CI compliance cleanup for test error handling

Status: Accepted
Date: 2025-12-30
Context:
- Motivation: restore just ci compliance and remove explicit panic/unwrap patterns in tests to align with AGENT error-handling rules.
- Constraints: keep coverage ≥ 80% and avoid new dependencies while satisfying clippy::pedantic.
Decision:
- Replace explicit panic!/unwrap usages in tests with Result-returning flows and let...else patterns.
- Exercise must-use values in tests to avoid lint violations.
Consequences:
- Positive outcomes: lint clean, tests remain deterministic, and coverage stays above the gate.
- Risks or trade-offs: slightly more verbose test code; added Result plumbing in tests.
Follow-up:
- Implementation tasks: keep new tests using Result and let...else patterns when adding coverage.
- Review checkpoints: re-run just ci after any test refactors.

Design notes

Tests now surface unexpected success paths as explicit error returns instead of panics.
Sse test responses are exercised via into_response to satisfy must-use lints.