From c596cf6c148051ff1181030826d7994a86cd66cd Mon Sep 17 00:00:00 2001
From: dgtlmoon <dgtlmoon@gmail.com>
Date: Fri, 17 Jul 2026 15:29:24 +0200
Subject: [PATCH] WIP

---
 .../blueprint/browser_steps/__init__.py       |   5 +-
 .../blueprint/settings/__init__.py            |  25 +--
 .../settings/templates/settings.html          |  14 +-
 .../blueprint/ui/browser_config.py            |   7 +-
 .../ui/templates/browsers-overview.html       |  68 +++++---
 .../content_fetchers/__init__.py              |  44 ++----
 changedetectionio/forms.py                    |   6 +-
 changedetectionio/model/Watch.py              | 148 ++++++++++++------
 changedetectionio/model/browser_config.py     | 139 +++++++---------
 changedetectionio/store/__init__.py           |  12 +-
 changedetectionio/store/updates.py            |  40 +++++
 .../test_custom_browser_url.py                |   9 +-
 .../tests/fetchers/test_content.py            |   9 +-
 .../tests/restock/test_restock.py             |   9 +-
 .../tests/test_access_control.py              |   5 +-
 .../tests/test_browser_config.py              | 112 +++++++++++++
 16 files changed, 449 insertions(+), 203 deletions(-)

diff --git a/changedetectionio/blueprint/browser_steps/__init__.py b/changedetectionio/blueprint/browser_steps/__init__.py
index 58be9a95..b9e2a307 100644
--- a/changedetectionio/blueprint/browser_steps/__init__.py
+++ b/changedetectionio/blueprint/browser_steps/__init__.py
@@ -266,9 +266,8 @@ def construct_blueprint(datastore: ChangeDetectionStore):
         # Resolve the fetcher backend for this watch so we can ask it to launch its own browser
         # if it supports that (e.g. CloakBrowser, which runs locally rather than via CDP)
         watch = datastore.data['watching'][watch_uuid]
-        fetcher_name = watch.get_fetch_backend or 'system'
-        if fetcher_name == 'system':
-            fetcher_name = datastore.data['settings']['application'].get('fetch_backend', 'html_requests')
+        # get_fetch_backend is fully resolved (group override / watch / 'system' -> global default).
+        fetcher_name = watch.get_fetch_backend
 
         browser, playwright_context = await acquire_browser_for_fetcher(fetcher_name, proxy=proxy, keepalive_ms=keepalive_ms)
 
diff --git a/changedetectionio/blueprint/settings/__init__.py b/changedetectionio/blueprint/settings/__init__.py
index 164436a6..9a1c76a4 100644
--- a/changedetectionio/blueprint/settings/__init__.py
+++ b/changedetectionio/blueprint/settings/__init__.py
@@ -66,17 +66,10 @@ def construct_blueprint(datastore: ChangeDetectionStore):
                                         extra_notification_tokens=datastore.get_unique_notification_tokens_available()
                                         )
 
-        # The global default fetch method is now the "Default browser": the always-present
-        # built-in engines + the user's saved browsers (no 'system' - this IS the system
-        # default). Everything else in the app resolves 'system' back to this value.
-        from changedetectionio.model.browser_config import list_builtin_browsers
-        default_browser_choices = [(b['id'], b['label']) for b in list_builtin_browsers()]
-        default_browser_choices += [(cid, e.get('label') or cid)
-                                    for cid, e in datastore.browser_config_store.all().items()]
-        form.application.form.fetch_backend.choices = default_browser_choices
-        form.application.form.fetch_backend.label.text = gettext('Default browser')
-        # Accept legacy raw-engine values / ids not in the (dynamic) choice list.
-        form.application.form.fetch_backend.validate_choice = False
+        # The global "Default browser" was migrated to the /browsers tab (its per-row radio
+        # writes settings.application.fetch_backend). Drop the inherited fetch_backend field so a
+        # settings save never renders, validates, or clobbers the default - /browsers owns it now.
+        del form.application.form.fetch_backend
 
         # Remove the last option 'System default'
         form.application.form.notification_format.choices.pop()
@@ -260,8 +253,18 @@ def construct_blueprint(datastore: ChangeDetectionStore):
         # Cost display: only when user configured their own key (not hosted/operator-managed)
         llm_show_costs = not llm_env_configured
 
+        # Read-only label for the global "Default browser" (managed on the /browsers tab).
+        from changedetectionio.model.browser_config import list_builtin_browsers
+        _default_id = datastore.get_default_backend()
+        _default_entry = datastore.browser_config_store.get(_default_id)
+        if _default_entry:
+            default_browser_label = _default_entry.get('label') or _default_id
+        else:
+            default_browser_label = dict((b['id'], b['label']) for b in list_builtin_browsers()).get(_default_id, _default_id)
+
         output = render_template("settings.html",
                                 active_plugins=active_plugins,
+                                default_browser_label=default_browser_label,
                                 api_key=datastore.data['settings']['application'].get('api_access_token'),
                                 llm_config=llm_config,
                                 llm_env_configured=llm_env_configured,
diff --git a/changedetectionio/blueprint/settings/templates/settings.html b/changedetectionio/blueprint/settings/templates/settings.html
index 1d5ffa63..5aadb105 100644
--- a/changedetectionio/blueprint/settings/templates/settings.html
+++ b/changedetectionio/blueprint/settings/templates/settings.html
@@ -100,14 +100,18 @@
             </div>
 
