feat(ci): redesign quarantine report for readability and error visibility

[JulianMaurin]

The CLI quarantine report was hard to scan in web-based CI consoles
(GitHub Actions). Test failures only showed names without error details,
forcing developers to scroll through test runner output to find
stacktraces. The report lacked visual hierarchy and mixed concerns.

Report improvements:

• Add intro section explaining what CI Insights does and linking to docs
• Display error stacktraces for unquarantined failures using box-drawing
  characters (┌ │ └─) for clear visual separation
• Use ══ heavy separators to frame the header and verdict sections
• Show "(no error details in JUnit report)" when failure has no exception
  attributes, so users understand the absence is expected
• Condense verdict into a framed block with consistent X/Y format
  (e.g. "1/2 failures quarantined", "all tests passed, no quarantine needed")
• Skip quarantine section entirely when no failures are detected

Error handling improvements:

• Display quarantine API errors inline in the report (not hidden in stderr)
  with ⚠️ section, explanation, and detail box
• Show all test failure stacktraces when quarantine check fails, treating
  all failures as unquarantined so users can still see what went wrong
• Display upload errors inline with clear messaging about impact
  ("Mergify CI Insights won't process these test results.
  Quarantine status and CI outcome are unaffected.")
• Remove redundant/confusing error messages (QUARANTINE_INFO_ERROR_MSG)

Architecture improvements:

• Separate concerns: move all display logic from quarantine.py to cli.py
• quarantine.check_and_update_failing_spans now returns a QuarantineResult
  dataclass instead of an int, carrying categorized span lists
• upload.upload() no longer prints — just uploads and raises on error
• junit.files_to_spans() returns (run_id, spans) tuple so cli.py controls
  the run ID display
• Extract _run_process test helper to eliminate ~20 lines of boilerplate
  per test case
• Move XML fixtures to tests/ci/fixtures/ directory

Test coverage:

• 15 test scenarios covering all report paths with full output assertions
• Add tests for: invalid XML, empty testsuites, no exception attributes,
  exception type only, None attributes, upload+quarantine combined errors,
  multiple report files, pluralization
• Consolidate duplicated tests from test_cli.py into
  junit_processing/test_cli.py
• Use realistic error messages (HTTP 422, httpx.ConnectError)

Co-Authored-By: Claude Opus 4.6 (1M context) noreply@anthropic.com

[mergify]

Merge Protections

Your pull request matches the following merge protections and will not be merged until they are valid.

🟢 🤖 Continuous Integration

Wonderful, this rule succeeded.

• all of:
  • check-success=ci-gate

🟢 👀 Review Requirements

Wonderful, this rule succeeded.

• any of:
  • #approved-reviews-by>=2
  • author = dependabot[bot]
  • author = mergify-ci-bot
  • author = renovate[bot]

🟢 Enforce conventional commit

Wonderful, this rule succeeded.

Make sure that we follow https://www.conventionalcommits.org/en/v1.0.0/

• title ~= ^(fix|feat|docs|style|refactor|perf|test|build|ci|chore|revert)(?:\(.+\))?:

🟢 🔎 Reviews

Wonderful, this rule succeeded.

• #changes-requested-reviews-by = 0
• #review-requested = 0
• #review-threads-unresolved = 0

🟢 📕 PR description

Wonderful, this rule succeeded.

• body ~= (?ms:.{48,})

[mergify]

🧪 CI Insights

Here's what we observed from your CI run for 37e10e6.

🟢 All jobs passed!

But CI Insights is watching 👀

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-03-16 10:48 UTC · Rule: default
• ✅ Checks passed · on draft merge queue: embarking main (c6ca9e9) and #1030 together #1031
• ✅ Merged — 2026-03-16 10:51 UTC · at 37e10e68fa1c813f8d46231a94c2a6319ec1ea9e

This pull request spent 2 minutes 31 seconds in the queue, including 2 minutes 17 seconds running CI.

Required conditions to merge

• all of [🛡 Merge Protections rule Enforce conventional commit]:
  • title ~= ^(fix|feat|docs|style|refactor|perf|test|build|ci|chore|revert)(?:\(.+\))?:
    • feat(ci): redesign quarantine report for readability and error visibility #1030
• all of [🛡 Merge Protections rule 👀 Review Requirements]:
  • any of:
    • #approved-reviews-by>=2
      • feat(ci): redesign quarantine report for readability and error visibility #1030
    • author = dependabot[bot]
      • feat(ci): redesign quarantine report for readability and error visibility #1030
    • author = mergify-ci-bot
      • feat(ci): redesign quarantine report for readability and error visibility #1030
    • author = renovate[bot]
      • feat(ci): redesign quarantine report for readability and error visibility #1030
• all of [🛡 Merge Protections rule 📕 PR description]:
  • body ~= (?ms:.{48,})
    • feat(ci): redesign quarantine report for readability and error visibility #1030
• all of [🛡 Merge Protections rule 🔎 Reviews]:
  • #changes-requested-reviews-by = 0
    • feat(ci): redesign quarantine report for readability and error visibility #1030
  • #review-requested = 0
    • feat(ci): redesign quarantine report for readability and error visibility #1030
  • #review-threads-unresolved = 0
    • feat(ci): redesign quarantine report for readability and error visibility #1030
• all of [🛡 Merge Protections rule 🤖 Continuous Integration]:
  • all of:
    • check-success=ci-gate