help: default the contextual layer off, and carry the help into the chooser

The contextual help was on by default, so a first run met a window with a "?"
beside every surface it had not asked to have explained; `contextual_help` now
defaults to false and the layer is asked for from the Help menu, from the
chooser's new help menu, or with Ctrl+H.

The source chooser runs before `App` exists, which makes it the window a user
who does not know how to start is looking at, so it now carries the same three
help affordances the window's Help view does: Documentation (the manual is
another process and needs nothing of the app), Enable contextual help (a row
whose check *is* the setting, written to the file the app reads a moment
later), and Guided tour. The tour is drawn on the app's own window, so the
chooser can only record the wish: it sets `Config::tour_pending` -- the value
`main()` owns and hands to both `choose_source()` and `run_ui()` -- and
`on_activate()` starts it once the window is up and laid out, through its own
callback so the readings can tell a request from the first-run auto-start.
The rows are the window's own `menu_button()`/`menu_toggle()`; `install_css()`
therefore runs from `choose_source()` (it is idempotent now) so the popover
gets the `.udpscope-menu` rules before it is shown.

Opening the manual could also fail with a message that blamed the handler
whatever was missing. `help_installed_path()` now resolves `help:<id>` the way
the specification does and the failure alert says which of the two it is: with
the set installed it names the viewer, without it it names the identifier, the
expected installed path and the install command. `show_help()` gained an
optional reporter, which `UDPSCOPE_PROBE_HELP_MS` uses for a new reading --
`[help] launch attempted= done= ok= error='' installed=` -- since a successful
launch leaves no window of ours to observe.

Tested: clean --clean-first build, three warnings as documented; test-ui 13/13
and test-help pass; no Gtk-CRITICAL in the help, helpui and chooser runs.

README.md

@@ -730,7 +730,11 @@ same session twice). Connector settings are stored even for a configuration with
 which is why those rows exist at all. The app's
 menu has **Configurations…**: the same list for the running source, with *Save this session* —
 a name and a note — and a delete button per row. Opening one saves the current session first, so
-switching is never the gesture that loses what it switches from.
+switching is never the gesture that loses what it switches from. Beside **Preferences…** the chooser
+also carries a **help menu** with the window's three help entries — the manual, the contextual-help
+toggle and the guided tour — because the chooser is shown to exactly the user who has not started yet
+and does not know how to; the tour is started by the app once its window is up (see
+[the help section](#the-help-submenu-the-contextual-help-and-the-guided-tour)).
 
 A session written before configurations existed is imported on first use as the configuration
 named `default`: copied into the directory, remembered as active, and the old file renamed to
@@ -901,14 +905,32 @@ button is a sibling of the heading's title, not an overlay on its corner, for th
 toolbar's icons are not overlaid either: an overlay child sits *on* whatever is under it, and the
 one surface whose corner is free (the plot) is the one that uses one.
 