             <div class="tab-pane-inner" id="fetching">
-                <div class="pure-control-group inline-radio">
-                    {{ render_field(form.application.form.fetch_backend, class="fetch-backend") }}
+                <div class="pure-control-group">
+                    <label>{{ _('Default browser') }}</label>
+                    <div class="default-browser-summary" style="margin:0.3em 0;">
+                        <strong style="margin-right:0.75em;">{{ default_browser_label }}</strong>
+                        <a class="pure-button button-small" href="{{ url_for('ui.browser_config.browsers_overview') }}">{{ _('Manage browsers &amp; set default')|safe }}</a>
+                    </div>
                     <span class="pure-form-message-inline">
-                        <p>{{ _('Use the <strong>Basic</strong> method (default) where your watched sites don\'t need Javascript to render.')|safe }}</p>
-                        <p>{{ _('The <strong>Chrome/Javascript</strong> method requires a network connection to a running WebDriver+Chrome server, set by the ENV var \'WEBDRIVER_URL\'.')|safe }}</p>
+                        <p>{{ _('Every watch uses this browser unless it (or its group) picks another one.')|safe }}</p>
+                        <p>{{ _('Add screen sizes, languages, timezones and choose the default on the <a href="%(url)s">Browsers</a> page.', url=url_for('ui.browser_config.browsers_overview'))|safe }}</p>
                     </span>
                 </div>
-                <fieldset class="pure-group" id="webdriver-override-options" data-visible-for="application-fetch_backend=html_webdriver">
+                <fieldset class="pure-group" id="webdriver-override-options">
                     <div class="pure-form-message-inline">
                         <strong>{{ _('If you\'re having trouble waiting for the page to be fully rendered (text missing etc), try increasing the \'wait\' time here.') }}</strong>
                         <br>
diff --git a/changedetectionio/blueprint/ui/browser_config.py b/changedetectionio/blueprint/ui/browser_config.py
index 8e4e2c65..edba309e 100644
--- a/changedetectionio/blueprint/ui/browser_config.py
+++ b/changedetectionio/blueprint/ui/browser_config.py
@@ -208,12 +208,15 @@ def construct_blueprint(datastore: ChangeDetectionStore):
     @browser_config_blueprint.route("/browsers/set-default/<string:config_id>", methods=['POST'])
     @login_optionally_required
     def browser_config_set_default(config_id):
-        # "Default" is the global system fetch_backend - the single source of truth that a
-        # watch/group set to 'system' resolves to. This is settable from here or from Settings.
+        # "Default browser" is the global settings.application.fetch_backend - the single source
+        # of truth a watch/group set to 'system' resolves to. This /browsers tab is now the only
+        # place it's set (the Settings page shows it read-only). Only usable (ready-to-use)
+        # built-in engines or saved browser configs may be the default.
         from changedetectionio.model.browser_config import list_builtin_browsers
         builtins = {b['id'] for b in list_builtin_browsers()}
         if config_id in builtins or datastore.browser_config_store.get(config_id):
             datastore.data['settings']['application']['fetch_backend'] = config_id
+            logger.debug(f"Default browser (settings.application.fetch_backend) set to '{config_id}'")
             flash(gettext("Default browser set"))
         else:
             flash(gettext("Browser config not found"), 'error')
diff --git a/changedetectionio/blueprint/ui/templates/browsers-overview.html b/changedetectionio/blueprint/ui/templates/browsers-overview.html
index b2d8608f..9d79c039 100644
--- a/changedetectionio/blueprint/ui/templates/browsers-overview.html
+++ b/changedetectionio/blueprint/ui/templates/browsers-overview.html
@@ -8,16 +8,27 @@
         <p class="pure-form-message-inline">
             {{ _('Save a browser once (its screen size, language, timezone…) and reuse it on any watch or group. Add a variation from one of the available browsers below.') }}
         </p>
+        <p class="pure-form-message-inline">
+            {{ _('The <strong>Default browser</strong> (chosen with the radio button below) is used by every watch unless the watch — or its group — picks another one. This is the same value shown on the <a href="%(url)s#fetching">Settings → Fetching</a> page.', url=url_for('settings.settings_page'))|safe }}
+        </p>
 
         {# ---- User-created browser variations ---- #}
         <h5 style="margin-top:1.5em">{{ _('Your browsers') }}</h5>
         {% if browser_configs %}
-        <table class="pure-table" style="width:100%; margin-top:0.5em;">
-            <thead><tr><th>{{ _('Name') }}</th><th>{{ _('Setup') }}</th><th></th><th></th></tr></thead>
+        <table class="pure-table browsers-table" style="width:100%; margin-top:0.5em;">
+            <thead><tr><th style="width:5em; text-align:center">{{ _('Default') }}</th><th>{{ _('Name') }}</th><th>{{ _('Setup') }}</th><th></th></tr></thead>
             <tbody>
                 {% for cid, entry in browser_configs.items() %}
                 {% set bc = entry.get('browser_config') or {} %}
-                <tr>
+                <tr class="{% if cid == default_browser_id %}is-default{% endif %}">
+                    <td style="text-align:center">
+                        <form method="POST" class="set-default-form" action="{{ url_for('ui.browser_config.browser_config_set_default', config_id=cid) }}">
+                            <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
+                            <input type="radio" class="browser-default-radio" name="browser_default" value="{{ cid }}"
+                                   title="{{ _('Set as the default browser') }}"
+                                   {% if cid == default_browser_id %}checked{% endif %}>
+                        </form>
+                    </td>
                     <td>
                         <strong>{{ entry.get('label') }}</strong>
                         <span class="browser-chip">{{ entry.get('base_fetcher') }}</span>
@@ -30,14 +41,6 @@
                         {% if bc.get('timezone_id') %}<span class="browser-chip">{{ bc.timezone_id }}</span>{% endif %}
                         {% if bc.get('block_resource_types') %}<span class="browser-chip">{{ _('no') }} {{ bc.block_resource_types|join(', ') }}</span>{% endif %}
                     </td>
-                    <td style="text-align:right; white-space:nowrap">
-                        {% if cid != default_browser_id %}
-                        <form method="POST" action="{{ url_for('ui.browser_config.browser_config_set_default', config_id=cid) }}" style="display:inline">
-                            <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
-                            <button class="pure-button button-small" type="submit">{{ _('Make default') }}</button>
-                        </form>
-                        {% endif %}
-                    </td>
                     <td style="text-align:right; white-space:nowrap">
                         <a class="pure-button button-small" href="{{ url_for('ui.browser_config.browser_config_edit', config_id=cid) }}">{{ _('Edit') }}</a>
                         <form method="POST" action="{{ url_for('ui.browser_config.browser_config_remove', config_id=cid) }}" style="display:inline"
@@ -57,12 +60,23 @@
         {# ---- Available base browsers - each offers "Add variation" ---- #}
         <h5 style="margin-top:2em">{{ _('Available browsers') }}</h5>
         {% if base_fetchers %}
-        <table class="pure-table" style="width:100%; margin-top:0.5em;">
-            <thead><tr><th>{{ _('Browser') }}</th><th>{{ _('Capabilities') }}</th><th></th><th></th></tr></thead>
+        <table class="pure-table browsers-table" style="width:100%; margin-top:0.5em;">
+            <thead><tr><th style="width:5em; text-align:center">{{ _('Default') }}</th><th>{{ _('Browser') }}</th><th>{{ _('Capabilities') }}</th><th></th><th></th></tr></thead>
             <tbody>
                 {% for f in base_fetchers %}
                 {% set fbc = f.browser_config or {} %}
-                <tr>
+                <tr class="{% if f.ready_to_use and f.name == default_browser_id %}is-default{% endif %}">
+                    <td style="text-align:center">
+                        {# Only ready-to-use engines can be the default (base-only engines aren't usable directly) #}
+                        {% if f.ready_to_use %}
+                        <form method="POST" class="set-default-form" action="{{ url_for('ui.browser_config.browser_config_set_default', config_id=f.name) }}">
+                            <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
+                            <input type="radio" class="browser-default-radio" name="browser_default" value="{{ f.name }}"
+                                   title="{{ _('Set as the default browser') }}"
+                                   {% if f.name == default_browser_id %}checked{% endif %}>
+                        </form>
+                        {% endif %}
+                    </td>
                     <td>
                         <strong>{{ f.description }}</strong>
                         {% if not f.ready_to_use %}<span class="browser-chip">{{ _('needs setup') }}</span>{% endif %}
@@ -74,14 +88,8 @@
                         {% endfor %}
                     </td>
                     <td style="text-align:right; white-space:nowrap">
-                        {# ready-to-use engines are usable directly: can be edited + made default #}
+                        {# ready-to-use engines are usable directly: they can be edited #}
                         {% if f.ready_to_use %}
-                            {% if f.name != default_browser_id %}
-                            <form method="POST" action="{{ url_for('ui.browser_config.browser_config_set_default', config_id=f.name) }}" style="display:inline">
-                                <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
-                                <button class="pure-button button-small" type="submit">{{ _('Make default') }}</button>
-                            </form>
-                            {% endif %}
                             <a class="pure-button button-small" href="{{ url_for('ui.browser_config.browser_config_edit', config_id=f.name) }}">{{ _('Edit') }}</a>
                         {% endif %}
                     </td>
@@ -102,6 +110,21 @@
     </div>
 </div>
 
