Feat/UI error category 325

[ivasuy]

Summary

Implements UI observability for failed executions by surfacing error_category on run list rows and step detail error panels, including category-specific guidance and diagnostics links. This addresses troubleshooting clarity requested in #325 by making it obvious whether failure came from LLM availability, concurrency pressure, agent/network issues, bad responses, or control-plane internals.

Type of change

• Bug fix
• New feature
• Refactor / cleanup
• Docs only
• Tests only
• CI / tooling
• Breaking change

Test plan

• cd control-plane/control-plane && go test ./internal/storage ./internal/handlers/ui
• npm --prefix control-plane/web/client run test -- src/test/pages/RunsPage.test.tsx src/test/components/StepDetail.test.tsx src/test/App.zero.test.tsx
• Manual verification in embedded UI:
  • /ui/runs: failed rows show category badge + diagnostics link
  • /ui/runs/:id: error card shows category badge + human-readable guidance + diagnostics link
  • /ui basename navigation works (no backend GET /dashboard 404)

Test coverage

• I ran tests for the surface(s) I changed locally.
• New code paths are covered by tests in this PR (no bare additions).
• If I removed code, I updated coverage-baseline.json in this PR only if the removal caused a legitimate regression and I called it out in the summary above.
• The coverage gate check is green in CI before requesting review.

Checklist

• I have read CONTRIBUTING.md (if present) and docs/DEVELOPMENT.md.
• Commits are signed and follow conventional-commits style.
• I have linked any related issues (Fixes feat(tests): add unit tests for vector memory handler functionality #123 / Closes test: add tests for TypeScript SDK utils (pattern, schema, httpAgents) #456).

Related issues / PRs

• Closes UI: Show error_category on failed executions #325
• Refs Hard to troubleshoot, agent stays running for hour #316
• Refs feat: execution resilience - LLM health, concurrency limits, retry, log streaming #319

UI screenshots

Runs list (failed row badges + diagnostics links)

Step detail (error category guidance + diagnostics link)

[github-actions]

Performance

SDK	Memory	Δ	Latency	Δ	Tests	Status
Python	9.4 KB	+4%	0.23 µs	-34%	✓	✓

✓ No regressions detected

[github-actions]

📊 Coverage gate

Thresholds from .coverage-gate.toml: per-surface ≥ 86%, aggregate ≥ 88%, max per-surface regression ≤ 1.0 pp, max aggregate regression ≤ 0.50 pp.

Surface	Current	Baseline	Δ
control-plane	87.40%	87.30%	↑ +0.10 pp	🟡
sdk-go	91.90%	90.70%	↑ +1.20 pp	🟢
sdk-python	93.66%	93.63%	↑ +0.03 pp	🟢
sdk-typescript	92.68%	92.56%	↑ +0.12 pp	🟢
web-ui	89.89%	90.01%	↓ -0.12 pp	🟡
aggregate	88.97%	89.01%	↓ -0.04 pp	🟡

✅ Gate passed

No surface regressed past the allowed threshold and the aggregate stayed above the floor.

[github-actions]

📐 Patch coverage gate

Threshold: 80% on lines this PR touches vs origin/main (from .coverage-gate.toml:thresholds.min_patch).

Surface	Touched lines	Patch coverage	Status
control-plane	28	100.00%	✅
sdk-go	0	—	➖ no changes
sdk-python	0	—	➖ no changes
sdk-typescript	0	—	➖ no changes
web-ui	133	90.00%	✅

✅ Patch gate passed

Every surface whose lines were touched by this PR has patch coverage at or above the threshold.