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+# Reset running session start to now (issue #33)
+
+## Problem
+
+Sometimes a session is started but a sizeable amount of time passes before play
+actually begins. The current UX to fix this is: edit the session, press "Set to
+now", submit. This is three steps across two pages.
+
+## Goal
+
+Add a one-click button in the session list — next to the existing "Finish
+session now", "Edit", and "Delete" buttons — that sets a running session's
+`timestamp_start` to the current time. A confirmation dialog protects against
+accidental clicks (the original start time is overwritten).
+
+## Scope
+
+- **Visibility:** the button shows only on running sessions (`timestamp_end is
+  None`), exactly like the green "Finish session now" button.
+- **Appearance:** gray button, new "reset" icon.
+- **Behavior:** confirm dialog before resetting; on confirm, sets
+  `timestamp_start = timezone.now()`, saves, and updates the row in place via
+  htmx.
+
+Out of scope: changing the existing Finish/Edit/Delete buttons; resetting end
+time; bulk operations.
+
+## Design
+
+### 1. New icon — `games/templates/icons/reset.html`
+
+A rotate/counterclockwise-arrow SVG signifying "reset". Styled like sibling
+icons (`text-black dark:text-white w-4 h-4`). Icons are auto-loaded by file stem
+(`common/icons.py`), so `Icon("reset")` resolves once the file exists — no
+registration needed.
+
+### 2. New view — `games/views/session.py`
+
+Mirrors the existing `end_session` view:
+
+```python
+@login_required
+def reset_session_start(request: HttpRequest, session_id: int) -> HttpResponse:
+    session = get_object_or_404(Session, id=session_id)
+    session.timestamp_start = timezone.now()
+    session.save()
+    if request.htmx:
+        return HttpResponse(_session_row_fragment(session))
+    return redirect("games:list_sessions")
+```
+
+`_session_row_fragment` already exists and is used by `end_session`.
+
+### 3. New URL — `games/urls.py`
+
+```python
+path(
+    "session/start/reset-to-now/from-list/<int:session_id>",
+    session.reset_session_start,
+    name="list_sessions_reset_session_start",
+),
+```
+
+### 4. Extend `ButtonGroup` — `common/components/primitives.py`
+
+The button-group button dict currently supports `href`, `slot`, `color`,
+`title`, `hx_get`, `hx_target`. Add two optional keys threaded through both
+`ButtonGroup()` and `_button_group_button()`:
+
+- `hx_confirm` — emitted as `hx-confirm` on the `<a>`; htmx shows a native
+  `confirm()` dialog before issuing the request.
+- `hx_swap` — emitted as `hx-swap` on the `<a>`; needed so the returned row
+  fragment replaces the row (`outerHTML`) rather than htmx's default.
+
+Both are additive and optional; existing callers are unaffected. Update the
+`ButtonGroup` docstring to list the new keys.
+
+### 5. Button in the session list — `games/views/session.py`
+
+Added to the `ButtonGroup` list in `list_sessions`, guarded the same way as the
+Finish button:
+
+```python
+{
+    "hx_get": reverse(
+        "games:list_sessions_reset_session_start", args=[session.pk]
+    ),
+    "hx_target": f"#session-row-{session.pk}",
+    "hx_swap": "outerHTML",
+    "hx_confirm": "Reset this session's start time to now?",
+    "slot": Icon("reset"),
+    "title": "Reset start to now",
+    "color": "gray",
+}
+if session.timestamp_end is None
+else {}
+```
+
+Placement: directly after the Finish button, before Edit.
+
+## Rationale: htmx for reset, plain href for Finish
+
+The reset button is htmx-driven (`hx-get` + `hx-target` + `hx-swap` +
+`hx-confirm`) so the confirm dialog and in-place row update come from htmx with
+no inline JS — consistent with the project's "no inline JS" convention. The
+existing Finish button uses a plain `href` (full-page navigation). This minor
+inconsistency is left as-is to keep the change focused; the reset view still
+returns a redirect for the non-htmx path, so it degrades gracefully.
+
+## Testing
+
+### Unit (`tests/`)
+
+- `reset_session_start` sets `timestamp_start` to ~now and saves.
+- Returns the row fragment when called via htmx; redirects to `list_sessions`
+  otherwise.
+- Session list renders the reset button only for running sessions
+  (`timestamp_end is None`), not for finished ones.
+
+### E2E (`e2e/`)
+
+- On the session list with a running session, click the reset button, accept the
+  confirm dialog (`page.on("dialog", lambda d: d.accept())`), and assert the
+  row's displayed start time updated to ~now.
+
+## No TypeScript build
+
+`hx-confirm` is built into htmx; no new custom element or `.ts` file, so `make
+ts` is not required for this change.