+<script>
+// Radio buttons live in per-row mini-forms (so each posts its own set-default action). They
+// share a name so they read as one group; on change we clear the others for instant feedback,
+// then submit — the server persists the choice and the reloaded page reflects it authoritatively.
+document.querySelectorAll('.browser-default-radio').forEach(function (radio) {
+    radio.addEventListener('change', function () {
+        if (!radio.checked) return;
+        document.querySelectorAll('.browser-default-radio').forEach(function (other) {
+            if (other !== radio) other.checked = false;
+        });
+        radio.closest('form').submit();
+    });
+});
+</script>
+
 <style>
 .browser-chip {
     display: inline-block;
@@ -113,6 +136,9 @@
     white-space: nowrap;
 }
 .browser-chip--default { background: #d4edda; color: #155724; }
+.browsers-table tr.is-default { background: rgba(21,87,36,0.06); }
+.browser-default-radio { transform: scale(1.3); cursor: pointer; }
+.set-default-form { margin: 0; display: inline; }
 .browser-empty {
     margin-top: 0.75em;
     padding: 2em;
diff --git a/changedetectionio/content_fetchers/__init__.py b/changedetectionio/content_fetchers/__init__.py
index 431720b5..f4711b14 100644
--- a/changedetectionio/content_fetchers/__init__.py
+++ b/changedetectionio/content_fetchers/__init__.py
@@ -106,18 +106,15 @@ def _log_fetcher_capabilities(fetcher_class, backend_name, uuid=None):
 
 
 def resolve_content_fetcher(watch, datastore):
-    """Single source of truth for resolving which content fetcher a watch should use.
+    """Build the concrete content-fetcher class + config for a watch.
 
-    Resolution order (room to grow):
-      1. Watch-level `fetch_backend`
-      2. (future) group-level default
-      3. System/global default from application settings
-
-    Also collapses the special backend forms into a concrete fetcher:
-      - 'system'                    -> global application default
+    *Which* browser/engine is selected is owned by the Watch model (watch.get_fetch_backend:
+    PDF / group override / watch / 'system' -> global Default browser). This function takes that
+    resolved selector and turns it into a fetcher instance, collapsing the special forms:
+      - a user browser-config id    -> its base_fetcher engine + its FetcherConfig
       - 'extra_browser_<key>'       -> html_webdriver + custom connection URL
-      - is_pdf watch                -> forced html_requests (browser PDF support incomplete)
       - html_webdriver + browser_steps -> playwright override (puppeteer steps incomplete)
+      - a deleted browser-config id -> raises BrowserConfigDoesntExist
 
     Returns:
         tuple: (fetcher_class, backend_name, custom_browser_connection_url, browser_config)
@@ -126,22 +123,15 @@ def resolve_content_fetcher(watch, datastore):
         resolved FetcherConfig to inject as `.browser_config`.
     """
     this_module = sys.modules[__name__]
-    from changedetectionio.model.browser_config import (
-        FetcherConfig, resolve_browser_config_override, BrowserConfigDoesntExist,
-    )
+    from changedetectionio.model.browser_config import FetcherConfig, BrowserConfigDoesntExist
 
     # Default behaviour = empty config (built-in engines / system default).
     browser_config = FetcherConfig()
 
-    # Selection order: a group override wins, else the watch's own selector value.
-    # The value is either a built-in engine name ('html_requests', 'html_webdriver',
-    # 'extra_browser_*'), the sentinel 'system', or the stable id of a user browser config.
-    override = resolve_browser_config_override(watch, datastore)
-    selected = override['config_id'] if override else watch.get('fetch_backend', 'system')
-
-    # 'system' -> the global default, which may itself be a browser-config id or an engine name.
-    if not selected or selected == 'system':
-        selected = datastore.data['settings']['application'].get('fetch_backend')
+    # THE single resolved selector for this watch (PDF / group override / watch / 'system' ->
+    # global default) - the Watch owns this chain so every codepath agrees. The value is a
+    # built-in engine name, 'extra_browser_*', or the stable id of a user browser config.
+    selected = watch.get_fetch_backend
 
     store = getattr(datastore, 'browser_config_store', None)
     entry = store.get(selected) if (store and selected) else None
@@ -170,15 +160,9 @@ def resolve_content_fetcher(watch, datastore):
             prefer_fetch_backend = 'html_webdriver'
             custom_browser_connection_url = connection[0].get('browser_connection_url')
 
-    # PDF should be html_requests because playwright will serve it up (so far) in an embedded page
-    # @todo https://github.com/dgtlmoon/changedetection.io/issues/2019
-    if getattr(watch, 'is_pdf', False):
-        logger.warning(
-            f"Watch {watch.get('uuid')} is_pdf detected (content-type/url) - forcing the "
-            f"'html_requests' fetcher because browser support isn't complete yet for "
-            f"saving/downloading the PDF. Overriding requested backend '{prefer_fetch_backend}'."
-        )
-        prefer_fetch_backend = "html_requests"
+    # PDF watches are already forced to 'html_requests' by Watch.get_fetch_backend (playwright
+    # can't render a PDF in-page yet - @todo https://github.com/dgtlmoon/changedetection.io/issues/2019),
+    # so no extra handling is needed here.
 
