diff --git a/.planning/ROADMAP.md b/.planning/ROADMAP.md
index 54d354f8..af516f13 100644
--- a/.planning/ROADMAP.md
+++ b/.planning/ROADMAP.md
@@ -501,8 +501,8 @@ Plans:
 
 Plans:
 - [x] 34-01-PLAN.md — Chat agent library: tool definitions, edit operations, context builder
-- [ ] 34-02-PLAN.md — Enhanced /api/chat route with tool calling for intent routing
-- [ ] 34-03-PLAN.md — Store applyEditOperations, ChatPanel tool result handling, end-to-end wiring
+- [x] 34-02-PLAN.md — Enhanced /api/chat route with tool calling for intent routing
+- [x] 34-03-PLAN.md — Store applyEditOperations, ChatPanel tool result handling, end-to-end wiring
 
 #### Phase 35: Large Workflow Handling
 
@@ -510,10 +510,12 @@ Plans:
 **Depends on**: Phase 34
 **Research**: Likely (chunking, context window strategies)
 **Research topics**: Token optimization for large payloads, base64 extraction/reinsertion, workflow summarization techniques
-**Plans**: TBD
+**Plans**: 3 plans
 
 Plans:
-- [ ] 35-01: TBD (run /gsd:plan-phase 35 to break down)
+- [ ] 35-01-PLAN.md — Binary stripping utility and rich workflow context builder (TDD)
+- [ ] 35-02-PLAN.md — Selection-aware subgraph extraction (TDD)
+- [ ] 35-03-PLAN.md — Client-side wiring, ChatPanel selection chip, API subgraph integration
 
