sam-pr-description

name	sam-pr-description
description	Create or update an evidence-backed description for a pull request, merge request, or equivalent change proposal using the actual base, immutable branch diff, complete file coverage, verified tests and safety claims, and deterministic validation. Use when asked to draft, rewrite, standardize, or remotely update a proposal description.

Sam PR Description

Generate a concise reviewer-focused description from the actual change. Default to a local draft and EN-US unless the user explicitly requests another language. Remain provider-, host-, model-, tool-, and stack-neutral.

Non-Negotiable Contract

• Never assume the target branch name.
• Never infer implementation, ticket, test, architecture, business-rule, or safety claims without evidence.
• Account for every changed file exactly once.
• Distinguish tests changed from commands actually run.
• Use Not applicable or Not verified instead of filling evidence gaps.
• Do not update a remote proposal unless the user explicitly requests it.
• Re-check the remote head immediately before an authorized update.
• Never expose secrets in context, reports, descriptions, commands, or receipts.

Resource Routing

• Run scripts/build_change_context.py for every draft.
• Read references/template.md before writing the body.
• Read references/output-contract.md before creating the evidence report.
• Run scripts/validate_description.py before returning or updating the body.

1. Resolve the Exact Base

Resolve in this order:

1. Explicit user-provided target.
2. Target of the existing remote proposal.
3. Repository or remote default branch proved by Git or platform metadata.
4. One concise question when the base remains unknown.

Do not fall back to a conventional branch name. Resolve base and head to immutable commits before inspecting the change.

2. Build the Change Context

Use a safe local checkout containing both refs. Preserve unrelated dirty work; use an isolated temporary clone or worktree when needed.

SAM_PR_DESCRIPTION_DIR="<absolute directory containing this SKILL.md>"
DESCRIPTION_TMP="$(mktemp -d)"
python3 "$SAM_PR_DESCRIPTION_DIR/scripts/build_change_context.py" \
  --repo "$DESCRIPTION_REPO" \
  --base "$TARGET_REF" \
  --head "$SOURCE_REF" \
  > "$DESCRIPTION_TMP/context.json"

Use --comparison direct only when the platform defines an exact base-to-head range. Never truncate an oversized patch or read a sensitive path into context.

3. Reconstruct Scope and Evidence

Read the complete manifest, commits, and relevant changed files. Record:

• Problem, intended outcome, why the change exists, and who benefits.
• Changed modules and every changed path.
• Observable behavior before, after, and intentionally unchanged.
• Business rules added, changed, or preserved by the diff.
• User, API, data, configuration, operational, and compatibility impact when relevant.
• Concrete failure modes, mitigations, remaining risks, rollout, monitoring, and recovery when relevant.
• Tests added or changed.
• Validation commands run with exact status.
• Ticket or proposal references present in user context, metadata, branch, or commits.

Treat reference candidates as candidates, not verified links. A positive claim must cite one or more evidence IDs in the temporary report.

4. Draft the Body

Follow references/template.md. Keep sections concise and adapt their content to the actual change:

• Write for a reader who did not implement the change.
• Lead with the problem, outcome, and observable behavior.
• Express business rules as conditions and outcomes.
• Pair each material risk with a mitigation or state that none is proven.
• Do not invent endpoint or payload fields for non-API work.
• Do not narrate files when a behavior-level summary is clearer.
• Do not mark checklist items complete without evidence.
• State unrun or blocked validation explicitly.
• Keep reviewer instructions focused on risk and behavior.

The body must be raw Markdown without an outer code fence, placeholders, HTML comments, or blank template instructions.

5. Build and Validate the Evidence Report

Create report.json using references/output-contract.md. Link concrete claims to evidence. Map every changed path to one body section.

python3 "$SAM_PR_DESCRIPTION_DIR/scripts/validate_description.py" \
  --context "$DESCRIPTION_TMP/context.json" \
  "$DESCRIPTION_TMP/report.json"

Fix the body or evidence mapping when validation fails. Do not weaken the validator, omit changed files, or relabel unverified claims to force success.

6. Update Remotely Only When Requested

For an explicit update request:

1. Set remote_update.requested to true.
2. Re-read the current remote head before the first write.
3. On head drift, set BLOCKED, record the error, and update nothing.
4. Use the available platform capability to replace only the description.
5. Record the confirmed receipt. On partial failure, preserve successful receipts, set PARTIAL, and do not blindly retry.
6. Revalidate the final report.

A local drafting request must remain NOT_REQUESTED with no receipts.

7. Return

Return only the validated description body when drafting locally. When a remote update was explicitly requested, return the body plus the confirmed update status or exact blocker. Remove temporary artifacts after capturing required receipts.