**Phase 144 final verification pass — complete, 100% green.**
- **Verified:** all 3 tasks already implemented in-tree — `document-modal.js` history-aware modal (one state-only entry per open: push on open, adopt on forward re-open, in-place `replaceState(prev)` on button/Escape/backdrop close, `closingViaBack`-guarded back-close, top-level popstate listener), `tests/unit/test_frontend_doc_modal.py` source pins, `tests/e2e/test_modal_back_button.py` (4 tests). No code fixes needed.
- **Tests:** `uv run pytest` → 3371 passed · `uv run pytest --cov=app --cov-report=term-missing` → 3371 passed, **app/ 99%** (gate >90%) · `uv run pytest tests/e2e/test_modal_back_button.py -v --no-cov` → 4 passed in isolation · regressions in isolation: `test_document_back_navigation.py` 3 passed, `test_kb_tree_nav.py` 4 passed · `uv run ruff check .` clean, `uv run pyright` 0 errors.
- **Completion criteria:** back closes modal (URL/view/drill untouched; second back navigates as usual) ✅ · back→forward re-opens same doc, no duplicate entry ✅ · button/Escape/backdrop close leaves no dead back step ✅ (state byte-identity + modal-free back chain; `replaceState` can't shrink `history.length` — documented deviation, locked design forbids `history.back()/go()`) · all gates green ✅ · no behavior change in completed phases (pre-phase pins + both regression E2Es green) ✅.
- **Docs:** README — one feature-description gap fixed (added the phase-144 Back/Forward modal behavior to the Chat section); all other README facts verified against code (routes, every `.env.example` var, all ~40 documented defaults vs `app/config.py`). AGENTS.md — verified consistent, no changes needed.
- **Decisions:** no live-infrastructure work touched; all changes left uncommitted in the working tree per harness protocol.
- **Next pending phase:** `145_git_source_links`.
