diff --git a/common/components/primitives.py b/common/components/primitives.py
index 182194e..500211d 100644
--- a/common/components/primitives.py
+++ b/common/components/primitives.py
@@ -328,6 +328,8 @@ def _button_group_button(
     title: str = "",
     hx_get: str = "",
     hx_target: str = "",
+    hx_swap: str = "",
+    hx_confirm: str = "",
 ) -> Element:
     """Generate a single button-group button (inner <button> inside <a>)."""
     color_classes = _GROUP_BUTTON_COLORS.get(color, _GROUP_BUTTON_COLORS["gray"])
@@ -337,6 +339,10 @@ def _button_group_button(
         a_attrs.append(("hx-get", hx_get))
     if hx_target:
         a_attrs.append(("hx-target", hx_target))
+    if hx_swap:
+        a_attrs.append(("hx-swap", hx_swap))
+    if hx_confirm:
+        a_attrs.append(("hx-confirm", hx_confirm))
     a_attrs.append(
         (
             "class",
@@ -361,7 +367,8 @@ def _button_group_button(
 def ButtonGroup(buttons: list[dict] | None = None) -> Element:
     """Generate a button group div.
 
-    Each button dict accepts: href, slot (required), color, title, hx_get, hx_target.
+    Each button dict accepts: href, slot (required), color, title, hx_get,
+    hx_target, hx_swap, hx_confirm.
     Empty dicts (no slot) are silently skipped — matching the template behavior
     for conditional buttons (e.g., end-session only when session is active).
     """
@@ -378,6 +385,8 @@ def ButtonGroup(buttons: list[dict] | None = None) -> Element:
                 title=btn.get("title", ""),
                 hx_get=btn.get("hx_get", ""),
                 hx_target=btn.get("hx_target", ""),
+                hx_swap=btn.get("hx_swap", ""),
+                hx_confirm=btn.get("hx_confirm", ""),
             )
         )
 
diff --git a/docs/superpowers/specs/2026-06-20-issue-33-reset-session-start-to-now-design.md b/docs/superpowers/specs/2026-06-20-issue-33-reset-session-start-to-now-design.md
new file mode 100644
index 0000000..bb51a8d
--- /dev/null
+++ b/docs/superpowers/specs/2026-06-20-issue-33-reset-session-start-to-now-design.md
@@ -0,0 +1,138 @@
+# 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 refreshes the list via htmx so
+  the new start time shows.
+
+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, but the htmx path returns an empty
+`204` with an `HX-Refresh: true` header instead of a row fragment:
+
+```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:
+        response = HttpResponse(status=204)
+        response["HX-Refresh"] = "true"
+        return response
+    return redirect("games:list_sessions")
+```
+
+**Why `HX-Refresh` and not a row swap:** `_session_row_fragment` (used by
+`end_session`) renders a legacy 4-column `<tr>` that no longer matches the live
+session-list table (6 columns, built inline by `list_sessions`) and carries no
+`id="session-row-{pk}"`. Swapping it into the current table would produce a
+malformed row. The list table is rebuilt server-side on every request, so a full
+htmx refresh is the simplest correct update — and consistent with the existing
+Finish button, which also does a full-page navigation.
+
+### 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
+{
+    "href": reverse(
+        "games:list_sessions_reset_session_start", args=[session.pk]
+    ),
+    "hx_get": reverse(
+        "games:list_sessions_reset_session_start", args=[session.pk]
+    ),
+    "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. `href` is a graceful
+fallback (the non-htmx view path redirects); `hx_get` + `hx_confirm` drive the
+confirm dialog and htmx refresh when JS is active.
+
+## Rationale: htmx confirm
+
+The confirm dialog comes from htmx's built-in `hx-confirm`, which only fires on
+htmx-driven requests — so the button must use `hx-get` (not just `href`). No
+inline JS is needed, consistent with the project's conventions.
+
+## 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.
diff --git a/e2e/test_session_reset_e2e.py b/e2e/test_session_reset_e2e.py
new file mode 100644
index 0000000..4b4090f
--- /dev/null
+++ b/e2e/test_session_reset_e2e.py
@@ -0,0 +1,46 @@
+"""Browser test for the session-list "Reset start to now" button (issue #33).
+
+Drives the real session list against pytest-django's ``live_server``: clicks the
+reset button on a running session, accepts the confirm dialog, and asserts the
+row's start time is updated in place via htmx.
+"""
+
+import datetime as dt
+
+import pytest
+from django.urls import reverse
+from playwright.sync_api import Page, expect
+
+from games.models import Game, Platform, Session
+
+
+@pytest.fixture
+def authenticated_page(live_server, page: Page, django_user_model) -> Page:
+    django_user_model.objects.create_user(username="tester", password="secret123")
+    page.goto(f"{live_server.url}{reverse('login')}")
+    page.fill('input[name="username"]', "tester")
+    page.fill('input[name="password"]', "secret123")
+    page.click('button:has-text("Login")')
+    page.wait_for_url(f"{live_server.url}/tracker**")
+    return page
+
+
+def test_reset_session_start_to_now(authenticated_page: Page, live_server):
+    page = authenticated_page
+    platform = Platform.objects.create(name="PC", icon="pc", group="PC")
+    game = Game.objects.create(name="Reset Game", platform=platform)
+    session = Session.objects.create(
+        game=game,
+        timestamp_start=dt.datetime(2020, 1, 1, 10, 0, tzinfo=dt.timezone.utc),
+    )
+
+    page.goto(f"{live_server.url}{reverse('games:list_sessions')}")
+
+    row = page.locator(f"#session-row-{session.id}")
+    expect(row).to_contain_text("2020")
+
+    page.on("dialog", lambda dialog: dialog.accept())
+    row.locator('button[title="Reset start to now"]').click()
+
+    # htmx swaps the row in place; the old 2020 start time is gone.
+    expect(row).not_to_contain_text("2020")
diff --git a/games/templates/icons/reset.html b/games/templates/icons/reset.html
new file mode 100644
index 0000000..e01b332
--- /dev/null
+++ b/games/templates/icons/reset.html
@@ -0,0 +1,11 @@
+<svg xmlns="http://www.w3.org/2000/svg"
+     viewBox="0 0 24 24"
+     fill="none"
+     stroke="currentColor"
+     stroke-width="2"
+     stroke-linecap="round"
+     stroke-linejoin="round"
+     class="text-black dark:text-white w-4 h-4">
+    <path d="M3 12a9 9 0 1 0 3-6.7L3 8" />
+    <path d="M3 3v5h5" />
+</svg>
diff --git a/games/urls.py b/games/urls.py
index ab1fa6e..700120f 100644
--- a/games/urls.py
+++ b/games/urls.py
@@ -147,6 +147,11 @@
         session.end_session,
         name="list_sessions_end_session",
     ),
+    path(
+        "session/start/reset-to-now/from-list/<int:session_id>",
+        session.reset_session_start,
+        name="list_sessions_reset_session_start",
+    ),
     path("session/list", session.list_sessions, name="list_sessions"),
     path("session/search", session.search_sessions, name="search_sessions"),
     path(
diff --git a/games/views/session.py b/games/views/session.py
index 45f6422..c93157f 100644
--- a/games/views/session.py
+++ b/games/views/session.py
@@ -144,6 +144,24 @@ def list_sessions(request: HttpRequest, search_string: str = "") -> HttpResponse
                             }
                             if session.timestamp_end is None
                             else {},
+                            {
+                                "href": reverse(
+                                    "games:list_sessions_reset_session_start",
+                                    args=[session.pk],
+                                ),
+                                "hx_get": reverse(
+                                    "games:list_sessions_reset_session_start",
+                                    args=[session.pk],
+                                ),
+                                "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 {},
                             {
                                 "href": reverse(
                                     "games:edit_session", args=[session.pk]
@@ -234,7 +252,7 @@ def add_session(request: HttpRequest, game_id: int = 0) -> HttpResponse:
             return redirect("games:list_sessions")
     else:
         if game_id:
-            game = Game.objects.get(id=game_id)
+            game = get_object_or_404(Game, id=game_id)
             form = SessionForm(
                 initial={
                     **initial,
@@ -379,6 +397,20 @@ def end_session(request: HttpRequest, session_id: int) -> HttpResponse:
     return redirect("games:list_sessions")
 
