test(lint): reduce warning debt in selected test suites

docs/plans/analysis/2026-02-16-codebase-audit-report.md

@@ -28,7 +28,7 @@ Current health snapshot:
 - `pnpm typecheck`: passing
 - `pnpm build`: passing
 - `pnpm test:run`: passing (`140/140` files, `1773/1773` tests)
-- `pnpm lint`: passing with warnings only (`0 errors`, `539 warnings`)
+- `pnpm lint`: passing with warnings only (`0 errors`, `501 warnings`)
 
 Top conclusions:
 - A critical Web UI security issue exists in markdown rendering (unsanitized HTML insertion).
@@ -126,7 +126,7 @@ Remediation update (2026-02-16):
 - Severity: Medium
 - Impact: CI noise, reduced confidence in static analysis, and slower defect detection.
 - Evidence:
-  - `pnpm -s lint` => `0 errors`, `539 warnings`
+  - `pnpm -s lint` => `0 errors`, `501 warnings`
   - Error concentration:
     - `src/daemon/models.ts` (90 errors)
     - `src/cli/tui.ts` (25 errors)
@@ -145,7 +145,7 @@ Remediation update (2026-02-16):
 
 Remediation update (2026-02-16):
 - Stage 1 complete: fixed all error-level ESLint violations in impacted high-error files so `pnpm lint` now passes with `0` errors.
-- Stage 2 pending: warning-burn-down remains (currently `539` warnings).
+- Stage 2 in progress: warning-burn-down reduced to `501` warnings via targeted low-risk test cleanup (non-null assertion removal).
 
 ### F-005 Medium: ESLint browser globals mismatch causes avoidable UI lint failures
 
@@ -449,7 +449,7 @@ pnpm -s lint
 
 Observed outcomes:
 - Typecheck/build/test: passing.
-- Lint: passing with warnings only (`0` errors, `539` warnings).
+- Lint: passing with warnings only (`0` errors, `501` warnings).
 
 Historical pre-remediation lint error concentration snapshot:
 - `src/daemon/models.ts`: 90 errors