docs: add PR metadata guardrails

Author: Copilot

.github/copilot-instructions.md

@@ -74,6 +74,8 @@ Always include `Closes #N` in **both** the commit message AND the PR body's "Rel
 
 **⚠️ CRITICAL:** When creating a pull request, the title and description must summarize **ALL changes in the branch**, not just the last commit.
 
+**⚠️ CRITICAL:** Once a pull request already exists, do **not** change its title or description unless the user explicitly asks you to do so.
+
 ### Before Creating Any PR
 
 1. Run `git log main..HEAD --oneline` to see ALL commits in the branch
@@ -86,6 +88,12 @@ Always include `Closes #N` in **both** the commit message AND the PR body's "Rel
    - New files added
    - Modified functionality
 
+### After a PR Already Exists
+
+1. Treat the current PR title and description as user-approved context unless the user explicitly asks for a change
+2. If the user does ask for an update, keep the title and description aligned with the **entire branch**, not just the latest iteration
+3. Do not overwrite a good PR summary just because you made a new commit, merged `main`, or addressed review feedback
+
 ### Common Mistake
 
 ❌ **Wrong:** PR titled after the most recent commit ("fix: resolve Windows test failures")  

.squad/templates/copilot-instructions.md

@@ -51,6 +51,8 @@ Always include `Closes #N` or `Fixes #N` in commit messages when the change reso
 
 When opening a PR:
 - **Title and description must summarize ALL changes in the branch**, not just the last commit. Use `git log main..HEAD --oneline` (or the appropriate base branch) to review all commits and write a comprehensive PR title and description.
+- Once a PR already exists, **do not change its title or description unless the user explicitly asks you to do so**.
+- If the user does ask for an update, preserve the full-branch summary instead of rewriting the PR around only the most recent iteration.
 - Reference the issue in **both** the commit message AND the PR body: `Closes #{issue-number}`. The PR body is a redundant safety net if commit message formatting fails.
 - If the issue had a `squad:{member}` label, mention the member: `Working as {member} ({role})`
 - If this is a 🟡 needs-review task, add to the PR description: `⚠️ This task was flagged as "needs review" — please have a squad member review before merging.`