[ci-coach] Rebalance cgo.yml unit test shards by measured execution time

CI Optimization Proposal

Summary

Pre-flight validation (deps-dev, lint, lint-errors, npm-ci, build, recompile, test-unit) all passed cleanly, so this run focused on optimization opportunities in cgo.yml's test matrix job.

Top Optimization

Rebalance unit test shards by measured execution time

• Type: Test suite restructuring
• Impact: High — cuts longest-running shard from ~82s to ~45s (~45% reduction), shrinking the test job's critical path
• Risk: Low — patterns still partition the full ^Test.* namespace exhaustively and mutually exclusively; no tests are skipped or duplicated
• Changes: .github/workflows/cgo.yml — changed the 5-way matrix.include pattern split from alphabetical ranges (A-C/D-G/H-M/N-R/S-Z) to time-balanced ranges (A-B/C/D-H/I-O/P-Z)
• Rationale: Analyzed go test -json timing data from /tmp/gh-aw/agent/test-results.json (recent CI run). Top-level test durations per starting letter showed TestC* alone took ~45s (237 tests) and the old A-C shard totalled ~82s, while other shards ranged 21–37s — a >2x imbalance. Since fail-fast: false matrix jobs run in parallel, the wall-clock time for the whole test job is bounded by its slowest shard. Regrouping by measured time (verified against the actual timing data) balances all 5 shards to 31–45s each.

Expected Impact

• Reduces test job wall-clock time by up to ~45% (bounded by previously-slowest shard A-C at 82s → new max shard C at ~45s)
• No change to total test count, coverage, or matrix breadth — same 5 parallel shards, just rebalanced boundaries

Validation Results

• YAML syntax validated via js-yaml parser: OK
• make lint: only pre-existing, unrelated JS warnings (37 warnings, 0 errors) and a missing golangci-lint binary in this sandbox (unrelated to this change; pre-flight validation step already confirmed lint passes with deps installed)
• Verified new pattern set is exhaustive/non-overlapping across the full test namespace by re-running the shard-timing analysis script against all 10,126 top-level test names

Metrics Baseline

• Pre-flight validation: all 7 steps passed (deps-dev, lint, lint-errors, npm-ci, build, recompile, test-unit)
• Source: /tmp/gh-aw/agent/test-results.json (raw go test -json stream from most recent CI run)

# Download the artifact from the workflow run
gh run download '32974386050' -n agent -D '/tmp/agent-32974386050'

# Resolve the bundle source ref, fetch it into a temporary ref, then create the local branch
bundle_path='/tmp/agent-32974386050/aw-ci-coach-rebalance-test-shards.bundle'
temp_ref='refs/bundles/create-pr-ci-coach-rebalance-test-shards-c9f637620d00abcc-04ef1541'
target_ref='refs/heads/ci-coach-rebalance-test-shards-c9f637620d00abcc'
bundle_source_ref=$(git bundle list-heads "$bundle_path" | awk '$2 ~ /^refs\/heads\// { print $2 }')
if [ -z "$bundle_source_ref" ]; then
  bundle_source_ref=$(git bundle list-heads "$bundle_path" | awk '$2 == "HEAD" { print $2 }')
fi
if [ "$(printf '%s\n' "$bundle_source_ref" | sed '/^$/d' | wc -l | tr -d ' ')" != "1" ]; then
  echo "Expected exactly one bundle source ref, found: $bundle_source_ref" >&2
  exit 1
fi
git fetch "$bundle_path" "${bundle_source_ref}:${temp_ref}"
git update-ref "$target_ref" "$temp_ref"
git checkout 'ci-coach-rebalance-test-shards-c9f637620d00abcc'
# Ensure the working tree matches the updated branch
git reset --hard
# Remove the temporary bundle ref
git update-ref -d "$temp_ref"

# Push the branch and create the pull request
git push origin ci-coach-rebalance-test-shards-c9f637620d00abcc
gh pr create --title '[ci-coach] Rebalance cgo.yml unit test shards by measured execution time' --base main --head ci-coach-rebalance-test-shards-c9f637620d00abcc --repo github/gh-aw

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• expires on Aug 28, 2026, 5:50 AM UTC-08:00