 ### 📋 v1.5 Store Refactoring (Planned)
 
diff --git a/src/lib/chat/subgraphExtractor.test.ts b/src/lib/chat/subgraphExtractor.test.ts
new file mode 100644
index 00000000..85d7b5a7
--- /dev/null
+++ b/src/lib/chat/subgraphExtractor.test.ts
@@ -0,0 +1,289 @@
+/**
+ * Tests for subgraphExtractor.ts
+ *
+ * Validates selection-aware subgraph extraction for context scoping.
+ */
+
+import { describe, it, expect } from "vitest";
+import type { WorkflowNode } from "@/types/nodes";
+import type { WorkflowEdge } from "@/types/workflow";
+import { extractSubgraph, SubgraphResult } from "./subgraphExtractor";
+
+// Helper to create test nodes
+function createNode(id: string, type: string, selected = false): WorkflowNode {
+  return {
+    id,
+    type: type as any,
+    position: { x: 0, y: 0 },
+    data: {},
+    selected,
+  };
+}
+
+// Helper to create test edges
+function createEdge(
+  source: string,
+  target: string,
+  sourceHandle = "image",
+  targetHandle = "image"
+): WorkflowEdge {
+  return {
+    id: `${source}-${target}`,
+    source,
+    target,
+    sourceHandle,
+    targetHandle,
+  };
+}
+
+describe("extractSubgraph", () => {
+  describe("No selection (empty array)", () => {
+    it("returns all nodes and edges when selectedNodeIds is empty", () => {
+      const nodes: WorkflowNode[] = [
+        createNode("A", "prompt"),
+        createNode("B", "nanoBanana"),
+        createNode("C", "output"),
+      ];
+      const edges: WorkflowEdge[] = [
+        createEdge("A", "B", "text", "text"),
+        createEdge("B", "C", "image", "image"),
+      ];
+
+      const result = extractSubgraph(nodes, edges, []);
+
+      expect(result.isScoped).toBe(false);
+      expect(result.selectedNodes).toHaveLength(3);
+      expect(result.selectedEdges).toHaveLength(2);
+      expect(result.restSummary).toBeNull();
+    });
+  });
+
+  describe("Select all nodes", () => {
+    it("returns all nodes with isScoped=true and empty restSummary", () => {
+      const nodes: WorkflowNode[] = [
+        createNode("A", "prompt"),
+        createNode("B", "nanoBanana"),
+        createNode("C", "output"),
+      ];
+      const edges: WorkflowEdge[] = [
+        createEdge("A", "B", "text", "text"),
+        createEdge("B", "C", "image", "image"),
+      ];
+
+      const result = extractSubgraph(nodes, edges, ["A", "B", "C"]);
+
+      expect(result.isScoped).toBe(true);
+      expect(result.selectedNodes).toHaveLength(3);
+      expect(result.selectedEdges).toHaveLength(2);
+      expect(result.restSummary).not.toBeNull();
+      expect(result.restSummary!.nodeCount).toBe(0);
+      expect(result.restSummary!.boundaryConnections).toHaveLength(0);
+    });
+  });
+
+  describe("Select one node in chain", () => {
+    it("selects middle node with incoming and outgoing boundary connections", () => {
+      const nodes: WorkflowNode[] = [
+        createNode("A", "prompt"),
+        createNode("B", "nanoBanana"),
+        createNode("C", "output"),
+      ];
+      const edges: WorkflowEdge[] = [
+        createEdge("A", "B", "text", "text"),
+        createEdge("B", "C", "image", "image"),
+      ];
+
+      const result = extractSubgraph(nodes, edges, ["B"]);
+
+      expect(result.isScoped).toBe(true);
+      expect(result.selectedNodes).toHaveLength(1);
+      expect(result.selectedNodes[0].id).toBe("B");
+      expect(result.selectedEdges).toHaveLength(0); // No edges fully within selection
+
+      expect(result.restSummary).not.toBeNull();
+      expect(result.restSummary!.nodeCount).toBe(2);
+      expect(result.restSummary!.boundaryConnections).toHaveLength(2);
+
+      const incoming = result.restSummary!.boundaryConnections.find(
+        (c) => c.direction === "incoming"
+      );
+      expect(incoming).toBeDefined();
+      expect(incoming!.selectedNodeId).toBe("B");
+      expect(incoming!.otherNodeId).toBe("A");
+      expect(incoming!.handleType).toBe("text");
+
+      const outgoing = result.restSummary!.boundaryConnections.find(
+        (c) => c.direction === "outgoing"
+      );
+      expect(outgoing).toBeDefined();
+      expect(outgoing!.selectedNodeId).toBe("B");
+      expect(outgoing!.otherNodeId).toBe("C");
+      expect(outgoing!.handleType).toBe("image");
+    });
+  });
+
+  describe("Select two connected nodes", () => {
+    it("includes edge between selected nodes", () => {
+      const nodes: WorkflowNode[] = [
+        createNode("A", "prompt"),
+        createNode("B", "nanoBanana"),
+        createNode("C", "output"),
+      ];
+      const edges: WorkflowEdge[] = [
+        createEdge("A", "B", "text", "text"),
+        createEdge("B", "C", "image", "image"),
+      ];
+
+      const result = extractSubgraph(nodes, edges, ["A", "B"]);
+
+      expect(result.isScoped).toBe(true);
+      expect(result.selectedNodes).toHaveLength(2);
+      expect(result.selectedEdges).toHaveLength(1);
+      expect(result.selectedEdges[0].id).toBe("A-B");
+
+      expect(result.restSummary).not.toBeNull();
+      expect(result.restSummary!.nodeCount).toBe(1);
+      expect(result.restSummary!.boundaryConnections).toHaveLength(1);
+
+      const boundary = result.restSummary!.boundaryConnections[0];
+      expect(boundary.direction).toBe("outgoing");
+      expect(boundary.selectedNodeId).toBe("B");
+      expect(boundary.otherNodeId).toBe("C");
+    });
+  });
+
+  describe("Select subset of chain", () => {
+    it("correctly identifies boundary connections for middle segment", () => {
+      const nodes: WorkflowNode[] = [
+        createNode("A", "prompt"),
+        createNode("B", "nanoBanana"),
+        createNode("C", "annotation"),
+        createNode("D", "output"),
+      ];
+      const edges: WorkflowEdge[] = [
+        createEdge("A", "B", "text", "text"),
+        createEdge("B", "C", "image", "image"),
+        createEdge("C", "D", "image", "image"),
+      ];
+
+      const result = extractSubgraph(nodes, edges, ["B", "C"]);
+
+      expect(result.isScoped).toBe(true);
+      expect(result.selectedNodes).toHaveLength(2);