-**Off means gone, not greyed.** The toggle removes the buttons rather than disabling them, and
-which buttons exist is decided by a data key rather than a list of pointers, so the math editor --
-whose heading is created afresh every time it opens -- cannot leave a stale pointer behind. The
-setting is `contextual_help` in `settings.toml`, written by
+**Off means gone, not greyed, and off is the default.** The toggle removes the buttons rather than
+disabling them, and which buttons exist is decided by a data key rather than a list of pointers, so
+the math editor -- whose heading is created afresh every time it opens -- cannot leave a stale
+pointer behind. The setting is `contextual_help` in `settings.toml`, written by
 `Settings`/`load_settings()`/`save_settings()`: the same file, the same three functions and the same
-`~/.config/udpscope/settings.toml` the Preferences dialog writes. The dialog's own rows start from
-`load_settings()`, so a save from there carries the two help keys through untouched; the Help menu's
-row is the only place that states `contextual_help`, which is why the row's check *is* the setting.
+`~/.config/udpscope/settings.toml` the Preferences dialog writes. **A fresh install has no such key
+and the default is `false`**, so a first run shows the window as anyone would expect it and the layer
+is asked for -- from the Help menu, from the source chooser's own help menu, or with `Ctrl+H`. The
+dialog's own rows start from `load_settings()`, so a save from there carries the two help keys
+through untouched; the Help menu's row is the only place in the *window* that states `contextual_help`
+(which is why the row's check *is* the setting), and the chooser's row states it too, before any
+window exists.
+
+**The source chooser carries the same three affordances, because it is shown to exactly the user who
+has not started yet.** Its header bar has a help `GtkMenuButton` beside *Preferences*, whose rows are
+the window's own `menu_button()`/`menu_toggle()` -- the same shape, and the same `.udpscope-menu`
+stylesheet, whose rules `choose_source()` installs before building them since the app installs them
+later. *Documentation* opens the manual directly (it is another process and needs nothing of the app),
+*Enable contextual help* writes the settings file the app reads a moment later, and *Guided tour*
+cannot start anything -- the tour is drawn on the app's window, which does not exist yet -- so it sets
+**`Config::tour_pending`**, the value `main()` owns and hands to both the chooser and the front end
+(`open_waveform` crosses the same way). Half a second and a half after the window is up, the same
+delay the first-run auto-start uses, the pending request starts the tour; it sets `tour_requested`
+rather than `tour_auto_started`, so the readings say which of the two it was. The chooser's rows show
+**no accelerators** -- the window prints `F1`/`Ctrl+T` because the window binds them, and this dialog
+binds none.
 
 **The guided tour is five steps on a `GtkOverlay`** inserted above the window's content: the plot,
 the side panel, the trigger, the signals and the status line. There is no popover anywhere in it and
@@ -2439,7 +2461,14 @@ identifier `org.udpscope.app` is the desktop file's own basename, so it is the `
 GApplication id and the install directory at once. The set is installed by an `install()` rule to
 `share/help/C/org.udpscope.app/` — the path the freedesktop Help System Specification's `help:` URI
 resolves — and `show_help()` hands `help:org.udpscope.app` to whatever the desktop registered for the
-scheme (Yelp on GNOME), reporting a launch failure with an alert rather than failing silently.
+scheme (Yelp on GNOME), reporting a launch failure with an alert rather than failing silently. That
+alert says **which** thing is missing, because the two have different fixes: `help_installed_path()`
+looks for the document under `$XDG_DATA_HOME/help/<lang>/org.udpscope.app/` then
+`$XDG_DATA_DIRS/help/<lang>/org.udpscope.app/`, so with the set installed the alert names the missing
+*viewer* (`yelp`), and without it the alert names the identifier, the expected installed path and the
+install command — `cmake --install build --prefix ~/.local`, which writes
+`~/.local/share/help/C/org.udpscope.app/`. A build tree has neither the installed copy nor a
+`help:` handler, and **either is enough to make `F1` do nothing**; that is the failure this names.
 `cmake --build build --target test-help` checks the set the way `test-ui` checks the `.ui` files:
 `yelp-check`'s offline subcommands (links, media, orphans, ids) and a `yelp-build html` render;
 `yelp-check validate` is left out because it fetches the Mallard RelaxNG schema over the network.
@@ -2447,7 +2476,11 @@ scheme (Yelp on GNOME), reporting a launch failure with an alert rather than fai
 (GTK4 has to be forced to the Cairo renderer or X11 reads the surface back blank).
 `UDPSCOPE_PROBE_HELP_MS` asserts the set is *present in the tree* — its
 `[help] topics=… index=… figures=…` reading — rather than parsing pages, since they are files now
-and not resources. Mallard is translatable with `itstool`, but only the `C` set is authored here.
+and not resources, and it **launches the manual too**: `[help] launch attempted=1 done=1 ok=1
+error='' installed=/home/…/.local/share/help/C/org.udpscope.app` is the reading, `ok=1` meaning the
+`help:` URI reached a registered handler and not that a window appeared (Yelp is another process and
+cannot map one headlessly). Mallard is translatable with `itstool`, but only the `C` set is authored
+here.
 
