diff --git a/.agents/phases/todo/85_mobile_menu_gate_overlap/00_phase.md b/.agents/phases/complete/85_mobile_menu_gate_overlap/00_phase.md
similarity index 100%
rename from .agents/phases/todo/85_mobile_menu_gate_overlap/00_phase.md
rename to .agents/phases/complete/85_mobile_menu_gate_overlap/00_phase.md
diff --git a/.agents/phases/todo/85_mobile_menu_gate_overlap/01_gate_below_header.md b/.agents/phases/complete/85_mobile_menu_gate_overlap/01_gate_below_header.md
similarity index 100%
rename from .agents/phases/todo/85_mobile_menu_gate_overlap/01_gate_below_header.md
rename to .agents/phases/complete/85_mobile_menu_gate_overlap/01_gate_below_header.md
diff --git a/.agents/phases/todo/85_mobile_menu_gate_overlap/02_e2e_pin_updates.md b/.agents/phases/complete/85_mobile_menu_gate_overlap/02_e2e_pin_updates.md
similarity index 100%
rename from .agents/phases/todo/85_mobile_menu_gate_overlap/02_e2e_pin_updates.md
rename to .agents/phases/complete/85_mobile_menu_gate_overlap/02_e2e_pin_updates.md
diff --git a/.agents/phases/todo/85_mobile_menu_gate_overlap/03_verify_and_commit.md b/.agents/phases/complete/85_mobile_menu_gate_overlap/03_verify_and_commit.md
similarity index 100%
rename from .agents/phases/todo/85_mobile_menu_gate_overlap/03_verify_and_commit.md
rename to .agents/phases/complete/85_mobile_menu_gate_overlap/03_verify_and_commit.md
diff --git a/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__00_phase.a1.err b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__00_phase.a1.err
new file mode 100644
index 0000000..e69de29
diff --git a/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__00_phase.a1.md b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__00_phase.a1.md
new file mode 100644
index 0000000..bef412d
--- /dev/null
+++ b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__00_phase.a1.md
@@ -0,0 +1,12 @@
+All verification complete. Final report:
+
+**Phase 85 final verification pass — all green** (tasks 01–03 already complete; independently re-verified from scratch)
+- Verified fix in tree: `styles.css` `.auth-gate` z-index 500→15 + rewritten stacking comment (no `z-index: 500` left); `index.html`/`document.html` comment-only; `token-gate.js` docstring-only (logic byte-identical); `test_mobile_hamburger_nav.py` real-click conversion + new `test_anonymous_toggle_tappable_with_gate_up`; new `tests/unit/test_gate_header_stacking.py` (3 pins); `test_api_tokens.py` untouched
+- `uv run pytest` → 1717 passed, 1 warning (exit 0)
+- `uv run pytest --cov=app --cov-report=term-missing` → TOTAL **99%** (>90%)
+- E2E in isolation: `test_mobile_hamburger_nav.py` **8 passed**; `test_api_tokens.py` **9 passed** (unchanged); `test_smoke.py` **3 passed**; `test_document_viewer.py` **7 passed**
+- `uv run ruff check . && uv run pyright` → clean / 0 errors
+- Live probe (375×812, anonymous, fresh server): on `/` and `/history.html` `elementFromPoint` at toggle → SVG `path`, never `#auth-gate`; real click opens menu (`aria-expanded=true`); exactly one visible nav link (Chat) + sign-in copy; Chat link topmost over gate; `#main` inert — criteria 1, 2, 3 confirmed directly
+- Criteria: (1) real-click menu on / + /history ✅ (2) dropdown above gate ✅ (3) anonymous contents + #main inert ✅ (4) admin byte-identical (phase-46 tests green) ✅ (5) doc-viewer gate under bar (CSS pin + doc-viewer suite) ✅ (6) full gate green ✅ (7) diff scoped to the 5 code files + new unit test + phase files, nothing in `app/` ✅ (8) commit + todo→complete move left to harness per executor rules (task files already in `complete/`)
+- Note: `.agents/remediation_plan.md` (untracked) is a pre-existing artifact of the earlier security audit — left untouched; a missing "N passed" line seen mid-pass was my own `-q`+addopts `-q` = `-qq` quirk, not a defect
+- Next pending phase: `86_history_page_width`
diff --git a/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__00_phase.a1.validate b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__00_phase.a1.validate
new file mode 100644
index 0000000..0914b55
--- /dev/null
+++ b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__00_phase.a1.validate
@@ -0,0 +1,85 @@
+........................................................................ [  4%]
+........................................................................ [  8%]
+........................................................................ [ 12%]
+........................................................................ [ 16%]
+........................................................................ [ 20%]
+........................................................................ [ 25%]
+........................................................................ [ 29%]
+........................................................................ [ 33%]
+........................................................................ [ 37%]
+........................................................................ [ 41%]
+........................................................................ [ 46%]
+........................................................................ [ 50%]
+........................................................................ [ 54%]
+........................................................................ [ 58%]
+........................................................................ [ 62%]
+........................................................................ [ 67%]
+........................................................................ [ 71%]
+........................................................................ [ 75%]
+........................................................................ [ 79%]
+........................................................................ [ 83%]
+........................................................................ [ 88%]
+........................................................................ [ 92%]
+........................................................................ [ 96%]
+.............................................................            [100%]
+=============================== warnings summary ===============================
+.venv/lib/python3.13/site-packages/fastapi/testclient.py:1
+  /var/home/ducoterra/Projects/Personal/brain_of_reese/.venv/lib/python3.13/site-packages/fastapi/testclient.py:1: StarletteDeprecationWarning: Using `httpx` with `starlette.testclient` is deprecated; install `httpx2` instead.