+      expect(result.selectedEdges).toHaveLength(1);
+      expect(result.selectedEdges[0].id).toBe("B-C");
+
+      expect(result.restSummary).not.toBeNull();
+      expect(result.restSummary!.nodeCount).toBe(2);
+      expect(result.restSummary!.boundaryConnections).toHaveLength(2);
+
+      const incoming = result.restSummary!.boundaryConnections.find(
+        (c) => c.direction === "incoming" && c.selectedNodeId === "B"
+      );
+      expect(incoming).toBeDefined();
+      expect(incoming!.otherNodeId).toBe("A");
+
+      const outgoing = result.restSummary!.boundaryConnections.find(
+        (c) => c.direction === "outgoing" && c.selectedNodeId === "C"
+      );
+      expect(outgoing).toBeDefined();
+      expect(outgoing!.otherNodeId).toBe("D");
+    });
+  });
+
+  describe("Type breakdown", () => {
+    it("correctly counts node types in unselected nodes", () => {
+      const nodes: WorkflowNode[] = [
+        createNode("A", "prompt"),
+        createNode("B", "prompt"),
+        createNode("C", "nanoBanana"),
+        createNode("D", "nanoBanana"),
+        createNode("E", "nanoBanana"),
+        createNode("F", "output"),
+      ];
+      const edges: WorkflowEdge[] = [];
+
+      const result = extractSubgraph(nodes, edges, ["A"]);
+
+      expect(result.isScoped).toBe(true);
+      expect(result.restSummary).not.toBeNull();
+      expect(result.restSummary!.nodeCount).toBe(5);
+      expect(result.restSummary!.typeBreakdown).toEqual({
+        prompt: 1,
+        nanoBanana: 3,
+        output: 1,
+      });
+    });
+  });
+
+  describe("Disconnected selected nodes", () => {
+    it("handles selection with no edges between selected nodes", () => {
+      const nodes: WorkflowNode[] = [
+        createNode("A", "prompt"),
+        createNode("B", "nanoBanana"),
+        createNode("C", "prompt"),
+        createNode("D", "output"),
+      ];
+      const edges: WorkflowEdge[] = [
+        createEdge("A", "B", "text", "text"),
+        createEdge("C", "D", "text", "image"),
+      ];
+
+      const result = extractSubgraph(nodes, edges, ["A", "C"]);
+
+      expect(result.isScoped).toBe(true);
+      expect(result.selectedNodes).toHaveLength(2);
+      expect(result.selectedEdges).toHaveLength(0); // No edges between A and C
+
+      expect(result.restSummary).not.toBeNull();
+      expect(result.restSummary!.nodeCount).toBe(2);
+      expect(result.restSummary!.boundaryConnections).toHaveLength(2);
+
+      // Both are outgoing since A->B and C->D
+      const outgoingConnections = result.restSummary!.boundaryConnections.filter(
+        (c) => c.direction === "outgoing"
+      );
+      expect(outgoingConnections).toHaveLength(2);
+    });
+  });
+
+  describe("Complex multi-handle scenario", () => {
+    it("handles multiple connections to same node with different handle types", () => {
+      const nodes: WorkflowNode[] = [
+        createNode("prompt1", "prompt"),
+        createNode("prompt2", "prompt"),
+        createNode("img1", "imageInput"),
+        createNode("gen", "nanoBanana"),
+        createNode("out", "output"),
+      ];
+      const edges: WorkflowEdge[] = [
+        createEdge("prompt1", "gen", "text", "text"),
+        createEdge("prompt2", "gen", "text", "text"),
+        createEdge("img1", "gen", "image", "image"),
+        createEdge("gen", "out", "image", "image"),
+      ];
+
+      const result = extractSubgraph(nodes, edges, ["gen"]);
+
+      expect(result.isScoped).toBe(true);
+      expect(result.selectedNodes).toHaveLength(1);
+      expect(result.selectedEdges).toHaveLength(0);
+
+      expect(result.restSummary).not.toBeNull();
+      expect(result.restSummary!.nodeCount).toBe(4);
+      expect(result.restSummary!.boundaryConnections).toHaveLength(4);
+
+      // 3 incoming (2 text from prompts, 1 image from img1)
+      const incoming = result.restSummary!.boundaryConnections.filter(
+        (c) => c.direction === "incoming"
+      );
+      expect(incoming).toHaveLength(3);
+
+      // 1 outgoing (to out)
+      const outgoing = result.restSummary!.boundaryConnections.filter(
+        (c) => c.direction === "outgoing"
+      );
+      expect(outgoing).toHaveLength(1);
+    });
+  });
+});
diff --git a/src/lib/chat/subgraphExtractor.ts b/src/lib/chat/subgraphExtractor.ts
new file mode 100644
index 00000000..5456bb79
--- /dev/null
+++ b/src/lib/chat/subgraphExtractor.ts
@@ -0,0 +1,54 @@
+/**
+ * Subgraph Extractor
+ *
+ * Splits a workflow into a detailed selected subgraph and a summary of the rest,
+ * based on React Flow's node.selected property. When users select nodes before
+ * chatting, the LLM gets focused context on the selection with a lightweight
+ * summary of the surrounding workflow.
+ */
+
+import type { WorkflowNode } from "@/types/nodes";
+import type { WorkflowEdge } from "@/types/workflow";
+
+/**
+ * Boundary connection between selected and unselected nodes
+ */
+export interface BoundaryConnection {
+  direction: "incoming" | "outgoing";
+  selectedNodeId: string;
+  otherNodeId: string;
+  handleType: string;
+}
+
+/**
+ * Result of subgraph extraction
+ */
+export interface SubgraphResult {
+  // When selectedNodeIds is empty, these are ALL nodes/edges (no scoping)
+  selectedNodes: WorkflowNode[];
+  selectedEdges: WorkflowEdge[];
+  // Summary of unselected nodes (null when no selection)
+  restSummary: {
+    nodeCount: number;
+    typeBreakdown: Record<string, number>;
+    boundaryConnections: BoundaryConnection[];
+  } | null;
+  isScoped: boolean; // true when selectedNodeIds is non-empty
+}
+
+/**
+ * Extract subgraph based on selected node IDs
+ *
+ * @param nodes - All workflow nodes
+ * @param edges - All workflow edges
+ * @param selectedNodeIds - IDs of selected nodes
+ * @returns Subgraph result with selected nodes/edges and rest summary
+ */
+export function extractSubgraph(
+  nodes: WorkflowNode[],
+  edges: WorkflowEdge[],
+  selectedNodeIds: string[]
+): SubgraphResult {
+  // TODO: Implement
+  throw new Error("Not implemented");
+}