fix(ci): quality-gate drops the 74s full-history checkout

fetch-depth:0 cost 74 of the job's 92 seconds; the three gates it feeds
take ~12s combined. Shallow checkout + exact-SHA fetches for the diff's
base/head (an exact-SHA fetch, not a guessed depth — long-lived
branches and merge queues still resolve), with a --deepen fallback for
push events whose 'before' is unusable. timeout right-sized 20→10 min.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/quality-gate.yml

@@ -29,11 +29,13 @@ concurrency:
 jobs:
   quality:
     runs-on: ubicloud-standard-8
-    timeout-minutes: 20
+    timeout-minutes: 10
     steps:
+      # Shallow checkout: fetch-depth:0 cost 74s of a 92s job for checks that
+      # take ~12s combined. The one history consumer (the added-lines diff)
+      # fetches its exact base/head SHAs below — an exact-SHA fetch, not a
+      # guessed depth, so long-lived branches and merge queues still resolve.
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v4
-        with:
-          fetch-depth: 0
       - uses: oven-sh/setup-bun@0c5077e51419868618aeaa5fe8019c62421857d6 # v2
         with:
           bun-version: 1.3.13
@@ -47,7 +49,15 @@ jobs:
           HEAD_SHA: ${{ github.event.pull_request.head.sha || github.sha }}
         run: |
           set -euo pipefail
+          # Exact-SHA shallow fetches: the checkout above is depth-1 of the
+          # merge ref; the diff needs the PR head + base objects specifically.
+          git fetch --no-tags --depth=1 origin "$HEAD_SHA" 2>/dev/null || true
+          git cat-file -e "${BASE_SHA}^{commit}" 2>/dev/null \
+            || git fetch --no-tags --depth=1 origin "$BASE_SHA" 2>/dev/null || true
           if ! git cat-file -e "${BASE_SHA}^{commit}" 2>/dev/null; then
+            # push with an unusable `before` (branch create / force push):
+            # deepen once so HEAD^ exists as the fallback base.
+            git fetch --no-tags --deepen=1 origin 2>/dev/null || true
             BASE_SHA=$(git rev-parse HEAD^)
           fi
           git diff --unified=0 --no-color "$BASE_SHA" "$HEAD_SHA" -- \