+    from starlette.testclient import TestClient as TestClient  # noqa
+
+-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
+================================ tests coverage ================================
+_______________ coverage: platform linux, python 3.13.13-final-0 _______________
+
+Name                           Stmts   Miss  Cover
+--------------------------------------------------
+app/__init__.py                    1      0   100%
+app/api/__init__.py                0      0   100%
+app/api/auth.py                   52      0   100%
+app/api/chat.py                  178      0   100%
+app/api/chats.py                 110      0   100%
+app/api/config.py                  7      0   100%
+app/api/doc_drafts.py             94      0   100%
+app/api/docs.py                   50      0   100%
+app/api/git_sources.py           212      0   100%
+app/api/health.py                 10      0   100%
+app/api/steering.py               42      0   100%
+app/api/suggestions.py            29      0   100%
+app/api/sync.py                   98      0   100%
+app/api/tokens.py                 28      0   100%
+app/config.py                    141      0   100%
+app/core/__init__.py               0      0   100%
+app/core/auth.py                  45      0   100%
+app/core/caching.py              108      0   100%
+app/core/debugging.py             29      2    93%
+app/core/docs_push.py             39      0   100%
+app/core/errors.py                 5      0   100%
+app/core/logging.py               13      0   100%
+app/core/rate_limit.py            44      0   100%
+app/core/security_headers.py      19      0   100%
+app/core/tokens.py                33      0   100%
+app/db.py                         21      0   100%
+app/main.py                       64      0   100%
+app/models.py                     94      0   100%
+app/rag/__init__.py                0      0   100%
+app/rag/agent.py                 222      0   100%
+app/rag/archive_upload.py        128      0   100%
+app/rag/chunker.py               206      4    98%
+app/rag/git_sources.py            14      0   100%
+app/rag/importer.py              180      3    98%
+app/rag/llm.py                   217      0   100%
+app/rag/overview.py               71      0   100%
+app/rag/prompts.py                88      0   100%
+app/rag/retriever.py             150      3    98%
+app/rag/scaffolding.py            55      0   100%
+app/rag/source_removal.py         41      0   100%
+app/rag/sources_meta.py           16      0   100%
+app/rag/suggestions.py            27      0   100%
+app/rag/summarizer.py             24      0   100%
+app/schemas.py                   232      0   100%
+--------------------------------------------------
+TOTAL                           3237     12    99%
+coverage gate: app/ 99% (>90%) OK
+All checks passed!
+0 errors, 0 warnings, 0 informations
+validation OK
diff --git a/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__01_gate_below_header.a1.err b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__01_gate_below_header.a1.err
new file mode 100644
index 0000000..e69de29
diff --git a/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__01_gate_below_header.a1.md b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__01_gate_below_header.a1.md
new file mode 100644
index 0000000..7321af2
--- /dev/null
+++ b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__01_gate_below_header.a1.md
@@ -0,0 +1,17 @@
+Task 01 complete — all green.
+
+**Implemented**
+- `frontend/assets/styles.css`: `.auth-gate` `z-index: 500 → 15` (the one-value fix, A1) + stacking comment rewritten to the phase-85 contract (15 gate < 20 header < 21 dropdown; skip-link 100 / 1000-family overlays unaffected; `#main` lock is JS, not z-order)
+- `frontend/index.html` / `frontend/document.html`: gate-section comments reworded (header stays reachable; `#main` stays inert) — markup byte-identical, comment-only
+- `frontend/assets/token-gate.js`: docstring sweep only — "only interactive surface" → "only CONTENT-level interactive surface" + phase-85 note; logic byte-identical
+- New `tests/unit/test_gate_header_stacking.py`: 3 source-level z-order pins (gate=15, header=20 with gate<header, mobile `.app-nav` keeps 21>15) + the gate still covers content (fixed/inset:0, `[hidden]` display:none)
+
+**Test / lint results**
+- `uv run pytest tests/unit/test_gate_header_stacking.py -v` → 3 passed
+- `uv run pytest --cov=app --cov-report=term-missing` → 1717 passed, `app/` TOTAL **99%** (>90% ✓)
+- `uv run ruff check .` → All checks passed; `uv run pyright` → 0 errors, 0 warnings
+- `git diff --stat` limited to the 4 frontend files (CSS value + comments only) + the new test; `grep "z-index: 500"` no longer matches anything
+
+**Decisions**: the dropdown's `z-index: 21` lives on the base `.app-nav` rule (shared with `.is-open`), so the pin targets `.app-nav` in the ≤640px block — same as the existing phase-46 pin; value 15 kept as owner-decided.
+
+**Next pending task**: `02_e2e_pin_updates.md` (same phase — real-click conversion + TODO-regression E2E pin).
diff --git a/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__01_gate_below_header.a1.validate b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__01_gate_below_header.a1.validate
new file mode 100644
index 0000000..0914b55
--- /dev/null
+++ b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__01_gate_below_header.a1.validate
@@ -0,0 +1,85 @@
+........................................................................ [  4%]
+........................................................................ [  8%]
+........................................................................ [ 12%]
+........................................................................ [ 16%]
+........................................................................ [ 20%]
+........................................................................ [ 25%]
+........................................................................ [ 29%]
+........................................................................ [ 33%]
+........................................................................ [ 37%]
+........................................................................ [ 41%]
+........................................................................ [ 46%]
+........................................................................ [ 50%]
+........................................................................ [ 54%]
+........................................................................ [ 58%]
+........................................................................ [ 62%]
+........................................................................ [ 67%]
+........................................................................ [ 71%]
+........................................................................ [ 75%]
+........................................................................ [ 79%]
+........................................................................ [ 83%]
+........................................................................ [ 88%]
+........................................................................ [ 92%]
+........................................................................ [ 96%]
+.............................................................            [100%]
+=============================== warnings summary ===============================
+.venv/lib/python3.13/site-packages/fastapi/testclient.py:1
+  /var/home/ducoterra/Projects/Personal/brain_of_reese/.venv/lib/python3.13/site-packages/fastapi/testclient.py:1: StarletteDeprecationWarning: Using `httpx` with `starlette.testclient` is deprecated; install `httpx2` instead.
+    from starlette.testclient import TestClient as TestClient  # noqa
+
+-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
+================================ tests coverage ================================
+_______________ coverage: platform linux, python 3.13.13-final-0 _______________
+
+Name                           Stmts   Miss  Cover
+--------------------------------------------------
+app/__init__.py                    1      0   100%
+app/api/__init__.py                0      0   100%
+app/api/auth.py                   52      0   100%
+app/api/chat.py                  178      0   100%
+app/api/chats.py                 110      0   100%
+app/api/config.py                  7      0   100%
+app/api/doc_drafts.py             94      0   100%
+app/api/docs.py                   50      0   100%
+app/api/git_sources.py           212      0   100%
+app/api/health.py                 10      0   100%
+app/api/steering.py               42      0   100%
+app/api/suggestions.py            29      0   100%
+app/api/sync.py                   98      0   100%
+app/api/tokens.py                 28      0   100%
+app/config.py                    141      0   100%
+app/core/__init__.py               0      0   100%
+app/core/auth.py                  45      0   100%
+app/core/caching.py              108      0   100%
+app/core/debugging.py             29      2    93%
+app/core/docs_push.py             39      0   100%
+app/core/errors.py                 5      0   100%
+app/core/logging.py               13      0   100%
+app/core/rate_limit.py            44      0   100%
+app/core/security_headers.py      19      0   100%
+app/core/tokens.py                33      0   100%
+app/db.py                         21      0   100%
+app/main.py                       64      0   100%
+app/models.py                     94      0   100%
+app/rag/__init__.py                0      0   100%
+app/rag/agent.py                 222      0   100%
+app/rag/archive_upload.py        128      0   100%
+app/rag/chunker.py               206      4    98%
+app/rag/git_sources.py            14      0   100%
+app/rag/importer.py              180      3    98%
+app/rag/llm.py                   217      0   100%
+app/rag/overview.py               71      0   100%
+app/rag/prompts.py                88      0   100%
+app/rag/retriever.py             150      3    98%
+app/rag/scaffolding.py            55      0   100%
+app/rag/source_removal.py         41      0   100%
+app/rag/sources_meta.py           16      0   100%
+app/rag/suggestions.py            27      0   100%
+app/rag/summarizer.py             24      0   100%
+app/schemas.py                   232      0   100%
+--------------------------------------------------
+TOTAL                           3237     12    99%
+coverage gate: app/ 99% (>90%) OK
+All checks passed!