     # Grab the right kind of 'fetcher' class (playwright, requests, plugin-provided, etc)
     if prefer_fetch_backend and hasattr(this_module, prefer_fetch_backend):
diff --git a/changedetectionio/forms.py b/changedetectionio/forms.py
index 81de3ae1..9070c856 100644
--- a/changedetectionio/forms.py
+++ b/changedetectionio/forms.py
@@ -1091,7 +1091,11 @@ class globalSettingsApplicationForm(commonSettingsForm):
                            render_kw={"placeholder": os.getenv('BASE_URL', _l('Not set'))}
                            )
     empty_pages_are_a_change =  BooleanField(_l('Treat empty pages as a change?'), default=False)
-    fetch_backend = RadioField(_l('Fetch Method'), default="html_requests", choices=content_fetchers.available_fetchers(), validators=[ValidateContentFetcherIsReady()])
+    # NOTE: the global "Default browser" is NOT a field here anymore - all browser choice was
+    # migrated to the /browsers tab (set-default writes settings.application.fetch_backend). The
+    # inherited commonSettingsForm.fetch_backend field is del()'d from this form in the settings
+    # blueprint so a settings save never touches the default. Watches still pick a browser via
+    # their own commonSettingsForm.fetch_backend (processor_text_json_diff_form).
     global_ignore_text = StringListField(_l('Ignore Text'), [ValidateListRegex()])
     global_subtractive_selectors = StringListField(_l('Remove elements'), [ValidateCSSJSONXPATHInput(allow_json=False)])
     ignore_whitespace = BooleanField(_l('Ignore whitespace'))
diff --git a/changedetectionio/model/Watch.py b/changedetectionio/model/Watch.py
index f30c8683..d2f691c1 100644
--- a/changedetectionio/model/Watch.py
+++ b/changedetectionio/model/Watch.py
@@ -361,62 +361,120 @@ class model(EntityPersistenceMixin, watch_base):
     def is_source_type_url(self):
         return self.get('url', '').startswith('source:')
 
+    @property
+    def browser_config_store(self):
+        """A read-only, file-backed view of browsers.json for THIS watch.
+
+        The Watch only holds the raw settings data dict (self._datastore), not the full
+        ChangeDetectionStore, so it can't reach the shared browser_config_store directly. The
+        per-path registry hands back that same shared (mtime-cached) instance so the watch can
+        self-resolve its browser config (id -> engine, group overrides) without threading the
+        store through every call, and without re-reading browsers.json per watch per render.
+        """
+        from changedetectionio.model.browser_config import get_browser_config_store
+        if not self._datastore_path:
+            return None
+        return get_browser_config_store(self._datastore_path)
+
+    @property
+    def _global_default_fetch_backend(self):
+        """The global 'Default browser' (settings.application.fetch_backend) - the single source
+        of truth that BOTH /browsers (per-row radio) and Settings->Fetching write. May be a
+        built-in engine name or a user browser-config id."""
+        if self._datastore:
+            return self._datastore['settings']['application'].get('fetch_backend', 'html_requests')
+        return 'html_requests'
+
+    @property
+    def browser_config_override(self):
+        """If a group/tag overrides this watch's browser config, describe it, else None.
+
+        Uses the group's dedicated enabler (browser_config_overrides_watch), NOT the coarse
+        legacy `overrides_watch` flag. Tags are checked in the watch's tag-list order; the first
+        one whose enabler is on and whose selected config still exists (a user browser OR a
+        built-in engine) wins. Returns {group_uuid, group_title, config_id, label} or None.
+        """
+        from changedetectionio.model.browser_config import list_builtin_browsers
+        if not self._datastore:
+            return None
+        tags = self._datastore['settings']['application'].get('tags', {})
+        store = self.browser_config_store
+        builtins = {b['id']: b for b in list_builtin_browsers()}
+        for tag_uuid in (self.get('tags') or []):
+            tag = tags.get(tag_uuid)
+            if not tag:
+                continue
+            if tag.get('browser_config_overrides_watch') and tag.get('browser_config'):
+                cid = tag.get('browser_config')
+                entry = store.get(cid) if store else None
+                if entry:
+                    label = entry.get('label')
+                elif cid in builtins:
+                    label = builtins[cid]['label']
+                else:
+                    continue  # dangling / unknown - don't apply, fall through
+                return {'group_uuid': tag_uuid, 'group_title': tag.get('title'),
+                        'config_id': cid, 'label': label}
+        return None
+
     @property
     def get_fetch_backend(self):
+        """THE fully-resolved browser/engine selector this watch fetches with.
+
+        Single source of truth for the whole app (content fetcher, watchlist status icon,
+        capability checks, browser steps). Resolution order:
+
+            1. PDF watches      -> 'html_requests' (chrome/playwright can't render a PDF in-page;
+                                    we fetch it and pdf2html the text instead)
+            2. group override   -> the overriding group's browser config id
+            3. the watch's own `fetch_backend`
+            4. 'system' / unset -> the global Default browser (_global_default_fetch_backend)
+
+        Never returns 'system'. The value is a user browser-config id, a built-in engine name
+        ('html_requests'/'html_webdriver'/...), or 'extra_browser_<key>'. Map it to the concrete
+        engine with .resolved_fetch_engine; build the fetcher class/config via
+        content_fetchers.resolve_content_fetcher (which consumes this).
         """
-        Get the fetch backend for this watch with special case handling.
-
-        CHAIN RESOLUTION OPPORTUNITY:
-        Currently returns watch.fetch_backend directly, but doesn't implement
-        Watch → Tag → Global resolution chain. With Pydantic:
-
-        @computed_field
-        def resolved_fetch_backend(self) -> str:
-            # Special case: PDFs always use html_requests
-            if self.is_pdf:
-                return 'html_requests'
-
-            # Watch override
-            if self.fetch_backend and self.fetch_backend != 'system':
-                return self.fetch_backend
-
-            # Tag override (first tag with overrides_watch=True wins)
-            for tag_uuid in self.tags:
-                tag = self._datastore.get_tag(tag_uuid)
-                if tag.overrides_watch and tag.fetch_backend:
-                    return tag.fetch_backend
-
-            # Global default
-            return self._datastore.settings.fetch_backend
-        """
-        # Maybe also if is_image etc?
-        # This is because chrome/playwright wont render the PDF in the browser and we will just fetch it and use pdf2html to see the text.
+        uuid = self.get('uuid')
         if self.is_pdf:
+            logger.debug(f"fetch_backend: watch {uuid} is_pdf -> forced 'html_requests'")
             return 'html_requests'
 
