fix(commit): reject empty split hunk selectors

packages/coding-agent/test/commit-split-hunk-validation.test.ts

@@ -0,0 +1,98 @@
+import { afterEach, describe, expect, it, vi } from "bun:test";
+import type { CommitAgentState } from "../src/commit/agentic/state";
+import { createSplitCommitTool } from "../src/commit/agentic/tools/split-commit";
+import * as git from "../src/utils/git";
+
+const STAGED_DIFF = `diff --git a/src/a.ts b/src/a.ts
+index 1111111..2222222 100644
+--- a/src/a.ts
++++ b/src/a.ts
+@@ -1,3 +1,3 @@
+ export function a() {
+-	return 1;
++	return 2;
+ }
+diff --git a/src/b.ts b/src/b.ts
+index 3333333..4444444 100644
+--- a/src/b.ts
++++ b/src/b.ts
+@@ -1,3 +1,3 @@
+ export function b() {
+-	return 1;
++	return 2;
+ }
+`;
+
+describe("split_commit hunk selector validation", () => {
+	afterEach(() => {
+		vi.restoreAllMocks();
+	});
+
+	it("rejects hunk index selectors that match no parsed hunk", async () => {
+		vi.spyOn(git, "diff").mockResolvedValue(STAGED_DIFF);
+		const state: CommitAgentState = {
+			overview: { files: ["src/a.ts", "src/b.ts"], stat: "", numstat: [], scopeCandidates: "", isWideScope: false },
+		};
+		const tool = createSplitCommitTool("/repo", state, []);
+
+		const result = await tool.execute(
+			"split-commit",
+			{
+				commits: [
+					{
+						changes: [{ path: "src/a.ts", hunks: { type: "indices", indices: [2] } }],
+						type: "fix",
+						scope: null,
+						summary: "Fixed invalid selector handling",
+					},
+					{
+						changes: [{ path: "src/b.ts", hunks: { type: "all" } }],
+						type: "fix",
+						scope: null,
+						summary: "Fixed split commit coverage",
+					},
+				],
+			},
+			undefined,
+			{} as never,
+		);
+
+		expect(result.details.valid).toBe(false);
+		expect(result.details.errors).toContain("Commit 1: No hunks selected for src/a.ts");
+		expect(state.splitProposal).toBeUndefined();
+	});
+
+	it("rejects line selectors that overlap no parsed hunk", async () => {
+		vi.spyOn(git, "diff").mockResolvedValue(STAGED_DIFF);
+		const state: CommitAgentState = {
+			overview: { files: ["src/a.ts", "src/b.ts"], stat: "", numstat: [], scopeCandidates: "", isWideScope: false },
+		};
+		const tool = createSplitCommitTool("/repo", state, []);
+
+		const result = await tool.execute(
+			"split-commit",
+			{
+				commits: [
+					{
+						changes: [{ path: "src/a.ts", hunks: { type: "lines", start: 50, end: 60 } }],
+						type: "fix",
+						scope: null,
+						summary: "Fixed invalid line selectors",
+					},
+					{
+						changes: [{ path: "src/b.ts", hunks: { type: "all" } }],
+						type: "fix",
+						scope: null,
+						summary: "Fixed split commit coverage",
+					},
+				],
+			},
+			undefined,
+			{} as never,
+		);
+
+		expect(result.details.valid).toBe(false);
+		expect(result.details.errors).toContain("Commit 1: No hunks selected for src/a.ts");
+		expect(state.splitProposal).toBeUndefined();
+	});
+});