Prepare Milestone Base

Announcement

At the start of execution, always post a visible message to the user:

"Loaded skill: prepare-milestone-base. Creating milestone branch..."

Inputs

• epic_issue_number: GitHub issue number of the milestone epic (e.g. 3).

Goal

Create a milestone/m{number} branch from the latest origin/master and push it to remote, ensuring a clean, deterministic starting point for milestone work. This branch serves as the integration branch for Mode A (milestone-driven development) as defined in coding-standards.md.

Guardrails

• No file edits, no commits.
• No tagging of any kind (lightweight or annotated).
• No merge, rebase, or history rewriting operations.
• This skill is strictly for branch creation and verification only.
• Refuse to proceed if the working tree is dirty (git status --porcelain not empty).
• If milestone branch exists remotely, require explicit user confirmation before proceeding.
• Keep all communication concise and professional. No emojis.
• milestone/* branches created by this skill are protected from deletion by prepare-base.md.

Procedure

0) Gather inputs

• If epic_issue_number is missing, ask:

  "What is the epic issue number?"

• Pause execution until provided.

1) Fetch epic issue and derive milestone number

• Fetch issue using GitHub CLI, including its assigned milestone:

  gh issue view {epic_issue_number} --json title,milestone
  

* If the epic has no milestone assigned, stop and ask the user to assign one
  on GitHub first. Do not proceed until confirmed, and do not fall back to
  parsing the epic issue's own title text.

* Extract milestone number using regex against the assigned milestone's
  **title** (`.milestone.title`), never the epic issue's own title:

  * Primary match: `M(\d+(?:\.\d+)?)`
  * Normalize the extracted number to lowercase form for all branch names
  (e.g. `M3` → use `3`, branch is `milestone/m3`; `M1.1` → use `1.1`, branch
  is `milestone/m1.1`).
  
* If multiple matches exist or no match is found in the milestone title:

  * Ask user to provide milestone number manually
  * Stop execution

---

### 2) Check working tree cleanliness

* Run:

  ```bash
  git status --porcelain
  ```
* If output is not empty:

  * Inform user:

    > "Working tree has uncommitted changes. Please commit or stash before continuing."
  * Stop execution

---

### 3) Determine branch existence

* Check remote:

  ```bash
  git ls-remote --heads origin milestone/m{number}
  ```
* Check local:

  ```bash
  git branch --list milestone/m{number}
  ```

### Branch decision logic

#### If branch exists (remote or local)

* Ask user:

  > "Branch milestone/m{number} already exists. Do you want to check it out and update it from origin/master?"
* Accept: `yes | y | confirm`
* Anything else: stop execution

If confirmed:

* `git fetch origin`
* `git switch milestone/m{number}` (not `git checkout` — `switch` refuses to
  silently detach onto a same-named tag left behind by a prior
  `close-milestone-watch` run; `checkout` would not)
* If `origin/milestone/m{number}` exists:
  * `git reset --hard origin/milestone/m{number}`
* If branch exists locally only (no remote counterpart):
  * Inform user: "Branch exists locally only; resetting to origin/master instead."
  * `git reset --hard origin/master`
* Continue to Step 5

---

#### If branch does NOT exist

Proceed to Step 4.

---

### 4) Create milestone branch

Always base from remote master (not local):

```bash
git fetch origin
git checkout -B milestone/m{number} origin/master
git push -u origin refs/heads/milestone/m{number}:refs/heads/milestone/m{number}
```

Use the fully-qualified refspec for the push, not the short name. A prior
closed milestone leaves behind a tag named `milestone/m{number}` (created by
`close-milestone-watch`), and a short-name push fails with "src refspec ...
matches more than one" once a same-named tag exists.

---

### 5) Verify state

* Confirm active branch:

  ```bash
  git branch --show-current
  ```
* Confirm remote existence:

  ```bash
  git ls-remote --heads origin milestone/m{number}
  ```

If either check fails:

* Inform user of failure
* Stop execution

---

### 6) Final confirmation

> "Branch milestone/m{number} is active locally and present on origin. Ready for milestone feature branches."

---

## Summary

Post:

> "Milestone branch **milestone/m{number}** created from **origin/master** and pushed to origin. Ready for sub-issue implementation."