feat(rust): port stack checkout to native Rust

[jd]

The Rust binary now serves mergify stack checkout <NAME>
natively. mergify_cli/stack/checkout.py,
mergify_cli/tests/stack/test_checkout.py, and the click
registration are removed in the same PR.

First GitHub-API-backed stack subcommand to land natively. The
slice introduces a shared mergify_stack::stack_context module
that resolves the per-command preamble — repository owner/repo,
GitHub API server URL, default branch prefix — that sync,
list, open, and push will all reuse when their ports
follow.

mergify_stack::stack_context:

• parse_slug — owner/repo extraction handling both
  https://github.com/o/r.git and git@github.com:o/r.git
  shapes, port of utils.get_slug.
• resolve_repo — explicit --repository OWNER/REPO
  takes precedence; otherwise we parse
  git config remote.<remote>.url.
• resolve_github_server — reads
  mergify-cli.github-server git config, falls back to
  https://api.github.com/, mirrors Python's https-coercion +
  /api/v3 suffix for GitHub Enterprise.
• resolve_default_branch_prefix — reads
  mergify-cli.stack-branch-prefix, falls back to
  stack/<author>.

mergify_stack::commands::checkout:

1. Normalises the NAME argument — strip any trailing
   /Ixxxx… Change-Id suffix (via the new
   change_id::strip_branch_suffix helper) and any leading
   <branch_prefix>/ so users can paste a leaf branch ref
   verbatim.
2. Searches GitHub for the stack's PRs via the existing
   mergify_stack::remote_changes::get_remote_changes.
3. Builds the open-PR chain from root to leaf — root is the PR
   whose base.ref doesn't start with the stack branch
   prefix; we walk up via head.ref → base.ref linking.
   Two roots surface as InvalidState, matching Python.
4. --dry-run short-circuits with the printed chain.
   Otherwise git fetch <remote> <leaf-head>,
   git checkout -b <local> <remote>/<leaf-head>,
   git branch --set-upstream-to=<remote>/<root-base>.

Binary handler resolves the trunk via --trunk REMOTE/BRANCH
or the existing mergify_stack::trunk::get_trunk fallback,
the token via mergify_core::auth::resolve_token, and the
author via either --author or GET /user against the
resolved client.

Coverage in crates/mergify-stack/src/commands/checkout.rs
(7 tests): the pure chain builder (root-to-leaf, closed-PR
filter, two-root detection, empty case) plus three end-to-end
run tests against wiremock — no-stacked-prs, dry-run returns
chain without touching git, name normalisation strips both the
Change-Id suffix and the branch prefix.

Co-Authored-By: Claude Opus 4.7 noreply@anthropic.com

Depends-On: #1521

[jd]

This pull request is part of a Mergify stack:

#	Pull Request	Link
1	feat(rust): port stack note to native Rust	#1515
2	feat(rust): port stack edit + add rebase-todo machinery	#1516
3	feat(rust): port stack drop to native Rust	#1517
4	feat(rust): port stack fixup to native Rust	#1518
5	feat(rust): port stack reword to native Rust	#1519
6	feat(rust): port stack reorder + stack move to native Rust	#1520
7	feat(rust): port stack squash to native Rust	#1521
8	feat(rust): port stack checkout to native Rust	#1522	👈
9	feat(rust): port stack sync to native Rust	#1523
10	feat(rust): port stack list + stack open to native Rust	#1524

[mergify]

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• depends-on=Mergifyio/mergify-cli#1515 [⛓️ feat(rust): port stack note to native Rust #1515 [stack]]
• depends-on=Mergifyio/mergify-cli#1516 [⛓️ feat(rust): port stack edit + add rebase-todo machinery #1516 [stack]]
• depends-on=Mergifyio/mergify-cli#1517 [⛓️ feat(rust): port stack drop to native Rust #1517 [stack]]
• depends-on=Mergifyio/mergify-cli#1518 [⛓️ feat(rust): port stack fixup to native Rust #1518 [stack]]
• depends-on=Mergifyio/mergify-cli#1519 [⛓️ feat(rust): port stack reword to native Rust #1519 [stack]]
• depends-on=Mergifyio/mergify-cli#1520 [⛓️ feat(rust): port stack reorder + stack move to native Rust #1520 [stack]]
• depends-on=Mergifyio/mergify-cli#1521 [⛓️ feat(rust): port stack squash to native Rust #1521 [stack]]

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• depends-on=Mergifyio/mergify-cli#1515 [⛓️ feat(rust): port stack note to native Rust #1515 [stack]]
• depends-on=Mergifyio/mergify-cli#1516 [⛓️ feat(rust): port stack edit + add rebase-todo machinery #1516 [stack]]
• depends-on=Mergifyio/mergify-cli#1517 [⛓️ feat(rust): port stack drop to native Rust #1517 [stack]]
• depends-on=Mergifyio/mergify-cli#1518 [⛓️ feat(rust): port stack fixup to native Rust #1518 [stack]]
• depends-on=Mergifyio/mergify-cli#1519 [⛓️ feat(rust): port stack reword to native Rust #1519 [stack]]
• depends-on=Mergifyio/mergify-cli#1520 [⛓️ feat(rust): port stack reorder + stack move to native Rust #1520 [stack]]
• depends-on=Mergifyio/mergify-cli#1521 [⛓️ feat(rust): port stack squash to native Rust #1521 [stack]]

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[jd]

Revision history

#	Type	Changes	Reason	Date
1	initial	0da0845		2026-06-03 21:01 UTC
2	rebase	0da0845 → b09a7f8 (rebase only)		2026-06-03 21:01 UTC