-        return self.get('fetch_backend')
+        override = self.browser_config_override
+        if override:
+            logger.debug(f"fetch_backend: watch {uuid} uses group '{override.get('group_title')}' "
+                         f"override -> '{override['config_id']}'")
+            return override['config_id']
+
+        selected = self.get('fetch_backend') or 'system'
+        if selected == 'system':
+            default = self._global_default_fetch_backend
+            logger.debug(f"fetch_backend: watch {uuid} 'system' -> global default '{default}'")
+            return default
+
+        logger.debug(f"fetch_backend: watch {uuid} -> watch-level '{selected}'")
+        return selected
+
+    @property
+    def resolved_fetch_engine(self):
+        """The concrete engine name behind .get_fetch_backend - maps a browser-config id to its
+        base_fetcher, or passes a built-in engine name straight through. Used for capability
+        checks and the watchlist status icon so they agree with what actually fetches the page."""
+        value = self.get_fetch_backend
+        store = self.browser_config_store
+        entry = store.get(value) if (store and value) else None
+        if entry:
+            return entry.get('base_fetcher') or 'html_webdriver'
+        return value or 'html_requests'
 
     @property
     def fetcher_supports_screenshots(self):
-        """Return True if the fetcher configured for this watch supports screenshots.
-
-        Resolves 'system' via self._datastore, then checks supports_screenshots on
-        the actual fetcher class. Works for built-in and plugin fetchers alike.
-        """
+        """True if the fetcher this watch resolves to supports screenshots. Honours group
+        overrides + browser-config ids (via .resolved_fetch_engine). Works for built-in and
+        plugin fetchers alike."""
         from changedetectionio import content_fetchers
         from changedetectionio.content_fetchers.base import FetcherCapabilities
-        from changedetectionio.model.browser_config import base_fetcher_for
-
-        # get_fetch_backend handles is_pdf; base_fetcher_for maps a browser-config id / 'system'
-        # to the concrete engine name (and PDF -> html_requests is preserved by get_fetch_backend).
-        fetch_backend = self.get_fetch_backend
-        if fetch_backend == 'html_requests':
-            fetcher_name = 'html_requests'
-        else:
-            fetcher_name = base_fetcher_for(fetch_backend, self._datastore)
-
-        # Shared capability model - handles an unknown/None fetcher class (all-False)
-        fetcher_class = getattr(content_fetchers, fetcher_name, None)
+        fetcher_class = getattr(content_fetchers, self.resolved_fetch_engine, None)
         return FetcherCapabilities.from_fetcher(fetcher_class).supports_screenshots
 
     @property
diff --git a/changedetectionio/model/browser_config.py b/changedetectionio/model/browser_config.py
index f89a94c8..d914640c 100644
--- a/changedetectionio/model/browser_config.py
+++ b/changedetectionio/model/browser_config.py
@@ -121,8 +121,9 @@ class BrowserConfigEntry(BaseModel):
     """One browsers.json entry (the id is the dict key, not stored in the entry).
 
     Note: there is deliberately no `is_default` here. The default browser is the global
-    application `fetch_backend` (a single source of truth that can point at a built-in engine
-    OR a browser-config id), so it doesn't live per-entry - see base_fetcher_for().
+    settings.application.fetch_backend (a single source of truth that can point at a built-in
+    engine OR a browser-config id), so it doesn't live per-entry - see
+    ChangeDetectionStore.get_default_backend() / Watch.get_fetch_backend.
     """
     label: str = ''
     base_fetcher: str = 'html_webdriver'
@@ -135,27 +136,44 @@ class BrowserConfigStore:
     def __init__(self, datastore_path, lock):
         self._path = os.path.join(datastore_path, 'browsers.json')
         self._lock = lock
+        # mtime-keyed cache of the parsed file. all()/get() are hit per-watch on every watchlist
+        # render + fetch resolution, so re-reading + re-parsing browsers.json each time is real
+        # amplification (cf. the favicon-glob fix). Cache the parsed dict and only re-read when
+        # the file's mtime changes - picks up edits (save bumps mtime) without staleness.
+        self._cache = None
+        self._cache_mtime = None
 
     # ---- low level load/save ----
     def all(self):
-        """Raw dict {id: entry-dict}. Empty dict when the file is absent."""
-        if not path.isfile(self._path):
+        """Raw dict {id: entry-dict}. Empty dict when the file is absent. mtime-cached."""
+        try:
+            mtime = os.path.getmtime(self._path)
+        except OSError:
+            # File absent (or unreadable) - nothing configured yet.
+            self._cache, self._cache_mtime = {}, None
             return {}
+        if self._cache is not None and self._cache_mtime == mtime:
+            return self._cache
         try:
             if HAS_ORJSON:
                 with open(self._path, 'rb') as f:
-                    return orjson.loads(f.read()) or {}
-            with open(self._path, encoding='utf-8') as f:
-                return json.load(f) or {}
+                    data = orjson.loads(f.read()) or {}
+            else:
+                with open(self._path, encoding='utf-8') as f:
+                    data = json.load(f) or {}
         except Exception as e:
             logger.error(f"Could not load browsers.json: {e}")
             return {}
+        self._cache, self._cache_mtime = data, mtime
+        return data
 
     def _save(self, configs):
         # Deferred import avoids a model -> store import cycle at module load.
         from changedetectionio.store.file_saving_datastore import save_json_atomic
         with self._lock:
             save_json_atomic(self._path, configs, label="browsers")
+        # Invalidate so the next all()/get() re-reads (its mtime will differ anyway).
+        self._cache, self._cache_mtime = None, None
 
     # ---- CRUD ----
     def get(self, config_id):
@@ -217,28 +235,24 @@ class BrowserConfigStore:
         return FetcherConfig(**(raw.get('browser_config') or {}))
 
 
-def base_fetcher_for(value, datastore):
-    """Map any fetch_backend value to the concrete engine/fetcher name.
+# One BrowserConfigStore instance per datastore path, so the mtime cache is shared by everything
+# reading browsers.json (the ChangeDetectionStore and every Watch, which only holds the data dict
+# + its path). The ChangeDetectionStore registers its own (lock-bearing) instance here so writes
+# and the watch-side reads go through the same cache.
+_STORE_REGISTRY = {}
 