 **The status bar is two tiers.** The bar itself shows one glance line: the activity badge, the
 display state (one word from a fixed set — `connecting`, `live`, `paused`, `armed`, `capturing`,

docs/claude/invariants-gtk-and-chrome.md

@@ -127,7 +127,10 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   honest without knowing which dialog it is. One `GtkWidget*` (or `AdwDialog*`) per window, nulled
   in its own close handler, is the shape that prevents the double-open defect. `close_help_windows()`
   (misnamed now) closes just the two dialogs; a failed *launch* is reported by the launcher's own
-  callback with a `GtkAlertDialog`, so a click that cannot open the manual says so.
+  callback with a `GtkAlertDialog`, so a click that cannot open the manual says so. That callback is
+  also `show_help()`'s **optional reporter** (`std::function<void(bool ok, const std::string& error)>`)
+  — the one hook that runs on the success path, where no window of ours is left to observe; the probe
+  uses it and nothing else does.
 - **`build_info.cpp` is generated, never committed.** `cmake/write_build_info.cmake` runs at
   configure time (so `add_executable` can name the file) and again on every build through
   `udpscope_build_info` (so the commit and the timestamp belong to the binary that is running).
@@ -149,7 +152,21 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   → `org.udpscope.app`), so it is the `.desktop` name, the GApplication id and the install
   directory at once; `UDPSCOPE_HELP_NAME` and `UDPSCOPE_HELP_DIR` are compiled in from that one
   place. `show_help()` opens `help:<id>` with `GtkUriLauncher` (Yelp runs in its own process, so
-  nothing here holds a pointer to it), and its failure callback shows a `GtkAlertDialog`.
+  nothing here holds a pointer to it), and its failure callback shows a `GtkAlertDialog`. That
+  failure is **careful about which thing is missing**: `gtk_uri_launcher_launch_finish()` reports a
+  launch that could not be handed over — the *handler's* absence — and cannot tell that from a
+  document that was never installed, so `help_installed_path()` walks the specification's own
+  `$XDG_DATA_HOME/help/<lang>/<id>/` then `$XDG_DATA_DIRS/help/<lang>/<id>/` for an `index.page` and
+  the dialog says which one it is: with the manual there, install a viewer (for example `yelp`); with
+  it absent, the identifier, the expected installed path and the install command
+  (`cmake --install build --prefix ~/.local`, which writes `~/.local/share/help/C/<id>/`) — and a
+  viewer as well, the second possibility the error alone cannot rule out. Reporting a missing
+  *document* as a missing *handler* is the defect that shape avoids.
+
+  `UDPSCOPE_PROBE_HELP_MS` launches it too, and its `[help] launch attempted= done= ok= error=''
+  installed=` line is the reading — `ok=1` is the URI handed to a viewer and not a window on screen,
+  since Yelp is another process and cannot map one headlessly; `installed=` sits beside it because a
+  failing `ok=0` has to be read against whether the document was there at all.
 
