refactor(main): eliminate unsafe runtime cast escapes

Tighten main/runtime dependency contracts to remove non-test `as never` and `as unknown as` usage so type drift surfaces during compile/test checks instead of at runtime.

backlog/tasks/task-105 - Eliminate-unsafe-non-test-runtime-casts-in-main-boundaries.md

@@ -1,10 +1,11 @@
 ---
 id: TASK-105
 title: Eliminate unsafe non-test runtime casts in main boundaries
-status: To Do
-assignee: []
+status: Done
+assignee:
+  - opencode-task105-unsafe-casts
 created_date: '2026-02-22 07:13'
-updated_date: '2026-02-22 07:13'
+updated_date: '2026-02-22 21:56'
 labels:
   - refactor
   - type-safety
@@ -36,15 +37,43 @@ Current scan shows repeated casts in dependency builders and runtime adapters, w
 
 ## Acceptance Criteria
 <!-- AC:BEGIN -->
-- [ ] #1 Non-test `as never` occurrences in `src/main.ts` and `src/main/runtime` are reduced to zero or documented narrow exceptions.
-- [ ] #2 Runtime dependency builders compile without unsafe production-path cast escapes.
-- [ ] #3 Contract regressions are caught by compile/test checks rather than runtime behavior.
+- [x] #1 Non-test `as never` occurrences in `src/main.ts` and `src/main/runtime` are reduced to zero or documented narrow exceptions.
+- [x] #2 Runtime dependency builders compile without unsafe production-path cast escapes.
+- [x] #3 Contract regressions are caught by compile/test checks rather than runtime behavior.
 <!-- AC:END -->
 
+## Implementation Plan
+
+<!-- SECTION:PLAN:BEGIN -->
+1) Baseline cast inventory in non-test scope (`src/main.ts`, `src/main/runtime/*`) using `rg` and record before-count in notes.
+2) Tighten runtime adapter contracts to remove `as never` escapes in `*-main-deps` modules: MPV/Jellyfin defaults, startup config deps, overlay visibility/options deps, field-grouping deps, CLI context deps, subtitle tokenization deps, dictionary runtime deps, tray/app deps, and MPV event bindings.
+3) Update `src/main.ts` boundary wiring to match tightened contracts and remove cast escapes in config hot-reload setters, dictionary lookup setters, MPV defaults/OSD wiring, MPV client factory constructor typing, tray creation, and overlay bootstrap callbacks.
+4) Re-run cast scan expecting zero non-test unsafe casts (or document narrow exceptions), run required gates (`bun run build`, `bun run test:core:src`), then attach before/after cast report and finalize AC/DoD.
+<!-- SECTION:PLAN:END -->
+
+## Implementation Notes
+
+<!-- SECTION:NOTES:BEGIN -->
+Executed TASK-105 implementation with runtime contract tightening across `src/main.ts` + `src/main/runtime/*` non-test files. Removed all unsafe `as never` / `as unknown as` casts in target scope by replacing unknown passthrough contracts with typed deps (MPV/Jellyfin runtime types, overlay/bootstrap deps, tokenizer/CLI deps, dictionary lookup function types, tray deps typing).
+
+Cast reduction report: baseline scan count = 42 non-test matches (`rg -n "as\\s+never|as\\s+unknown\\s+as" src/main.ts src/main/runtime --glob '!**/*.test.ts'`), after changes = 0 matches with same command.
+
+Verification: targeted runtime cast-refactor tests passed (`bun test ...` across 19 files, 35 pass / 0 fail). Required core lane passed: `bun run test:core:src` => 236 pass / 6 skip / 0 fail.
+
+Blocker: `bun run build` currently fails on pre-existing unrelated typing issues in `src/anki-integration/note-update-workflow.test.ts` (6 TS errors). No remaining build errors from TASK-105 touched files.
+
+Follow-up verification rerun after concurrent compile-fix pass: `bun run build` now succeeds on current HEAD (tsc + renderer build + packaging copy step). DoD build gate unblocked.
+<!-- SECTION:NOTES:END -->
+
+## Final Summary
+
+<!-- SECTION:FINAL_SUMMARY:BEGIN -->
+Eliminated unsafe non-test runtime cast escapes in `src/main.ts` and `src/main/runtime/*` by tightening runtime dependency-builder contracts (MPV/Jellyfin, overlay/bootstrap, CLI/tokenizer, dictionary/tray boundaries) and removing `as never` / `as unknown as` patterns in production paths. Captured cast reduction evidence (42 -> 0 matches in scoped scan), validated focused runtime suites (35 pass), and revalidated required gates (`bun run test:core:src`, `bun run build`) on current HEAD.
+<!-- SECTION:FINAL_SUMMARY:END -->
+
 ## Definition of Done
 <!-- DOD:BEGIN -->
-- [ ] #1 Cast reduction report attached in task notes (before/after counts).
-- [ ] #2 `bun run build` and `bun run test:core:src` pass.
-- [ ] #3 Any remaining exceptions have explicit rationale in code comments or task notes.
+- [x] #1 Cast reduction report attached in task notes (before/after counts).
+- [x] #2 `bun run build` and `bun run test:core:src` pass.
+- [x] #3 Any remaining exceptions have explicit rationale in code comments or task notes.
 <!-- DOD:END -->
-