).toBe(true);
+  });
+  it('moved past slop = not a tap (it is a drag/pan)', () => {
+    expect(isTap(120, 40)).toBe(false);
+  });
+  it('held too long = not a tap (it is a long-press)', () => {
+    expect(isTap(600, 2)).toBe(false);
+  });
+});
+
+describe('isLongPress', () => {
+  it('held + still = long-press', () => {
+    expect(isLongPress(600, 4)).toBe(true);
+  });
+  it('moved = not a long-press', () => {
+    expect(isLongPress(600, 40)).toBe(false);
+  });
+  it('quick = not a long-press', () => {
+    expect(isLongPress(120, 2)).toBe(false);
+  });
+  it('tap and long-press are mutually exclusive across the boundary', () => {
+    expect(isTap(499, 0)).toBe(true);
+    expect(isLongPress(499, 0)).toBe(false);
+    expect(isTap(500, 0)).toBe(false);
+    expect(isLongPress(500, 0)).toBe(true);
+  });
+});
+
+describe('touchHitSize', () => {
+  it('enforces the 44px minimum on touch, never shrinking a larger control', () => {
+    expect(touchHitSize(16, true)).toBe(MIN_TOUCH_TARGET);
+    expect(touchHitSize(24, true)).toBe(44);
+    expect(touchHitSize(60, true)).toBe(60);
+  });
+  it('leaves the visual size untouched on a mouse pointer', () => {
+    expect(touchHitSize(16, false)).toBe(16);
+  });
+});
+
+describe('distance', () => {
+  it('is euclidean', () => {
+    expect(distance(0, 0, 3, 4)).toBe(5);
+    expect(distance(1, 1, 1, 1)).toBe(0);
+  });
+});
+
+describe('isCoarsePointer', () => {
+  it('does not throw without a browser matchMedia', () => {
+    expect(typeof isCoarsePointer()).toBe('boolean');
+  });
+});
diff --git a/packages/web/src/lib/touchInteraction.ts b/packages/web/src/lib/touchInteraction.ts
new file mode 100644
index 00000000..4467caa8
--- /dev/null
+++ b/packages/web/src/lib/touchInteraction.ts
@@ -0,0 +1,51 @@
+/**
+ * Pure touch-interaction logic for the graph (#29 mobile touch overhaul). The D3
+ * layer feeds raw touch timing/movement here and applies the verdicts; keeping
+ * the thresholds + classification here makes them unit-testable without a DOM.
+ *
+ * Gestures on a node:
+ *  - tap         → select / open (short, didn't move)
+ *  - long-press  → context menu (held, didn't move)
+ *  - drag/pan    → move the node or pan the canvas (moved past the slop)
+ */
+export const MIN_TOUCH_TARGET = 44; // px — WCAG 2.5.5 / Apple HIG minimum
+export const TAP_MAX_MS = 500;      // held longer (without moving) = long-press
+export const TAP_MAX_MOVE_PX = 10;  // moved farther = drag/pan, not a tap
+
+export function distance(ax: number, ay: number, bx: number, by: number): number {
+  return Math.hypot(ax - bx, ay - by);
+}
+
+/** A quick touch that didn't move = a tap (select/open). */
+export function isTap(
+  durationMs: number,
+  movePx: number,
+  { maxMs = TAP_MAX_MS, maxMove = TAP_MAX_MOVE_PX } = {},
+): boolean {
+  return durationMs >= 0 && durationMs < maxMs && movePx <= maxMove;
+}
+
+/** A held touch that didn't move = a long-press (context menu). */
+export function isLongPress(
+  durationMs: number,
+  movePx: number,
+  { minMs = TAP_MAX_MS, maxMove = TAP_MAX_MOVE_PX } = {},
+): boolean {
+  return durationMs >= minMs && movePx <= maxMove;
+}
+
+/**
+ * The hit-area side length for an on-canvas control. On touch we guarantee at
+ * least MIN_TOUCH_TARGET regardless of how small the icon is drawn; on a mouse
+ * pointer the visual size is fine.
+ */
+export function touchHitSize(visualPx: number, isTouch: boolean, min = MIN_TOUCH_TARGET): number {
+  return isTouch ? Math.max(min, visualPx) : visualPx;
+}
+
+/** Coarse-pointer (touch) detection; safe in non-browser/test contexts. */
+export function isCoarsePointer(): boolean {
+  return typeof window !== 'undefined'
+    && typeof window.matchMedia === 'function'
+    && window.matchMedia('(pointer: coarse)').matches;
+}
diff --git a/tests/e2e/mobile/touch-graph.spec.ts b/tests/e2e/mobile/touch-graph.spec.ts
new file mode 100644
index 00000000..e26fda11
--- /dev/null
+++ b/tests/e2e/mobile/touch-graph.spec.ts
@@ -0,0 +1,33 @@
+import { test, expect } from '@playwright/test';
+import { login, TEST_USERS } from '../../lib/auth';
+
+/**
+ * Mobile touch overhaul (#29). On a phone the graph defaults to LOCKED (touch
+ * pans the canvas), but a single TAP on a node must still open it — the primary
+ * way to inspect/edit on touch. Verifies tap-to-open works under a real touch
+ * context (not a synthetic mouse click).
+ */
+test.use({ viewport: { width: 390, height: 844 }, hasTouch: true });
+
+test.describe('mobile graph touch @mobile @touch', () => {
+  test('single tap on a node opens the inspector (even while locked)', async ({ page }) => {
+    test.setTimeout(90000);
+    await login(page, TEST_USERS.ADMIN);
+    // Land deterministically on the graph view.
+    await page.evaluate(() => localStorage.setItem('graphdone:viewMode', 'graph'));
+    await page.reload({ waitUntil: 'domcontentloaded' });
+    await page.waitForSelector('.node-bg', { timeout: 30000 });
+    await page.waitForTimeout(4000); // let physics settle
+
+    // The graph starts locked on a phone (pan-by-touch is the default nav).
+    const lock = page.getByTestId('graph-lock-toggle');
+    await expect(lock).toBeVisible();
+
+    // Inspector is not open yet.
+    await expect(page.getByTestId('node-inspector')).toHaveCount(0);
+
+    // A real touch TAP on a node card opens the inspector.
+    await page.locator('.node-bg').first().tap();
+    await expect(page.getByTestId('node-inspector')).toBeVisible({ timeout: 8000 });
+  });
+});