   `UDPSCOPE_PROBE_HELP_MS` no longer parses pages — they are files, not markup in a resource — so
   its `[help]` line asserts the set is *there*: `topics` (the `.page` files other than
@@ -163,6 +180,25 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   (GTK4 must be forced to the Cairo renderer, `GSK_RENDERER=cairo`, or the X11 surface reads back
   blank). Mallard is translatable with `itstool`, but there is no i18n set-up here: only the `C`
   set is authored.
+- **The chooser carries the same help affordances as the window, and the tour request crosses as a
+  value — not a global.** The source chooser runs *before* `App` exists, so a user who has not started
+  yet is the one least able to find the help; its header bar therefore has a help `GtkMenuButton`
+  (the `.ui` holds the button, code holds the rows) whose three entries are the window's Help view's
+  the same way — `ui_impl::menu_button()`/`menu_toggle()`, the app's own row shape — with the
+  `.udpscope-menu` class on the popover. That class's rules only exist once `install_css()` has run, so
+  `choose_source()` calls it before building the rows (`install_css()` is idempotent precisely because
+  it now has two callers; the app's `on_activate()` still calls it and is a no-op by then). The rows
+  show **no accelerators**: the window's Help view prints `F1`/`Ctrl+T` because the window binds them,
+  and this dialog binds none, so a key printed here would be documentation that does nothing.
+  *Documentation* calls `show_help()` straight from the chooser (the manual is another process and
+  needs nothing of the app); *Enable contextual help* writes the settings file, which is what the app
+  reads when it starts a moment later; *Guided tour* cannot start anything — the tour is drawn on the
+  app's own window — so it sets **`Config::tour_pending`**, the one value `main()` owns and hands to
+  both `choose_source()` and `run_ui()` (`open_waveform` and the preferences' relative time cross the
+  same way). `on_activate()` schedules `tour_start_requested()` 1.5 s later, the same delay the
+  first-run auto-start uses, and **that callback is separate from `tour_autostart()` on purpose**: it
+  sets `tour_requested`, not `tour_auto_started`, so `help layer:` says which of the two started the
+  tour instead of conflating a user's request with a first run.
 - **A `GtkPaned` hands its start child at least its minimum unless the position says otherwise.**
   Putting the events pane in a paned is what makes its width the user's to drag -- but with the
   position left alone, `shrink-start-child` or not, the pane's minimum is reserved as an empty column