+0 errors, 0 warnings, 0 informations
+validation OK
diff --git a/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__02_e2e_pin_updates.a1.err b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__02_e2e_pin_updates.a1.err
new file mode 100644
index 0000000..e69de29
diff --git a/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__02_e2e_pin_updates.a1.md b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__02_e2e_pin_updates.a1.md
new file mode 100644
index 0000000..6dc01c4
--- /dev/null
+++ b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__02_e2e_pin_updates.a1.md
@@ -0,0 +1,19 @@
+All green. Task 02 is complete.
+
+**Implemented**
+- `tests/e2e/test_mobile_hamburger_nav.py`: retired `_js_open_menu` (JS-dispatch drive) — anonymous tests now use the real-click helper `_open_menu` (`page.click("#nav-toggle")`), docstring rewritten to the phase-85 contract (gate z 15 below header z 20)
+- New regression pin `test_anonymous_toggle_tappable_with_gate_up`: with the gate up (`#main` inert), `elementFromPoint` at the toggle center resolves to the toggle/SVG child, never `#auth-gate`; real click opens the menu above the gate (Chat link visible + topmost at its center, gate still up); Esc settles closed
+- Module docstring: phase-85 stacking paragraph + numbered mapping entry; all phase-79 "intercepted by the gate" test docstrings/comments swept (assertions kept exactly: one visible "Chat" link, Esc refocus, outside-click at (10,780) doesn't close, 180ms pins)
+- `test_api_tokens.py`: verified no hamburger pins (grep clean); run unchanged, green
+
+**Results**
+- `uv run pytest tests/e2e/test_mobile_hamburger_nav.py -v --no-cov` → 8 passed (isolation)
+- `uv run pytest tests/e2e/test_api_tokens.py -v --no-cov` → 9 passed, file unchanged (isolation)
+- `uv run pytest tests/e2e/test_smoke.py -v --no-cov` → 3 passed
+- `uv run pytest --cov=app --cov-report=term-missing` → 1717 passed, coverage 99% (>90%)
+- `uv run ruff check . && uv run pyright` → clean
+- Criterion grep `querySelector('#nav-toggle').click()` → no matches; my diff touches only the one E2E file (frontend changes in tree are task-01's, committed atomically by the harness at phase end)
+
+**Deviations** — none; the JS helper was folded into `_open_menu` rather than duplicated (identical real-click body + same 3 assertions).
+
+**Next pending task:** `.agents/phases/todo/85_mobile_menu_gate_overlap/03_verify_and_commit.md`
diff --git a/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__02_e2e_pin_updates.a1.validate b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__02_e2e_pin_updates.a1.validate
new file mode 100644
index 0000000..0914b55
--- /dev/null
+++ b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__02_e2e_pin_updates.a1.validate
@@ -0,0 +1,85 @@
+........................................................................ [  4%]
+........................................................................ [  8%]
+........................................................................ [ 12%]
+........................................................................ [ 16%]
+........................................................................ [ 20%]
+........................................................................ [ 25%]
+........................................................................ [ 29%]
+........................................................................ [ 33%]
+........................................................................ [ 37%]
+........................................................................ [ 41%]
+........................................................................ [ 46%]
+........................................................................ [ 50%]
+........................................................................ [ 54%]
+........................................................................ [ 58%]
+........................................................................ [ 62%]
+........................................................................ [ 67%]
+........................................................................ [ 71%]
+........................................................................ [ 75%]
+........................................................................ [ 79%]
+........................................................................ [ 83%]
+........................................................................ [ 88%]
+........................................................................ [ 92%]
+........................................................................ [ 96%]
+.............................................................            [100%]
+=============================== warnings summary ===============================
+.venv/lib/python3.13/site-packages/fastapi/testclient.py:1
+  /var/home/ducoterra/Projects/Personal/brain_of_reese/.venv/lib/python3.13/site-packages/fastapi/testclient.py:1: StarletteDeprecationWarning: Using `httpx` with `starlette.testclient` is deprecated; install `httpx2` instead.
+    from starlette.testclient import TestClient as TestClient  # noqa
+
+-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
+================================ tests coverage ================================
+_______________ coverage: platform linux, python 3.13.13-final-0 _______________
+
+Name                           Stmts   Miss  Cover
+--------------------------------------------------
+app/__init__.py                    1      0   100%
+app/api/__init__.py                0      0   100%
+app/api/auth.py                   52      0   100%
+app/api/chat.py                  178      0   100%
+app/api/chats.py                 110      0   100%
+app/api/config.py                  7      0   100%
+app/api/doc_drafts.py             94      0   100%
+app/api/docs.py                   50      0   100%
+app/api/git_sources.py           212      0   100%
+app/api/health.py                 10      0   100%
+app/api/steering.py               42      0   100%
+app/api/suggestions.py            29      0   100%
+app/api/sync.py                   98      0   100%
+app/api/tokens.py                 28      0   100%
+app/config.py                    141      0   100%
+app/core/__init__.py               0      0   100%
+app/core/auth.py                  45      0   100%
+app/core/caching.py              108      0   100%
+app/core/debugging.py             29      2    93%
+app/core/docs_push.py             39      0   100%
+app/core/errors.py                 5      0   100%
+app/core/logging.py               13      0   100%
+app/core/rate_limit.py            44      0   100%
+app/core/security_headers.py      19      0   100%
+app/core/tokens.py                33      0   100%
+app/db.py                         21      0   100%
+app/main.py                       64      0   100%
+app/models.py                     94      0   100%
+app/rag/__init__.py                0      0   100%
+app/rag/agent.py                 222      0   100%
+app/rag/archive_upload.py        128      0   100%
+app/rag/chunker.py               206      4    98%
+app/rag/git_sources.py            14      0   100%
+app/rag/importer.py              180      3    98%
+app/rag/llm.py                   217      0   100%
+app/rag/overview.py               71      0   100%
+app/rag/prompts.py                88      0   100%
+app/rag/retriever.py             150      3    98%
+app/rag/scaffolding.py            55      0   100%
+app/rag/source_removal.py         41      0   100%
+app/rag/sources_meta.py           16      0   100%
+app/rag/suggestions.py            27      0   100%
+app/rag/summarizer.py             24      0   100%
+app/schemas.py                   232      0   100%
+--------------------------------------------------
+TOTAL                           3237     12    99%
+coverage gate: app/ 99% (>90%) OK
+All checks passed!
