Add test for combined task and user prompt parsing

[Copilot]

The codebase combines task prompts and user prompts with a --- delimiter before parsing, but lacked a test verifying this combined content parses correctly through taskparser.ParseTask.

Changes

• Added test case "both task prompt and user prompt parse correctly" in TestUserPrompt
  • Verifies text blocks, slash commands, and parameter substitution work in both prompts
  • Validates delimiter preservation and content ordering
  • Includes proper error handling for string index validation

Example

createTask(t, dir, "parse-test", "", "Task prompt with text\n/task-command arg1\nMore task text\n")
createCommand(t, dir, "task-command", "", "Task command output ${param1}")
createCommand(t, dir, "user-command", "", "User command output ${param2}")

opts: []Option{
    WithUserPrompt("User prompt with text\n/user-command arg2\nMore user text"),
    WithParams(taskparser.Params{
        "param1": []string{"value1"},
        "param2": []string{"value2"},
    }),
}

// Verifies both commands expand correctly and content maintains order

Original prompt

Write a test here we have both task prompt and user prompt. Verify that is parses.

---

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[Copilot]

Pull request overview

This PR adds a comprehensive test case to verify that the system correctly combines and parses both task prompts and user prompts when both are present. The test ensures that the --- delimiter is preserved, slash commands are expanded in both prompts, parameter substitution works correctly, and content ordering is maintained.

Key Changes

• Added test case "both task prompt and user prompt parse correctly" to the TestUserPrompt table-driven test
• Validates slash command expansion with parameter substitution in both task and user prompts
• Verifies delimiter presence and correct ordering of combined content

[Copilot]

This check is redundant because the previous assertions on lines 1682-1693 already verify that both strings are present using strings.Contains. If those checks pass, then taskIdx and userIdx cannot be -1. Consider removing this check since it's already covered by earlier assertions.

Suggested change

	if taskIdx == -1 || userIdx == -1 {
	t.Error("expected both task and user prompt text to be found in result")
	} else if taskIdx >= userIdx {
	if taskIdx >= userIdx {