docs/claude/probe-readings.md

@@ -395,17 +395,21 @@ Two lines of the self-check output are assertions in disguise:
   on the first tick for the same reason the toolbar's are. **Both must read `(ok)`**: the page titles are
   empty on purpose, so an icon that does not resolve leaves a *blank* pill, and a blank pill looks
   exactly like a page with nothing in it.
-- `help layer: contextual=on hints=8 ids={events plot status cursors measures trigger signals window} icon=dialog-question-symbolic(ok); tour=idle steps=5 step=0 auto=1` (in the exit
+- `help layer: contextual=on hints=8 ids={events plot status cursors measures trigger signals window} icon=dialog-question-symbolic(ok); tour=idle steps=5 step=0 auto=1 requested=0` (in the exit
   dump, beside `switcher:`) — the help affordance layer as the last tick found it. **`hints=` must equal
   the number of ids**, and the ids are the surfaces the contextual help is on: the eight of the window
   itself, and `math` only while the math editor is open (its heading lives in a builder that is rebuilt
-  on every opening, so it is not one of the window's own). `contextual=off` beside `hints=0` is the
-  toggle's other state — **off is *gone*, not greyed**, so a non-zero count with `off` is a row that hid
-  its buttons instead of removing them. **`icon=` must read `(ok)`**: a `?"` whose name Adwaita lacks is a
+  on every opening, so it is not one of the window's own). The layer is **off by default**
+  (`contextual_help` in `settings.toml` is false for a missing file), so a fresh-config run reads
+  `contextual=off hints=0` and that line above is the state *after* the Help row was switched on;
+  `contextual=off` beside a non-zero count is the toggle not having removed its buttons — **off is
+  *gone*, not greyed**. **`icon=` must read `(ok)`**: a `?"` whose name Adwaita lacks is a
   *blank* control that still works, the failure the pane [edit] buttons already paid for once. `tour=`
-  is `running`/`idle` with the plan's `steps=` and the current `step=`, and `auto=1` is the first-run
+  is `running`/`idle` with the plan's `steps=` and the current `step=`; `auto=1` is the first-run
   auto-start having fired *in this process* — the flag is `tour_seen` in `settings.toml`, so a second run
-  against the same config directory reads `auto=0`.
+  against the same config directory reads `auto=0` — and `requested=1` is the **chooser's** "Guided tour"
+  (`Config::tour_pending`) having been carried into this run instead, which is `auto=0` because it is not
+  the auto-start.
 - `help figures: trigger_head=X,Y,W,H trigger_summary=… trigger_panel=… signal_list=… side_switcher=… side_stack=… window_button=… status_label=… header_bar=… plot=…` (in the exit
   dump, beside `help layer:`) — the **window-coordinate** rectangle of each surface the help's annotated
   figures label, `x,y,width,height`, or `-1,-1,0,0` for a surface that is **not on screen**. It is
@@ -634,7 +638,7 @@ Two lines of the self-check output are assertions in disguise:
   so the panes the tick rewrites are measured directly. The `[width-probe]` lines are the
   per-change detail behind the `axes.w changes` count, and a step over 100 px dumps the widget
   tree's wide subtrees — that is what the documented, intermittent ~320 px step wants read.
-- `[help] topics=14 index=1 figures=3 dir=/…/help/C/org.udpscope.app; shortcuts: app=14 plot=14 tables=28 ui=28 ui_accel=21 ui_icon=7 ui_bare=0; about version=… commit=… built=… settings=… icon=org.udpscope.app; closed ok` (stderr, `UDPSCOPE_PROBE_HELP_MS`) — the manual is a Mallard set on disk now, not a GResource in the binary, so this is a **file-system reading**: `topics` is the `.page` files other than `index.page`, `index` must be 1, and `figures` counts the screenshots under `figures/`. **`topics=0 index=0` means the manual is missing** from `dir` (the source directory the build was configured from, `UDPSCOPE_HELP_DIR`) — the finding the old `parsed != pages` used to name. The manual itself opens in Yelp, another process, which this probe does not and cannot exercise. The `shortcuts:` numbers are the shortcut overview four ways.
+- `[help] topics=14 index=1 figures=3 dir=/…/help/C/org.udpscope.app; shortcuts: app=14 plot=14 tables=28 ui=28 ui_accel=21 ui_icon=7 ui_bare=0; about version=… commit=… built=… settings=… icon=org.udpscope.app; closed ok` (stderr, `UDPSCOPE_PROBE_HELP_MS`) — the manual is a Mallard set on disk now, not a GResource in the binary, so this is a **file-system reading**: `topics` is the `.page` files other than `index.page`, `index` must be 1, and `figures` counts the screenshots under `figures/`. **`topics=0 index=0` means the manual is missing** from `dir` (the source directory the build was configured from, `UDPSCOPE_HELP_DIR`) — the finding the old `parsed != pages` used to name. The manual itself opens in Yelp, another process, which the probe now launches and reports (the `[help] launch` line below). The `shortcuts:` numbers are the shortcut overview four ways.
 `app` and `plot` are the rows in the C tables -- what the application actually *handles* -- and `tables`
 is their sum. `ui`, `ui_accel`, `ui_icon` and `ui_bare` are what `src/ui/shortcuts.ui` *declares*, read
 out of the resource with a markup parse rather than off the built widgets, because a tree walk counts
@@ -642,7 +646,8 @@ every row twice: `GtkShortcutsWindow` reaches each one from more than one place
