fix(design-decision-gate): handle >300-file PRs without HTTP 406 abort

[Copilot]

The Pre-fetch ADR gate PR context step called gh pr diff unconditionally. For PRs with >300 changed files the GitHub diff API returns HTTP 406, and set -euo pipefail killed the step before the agent could run.

Changes

• Fetch order — pr-files.json (paginated) is now fetched before gh pr diff so the file count is known before attempting the diff call.
• File-count guard — When FILE_COUNT > 300, the diff call is skipped entirely; a descriptive notice is written to pr.diff and a ::warning:: annotation is emitted instead of exiting 1.
• Extended summary — adr-prefetch-summary.json gains two new fields:
  • file_count — total changed files
  • diff_available — boolean (computed via jq -n to avoid shell edge cases)
• Agent prompt — Fallback instruction for pr.diff now branches on diff_available: when false, directs the agent to use pr-files.json for file-level analysis and explicitly suppresses the mcp__github__get_pull_request_diff call (which would also 406).
• .gitattributes — Replaced the two path-specific *.lock.yml entries with a single *.lock.yml linguist-generated=true merge=ours pattern so all .lock.yml files anywhere in the repository are collapsed by default in GitHub PR diffs.

FILE_COUNT=$(jq 'length' /tmp/gh-aw/agent/pr-files.json)

if [ "$FILE_COUNT" -gt 300 ]; then
  echo "::warning::PR has $FILE_COUNT changed files (exceeds the 300-file GitHub diff API limit). Skipping full diff; file listing is available in pr-files.json."
  printf '# Diff unavailable: PR has %s changed files ...\n' "$FILE_COUNT" \
    > /tmp/gh-aw/agent/pr.diff
else
  gh pr diff "$PR_NUMBER" --repo "$EXPR_GITHUB_REPOSITORY" > /tmp/gh-aw/agent/pr.diff
fi

[pelikhan]

@copilot diff should ignore **/*.lock.yml files

[Copilot]

@copilot diff should ignore **/*.lock.yml files

Done in 3db1be8. Replaced the two path-specific entries (.github/workflows/*.lock.yml and pkg/cli/workflows/*.lock.yml) with a single *.lock.yml linguist-generated=true merge=ours line that covers all .lock.yml files anywhere in the repository.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates the design decision gate workflow to gracefully handle PRs with very large file counts by avoiding diff retrieval when it would exceed GitHub’s diff limitations.

Changes:

• Skip fetching the full PR diff when the PR changes more than 300 files; emit a notice file instead.
• Add file_count and diff_available to the prefetch summary JSON to guide downstream behavior.
• Broaden .gitattributes rules for *.lock.yml and adjust workflow lockfile handling.

Show a summary per file

File	Description
.github/workflows/design-decision-gate.md	Adds file-count check, conditional diff fetch, and propagates file_count/diff_available into the summary + instructions.
.github/workflows/design-decision-gate.lock.yml	Regenerates the locked workflow with the new prefetch logic and summary fields.
.gitattributes	Broadens *.lock.yml handling and adds an extra workflow lockfile rule.

Copilot's findings

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• Files reviewed: 3/3 changed files
• Comments generated: 3