+0 errors, 0 warnings, 0 informations
+validation OK
diff --git a/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__03_verify_and_commit.a1.err b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__03_verify_and_commit.a1.err
new file mode 100644
index 0000000..e69de29
diff --git a/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__03_verify_and_commit.a1.md b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__03_verify_and_commit.a1.md
new file mode 100644
index 0000000..67ce83c
--- /dev/null
+++ b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__03_verify_and_commit.a1.md
@@ -0,0 +1,11 @@
+Screenshot confirms the fix visually: the anonymous menu (Chat + Sign in) renders **above** the gate card. Phase 85 is fully gated.
+
+**Report — Phase 85, task 03 (verify & commit)**
+
+- Full gate green: `uv run pytest` → 1717 passed; `--cov=app` → TOTAL **99%** (>90% floor, no `app/` change)
+- E2E in isolation: `test_mobile_hamburger_nav.py` → 8 passed (real-click contract + new `elementFromPoint` pin); `test_api_tokens.py` → 9 passed, **file unchanged** (phase-79 lock contract intact); `test_smoke.py` → 3 passed; `test_document_viewer.py` → 7 passed
+- `uv run ruff check . && uv run pyright` → clean (0 errors/warnings)
+- Live check (dev server :8000, 375×812, not signed in): 12/12 checks passed — real tap opens the menu above the gate (Chat + sign-in visible, token card behind/below), `elementFromPoint` at toggle resolves to the SVG (never `#auth-gate`), wrong-token error line + menu independence (Esc closes, gate stays), admin menu unchanged; log + 2 screenshots in `.agents/reports/85_mobile_menu_gate_overlap/`
+- Working tree verified: only `styles.css` (z 500→15 + comment), `index.html`/`document.html` (comments only), `token-gate.js` (docstring only), `test_mobile_hamburger_nav.py`, new `tests/unit/test_gate_header_stacking.py` + phase files — nothing in `app/`, `pyproject.toml`, `uv.lock`
+- Deviation (per executor rules, overrides task steps 3–4): **no `git commit` made and phase dir not moved** — all changes left in the working tree for the harness's single atomic phase commit and the `todo/ → complete/` move
+- Next pending task: none in this phase (task 03 was the last); following phases: `86_history_page_width`, `87_big_read_progress`
diff --git a/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__03_verify_and_commit.a1.validate b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__03_verify_and_commit.a1.validate
new file mode 100644
index 0000000..0914b55
--- /dev/null
+++ b/.agents/reports/85_mobile_menu_gate_overlap/85_mobile_menu_gate_overlap__03_verify_and_commit.a1.validate
@@ -0,0 +1,85 @@
+........................................................................ [  4%]
+........................................................................ [  8%]
+........................................................................ [ 12%]
+........................................................................ [ 16%]
+........................................................................ [ 20%]
+........................................................................ [ 25%]
+........................................................................ [ 29%]
+........................................................................ [ 33%]
+........................................................................ [ 37%]
+........................................................................ [ 41%]
+........................................................................ [ 46%]
+........................................................................ [ 50%]
+........................................................................ [ 54%]
+........................................................................ [ 58%]
+........................................................................ [ 62%]
+........................................................................ [ 67%]
+........................................................................ [ 71%]
+........................................................................ [ 75%]
+........................................................................ [ 79%]
+........................................................................ [ 83%]
+........................................................................ [ 88%]
+........................................................................ [ 92%]
+........................................................................ [ 96%]
+.............................................................            [100%]
+=============================== warnings summary ===============================
+.venv/lib/python3.13/site-packages/fastapi/testclient.py:1
+  /var/home/ducoterra/Projects/Personal/brain_of_reese/.venv/lib/python3.13/site-packages/fastapi/testclient.py:1: StarletteDeprecationWarning: Using `httpx` with `starlette.testclient` is deprecated; install `httpx2` instead.
+    from starlette.testclient import TestClient as TestClient  # noqa
+
+-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
+================================ tests coverage ================================
+_______________ coverage: platform linux, python 3.13.13-final-0 _______________
+
+Name                           Stmts   Miss  Cover
+--------------------------------------------------
+app/__init__.py                    1      0   100%
+app/api/__init__.py                0      0   100%
+app/api/auth.py                   52      0   100%
+app/api/chat.py                  178      0   100%
+app/api/chats.py                 110      0   100%
+app/api/config.py                  7      0   100%
+app/api/doc_drafts.py             94      0   100%
+app/api/docs.py                   50      0   100%
+app/api/git_sources.py           212      0   100%
+app/api/health.py                 10      0   100%
+app/api/steering.py               42      0   100%
+app/api/suggestions.py            29      0   100%
+app/api/sync.py                   98      0   100%
+app/api/tokens.py                 28      0   100%
+app/config.py                    141      0   100%
+app/core/__init__.py               0      0   100%
+app/core/auth.py                  45      0   100%
+app/core/caching.py              108      0   100%
+app/core/debugging.py             29      2    93%
+app/core/docs_push.py             39      0   100%
+app/core/errors.py                 5      0   100%
+app/core/logging.py               13      0   100%
+app/core/rate_limit.py            44      0   100%
+app/core/security_headers.py      19      0   100%
+app/core/tokens.py                33      0   100%
+app/db.py                         21      0   100%
+app/main.py                       64      0   100%
+app/models.py                     94      0   100%
+app/rag/__init__.py                0      0   100%
+app/rag/agent.py                 222      0   100%
+app/rag/archive_upload.py        128      0   100%
+app/rag/chunker.py               206      4    98%
+app/rag/git_sources.py            14      0   100%
+app/rag/importer.py              180      3    98%
+app/rag/llm.py                   217      0   100%
+app/rag/overview.py               71      0   100%
+app/rag/prompts.py                88      0   100%
+app/rag/retriever.py             150      3    98%
+app/rag/scaffolding.py            55      0   100%
+app/rag/source_removal.py         41      0   100%
+app/rag/sources_meta.py           16      0   100%
+app/rag/suggestions.py            27      0   100%
+app/rag/summarizer.py             24      0   100%
+app/schemas.py                   232      0   100%
+--------------------------------------------------
+TOTAL                           3237     12    99%
+coverage gate: app/ 99% (>90%) OK
+All checks passed!
