repro: focus on jammy x86, bump iterations, run 5 replicas

Drop noble + arm legs (binary is x86 only and noble is a control we don't
need to re-verify). Run 5 parallel replicas of jammy x86 to amortize the
~0.1-1% per-launch crash rate observed in CI.

Per replica: 3000 iterations x 8 parallel launches = 24k browser starts
per replica, 120k total across the matrix. At a 0.18% rate, expected ~216
SIGSEGV events; if zero, the bug is conditional on something Playwright
sets up that this minimal repro doesn't.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: yury-s

.github/workflows/repro_chs_jammy.yml

@@ -3,54 +3,49 @@
 # from Chrome for Testing, launches it in a tight loop with the same flags
 # Playwright uses, and counts SIGSEGV exits.
 #
-# Mirrors test_docker.yml's matrix and `--ipc=host` exactly so the runtime
-# environment is identical to the failing job, modulo the Java/Playwright
-# layer.
+# Mirrors test_docker.yml's `--ipc=host` and ubuntu:jammy container exactly.
+# Runs 5 parallel replicas to amortize the ~0.1-1% per-launch crash rate.
 name: Repro CHS jammy SIGSEGV
 
 on:
   workflow_dispatch:
     inputs:
       iterations:
-        description: Launches per matrix leg
-        default: '300'
+        description: Launches per replica
+        default: '3000'
       parallel:
-        description: Concurrent launches
-        default: '4'
+        description: Concurrent launches per replica
+        default: '8'
       chrome_version:
-        description: Chrome for Testing version (e.g. 148.0.7778.96)
+        description: Chrome for Testing version
         default: '148.0.7778.96'
   push:
     branches:
       - 'repro/**'
 
 jobs:
   repro:
-    name: Repro (${{ matrix.flavor }}, ${{ matrix.runs-on }})
+    name: Repro jammy x86 (replica ${{ matrix.replica }})
     timeout-minutes: 60
-    runs-on: ${{ matrix.runs-on }}
+    runs-on: ubuntu-24.04
     strategy:
       fail-fast: false
       matrix:
-        flavor: [jammy, noble]
-        runs-on: [ubuntu-24.04, ubuntu-24.04-arm]
+        replica: [1, 2, 3, 4, 5]
     steps:
       - uses: actions/checkout@v6
 
       - name: Build Docker image
         run: |
-          # Override the FROM line to match the matrix flavor.
-          sed "s|^FROM ubuntu:.*$|FROM ubuntu:${{ matrix.flavor }}|" \
-              tools/chs-repro/Dockerfile > tools/chs-repro/Dockerfile.${{ matrix.flavor }}
           docker build \
             --build-arg CHROME_VERSION=${{ inputs.chrome_version || '148.0.7778.96' }} \
-            -t chs-repro:${{ matrix.flavor }} \
-            -f tools/chs-repro/Dockerfile.${{ matrix.flavor }} \
+            -t chs-repro:jammy \
+            -f tools/chs-repro/Dockerfile \
             tools/chs-repro
 
       - name: Run repro (--ipc=host, matches test_docker.yml)
         run: |
           docker run --rm --ipc=host \
-            -e ITERATIONS=${{ inputs.iterations || '300' }} \
-            -e PARALLEL=${{ inputs.parallel || '4' }} \
-            chs-repro:${{ matrix.flavor }}
+            -e ITERATIONS=${{ inputs.iterations || '3000' }} \
+            -e PARALLEL=${{ inputs.parallel || '8' }} \
+            chs-repro:jammy