test(P02): backend test coverage — 4 new suites, 353 tests passing

---ci---
project: ci
phase: 2
milestone: v0.5
status: complete
decisions:
  - id: D-024
    decision: Phase 2 Backend Test Coverage complete
    rationale: All TEST requirements covered; 31 suites, 353 tests passing
    confidence: 0.95
    alternatives: []
requirements:
  covered: [TEST-01, TEST-02, TEST-03, TEST-04]
---/ci---

src/backends/tool-registry-extended.test.ts

@@ -0,0 +1,135 @@
+import * as fs from "node:fs";
+import * as path from "node:path";
+import * as os from "node:os";
+import { ToolRegistry, TOOL_DEFINITIONS } from "../backends/tool-registry.js";
+
+describe("ToolRegistry Extended", () => {
+  let tempDir: string;
+  let registry: ToolRegistry;
+
+  beforeEach(() => {
+    tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "ci-tool-registry-ext-"));
+    registry = new ToolRegistry(tempDir);
+  });
+
+  afterEach(() => {
+    fs.rmSync(tempDir, { recursive: true, force: true });
+  });
+
+  describe("readFile edge cases", () => {
+    it("reads empty file", () => {
+      const filePath = path.join(tempDir, "empty.txt");
+      fs.writeFileSync(filePath, "");
+      const result = registry.execute({ name: "readFile", arguments: { path: filePath } });
+      expect(result.content).toBe("");
+      expect(result.isError).toBeFalsy();
+    });
+
+    it("reads file with unicode content", () => {
+      const filePath = path.join(tempDir, "unicode.txt");
+      fs.writeFileSync(filePath, "héllo wörld 🌍");
+      const result = registry.execute({ name: "readFile", arguments: { path: filePath } });
+      expect(result.content).toBe("héllo wörld 🌍");
+    });
+
+    it("handles unreadable file gracefully", () => {
+      if (process.getuid?.() === 0) return;
+      const filePath = path.join(tempDir, "unreadable.txt");
+      fs.writeFileSync(filePath, "data");
+      fs.chmodSync(filePath, 0o000);
+      const result = registry.execute({ name: "readFile", arguments: { path: filePath } });
+      expect(result.isError).toBe(true);
+      fs.chmodSync(filePath, 0o644);
+    });
+  });
+
+  describe("writeFile edge cases", () => {
+    it("overwrites existing file", () => {
+      const filePath = path.join(tempDir, "overwrite.txt");
+      fs.writeFileSync(filePath, "old");
+      const result = registry.execute({ name: "writeFile", arguments: { path: filePath, content: "new" } });
+      expect(result.isError).toBeFalsy();
+      expect(fs.readFileSync(filePath, "utf-8")).toBe("new");
+    });
+
+    it("creates nested directories", () => {
+      const filePath = path.join(tempDir, "a", "b", "c", "deep.txt");
+      const result = registry.execute({ name: "writeFile", arguments: { path: filePath, content: "deep" } });
+      expect(result.isError).toBeFalsy();
+      expect(fs.readFileSync(filePath, "utf-8")).toBe("deep");
+    });
+  });
+
+  describe("editFile edge cases", () => {
+    it("replaces only first occurrence", () => {
+      const filePath = path.join(tempDir, "multi.txt");
+      fs.writeFileSync(filePath, "aaa bbb aaa");
+      const result = registry.execute({ name: "editFile", arguments: { path: filePath, old: "aaa", new: "zzz" } });
+      expect(result.isError).toBeFalsy();
+      expect(fs.readFileSync(filePath, "utf-8")).toBe("zzz bbb aaa");
+    });
+
+    it("handles empty old string", () => {
+      const filePath = path.join(tempDir, "empty-old.txt");
+      fs.writeFileSync(filePath, "hello");
+      const result = registry.execute({ name: "editFile", arguments: { path: filePath, old: "", new: "X" } });
+      expect(fs.readFileSync(filePath, "utf-8")).toContain("X");
+    });
+  });
+
+  describe("runBash edge cases", () => {
+    it("respects cwd argument", () => {
+      const subDir = path.join(tempDir, "subdir");
+      fs.mkdirSync(subDir);
+      const result = registry.execute({ name: "runBash", arguments: { command: "pwd", cwd: subDir } });
+      expect(result.content).toContain("subdir");
+      expect(result.isError).toBeFalsy();
+    });
+
+    it("respects timeout argument", () => {
+      const result = registry.execute({ name: "runBash", arguments: { command: "sleep 100", timeout: 500 } });
+      expect(result.isError).toBe(true);
+    });
+
+    it("captures stderr in error output", () => {
+      const result = registry.execute({ name: "runBash", arguments: { command: "echo error >&2 && exit 1" } });
+      expect(result.isError).toBe(true);
+      expect(result.content).toContain("error");
+    });
+  });
+
+  describe("glob edge cases", () => {
+    it("finds files in subdirectories", () => {
+      const subDir = path.join(tempDir, "src");
+      fs.mkdirSync(subDir);
+      fs.writeFileSync(path.join(subDir, "app.ts"), "");
+      fs.writeFileSync(path.join(subDir, "util.ts"), "");
+      const result = registry.execute({ name: "glob", arguments: { pattern: "**/*.ts" } });
+      const matches = JSON.parse(result.content);
+      expect(matches.length).toBeGreaterThanOrEqual(2);
+    });
+
+    it("returns empty array for no matches", () => {
+      const result = registry.execute({ name: "glob", arguments: { pattern: "*.xyz" } });
+      const matches = JSON.parse(result.content);
+      expect(matches).toEqual([]);
+    });
+  });
+
+  describe("grep edge cases", () => {
+    it("supports include pattern filter", () => {
+      fs.writeFileSync(path.join(tempDir, "app.ts"), "const x = 1;\n");
+      fs.writeFileSync(path.join(tempDir, "app.js"), "const x = 1;\n");
+      const result = registry.execute({ name: "grep", arguments: { pattern: "const", include: "*.ts" } });
+      const matches = JSON.parse(result.content);
+      expect(matches.every((m: { file: string }) => m.file.endsWith(".ts"))).toBe(true);
+    });
+
+    it("returns empty for no matches", () => {
+      fs.writeFileSync(path.join(tempDir, "app.ts"), "nothing interesting\n");
+      const result = registry.execute({ name: "grep", arguments: { pattern: "NONEXISTENT_PATTERN_XYZ", include: "*.ts" } });
+      const matches = JSON.parse(result.content);
+      expect(matches).toEqual([]);
+    });
+  });
+});