+0 errors, 0 warnings, 0 informations
+validation OK
diff --git a/.agents/reports/85_mobile_menu_gate_overlap/livecheck_admin_menu.png b/.agents/reports/85_mobile_menu_gate_overlap/livecheck_admin_menu.png
new file mode 100644
index 0000000..953aac7
Binary files /dev/null and b/.agents/reports/85_mobile_menu_gate_overlap/livecheck_admin_menu.png differ
diff --git a/.agents/reports/85_mobile_menu_gate_overlap/livecheck_anonymous_menu_over_gate.png b/.agents/reports/85_mobile_menu_gate_overlap/livecheck_anonymous_menu_over_gate.png
new file mode 100644
index 0000000..4ad172b
Binary files /dev/null and b/.agents/reports/85_mobile_menu_gate_overlap/livecheck_anonymous_menu_over_gate.png differ
diff --git a/frontend/assets/styles.css b/frontend/assets/styles.css
index 848036e..d5291d0 100644
--- a/frontend/assets/styles.css
+++ b/frontend/assets/styles.css
@@ -1631,23 +1631,28 @@ details.thinking .thinking-text ul { margin: 0 0 0.5rem; }
 /* Phase 79 (task 05): the in-app token gate — the gate surface of the
    two token-only pages (the shell + the document viewer, one shared
    .auth-gate markup each). A body-level FIXED overlay (the
-   body-level doc-modal precedent): while visible it is the ONLY
-   interactive surface — assets/token-gate.js locks the root (#main,
-   inert) so focus and keyboard traversal stay inside the gate
-   (WCAG, the inert-pair contract).
-   Stacking: z-index 500 — above the app content (the sticky header is
-   20, the skip-link 100) but BELOW the doc-modal (1000), which can
-   only be opened from the unlocked app anyway. Solid --bg: the canvas
-   + grid texture live on <html> (the body stays transparent), so the
-   overlay reads as the app's own surface — no blur (the phase-08
-   perf anchor).
+   body-level doc-modal precedent): while visible it is the only
+   CONTENT-level interactive surface — assets/token-gate.js locks the
+   root (#main, inert) so focus and keyboard traversal stay inside
+   the gate (WCAG, the inert-pair contract).
+   Stacking (phase 85, TODO.md L3): z-index 15 — ABOVE all app
+   content (static) but BELOW the sticky header (20) and its mobile
+   dropdown (21, inside the header's stacking context): the
+   unauthenticated visitor keeps a reachable hamburger + menu while
+   the gate still covers and locks the app content (#main stays
+   inert — the lock is JS, not z-order — phase 79). The skip-link
+   (100) and the 1000-family overlays (doc-modal, sync backdrop) are
+   unaffected — all above 15; the doc-modal can only be opened from
+   the unlocked app anyway. Solid --bg: the canvas + grid texture
+   live on <html> (the body stays transparent), so the overlay reads
+   as the app's own surface — no blur (the phase-08 perf anchor).
    The centered card reuses the #sources-gate visual language
    (surface card + hairline + glyph + heading + sub + action) in a
    tighter column. */
 .auth-gate {
   position: fixed;
   inset: 0;
-  z-index: 500;
+  z-index: 15;
   display: flex; /* the card is the only in-flow child — margin: auto centers it */
   overflow-y: auto; /* short viewports: the card scrolls fully into view */
   background: var(--bg);
diff --git a/frontend/assets/token-gate.js b/frontend/assets/token-gate.js
index 8de5944..d18300e 100644
--- a/frontend/assets/token-gate.js
+++ b/frontend/assets/token-gate.js
@@ -193,9 +193,13 @@ export async function mountGate(lockRoot, onAuthed) {
 
   /* Anonymous: reveal the gate (drop hidden AND inert — the inert-pair
      contract), lock the app, focus the token input. The gate is the
-     only interactive surface while visible: the lock root is inert,
-     so Tab never reaches the locked app (the composer on the shell,
-     the content on the viewer). */
+     only CONTENT-level interactive surface while visible: the lock
+     root is inert, so Tab never reaches the locked app (the composer
+     on the shell, the content on the viewer). The header was never
+     the lock root (and is never inert) — it was only visually
+     covered pre-phase-85: the gate's z-index (15) now sits below the
+     header (20), so the mobile hamburger + menu stay reachable while
+     the app content stays inert-locked (TODO.md L3). */
   if (gate) {
     gate.hidden = false;
     gate.inert = false;
diff --git a/frontend/document.html b/frontend/document.html
index 86183a7..1ed7474 100644
--- a/frontend/document.html
+++ b/frontend/document.html
@@ -162,7 +162,10 @@
        root; the existing boot sequence (whoami → load content) runs
        as onAuthed — an admin (or a validly cached token user) gets
        it immediately, the gate never shows. SHIPS hidden + inert
-       (the phase-16 ship-hidden pattern). -->
+       (the phase-16 ship-hidden pattern). Phase 85 (TODO.md L3):
+       same stacking as the shell gate — the overlay (z-index 15)
+       sits below the viewer's sticky bar (20), so the hamburger +
+       menu stay reachable while #main stays inert-locked. -->
   <section class="auth-gate" id="doc-auth-gate" hidden inert aria-labelledby="doc-auth-gate-title">
     <div class="auth-gate-card">
       <div class="auth-gate-glyph" aria-hidden="true">
diff --git a/frontend/index.html b/frontend/index.html
index 43892fb..448e3a2 100644
--- a/frontend/index.html
+++ b/frontend/index.html
@@ -896,9 +896,13 @@
 
   <!-- Phase 79 (task 05): the in-app token gate — a body-level
        position:fixed; inset:0 overlay (the body-level doc-modal
-       precedent) that is the ONLY interactive surface while visible:
-       assets/token-gate.js locks #main (inert) so focus and keyboard
-       traversal stay in the gate (WCAG, the inert-pair contract). It
+       precedent) that is the only CONTENT-level interactive surface
+       while visible: assets/token-gate.js locks #main (inert) so
+       focus and keyboard traversal stay in the gate (WCAG, the
+       inert-pair contract). Phase 85 (TODO.md L3): the overlay sits
+       BELOW the sticky header (z-index 15 < 20) — it covers #main's
+       content region visually, but the header (hamburger + menu)
+       stays reachable for the unauthenticated visitor. It
        SHIPS hidden + inert (the phase-16 ship-hidden pattern) — an
        authenticated boot (admin, or a valid cached token re-authed
        silently at mount) never shows it for a frame. The gate is the
diff --git a/tests/e2e/test_mobile_hamburger_nav.py b/tests/e2e/test_mobile_hamburger_nav.py
index d84e496..1dfc9c1 100644
--- a/tests/e2e/test_mobile_hamburger_nav.py
+++ b/tests/e2e/test_mobile_hamburger_nav.py
@@ -15,6 +15,14 @@ visibility contract intact INSIDE the menu; at >640px the bar is
 byte-identical to pre-phase-46 (hamburger absent, inline pills). No
 document is ever needed — the suite exercises the shared header only.
