Rename the GitHub CLI extension to gh gitsim

gh names an extension's command after its gh-<name> folder and script,
so integrations/gh-sim becomes integrations/gh-gitsim, run as
gh gitsim pr 42. The script's messages, refs, and temporary worktree,
the README, and CONTRIBUTING use the new name. The README's star link
now jumps to the top of the page, as git-dummy's does.

Signed-off-by: Jacob Stopak <jacob@initialcommit.io>

Author: initialcommit-io

CONTRIBUTING.md

@@ -54,7 +54,7 @@ $ git-sim merge dev
 - `src/git_sim/render/`: the static renderer, which draws the SVG, PNG, and JPG output and the interactive page
 - `src/git_sim/live.py`, `preflight.py`, `mcp_server.py`, `claude_hook.py`: live mode, pre-flight, the MCP server, and the agent hook
 - `vscode/`: the VS Code extension
-- `integrations/`: the GitHub CLI extension (`gh sim`) and the GitHub Action
+- `integrations/`: the GitHub CLI extension (`gh gitsim`) and the GitHub Action
 - `docs/img/`: the README's images
 - `scripts/`: the scripts that draw the README's graphs
 

README.md

@@ -965,31 +965,31 @@ Pull requests from forks get a read-only token, which can't post comments, so se
 </details>
 
 <details>
-<summary>GitHub CLI: gh sim</summary>
+<summary>GitHub CLI: gh gitsim</summary>
 
 With the [GitHub CLI](https://github.com/cli/cli#installation) installed and logged in (`gh auth login`), install the extension from a clone of this repo:
 
 ```console
 $ git clone https://github.com/initialcommit-com/git-sim.git ~/git-sim
-$ cd ~/git-sim/integrations/gh-sim
+$ cd ~/git-sim/integrations/gh-gitsim
 $ gh extension install .
 ```
 
 Then, inside a clone of the pull request's repo:
 
 ```console
-$ gh sim pr 42           # what merging pull request #42 into its base would do
-$ gh sim pr 42 rebase    # what rebasing it onto its base would do
+$ gh gitsim pr 42           # what merging pull request #42 into its base would do
+$ gh gitsim pr 42 rebase    # what rebasing it onto its base would do
 ```
 
-`gh sim pr` simulates in a temporary worktree, so your checkout and branches are never touched. Any other `gh sim` command is the same as running git-sim. On Windows, `gh` runs the extension with the bash from Git for Windows.
+`gh gitsim pr` simulates in a temporary worktree, so your checkout and branches are never touched. Any other `gh gitsim` command is the same as running git-sim. On Windows, `gh` runs the extension with the bash from Git for Windows.
 
 </details>
 
 ## Support git-sim
 
 Git-Sim is Free and Open-Source Software (FOSS). Your support will help me work on it (and other Git projects) full time!
-- ⭐ [Star the repo](https://github.com/initialcommit-com/git-sim)
+- ⭐ [Star the repo](#top)
 - [Sponsor Git-Sim on GitHub](https://github.com/sponsors/initialcommit-com)
 - [Support Git-Sim via Patreon](https://patreon.com/user?u=92322459)
 

integrations/gh-gitsim/gh-gitsim

@@ -0,0 +1,63 @@
+#!/usr/bin/env bash
+# gh gitsim: git-sim as a GitHub CLI extension.
+#
+#   gh gitsim <git-sim arguments>         the same as running git-sim
+#   gh gitsim pr <number> [merge|rebase]  what merging (or rebasing) a pull request
+#                                         into its base would do, on this repository
+#
+# `gh gitsim pr` never touches your checkout: it fetches the pull request's head
+# and base into a temporary worktree, runs git-sim there, and removes it.
+#
+# Install:  gh extension install .   (from this folder, in a clone of git-sim)
+# Needs:    git-sim on the PATH (pipx install git-sim) and gh logged in.
+set -euo pipefail
+
+if ! command -v git-sim >/dev/null 2>&1; then
+  echo "gh gitsim: git-sim is not installed. Run: pipx install git-sim" >&2
+  exit 1
+fi
+
+if [ "${1:-}" != "pr" ]; then
+  exec git-sim "$@"
+fi
+
+shift
+number="${1:-}"
+mode="${2:-merge}"
+if [ -z "$number" ]; then
+  echo "usage: gh gitsim pr <number> [merge|rebase]" >&2
+  exit 2
+fi
+case "$mode" in merge|rebase) ;; *) echo "gh gitsim pr: the mode is merge or rebase, not '$mode'" >&2; exit 2;; esac
+
+read -r head base < <(gh pr view "$number" --json headRefName,baseRefName --jq '[.headRefName, .baseRefName] | @tsv')
+if [ -z "$head" ] || [ -z "$base" ]; then
+  echo "gh gitsim pr: could not read pull request #$number" >&2
+  exit 1
+fi
+
+remote="$(git config --get "branch.$base.remote" 2>/dev/null || echo origin)"
+echo "gh gitsim: fetching #$number ($head -> $base) from $remote"
+git fetch -q "$remote" "refs/pull/$number/head:refs/gh-gitsim/pr-$number" "$base"
+
+worktree="$(mktemp -d "${TMPDIR:-/tmp}/gh-gitsim.XXXXXX")"
+cleanup() {
+  git worktree remove --force "$worktree" >/dev/null 2>&1 || true
+  git branch -D "gh-gitsim/pr-$number" >/dev/null 2>&1 || true
+  git update-ref -d "refs/gh-gitsim/pr-$number" >/dev/null 2>&1 || true
+}
+trap cleanup EXIT
+
+# The base as the remote has it, checked out detached in the worktree, with
+# the pull request's head as a local branch git-sim can name.
+git worktree add -q --detach "$worktree" "$remote/$base"
+git branch -q -f "gh-gitsim/pr-$number" "refs/gh-gitsim/pr-$number"
+
+cd "$worktree"
+if [ "$mode" = "rebase" ]; then
+  # What the pull request's commits look like replayed onto the base.
+  git switch -q -C "gh-gitsim/pr-$number" "refs/gh-gitsim/pr-$number"
+  git-sim rebase "$remote/$base"
+else
+  git-sim merge "gh-gitsim/pr-$number"
+fi