Ignore symlinked pull request templates

[skarim]

gh stack submit and gh stack link prefill a new PR's body from the repository's pull request template. Template discovery in internal/pr read each candidate path with os.ReadFile, which follows symlinks. A template that is a symlink — for example .github/pull_request_template.md pointing to a file outside the repository — was therefore read through to its target, and that file's contents were used as the PR body.

This reuses cli/cli's githubtemplate package (already a dependency) for template discovery instead of the hand-rolled path list. It's the same code gh pr create uses, and it skips symlinked templates, so only regular template files inside the repository are read. FindTemplate keeps the same signature, so the submit and link callers are unchanged.

Behavior

• A pull request template that is a symlink is ignored; submit / link fall back to the default PR body (commit message + footer) as if no template were present.
• Two changes come with reusing githubtemplate:
  • YAML front-matter is stripped from the template, matching gh pr create.
  • Template filename matching is slightly broader — hyphenated (pull-request-template.md) and non-.md variants are now recognized.

Changes

internal/pr/template.go:

• FindTemplate now delegates to githubtemplate.FindLegacy + githubtemplate.ExtractContents (trimmed), replacing the manual candidate-path list and os.ReadFile loop. Symlinked templates are skipped.

Testing

internal/pr/template_test.go:

• Existing discovery tests still pass; adds a symlinked-template case (ignored), a front-matter-stripping case, and a hyphenated-filename case.

cmd/submit_test.go / cmd/link_test.go:

• Adds gh stack submit --auto and gh stack link cases confirming a symlinked template is not read into the created PR body and the default footer body is used instead.

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[Copilot]

Pull request overview

This PR fixes a subtle information-disclosure / correctness issue in PR template discovery. gh stack submit and gh stack link prefill a new PR body from the repository's pull request template; the previous implementation in internal/pr/template.go read candidate paths with os.ReadFile, which follows symlinks — so a symlinked pull_request_template.md pointing outside the repo would be read through to its target. The fix reuses cli/cli's githubtemplate package (the same code gh pr create uses), which ignores symlinked templates while keeping FindTemplate's signature intact.

Changes:

• Replaced the manual candidate-path list + os.ReadFile loop with githubtemplate.FindLegacy + githubtemplate.ExtractContents (trimmed), so symlinked templates are skipped.
• Side effects of the reuse: YAML front-matter is now stripped (matching gh pr create), and filename matching is broadened to hyphenated/non-.md variants.
• Added tests for symlink-ignoring, front-matter stripping, and hyphenated names at the unit level, plus end-to-end coverage in submit and link.

Show a summary per file

File	Description
internal/pr/template.go	Delegates FindTemplate to githubtemplate.FindLegacy/ExtractContents, dropping the symlink-following os.ReadFile loop.
internal/pr/template_test.go	Adds unit tests for symlink-ignored, front-matter-stripped, and hyphenated-name templates.
cmd/submit_test.go	Adds submit --auto test confirming a symlinked template is not read into the PR body (footer fallback used).
cmd/link_test.go	Adds link test confirming a symlinked template is not read into the PR body (footer fallback used).

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 0
• Review effort level: Medium