 
+@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:
+        # The list table is rebuilt server-side per request; a full refresh
+        # avoids swapping in a row fragment whose layout could drift from it.
+        response = HttpResponse(status=204)
+        response["HX-Refresh"] = "true"
+        return response
+    return redirect("games:list_sessions")
+
+
 @login_required
 def delete_session(request: HttpRequest, session_id: int = 0) -> HttpResponse:
     session = get_object_or_404(Session, id=session_id)
diff --git a/tests/test_rendered_pages.py b/tests/test_rendered_pages.py
index 3e63b1d..cacf524 100644
--- a/tests/test_rendered_pages.py
+++ b/tests/test_rendered_pages.py
@@ -13,6 +13,7 @@
 from django.contrib.auth.models import User
 from django.test import TestCase
 from django.urls import reverse
+from django.utils import timezone
 
 from games.models import Game, GameStatusChange, Platform, Purchase, Session
 
@@ -247,6 +248,47 @@ def test_session_row_fragment_via_htmx(self):
         self.assertIn(self.game.name, html)
         self.assertNoEscapedTags(html)
 
+    def test_reset_session_start_to_now_via_htmx(self):
+        # The inline "reset start" endpoint sets timestamp_start to now and
+        # asks htmx to refresh the list (the table is rebuilt server-side).
+        running = Session.objects.create(
+            game=self.game,
+            timestamp_start=datetime(2020, 1, 1, 10, 0, tzinfo=ZONEINFO),
+        )
+        before = timezone.now()
+        resp = self.client.get(
+            reverse("games:list_sessions_reset_session_start", args=[running.id]),
+            HTTP_HX_REQUEST="true",
+        )
+        self.assertEqual(resp["HX-Refresh"], "true")
+        running.refresh_from_db()
+        self.assertGreaterEqual(running.timestamp_start, before)
+
+    def test_reset_session_start_redirects_without_htmx(self):
+        running = Session.objects.create(
+            game=self.game,
+            timestamp_start=datetime(2020, 1, 1, 10, 0, tzinfo=ZONEINFO),
+        )
+        resp = self.client.get(
+            reverse("games:list_sessions_reset_session_start", args=[running.id])
+        )
+        self.assertRedirects(resp, reverse("games:list_sessions"))
+
+    def test_reset_button_only_shown_for_running_sessions(self):
+        running = Session.objects.create(
+            game=self.game,
+            timestamp_start=datetime(2020, 1, 1, 10, 0, tzinfo=ZONEINFO),
+        )
+        html = self.get("games:list_sessions").content.decode()
+        self.assertIn(
+            reverse("games:list_sessions_reset_session_start", args=[running.id]),
+            html,
+        )
+        self.assertNotIn(
+            reverse("games:list_sessions_reset_session_start", args=[self.session.id]),
+            html,
+        )
+
     # --- statuschange --------------------------------------------------------
 
     def test_statuschange_list_and_delete(self):