fix(workflows): render gate show_file contents in the interactive prompt

[doquanghuy]

Description

Closes #2809.

The built-in gate step accepts a show_file config field. The value was read, template-expanded, and stored in output["show_file"], but its contents were never displayed at the interactive prompt — the operator was asked to approve/reject without seeing the referenced file.

This renders show_file inside the interactive gate prompt, before the options. A missing or undecodable file degrades to a short one-line notice instead of raising, so a misconfigured path never breaks the prompt.

What changed

• GateStep._prompt(...) now accepts show_file and prints its contents (each line within the gate box) before the options.
• New GateStep._read_show_file(...) helper reads the file as UTF-8 and returns a (could not read file: …) / (file is empty) notice on error/empty instead of raising.

Compatibility

• Non-interactive (PAUSED) path is unchanged — the file is not read when stdin is not a TTY.
• Exit codes, on_reject handling, and resume semantics are unchanged.
• Gates without show_file produce byte-identical output to before.

Testing

• Tested locally with uv run specify --help
• Ran existing tests with uv sync --extra test && uv run pytest — 3310 passed, 40 skipped
• Tested with a sample project (if applicable)

Added three targeted tests in tests/test_workflows.py::TestGateStep:

• interactive prompt renders show_file contents and returns the chosen option;
• a missing show_file shows the notice and does not crash;
• the non-interactive path still PAUSES and preserves output["show_file"] without reading the file.

AI Disclosure

• I did not use AI assistance for this contribution
• I did use AI assistance (describe below)

Used Claude to trace the bug in gate/__init__.py, draft the fix and tests, and write this PR body. The behaviour was reproduced and the diff reviewed locally before submission.

[Copilot]

Pull request overview

This PR fixes the built-in workflow gate step so that a configured show_file is actually rendered in the interactive prompt, allowing operators to review the referenced file contents before choosing approve/reject. It adds a bounded, non-throwing file-read helper and extends test coverage around the interactive/non-interactive behaviors.

Changes:

• Render show_file contents inside the interactive gate prompt (before the options).
• Add _read_show_file() helper that caps output length and degrades to a one-line notice on read/decode errors.
• Add targeted tests covering interactive rendering, missing files, non-interactive pause behavior, empty files, and truncation.

Show a summary per file

File	Description
src/specify_cli/workflows/steps/gate/__init__.py	Passes show_file into the gate prompt and safely renders file contents with truncation/error notices.
tests/test_workflows.py	Adds regression tests for interactive rendering and safe behavior across missing/empty/large files and non-interactive runs.

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• Files reviewed: 2/2 changed files
• Comments generated: 1