-    Accepts a user browser-config id, a built-in engine name ('html_requests'/'html_webdriver'/
-    'extra_browser_*'), or the sentinel 'system'. This is the single place the rest of the
-    codebase should go through when it needs the *engine* behind a watch/global fetch_backend
-    (capability checks, screenshot support, etc.). 'system' resolves to the global default,
-    which may itself be a browser-config id.
-    """
-    # `datastore` may be the ChangeDetectionStore (has .browser_config_store and .data) or the
-    # raw settings data dict (Watch._datastore). Tolerate both; browser-config lookups are only
-    # possible when the store object is available.
-    store = getattr(datastore, 'browser_config_store', None)
-    data = getattr(datastore, 'data', datastore)
-    entry = store.get(value) if (store and value) else None
-    if entry:
-        return entry.get('base_fetcher') or 'html_webdriver'
-    if not value or value == 'system':
-        gd = data['settings']['application'].get('fetch_backend', 'html_requests')
-        gd_entry = store.get(gd) if (store and gd) else None
-        return (gd_entry.get('base_fetcher') if gd_entry else gd) or 'html_requests'
-    return value
+
+def register_browser_config_store(datastore_path, store):
+    _STORE_REGISTRY[datastore_path] = store
+
+
+def get_browser_config_store(datastore_path):
+    """The shared BrowserConfigStore for a datastore path (created read-only if none registered)."""
+    store = _STORE_REGISTRY.get(datastore_path)
+    if store is None:
+        store = BrowserConfigStore(datastore_path, lock=None)
+        _STORE_REGISTRY[datastore_path] = store
+    return store
 
 
 def list_builtin_browsers():
@@ -278,20 +292,24 @@ def _system_default_label(datastore):
     return gettext('Default (system settings)')
 
 
-def resolve_watch_fetcher_engine(watch, datastore):
-    """The concrete engine name that will actually fetch this watch.
+# --- Thin free-function delegators --------------------------------------------------------
+# The resolution chain (PDF / group override / watch / 'system' -> global default) lives on the
+# Watch model now (Watch.get_fetch_backend & friends) - only watches fetch, so the watch owns
+# "what do I fetch with?". These wrappers keep the historical (watch, datastore) call shape for
+# templates/blueprints/tests; `datastore` is accepted but unused (the Watch self-resolves).
 
-    Single place that mirrors resolve_content_fetcher's *selection*: a group override wins,
-    else the watch's own browser selection (a browser-config id or engine name or 'system'),
-    then mapped to the underlying engine. Used by capability checks and the watchlist status
-    icon so they all agree with what fetches the page.
-    """
-    override = resolve_browser_config_override(watch, datastore)
-    selected = override['config_id'] if override else watch.get('fetch_backend', 'system')
-    return base_fetcher_for(selected, datastore)
+def resolve_watch_fetcher_engine(watch, datastore=None):
+    """The concrete engine name that will actually fetch this watch. See Watch.resolved_fetch_engine."""
+    return watch.resolved_fetch_engine
 
 
-def resolve_watch_browser_display(watch, datastore):
+def resolve_browser_config_override(watch, datastore=None):
+    """If a group/tag overrides this watch's browser config, describe it, else None.
+    See Watch.browser_config_override."""
+    return watch.browser_config_override
+
+
+def resolve_watch_browser_display(watch, datastore=None):
     """Display info for the watchlist status icon: which browser a watch effectively uses.
 
     Returns dict: {engine, browser_type, label, is_named, group_title} where `label` is the
@@ -300,13 +318,10 @@ def resolve_watch_browser_display(watch, datastore):
     override supplies it.
     """
     from changedetectionio import content_fetchers
-    store = getattr(datastore, 'browser_config_store', None)
-
-    override = resolve_browser_config_override(watch, datastore)
-    selected = override['config_id'] if override else watch.get('fetch_backend', 'system')
-    if not selected or selected == 'system':
-        selected = datastore.data['settings']['application'].get('fetch_backend', 'html_requests')
+    store = watch.browser_config_store
+    override = watch.browser_config_override
 
+    selected = watch.get_fetch_backend
     entry = store.get(selected) if (store and selected) else None
     if entry:
         engine = entry.get('base_fetcher') or 'html_webdriver'
@@ -326,37 +341,3 @@ def resolve_watch_browser_display(watch, datastore):
         'is_named': is_named,
         'group_title': override['group_title'] if override else None,
     }
-
-
-def resolve_browser_config_override(watch, datastore):
-    """If a group/tag overrides this watch's browser config, describe it, else None.
-
-    Uses the group's own dedicated enabler (browser_config_overrides_watch), NOT the coarse
-    legacy `overrides_watch` flag. Tags are checked in the watch's tag-list order; the first
-    one whose enabler is on and whose selected config still exists wins (deterministic).
-
-    Returns: {group_uuid, group_title, config_id, label} or None.
-    """
-    tags = datastore.data['settings']['application'].get('tags', {})
-    builtins = {b['id']: b for b in list_builtin_browsers()}
-    for tag_uuid in (watch.get('tags') or []):
-        tag = tags.get(tag_uuid)
-        if not tag:
-            continue
-        if tag.get('browser_config_overrides_watch') and tag.get('browser_config'):
-            cid = tag.get('browser_config')
-            entry = datastore.browser_config_store.get(cid)
-            # The override may point at a user browser (uuid) OR a built-in engine (id == name).
-            if entry:
-                label = entry.get('label')
-            elif cid in builtins:
-                label = builtins[cid]['label']
-            else:
-                continue  # dangling / unknown - don't apply
-            return {
-                'group_uuid': tag_uuid,
-                'group_title': tag.get('title'),
-                'config_id': cid,
-                'label': label,
-            }
-    return None
diff --git a/changedetectionio/store/__init__.py b/changedetectionio/store/__init__.py
index 6ec61170..edcf1b27 100644
--- a/changedetectionio/store/__init__.py
+++ b/changedetectionio/store/__init__.py
@@ -61,12 +61,22 @@ class ChangeDetectionStore(DatastoreUpdatesMixin, FileSavingDataStore):
 
         # Named browser configs (browsers.json) - optional, backup-friendly, lazy-loaded.
         # Set here in __init__ so it exists on every path (fresh install included).
-        from changedetectionio.model.browser_config import BrowserConfigStore
+        from changedetectionio.model.browser_config import BrowserConfigStore, register_browser_config_store
         self.browser_config_store = BrowserConfigStore(self.datastore_path, self.lock)
+        # Share this (lock-bearing, mtime-cached) instance with Watch objects, which only hold
+        # the data dict + their path and reach the store via the per-path registry.
+        register_browser_config_store(self.datastore_path, self.browser_config_store)
 
         self.save_version_copy_json_db(version_tag)
         self.reload_state(datastore_path=datastore_path, include_default_watches=include_default_watches, version_tag=version_tag)
 
+    def get_default_backend(self):
+        """The global "Default browser" (settings.application.fetch_backend) - the single source
+        of truth a watch/group set to 'system' resolves to. Set only on the /browsers tab
+        (its per-row radio); the Settings page shows it read-only. May be a built-in engine name
+        or a user browser-config id. See Watch.get_fetch_backend for the per-watch resolution."""
+        return self.__data['settings']['application'].get('fetch_backend', 'html_requests')
+
     def save_version_copy_json_db(self, version_tag):
         """
         Create version-tagged backup of changedetection.json.
diff --git a/changedetectionio/store/updates.py b/changedetectionio/store/updates.py
index f367ff09..e1bfd916 100644
--- a/changedetectionio/store/updates.py
+++ b/changedetectionio/store/updates.py
@@ -871,4 +871,44 @@ class DatastoreUpdatesMixin:
             restock.pop('prev_price', None)
             watch.commit()
 