 
+Phase 85 (TODO.md L3): the anonymous visitor meets the token gate —
+but the gate (z-index 15) now sits BELOW the sticky header (z 20), so
+a REAL tap on ``#nav-toggle`` reaches the toggle for anonymous
+visitors exactly as for admin: every test in this suite drives the
+menu with real clicks (the phase-79 JS-dispatched workaround for the
+gate-overlay interception is retired — the gate covers only ``#main``,
+which stays ``inert``; it no longer covers the header).
+
 The conftest ``page`` fixture is 1280×800, so the mobile tests create
 fresh 375×812 pages via the session ``browser`` fixture (one page per
 test; the reduced-motion test gets its own context).
@@ -29,20 +37,24 @@ Test → story mapping (Playwright Mapping Rule):
 2. ``test_anonymous_menu_contents`` — anonymous at 375px: the menu
    shows EXACTLY one visible link ("Chat"); the three admin-only links
    stay ``hidden`` inside the menu; the open flips ``aria-expanded``.
-3. ``test_admin_menu_contents`` — admin at 375px: the menu shows all
+3. ``test_anonymous_toggle_tappable_with_gate_up`` — the TODO.md L3
+   regression pin: anonymous toggle tappable with the gate up —
+   ``elementFromPoint`` at the toggle center never ``#auth-gate``,
+   real click opens the menu above the gate.
+4. ``test_admin_menu_contents`` — admin at 375px: the menu shows all
    four links (the whoami reveal works inside the menu).
-4. ``test_link_click_navigates_and_closes`` — admin at 375px: clicking
+5. ``test_link_click_navigates_and_closes`` — admin at 375px: clicking
    "RAG" navigates to /sources.html and the menu on the arrival
    page ships closed.
-5. ``test_esc_and_outside_close`` — Esc closes AND returns focus to the
+6. ``test_esc_and_outside_close`` — Esc closes AND returns focus to the
    toggle; an outside click does NOT close (accepted — see the test
    docstring for why).
-6. ``test_animation_and_reduced_motion`` — motion allowed: the
+7. ``test_animation_and_reduced_motion`` — motion allowed: the
    180ms opacity/transform transition pair is live and the open flips
    class + aria; ``reducedMotion: "reduce"``: no transition in EITHER
    state (the .is-open state included — the specificity trap) and
    open/close still works.
-7. ``test_desktop_unchanged`` — 1280×800 regression: the hamburger is
+8. ``test_desktop_unchanged`` — 1280×800 regression: the hamburger is
    ``display: none`` and the inline nav renders in the bar exactly as
    before (admin: all four links, all inside the header band).
 """
@@ -105,6 +117,13 @@ def _visible_nav_links(page: Page) -> list[str]:
 
 
 def _open_menu(page: Page) -> None:
+    """Open the menu with a REAL click on the toggle.
+
+    Phase 85 (TODO.md L3): the gate (z-index 15) sits BELOW the sticky
+    header (z 20), so a real tap reaches the toggle for anonymous
+    visitors too — the phase-79 JS-dispatched workaround (the gate then
+    covered the header at z 500 and intercepted the click) is retired,
+    and every test in this suite uses this one real-click helper."""
     page.click("#nav-toggle")
     expect(page.locator("#nav-toggle")).to_have_attribute("aria-expanded", "true")
     # to_have_class(string) is an EXACT match on the class attribute —
@@ -113,20 +132,6 @@ def _open_menu(page: Page) -> None:
     expect(page.locator("#app-nav")).to_have_css("opacity", "1")
 
 
-def _js_open_menu(page: Page) -> None:
-    """Phase 79 (task 05): the in-app token gate is a full-viewport
-    overlay for ANONYMOUS visitors — it physically covers the header,
-    so a real click on #nav-toggle is intercepted by the gate (the gate
-    is the only interactive surface; the header is locked out with the
-    rest of the page). The binding is identical, so the menu contract
-    is driven programmatically: a JS-dispatched click runs the exact
-    same listener a real click would."""
-    page.evaluate("() => document.querySelector('#nav-toggle').click()")
-    expect(page.locator("#nav-toggle")).to_have_attribute("aria-expanded", "true")
-    expect(page.locator("#app-nav")).to_have_class(re.compile(r"\bis-open\b"))
-    expect(page.locator("#app-nav")).to_have_css("opacity", "1")
-
-
 def _assert_menu_closed(page: Page) -> None:
     expect(page.locator("#nav-toggle")).to_have_attribute("aria-expanded", "false")
     assert "is-open" not in (page.locator("#app-nav").get_attribute("class") or ""), (
@@ -205,17 +210,17 @@ def test_anonymous_menu_contents(
     preserved by reusing the same <nav> element); opening flips
     aria-expanded true.
 
-    Phase 79 (task 05): the anonymous visitor meets the token gate — a
-    full-viewport overlay that covers the header — so the toggle is
-    driven programmatically (the binding is identical; see
-    _js_open_menu)."""
