Skill: PR Description

Create or update PR description based on git diff.

Inputs

• PR number — required when updating an existing PR; provided by the user (referred to as <pr-number> below)
• Base branch — detect dynamically; do not assume main:

  BASE=$(gh repo view --json defaultBranchRef -q .defaultBranchRef.name)

  If the user names a different base (e.g. develop), use that instead.

Steps

1. Gather context:
   • Refresh the base first: git fetch origin "$BASE". gh repo view hands back a branch name; it does not update the local remote-tracking ref, and a stale origin/$BASE describes commits that merged upstream days ago as if they were this PR's.
   • For new PR: git diff "origin/$BASE"...HEAD and git log "origin/$BASE"..HEAD --oneline
   • For existing PR: gh pr diff <pr-number>, and its current body: gh pr view <pr-number> --json title,body. An update is a merge, not a rewrite: a body often carries hand-written limitations, verification evidence and issue links that the diff cannot reconstruct, and --body-file replaces all of it silently. Carry that content forward, and only rewrite what the diff has actually made wrong.
2. Generate description in this format:

## Changes

### Summary

[Brief summary of changes - 1-3 sentences]

### Business Context

[Business/technical context - why was this change needed. Infer from branch name, commits, and code changes. Remove this section if unclear.]

### Changes

[Technical approach - main architectural decisions, main changes. Use bullet points.]

### Architecture

[Diagrams, for an architectural change only — see Rules. Reference each attached image as `![alt](./name.png)` with one sentence saying what the reader should take from it. Remove this section for a change with no architectural shape.]

### Verification

[Example queries, commands, or steps to verify the changes work correctly. When the change is observable through the project's own tracing/observability backend (new or changed spans, telemetry attributes, logged events — check whether the repo has one before assuming), include links or excerpts from example traces you actually produced — see Rules.]

### Linked Issues

[Link to any relevant issues or tickets found in branch name or commits. Remove this section if none found.]

3. Execute (write the body to a file and pass --body-file; a long body with backticks does not survive --body "…" intact):
   • New PR: gh pr create --base "$BASE" --title "<title>" --body-file body.md
   • Existing PR: gh pr edit <pr-number> --body-file body.md
   • Diagrams go in the body as mermaid, so there is nothing to upload and no asset URL to go stale. gh has no image-upload flag - --attach is not a flag gh pr create or gh pr edit has ever exposed - and a local PNG referenced by path renders as a broken image for every reviewer.
4. Return the PR URL.

Rules

• No "Test plan" or "Generated with..." sections
• Keep descriptions concise
• Use present tense ("Add", "Update", "Remove")
• Omit Business Context and Linked Issues sections when there's nothing to fill in — don't leave placeholders
• Include trace/log evidence for observable changes, when the repo has the means to produce it. When the change produces or alters observability (new/changed spans, telemetry attributes, structured logs) and the project has a tracing or logging backend, link to or excerpt example traces/log lines you actually produced in the Verification section — one per meaningful path (happy path + key error paths), using that backend's own link format (e.g. a dashboard deep-link, a log query, a captured span tree). Only cite evidence you genuinely produced — never fabricate ids, URLs, or output. If the project has no such backend, or the change isn't observable through one, skip this and verify with the project's normal test/run commands instead.
• Attach diagrams for an architectural change. When a change adds or reshapes a flow across components — a new tool or service path, a new gate, a state machine, a cross-channel behaviour — put images in the Architecture section rather than making the reviewer rebuild the shape from the diff. Two usually suffice: one component/flow diagram (who calls what, and what each outcome writes) and one sequence diagram (the call order, with the refusal branches). Put the mermaid straight in the body, in a fenced ```mermaid block: GitHub renders it in a pull request description, so the diagram needs no renderer, no uploaded asset and no version of anything. It also stays readable in the diff and as text, which a PNG does not. A committed architecture doc's diagram belongs wherever this repo keeps those instead, e.g. docs/architecture.md, a docs/architecture/ directory, or an ADR. Diagram the mechanism the PR actually changes, including its failure paths; a box-and-arrow restatement of the module tree earns nothing. Skip the section for a fix, a test-only change, or a one-file tweak.