+    def update_34(self):
+        """Make the global 'Default browser' a concrete, valid selection for the /browsers tab.
+
+        All browser choice is managed on /browsers now; the default is
+        settings.application.fetch_backend (the single source of truth that the per-row radio
+        writes and every watch/group set to 'system' resolves to). Older installs may hold a
+        blank/missing value, the sentinel 'system', or a browser-config id that has since been
+        deleted - any of which would leave the /browsers "Default" radio with nothing selected
+        (and a watch on 'system' with no concrete engine). Normalise those to a concrete built-in
+        engine, honouring DEFAULT_FETCH_BACKEND (the same env var fresh installs use), else
+        'html_requests'.
+
+        Concrete values already stored - a built-in engine name (e.g. 'html_webdriver'), an
+        'extra_browser_*' key, or a still-existing saved browser-config id - are left untouched.
+        Idempotent.
+        """
+        app = self.data['settings']['application']
+        current = app.get('fetch_backend')
+
+        def _is_valid_default(value):
+            if not value or value == 'system':
+                return False
+            if value.startswith('extra_browser_'):
+                return True
+            # A saved browser config?
+            if self.browser_config_store.get(value):
+                return True
+            # A built-in engine that actually exists in this build?
+            from changedetectionio import content_fetchers
+            return hasattr(content_fetchers, value)
+
+        if _is_valid_default(current):
+            return  # already a concrete, resolvable default - nothing to do
+
+        default = os.getenv('DEFAULT_FETCH_BACKEND', 'html_requests') or 'html_requests'
+        app['fetch_backend'] = default
+        logger.info(
+            f"update_34: normalised global Default browser (fetch_backend) from '{current}' to '{default}'"
+        )
+
 
diff --git a/changedetectionio/tests/custom_browser_url/test_custom_browser_url.py b/changedetectionio/tests/custom_browser_url/test_custom_browser_url.py
index 514a9965..dfab5c8b 100644
--- a/changedetectionio/tests/custom_browser_url/test_custom_browser_url.py
+++ b/changedetectionio/tests/custom_browser_url/test_custom_browser_url.py
@@ -19,7 +19,6 @@ def do_test(client, live_server, make_test_use_extra_browser=False):
         url_for("settings.settings_page"),
         data={"application-empty_pages_are_a_change": "",
               "requests-time_between_check-minutes": 180,
-              'application-fetch_backend': "html_webdriver",
               'requests-extra_browsers-0-browser_connection_url': 'ws://sockpuppetbrowser-custom-url:3000',
               'requests-extra_browsers-0-browser_name': custom_browser_name
               },
@@ -28,6 +27,14 @@ def do_test(client, live_server, make_test_use_extra_browser=False):
 
     assert b"Settings updated." in res.data
 
+    # The global "Default browser" is now chosen on the /browsers tab (was the settings-page
+    # application-fetch_backend radio). Make html_webdriver the default.
+    res = client.post(
+        url_for("ui.browser_config.browser_config_set_default", config_id="html_webdriver"),
+        follow_redirects=True
+    )
+    assert b"Default browser set" in res.data
+
     # Add our URL to the import page
     uuid = client.application.config.get('DATASTORE').add_watch(url=test_url)
     client.get(url_for("ui.form_watch_checknow"), follow_redirects=True)
diff --git a/changedetectionio/tests/fetchers/test_content.py b/changedetectionio/tests/fetchers/test_content.py
index 89623fdc..22921e3e 100644
--- a/changedetectionio/tests/fetchers/test_content.py
+++ b/changedetectionio/tests/fetchers/test_content.py
@@ -17,7 +17,6 @@ def test_fetch_webdriver_content(client, live_server, measure_memory_usage, data
         data={
             "application-empty_pages_are_a_change": "",
             "requests-time_between_check-minutes": 180,
-            'application-fetch_backend': "html_webdriver",
             'application-ui-favicons_enabled': "y",
         },
         follow_redirects=True
@@ -25,6 +24,14 @@ def test_fetch_webdriver_content(client, live_server, measure_memory_usage, data
 
     assert b"Settings updated." in res.data
 
+    # The global "Default browser" is now set on the /browsers tab (was application-fetch_backend
+    # on the settings page). Make html_webdriver the default so 'system' watches use it.
+    res = client.post(
+        url_for("ui.browser_config.browser_config_set_default", config_id="html_webdriver"),
+        follow_redirects=True
+    )
+    assert b"Default browser set" in res.data
+
     # Add our URL to the import page
     res = client.post(
         url_for("imports.import_page"),
diff --git a/changedetectionio/tests/restock/test_restock.py b/changedetectionio/tests/restock/test_restock.py
index d097c82f..e10ae08c 100644
--- a/changedetectionio/tests/restock/test_restock.py
+++ b/changedetectionio/tests/restock/test_restock.py
@@ -195,11 +195,18 @@ def test_restock_detection(client, live_server, measure_memory_usage, datastore_
         url_for("settings.settings_page"),
         data={"application-empty_pages_are_a_change": "y",
               "requests-time_between_check-minutes": 180,
-              'application-fetch_backend': fetch_backend,
               },
         follow_redirects=True
     )
 
+    # The global "Default browser" is now set on the /browsers tab (was the settings-page
+    # application-fetch_backend radio).
+    res = client.post(
+        url_for("ui.browser_config.browser_config_set_default", config_id=fetch_backend),
+        follow_redirects=True
+    )
+    assert b"Default browser set" in res.data
+
     #####################
     # Set this up for when we remove the notification from the watch, it should fallback with these details
     res = client.post(
diff --git a/changedetectionio/tests/test_access_control.py b/changedetectionio/tests/test_access_control.py
index 9ef91a99..4dd12e97 100644
--- a/changedetectionio/tests/test_access_control.py
+++ b/changedetectionio/tests/test_access_control.py
@@ -152,7 +152,9 @@ def test_check_access_control(app, client, live_server, measure_memory_usage, da
         assert b"Import" in res.data
         assert b"/logout" in res.data
         assert b"time_between_check-minutes" in res.data
-        assert b"fetch_backend" in res.data
+        # The global browser default moved to the /browsers tab; the settings page now shows it
+        # read-only as "Default browser" (the editable radio was removed).
+        assert b"Default browser" in res.data
 
         ##################################################
         # Remove password button, and check that it worked
@@ -161,7 +163,6 @@ def test_check_access_control(app, client, live_server, measure_memory_usage, da
             url_for("settings.settings_page"),
             data={
                 "requests-time_between_check-minutes": 180,
-                "application-fetch_backend": "html_webdriver",
                 "application-removepassword_button": "Remove password"
             },
             follow_redirects=True,
diff --git a/changedetectionio/tests/test_browser_config.py b/changedetectionio/tests/test_browser_config.py
index 59be16a4..1f4d355a 100644
--- a/changedetectionio/tests/test_browser_config.py
+++ b/changedetectionio/tests/test_browser_config.py
@@ -352,6 +352,118 @@ def test_group_browser_config_override(client, live_server, measure_memory_usage
     assert b"French mobile" in res.data      # from group ...
 
