The current CI status templates were a first pass that shows everything. This PR makes the template layout selectable and adds a second, DX-focused style — Strata — that answers, in priority order: what broke → how to fix/repro it → why it was slow. The existing layout is preserved as Kilgore (the default), byte-identical to today.

Stacked on #1258 — that PR finalizes the per-failure repro data model this builds on. Review/merge #1258 first.

How it works

A style is a bundle of the three top-level Jinja2 templates a surface may need — summary + details (check surfaces) and body (the aggregated PR/MR comment) — selected by a new style arg on every status feature:

def config(ctx):
    for name in ctx.tasks:
        ctx.tasks[name].features[GithubStatusComments].args.style = "strata"
        ctx.tasks[name].features[GithubStatusChecks].args.style = "strata"

resolve_style(name, overrides) layers the existing per-key templates arg on top of the named style, so you can pick a style and replace just one slot — that's how custom variants are expressed, no new mechanism:

args.style = "strata"
args.templates = {"details": "<my jinja2>"}   # strata everywhere else, custom details

Wired into all five status features: GitHub status checks, GitHub PR comment, GitLab commit statuses, GitLab MR comment, Buildkite annotation.

What Strata looks like

Verdict-led, compact, aggregated PR comment:

## ✨ Aspect Workflows
### ❌ 1 task failed

- ❌ build (build-task) · ⏱ 42s · ✨ Aspect · 🐙 GitHub Actions · ☑️ Check<br>💬 Bazel build failed
- 🔄 test (test-task) · ⏱ 1m 18s · ✨ Aspect<br>💬 Bazel test running... (13/60 tests run)
- ✅ lint (lint-task) · ⏱ 24s · ✨ Aspect<br>💬 Lint complete (clean)

On a check surface, the body leads with a verdict heading + a KPI strip — a fenced, monospace, threshold-emoji health line that stands in for the web UI's colored tiles (markdown has no color):

🟡 Cache hit   78%     4,498 / 5,768 actions
🟢 Parallelism 6.2×    cpu 26m
🟡 Wall time   4m12s   crit path 1m50s (44%)

— then What broke (each failure's snippet open, with that failure's repro command right beneath it), then whole-run Fix / Reproduce, with the passed/cached rollup and the performance/invocation detail collapsed below. The performance block auto-expands on a "Passed, but slow" verdict.

Design synthesized from three independent design passes, drawing on BuildBuddy's results UI and the new Strata web UI in silo.

Changes are visible to end-users: yes

• Searched for relevant documentation and updated as needed: yes (docsite PR linked below)
• Breaking change (forces users to change their own code or config): no
• Suggested release notes appear below: yes

Suggested release notes

• Status surfaces (GitHub/GitLab PR comment, GitHub status check, GitLab commit status, Buildkite annotation) now support a style arg. strata is a new DX-focused layout — a verdict + a compact cache/parallelism/wall KPI strip, failure snippets shown with their repro commands inline, and reference sections collapsed. The original full report is kilgore (default, unchanged).
• Custom variants: layer per-key templates overrides on top of any style.

Test plan

• New test cases added
  • lib/template_styles_test.axl — 20 unit tests: resolve_style selection + override layering, compute_strata_kpi thresholds (cache/parallelism/critical-path-share), verdict words, slow-but-passing detection, verdict-without-metrics
  • Strata render passes added to test-template-snapshots, test-pr-comment-snapshots, and the inline-snippet render test in .aspect/axl.axl
• Covered by existing test cases (Kilgore output unchanged across all snapshot suites)
• Full local regression green: aspect tests axl (851), test-template-styles (20), all 7 snapshot suites, test-repro-commands/test-bazel-results/test-bazel-runner, cargo test -p aspect-cli (40)
• Live verification of the PR-comment + GitHub status-check surfaces with style = "strata" (in progress)