phase: 175_history_pagination

All criteria verified. This pass found no defects — the phase was fully implemented by prior task runs, and every gate is green.

**Phase 175 final verification pass — report**

- Verified tasks 01–03 implementation in-tree: `list_chats` `?limit=` (25, 1–100) / `?offset=` + `func.count` `total`; `SavedChatList.total` required; `#history-pager` below `#history-table-wrap` (hidden default, aria-labels, aria-hidden SVGs); `history.js` `PAGE_SIZE=25`/offset state, parameterized fetch, `updatePager`, refresh-keeps-current-page; CSS pill union + ≤640px block. No code changes were needed.
- Full suite: `uv run pytest --cov=app --cov-report=term-missing` → **exit 0, TOTAL 99%** (>90% gate).
- `uv run ruff check .` → all checks passed; `uv run pyright` → 0 errors, 0 warnings.
- Phase E2E in isolation: `uv run pytest tests/e2e/test_history_pagination.py -v --no-cov` → **9 passed** (page 1-of-2 / 2-of-2 walk, replace-not-append, refresh-on-page-2, delete-to-empty + single-page hide, anonymous no-fetch, 375px mobile, a11y/no-CDN).
- Regression set, each in isolation: test_chat_history 5✓, test_history_page_width 5✓, test_share_chat 4✓, test_stale_saved_chats 3✓, test_history_copy 1✓; integration `test_chats_api.py` green (incl. updated `test_list_empty` two-key pin and all five new pagination pins).
- Completion criteria: all nine boxes satisfied (API slice/422/honest-total pins ✓; E2E walk + status lines ✓; refresh/delete/hide ✓; anonymous gate ✓; mobile ✓; gates ✓; E2E + regression ✓; docs ✓; commit/phase-move is the harness's).
- Documentation: README.md reviewed in full — the saved-chats section already carries the `?limit=`/`?offset=`/`total` contract from this phase; all 31 `.env.example` vars documented; AGENTS.md verified accurate. **Consistent — no changes needed.**
- Deviations: none. No defects found in previously completed work.
- Next pending phase: none — 175 is the only entry in `todo/`.

app/api/chats.py

@@ -27,9 +27,15 @@ payload is the exact ``bor.chat.v1`` localStorage record shape
 (phase 14 — raw text, never HTML), so a saved chat restores
 pixel-identical through the existing ``renderStoredMessage`` path.
 
-Routes: ``GET`` (list, latest activity first — no payloads, but the
-phase-51 ``share_url`` and the phase-53 ``stale`` flag so the
-History's Share and Stale columns render without a second fetch),
+Routes: ``GET`` (list — paginated, phase 175 task 01: ``limit``
+(default 25, clamped 1–100) + ``offset`` (default 0); out-of-range
+values 422 via FastAPI's field-message validation — no hand-rolled
+checks — and the body reports the full ``total`` (one small count
+query per request) so a client can walk the pages; rows are one
+PAGE in the History page's table order, latest activity first
+(``updated_at desc, id desc``); no payloads, but the phase-51
+``share_url`` and the phase-53 ``stale`` flag so the History's
+Share and Stale columns render without a second fetch),
 ``POST`` (create — auto-title from the first question
 when no ``title`` is supplied; (phase 51, task 02) ``share: true`` sets
 the token in the SAME commit — the save-then-share contract;
@@ -74,9 +80,9 @@ from __future__ import annotations
 import uuid
 from pathlib import Path
 
-from fastapi import APIRouter, Depends, HTTPException, Response
+from fastapi import APIRouter, Depends, HTTPException, Query, Response
 from fastapi.responses import FileResponse, JSONResponse
-from sqlalchemy import select, text
+from sqlalchemy import func, select, text
 from sqlalchemy.orm import Session
 
 from app.config import get_settings
@@ -173,20 +179,41 @@ def _to_row(row: SavedChat, current_version: int) -> SavedChatRow:
     dependencies=[Depends(require_admin)],  # management surface (phase 55)
 )
 def list_chats(
+    limit: int = Query(25, ge=1, le=100),  # noqa: B008
+    offset: int = Query(0, ge=0),  # noqa: B008
     db: Session = Depends(get_db),  # noqa: B008
 ) -> SavedChatList:
-    """All saved chats, latest activity first (``updated_at desc, id
-    desc``) — the History page's table order, admin-only (the owner's
-    History surface; phase 55 moved the gate per-route). Each row
-    carries the
-    phase-53 ``stale`` flag: the current generation is read ONCE per
-    request (one PK read of the seeded row) and compared against every
-    row's stamp in the serializer helpers — no per-row queries."""
+    """One PAGE of the saved chats (phase 175, task 01), latest
+    activity first (``updated_at desc, id desc``) — the History
+    page's table order, admin-only (the owner's History surface;
+    phase 55 moved the gate per-route).
+
+    ``limit`` (default 25, clamped 1–100) and ``offset`` (default 0)
+    are FastAPI-validated: ``limit=0`` / ``limit=101`` / ``offset=-1``
+    422 with the house field-message contract (no hand-rolled checks).
+    A bare ``GET`` is the first 25 rows; an offset beyond the end is
+    honest — an empty ``chats`` list with the real ``total``.
+
+    ``total`` is the FULL count across all saved chats: one small
+    ``count`` query per request (two small queries total; the
+    once-per-request ``current_sources_version`` read is untouched),
+    so a client can walk the pages and know when it has seen them
+    all. Each row carries the phase-53 ``stale`` flag: the current
+    generation is read ONCE per request (one PK read of the seeded
+    row) and compared against every row's stamp in the serializer
+    helpers — no per-row queries."""
     current_version = current_sources_version(db)
     rows = db.scalars(
-        select(SavedChat).order_by(SavedChat.updated_at.desc(), SavedChat.id.desc())
+        select(SavedChat)
+        .order_by(SavedChat.updated_at.desc(), SavedChat.id.desc())
+        .offset(offset)
+        .limit(limit)
     ).all()
-    return SavedChatList(chats=[_to_row(row, current_version) for row in rows])
+    total = db.scalar(select(func.count(SavedChat.id))) or 0
+    return SavedChatList(
+        chats=[_to_row(row, current_version) for row in rows],
+        total=total,
+    )
 
 
 @router.post("", response_model=SavedChatOut, status_code=201)