 
+def test_settings_default_browser_is_readonly_and_browsers_tab_owns_it(client, live_server, measure_memory_usage, datastore_path):
+    """All browser choice moved to /browsers. The Settings->Fetching page shows the global
+    Default browser read-only (no editable radio) and a settings save must NOT clobber it."""
+    datastore = client.application.config.get('DATASTORE')
+
+    _add_browser(client, label="Settings Default", viewport_width=800)
+    cid = list(datastore.browser_config_store.all())[0]
+    client.post(url_for("ui.browser_config.browser_config_set_default", config_id=cid), follow_redirects=True)
+    assert datastore.data['settings']['application']['fetch_backend'] == cid
+
+    # Settings page shows the read-only summary (label + link to /browsers) and NO editable radio.
+    res = client.get(url_for("settings.settings_page"))
+    assert b"Default browser" in res.data
+    assert b"Settings Default" in res.data
+    assert url_for("ui.browser_config.browsers_overview").encode() in res.data
+    assert b'name="application-fetch_backend"' not in res.data
+
+    # A settings save (the form no longer carries fetch_backend) leaves the default untouched.
+    res = client.post(url_for("settings.settings_page"),
+                      data={"requests-time_between_check-minutes": 180,
+                            "application-empty_pages_are_a_change": ""},
+                      follow_redirects=True)
+    assert b"Settings updated." in res.data
+    assert datastore.data['settings']['application']['fetch_backend'] == cid
+
+
+def test_browsers_overview_default_radio(client, live_server, measure_memory_usage, datastore_path):
+    """Each usable browser row exposes a radio to set it as default; the current default is checked."""
+    import re
+    datastore = client.application.config.get('DATASTORE')
+    _add_browser(client, label="Radio Mobile", viewport_width=390)
+    cid = list(datastore.browser_config_store.all())[0]
+    client.post(url_for("ui.browser_config.browser_config_set_default", config_id=cid), follow_redirects=True)
+
+    res = client.get(url_for("ui.browser_config.browsers_overview"))
+    assert b'class="browser-default-radio"' in res.data
+    # Built-in engines each have a radio too (usable ones)
+    assert b'value="html_webdriver"' in res.data
+    # The checked radio is our default config id
+    checked = re.findall(rb'<input type="radio"[^>]*?>', res.data)
+    assert any(cid.encode() in tag and b'checked' in tag for tag in checked)
+
+
+def test_watch_get_fetch_backend_resolution_chain(client, live_server, measure_memory_usage, datastore_path):
+    """Watch.get_fetch_backend owns the whole chain: PDF / watch / 'system'->global / group override."""
+    datastore = client.application.config.get('DATASTORE')
+
+    # Global Default browser = html_webdriver (what /browsers set-default writes)
+    datastore.data['settings']['application']['fetch_backend'] = 'html_webdriver'
+
+    uuid = datastore.add_watch(url="https://example.com")
+    watch = datastore.data['watching'][uuid]
+
+    # 'system' resolves to the global default (and maps to the same engine)
+    watch['fetch_backend'] = 'system'
+    assert watch.get_fetch_backend == 'html_webdriver'
+    assert watch.resolved_fetch_engine == 'html_webdriver'
+
+    # A watch-level choice wins over the global default
+    watch['fetch_backend'] = 'html_requests'
+    assert watch.get_fetch_backend == 'html_requests'
+
+    # PDF forces html_requests regardless of the selected browser
+    watch['fetch_backend'] = 'html_webdriver'
+    watch['url'] = 'https://example.com/doc.pdf'
+    assert watch.get_fetch_backend == 'html_requests'
+    watch['url'] = 'https://example.com'
+
+    # A group override beats the watch's own selection
+    tag_uuid = datastore.add_tag("Force webdriver")
+    client.post(url_for("tags.form_tag_edit_submit", uuid=tag_uuid),
+                data={'title': 'Force webdriver', 'browser_config_overrides_watch': 'y',
+                      'browser_config': 'html_webdriver'}, follow_redirects=True)
+    watch['fetch_backend'] = 'html_requests'
+    watch['tags'] = [tag_uuid]
+    assert watch.get_fetch_backend == 'html_webdriver'
+
+
+def test_update_34_normalises_default_browser(client, live_server, measure_memory_usage, datastore_path):
+    """update_34 turns a blank/'system'/dangling global default into a concrete built-in engine,
+    but leaves an already-valid default (engine name or saved config id) untouched."""
+    datastore = client.application.config.get('DATASTORE')
+    app = datastore.data['settings']['application']
+
+    # Blank -> concrete default
+    app['fetch_backend'] = ''
+    datastore.update_34()
+    assert app['fetch_backend'] in ('html_requests', 'html_webdriver')
+
+    # 'system' at the global level is invalid (it IS the system default) -> normalised
+    app['fetch_backend'] = 'system'
+    datastore.update_34()
+    assert app['fetch_backend'] != 'system'
+
+    # A dangling browser-config id -> normalised to a concrete engine
+    app['fetch_backend'] = 'deleted-id-9999'
+    datastore.update_34()
+    assert app['fetch_backend'] != 'deleted-id-9999'
+
+    # A valid built-in engine is left untouched (idempotent)
+    app['fetch_backend'] = 'html_webdriver'
+    datastore.update_34()
+    assert app['fetch_backend'] == 'html_webdriver'
+
+    # A valid saved browser-config id is left untouched
+    _add_browser(client, label="Keeper", viewport_width=800)
+    cid = list(datastore.browser_config_store.all())[0]
+    app['fetch_backend'] = cid
+    datastore.update_34()
+    assert app['fetch_backend'] == cid
+
+
 def test_group_override_with_builtin_browser(client, live_server, measure_memory_usage, datastore_path):
     """A group can also override with a built-in engine (e.g. html_webdriver), not just a user browser."""
     from changedetectionio.model.browser_config import resolve_browser_config_override