input prompter improvements

[skarim]

Improve input prompts with inline prefix prefill and colored text

Previously, when gh stack add or gh stack init prompted for a branch name with a prefix configured, the prefix was mentioned parenthetically in the prompt message (e.g. "will be prefixed with feat/") and silently prepended to whatever the user typed. This made it hard to see or edit the full branch name, and easy to accidentally double-prefix.

This PR introduces an inputWithPrefill helper that places the prefix directly in the editable input field (e.g. the cursor starts after feat/), so the user can see, append to, or modify the full branch name in-place. The user's typed text is rendered in cyan for visual distinction from the prompt.

Changes:

• Add inputWithPrefill() to cmd/utils.go using terminal.RuneReader.ReadLineWithDefault to render editable prefill text with cyan coloring via mgutz/ansi
• Add InputFn hook to config.Config, following the existing SelectFn/ConfirmFn pattern, for test injection of text input responses
• Update cmd/add.go to pre-fill the prefix in the branch name prompt and use the raw input as the branch name (no silent prepend)
• Update cmd/init.go (promptBranchName) to use inputWithPrefill with the prefix pre-filled, removing the separate "will be prefixed with" message and the post-hoc prefix concatenation
• Update cmd/submit.go PR title prompt to use inputWithPrefill for consistent styling across all input prompts
• Fix arrow direction in printWhatsNext from → to ← to correctly reflect the base-branch relationship (main ← branch1 ← branch2)

Tests:

• TestAdd_PromptPrefillsPrefix — verifies prefix/ is passed as the default value and the full input is used as the branch name
• TestAdd_PromptNoPrefixEmptyDefault — verifies empty default when no prefix is configured
• TestAdd_PromptUserModifiesPrefix — verifies user can replace the pre-filled prefix entirely and the verbatim input is used

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[Copilot]

Pull request overview

This PR improves interactive text input prompting in gh-stack by introducing an editable prefilled input experience (instead of showing defaults in parentheses), and wiring a new test hook to mock text input prompts. It also tweaks the “What’s next” init output to display the stack chain with left-pointing arrows.

Changes:

• Added Config.InputFn to allow tests to mock freeform text input prompts.
• Implemented inputWithPrefill and switched init, add, and submit PR-title prompts to use editable prefill text.
• Updated init “Created stack” chain formatting (main ← branch) and adjusted tests accordingly.

Show a summary per file

File	Description
internal/config/config.go	Adds InputFn hook to Config for test-time prompt mocking.
cmd/utils.go	Adds inputWithPrefill helper using rune-reader raw input + ANSI coloring.
cmd/submit.go	Uses inputWithPrefill for PR title prompting (interactive, non---auto).
cmd/init.go	Uses inputWithPrefill for prefix/branch prompts; changes init chain arrow direction.
cmd/init_test.go	Updates expectation for new main ← my-feature chain rendering.
cmd/add.go	Uses inputWithPrefill for interactive branch naming with prefix prefill.
cmd/add_test.go	Adds tests asserting prompt defaults/prefix prefill behavior for add.

Copilot's findings

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Comments suppressed due to low confidence (2)

cmd/add.go:168

• With a non-empty prefix, the default prefill is prefix + "/". If the user accepts the prefill without adding a suffix (or deletes the suffix), the branch name can end up as prefix/, which is not a valid git ref name. Please add validation to reject names that end with "/" (and ideally validate the ref name before calling git.CreateBranch).

			// Pre-fill the prompt with the prefix so the user can see
			// (and optionally edit) the full branch name.
			prefill := ""
			if s.Prefix != "" {
				prefill = s.Prefix + "/"
			}
			for {
				input, err := inputWithPrefill(cfg, "Enter a name for the new branch:", prefill)
				if err != nil {
					if isInterruptError(err) {
						printInterrupt(cfg)
						return ErrSilent
					}
					return fmt.Errorf("could not read branch name: %w", err)
				}
				if input == "" {
					cfg.Warningf("branch name cannot be empty, please try again")
					continue
				}
				branchName = input
				break

cmd/init.go:455

• Similar to cmd/add.go, when prefix != "" the prefill becomes prefix + "/", which makes it easy for the user to submit prefix/ as the full branch name. Since the only validation is branchName == "", this can allow an invalid ref name through until branch creation fails. Add validation to reject trailing-slash names (and ideally run git.ValidateRefName on the final branch name).

	prefill := ""
	prompt := "What's the name of the first branch:"
	if prefix != "" {
		prompt = "Enter a name for the first branch:"
		prefill = prefix + "/"
	}
	branchName, err := inputWithPrefill(cfg, prompt, prefill)
	if err != nil {
		if isInterruptError(err) {
			printInterrupt(cfg)
			return "", ErrSilent
		}
		cfg.Errorf("failed to read branch name: %s", err)
		return "", ErrSilent
	}
	branchName = strings.TrimSpace(branchName)
	if branchName == "" {
		cfg.Errorf("branch name cannot be empty")
		return "", ErrInvalidArgs
	}
	return branchName, nil

• Files reviewed: 7/7 changed files
• Comments generated: 4