+    Phase 85 (TODO.md L3): the anonymous visitor meets the token gate
+    — but the gate (z 15) now sits BELOW the header (z 20), so the
+    toggle is a real, tappable target and the menu is driven with a
+    real click exactly as for admin."""
     page = _mobile_page(browser)
     try:
         page.goto(app_url)
         _wait_settled_anonymous(page)
         _assert_menu_closed(page)
 
-        _js_open_menu(page)
+        _open_menu(page)
         assert _visible_nav_links(page) == ["Chat"], (
             "anonymous: the menu must show exactly one visible link (Chat)"
         )
@@ -223,7 +228,96 @@ def test_anonymous_menu_contents(
             expect(page.locator(sel)).to_be_hidden()
 
         # A second click closes it again — aria-expanded round-trips.
-        page.evaluate("() => document.querySelector('#nav-toggle').click()")
+        page.click("#nav-toggle")
+        _assert_menu_closed(page)
+    finally:
+        page.close()
+
+
+def test_anonymous_toggle_tappable_with_gate_up(
+    browser: Browser, app_url: str, db_ready: None
+) -> None:
+    """TODO.md L3 regression pin (phase 85): the anonymous visitor meets
+    the token gate, but the gate (z-index 15) sits BELOW the sticky
+    header (z 20) — so the toggle is a REAL, tappable target:
+    ``document.elementFromPoint`` at the toggle center resolves to the
+    toggle itself (or its SVG child), NEVER ``#auth-gate`` (the exact
+    probe that returned the gate in the bug reproduction), and a real
+    click opens the menu ABOVE the gate — the "Chat" link visible with
+    the gate still up (the dropdown's z context, 21 inside the
+    header's 20, paints over the gate's 15). The lock is untouched:
+    ``#main`` stays ``inert``. Leaves the page clean — Esc settles the
+    menu closed."""
+    page = _mobile_page(browser)
+    try:
+        page.goto(app_url)
+        _wait_settled_anonymous(page)
+
+        # The gate is up and the app is locked (the phase-79 contract)…
+        expect(page.locator("#auth-gate")).to_be_visible(timeout=30_000)
+        assert page.evaluate("() => document.getElementById('main').inert === true"), (
+            "the gate must keep #main inert while it is up"
+        )
+
+        # …but the probe at the toggle center no longer resolves to the
+        # gate: it hits the toggle itself or a descendant of it (the
+        # SVG path) — the exact probe that returned #auth-gate in the
+        # bug reproduction (TODO.md L3).
+        probe = page.evaluate(
+            """() => {
+                const t = document.querySelector('#nav-toggle');
+                const r = t.getBoundingClientRect();
+                const el = document.elementFromPoint(
+                    r.left + r.width / 2, r.top + r.height / 2);
+                return {
+                    id: el ? el.id : null,
+                    tag: el ? el.tagName.toLowerCase() : null,
+                    toggle_or_descendant: el !== null && t.contains(el),
+                };
+            }"""
+        )
+        assert probe["id"] != "auth-gate", (
+            f"the toggle center must not resolve to the gate, "
+            f"got <{probe['tag']} id={probe['id']!r}> (the phase-79 bug)"
+        )
+        assert probe["toggle_or_descendant"], (
+            f"the toggle center must resolve to the toggle or its SVG "
+            f"child, got <{probe['tag']} id={probe['id']!r}>"
+        )
+
+        # A REAL click opens the menu (the owner's exact scenario —
+        # "clicking it … does not expand the menu" is fixed), and the
+        # menu is ABOVE the gate: with the gate still up the
+        # dropdown's "Chat" link is visible, and the topmost element at
+        # its center is the link (or a descendant), never #auth-gate.
+        _open_menu(page)
+        expect(page.locator("#auth-gate")).to_be_visible()
+        chat = page.locator("#app-nav a[href='/']")
+        expect(chat).to_be_visible()
+        link_probe = page.evaluate(
+            """() => {
+                const a = document.querySelector("#app-nav a[href='/']");
+                const r = a.getBoundingClientRect();
+                const el = document.elementFromPoint(
+                    r.left + r.width / 2, r.top + r.height / 2);
+                return {
+                    id: el ? el.id : null,
+                    tag: el ? el.tagName.toLowerCase() : null,
+                    link_or_descendant: el !== null && a.contains(el),
+                };
+            }"""
+        )
+        assert link_probe["id"] != "auth-gate", (
+            f"the open dropdown must paint ABOVE the gate, the Chat "
+            f"link center resolved to the gate ({link_probe!r})"
+        )
+        assert link_probe["link_or_descendant"], (
+            f"the Chat link must be the topmost target at its center, "
+            f"got <{link_probe['tag']} id={link_probe['id']!r}>"
+        )
+
+        # Leave the page clean: Esc settles it closed.
+        page.keyboard.press("Escape")
         _assert_menu_closed(page)
     finally:
         page.close()
@@ -303,11 +397,10 @@ def test_esc_and_outside_close(
         page.goto(app_url)
         _wait_settled_anonymous(page)
 
-        # Phase 79 (task 05): the anonymous visitor's toggle click is
-        # intercepted by the gate overlay — drive the identical binding
-        # programmatically (see _js_open_menu).
+        # Phase 85 (TODO.md L3): the gate (z 15) sits below the header
+        # (z 20) — the real click reaches the anonymous toggle too.
         # Esc closes + refocuses the opener.
-        _js_open_menu(page)
+        _open_menu(page)
         page.keyboard.press("Escape")
         _assert_menu_closed(page)
         assert page.evaluate("() => document.activeElement.id") == "nav-toggle", (
@@ -316,10 +409,11 @@ def test_esc_and_outside_close(
 
         # Outside click: the menu STAYS open (accepted behavior — the
         # locked close set is Esc + link + resize, not backdrop click).
-        # Phase 79 (task 05): for the anonymous visitor the "outside"
-        # point is the gate overlay itself — a REAL mouse click below
-        # the centered card (outside the nav, intercepted by the gate).
-        _js_open_menu(page)
+        # Phase 85: for the anonymous visitor the "outside" point is
+        # the gate overlay itself — a REAL mouse click below the
+        # centered card, outside the nav (the gate covers the content
+        # but no longer the header; it carries no close listener).
+        _open_menu(page)
         page.mouse.click(10, 780)  # the gate overlay — a neutral, non-nav point
         expect(page.locator("#nav-toggle")).to_have_attribute("aria-expanded", "true")
         assert "is-open" in (page.locator("#app-nav").get_attribute("class") or ""), (
@@ -364,9 +458,9 @@ def test_animation_and_reduced_motion(
             f"got {report['property']!r}"
         )
         # Opening flips class + aria together (the animated state).
-        # Phase 79 (task 05): the anonymous toggle click is intercepted
-        # by the gate overlay — programmatic drive, same binding.
-        _js_open_menu(page)
+        # Phase 85: the gate sits below the header — the real click
+        # reaches the anonymous toggle.
+        _open_menu(page)
         page.keyboard.press("Escape")
         _assert_menu_closed(page)
     finally:
@@ -389,9 +483,9 @@ def test_animation_and_reduced_motion(
         assert _stilled("#app-nav") == "0s", (
             f"reduced motion: closed state must not transition, got {_stilled('#app-nav')!r}"
         )
-        # Phase 79 (task 05): programmatic drive (the gate overlay
-        # intercepts the anonymous real click — same binding).
