* test: raise statement coverage to 90% and enforce it in CI
Add unit tests across the cmd and internal packages to bring total
statement coverage above 90%, and gate future regressions.
- Cover CLI helpers, provider TUI handlers, resume/manifest paths, and
error branches in config, llm, llmloop, scan, session, agent, viewer,
mcp, pathutil, and telemetry.
- Raise the coverage threshold from 80% to 90% in the Makefile
(COVERAGE_THRESHOLD) and in the CI "Check coverage threshold" step.
- Ignore generated coverage.out and coverage.html artifacts.
Total statement coverage is now 90.5%, measured consistently by both
`make coverage` and the CI `go test ./...` scope.
* test: widen statement coverage margin with environment-independent unit tests
Add table-driven unit tests for pure, environment-independent functions to
raise the statement-coverage safety margin above the 90% threshold:
- session.ResumeState.ValidateScanOptions (70% -> 100%)
- rules.SystemRule.UnmarshalJSON error branches (71% -> 82%)
- llmloop.stripMarkdownFences no-newline branch (82% -> 100%)
- diff.firstLine empty/blank-input branch
- diff.extractCodeBlock missing-newline and no-closing-fence branches
- main.truncate n<=1 and normalization branches
- agent.Agent nil-receiver accessor guards