-        _js_open_menu(rpage)
+        # Phase 85: real drive (the gate no longer intercepts the
+        # anonymous click — it sits below the header).
+        _open_menu(rpage)
         expect(rpage.locator("#nav-toggle")).to_have_attribute("aria-expanded", "true")
         expect(rpage.locator("#app-nav")).to_have_class(re.compile(r"\bis-open\b"))
         assert _stilled("#app-nav") == "0s", (
diff --git a/tests/unit/test_gate_header_stacking.py b/tests/unit/test_gate_header_stacking.py
new file mode 100644
index 0000000..692e8ec
--- /dev/null
+++ b/tests/unit/test_gate_header_stacking.py
@@ -0,0 +1,126 @@
+"""Unit: the gate-below-header z-order contract (phase 85, task 01).
+
+TODO.md L3 (owner bug report, 2026-09-07): "Only on the chat page, and
+only when navigating there directly, does the hamburger menu on mobile
+not work. … This makes the menu inaccessible on mobile."
+
+Bug basis (confirmed by live reproduction): the phase-79 token gate
+ships as a full-viewport overlay at ``z-index: 500`` — ABOVE the sticky
+``.app-header`` (20) — so for an unauthenticated visitor
+``document.elementFromPoint`` at the ``#nav-toggle`` center returned
+``#auth-gate`` in every shell view: a real tap on the hamburger was
+intercepted by the overlay and the menu could never open. (The chat
+page was just the entry point; the gate broke the menu on every view.
+``login.html`` has no gate, which is why the owner saw it work "when
+logging in".)
+
+The fix is ONE CSS value (owner decision A1): ``.auth-gate`` moves to
+``z-index: 15`` — above all app content (static) but BELOW the sticky
+header (20) and its mobile dropdown (21, inside the header's stacking
+context). The gate still covers and locks the app content (``#main``
+stays ``inert`` — the lock is JS, not z-order — phase 79); only the
+header's VISUAL lock is lifted. This module pins the three z-order
+values at source level (the house pattern of
+``tests/unit/test_hamburger_nav.py``: read ``styles.css`` as text, no
+browser) so the regression that put the gate at 500 cannot return.
+"""
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+FRONTEND = Path(__file__).resolve().parents[2] / "frontend"
+STYLES_CSS = FRONTEND / "assets" / "styles.css"
+
+
+def _text(path: Path) -> str:
+    assert path.is_file(), f"missing frontend file: {path}"
+    return path.read_text(encoding="utf-8")
+
+
+def _css() -> str:
+    """styles.css with comments stripped (a comment may legally carry
+    braces — the brace-matching helpers below must never see them)."""
+    return re.sub(r"/\*.*?\*/", "", _text(STYLES_CSS), flags=re.S)
+
+
+def _media_block(css: str, query: str) -> str:
+    """The full text of the FIRST ``@media <query>`` block (brace-matched,
+    nested rules included verbatim)."""
+    m = re.search(re.escape(query) + r"[^{]*\{", css)
+    assert m, f"missing {query!r} media query in styles.css"
+    depth = 0
+    for i in range(m.end() - 1, len(css)):
+        if css[i] == "{":
+            depth += 1
+        elif css[i] == "}":
+            depth -= 1
+            if depth == 0:
+                return css[m.start() : i + 1]
+    raise AssertionError(f"unbalanced braces in {query!r} media block")
+
+
+def _rule_block(css: str, selector: str) -> str:
+    """The first rule body for ``selector`` (e.g. ``.auth-gate``). The
+    ``\\s*\\{`` requires the opening brace right after the selector, so a
+    decorated variant (``.auth-gate[hidden]``) is never matched."""
+    m = re.search(r"(?<![\w-])" + re.escape(selector) + r"\s*\{([^}]*)\}", css)
+    assert m, f"missing rule for {selector!r}"
+    return m.group(1)
+
+
+def _z_index(block: str) -> int:
+    m = re.search(r"z-index:\s*(\d+)", block)
+    assert m, "the rule must carry an explicit z-index"
+    return int(m.group(1))
+
+
+def test_auth_gate_sits_below_the_sticky_header() -> None:
+    """THE regression pin: the .auth-gate overlay carries z-index 15 —
+    below the sticky .app-header (20), so taps on the bar (and the
+    hamburger) reach the bar for the unauthenticated visitor instead of
+    the overlay (TODO.md L3). The old 500 (above the header) must not
+    return."""
+    css = _css()
+    gate = _z_index(_rule_block(css, ".auth-gate"))
+    header = _z_index(_rule_block(css, ".app-header"))
+    assert gate == 15, f".auth-gate must be pinned at z-index 15 (found {gate})"
+    assert header == 20, f".app-header must keep z-index 20 (found {header})"
+    assert gate < header, (
+        "the gate must sit BELOW the header — otherwise the overlay "
+        "intercepts the #nav-toggle again (the phase-79 bug)"
+    )
+
+
+def test_auth_gate_still_covers_the_app_content() -> None:
+    """The lock is JS, not z-order (phase 79): the rest of the overlay
+    contract is untouched — body-level fixed full-viewport cover
+    (position:fixed + inset:0), and the [hidden] state stays
+    display:none (the ship-hidden skeleton contract)."""
+    css = _css()
+    block = _rule_block(css, ".auth-gate")
+    assert "position: fixed" in block, ".auth-gate must stay position:fixed"
+    assert "inset: 0" in block, ".auth-gate must still cover the full viewport"
+    hidden = _rule_block(css, ".auth-gate[hidden]")
+    assert "display: none" in hidden, (
+        ".auth-gate[hidden] must stay display:none (ship-hidden)"
+    )
+
+
+def test_mobile_dropdown_stays_above_the_gate() -> None:
+    """The mobile dropdown (.app-nav, ≤640px — the z-index lives on the
+    base rule, shared by the closed and the .is-open states) keeps
+    z-index 21 = header + 1 (the phase-46 relationship pinned in
+    test_hamburger_nav): inside the header's stacking context the open
+    menu paints above the bar content AND above the gate (15)."""
+    css = _css()
+    mobile = _media_block(css, "@media (max-width: 640px)")
+    assert _z_index(_rule_block(mobile, ".app-nav")) == 21, (
+        "the mobile .app-nav must keep z-index 21 (header 20 + 1)"
+    )
+    # The header (20) itself is global (outside media queries) — the
+    # ≤640px block restyles it but never changes its stacking level,
+    # so the dropdown's 21 stays the header's own +1 on mobile too.
+    assert _z_index(_rule_block(mobile, ".app-nav")) > 15, (
+        "the open menu must paint above the gate (21 > 15)"
+    )