 **`ui` must equal `tables`** -- two lists of one thing, and a row in one but not the other is a gesture
 that works and is not documented, or is documented and does nothing -- and **`ui_bare` must be zero**: a
 row with no accelerator and no icon is a cell reading "No Shortcut". `ui_accel + ui_icon == ui`, so those
-two also catch a row whose accelerator went missing. `settings=` must be a real path (the same one the About dialog shows). **`icon=` must read `org.udpscope.app`** — it is read back through `adw_about_dialog_get_application_icon()` while the dialog is open, so the dialog is asserted to *carry* the icon rather than merely to open (a `set_application_icon()` lost in an edit leaves a dialog that opens, looks almost right, and shows a generic placeholder). `closed ok` with **no `Gtk-CRITICAL`** is as much a crash test of the two dialogs built, presented and closed in one run as it is a state check: they are closed by **two different calls**, so a mismatched pair crashes or leaks here. One is a `GtkWindow` (the shortcut overview, `gtk_window_close()`/`::close-request`); the About dialog is an `AdwDialog` and closes with `adw_dialog_close()`, cleared on `::closed`. The manual is *not* one of them — it opens in Yelp, a separate process, so there is nothing here to open, read back or close.
+two also catch a row whose accelerator went missing. `settings=` must be a real path (the same one the About dialog shows). **`icon=` must read `org.udpscope.app`** — it is read back through `adw_about_dialog_get_application_icon()` while the dialog is open, so the dialog is asserted to *carry* the icon rather than merely to open (a `set_application_icon()` lost in an edit leaves a dialog that opens, looks almost right, and shows a generic placeholder). `closed ok` with **no `Gtk-CRITICAL`** is as much a crash test of the two dialogs built, presented and closed in one run as it is a state check: they are closed by **two different calls**, so a mismatched pair crashes or leaks here. One is a `GtkWindow` (the shortcut overview, `gtk_window_close()`/`::close-request`); the About dialog is an `AdwDialog` and closes with `adw_dialog_close()`, cleared on `::closed`. The manual is *not* one of them — it opens in Yelp, a separate process, so there is no window of ours to read back or close; the line below is the reading of that path instead.
+- `[help] launch attempted=1 done=1 ok=1 error='' installed=/home/…/.local/share/help/C/org.udpscope.app` (stderr, `UDPSCOPE_PROBE_HELP_MS`, a moment after the line above) — the **launch of the manual**, the one part of the help path no other reading reaches: a successful launch leaves no window of ours, so nothing else can say whether `show_help()` did anything at all. `attempted=` is set at the call (`0` would be a probe that never got as far as calling it); `done=` says the asynchronous callback ran, and **`done=0` is the reading for a launch that never called back**; `ok=1` is the `help:` URI handed to a viewer, `ok=0` with the launcher's `error=` text is a launch that failed. **`ok` is not "a window appeared"**: Yelp is another process, and under a headless X server it cannot map one — the launch is *this* process's half (the URI reached a registered handler), which is exactly what the desktop does when a user presses F1, and what an absent handler or an uninstalled viewer breaks. `installed=` is `help_installed_path()`'s answer — the `$XDG_DATA_HOME`/`$XDG_DATA_DIRS` directory the document was found in, or `(not found)` — and it is what a failing `ok=0` should be read beside, because the launch error alone cannot tell a missing document from a missing handler. On a machine with the set installed by `cmake --install build --prefix ~/.local` and `yelp` present, the line reads `ok=1 … installed=~/.local/share/help/C/org.udpscope.app`. A **failure** leaves the launcher's `GtkAlertDialog` up on purpose — that is what a user gets, and the probe must not report a failed path as a silence.
 - `[menu] N 'label' accel='key' h=P label_x=X accel_right=R/W order=D ok=O`, one line per row,
   then `[menu] rows=R expected=E order=D rows_bad=B popover_visible=V mapped=M button_mapped=B`
   and `[menu] status pos=top bubble=WxH button_top=T button_right=R fits=F` (stderr,
@@ -671,7 +676,10 @@ two also catch a row whose accelerator went missing. `settings=` must be a real
   run against the same config directory, which is the assertion that the flag persisted. Then:
   - `[helpui] contextual on: hints=8 ids={events plot status cursors measures trigger signals window}` —
     the eight "?" affordances, by id. The layer's ninth surface, `math`, is not here: its host exists
-    only while the math editor window is open.
+    only while the math editor window is open. **On a fresh config this reads `hints=0 ids={}`**, because
+    the layer is off by default; the example is the state after the row below was switched on, and a
+    fresh run's `hints=0` beside a `settings.toml` with no `contextual_help` key is the default being
+    read rather than assumed.
   - `[helpui] main view: rows=7 help_row=1` and one `[helpui] entry N '<label>' accel='<key>' order=O`
     per row of the **Help view** — `entry 0 'Back'` with no accelerator and then the four the submenu
     promises: `entry 1 'Keyboard shortcuts' accel='Ctrl+/'`, `entry 2 'Documentation' accel='F1'`,
@@ -679,7 +687,9 @@ two also catch a row whose accelerator went missing. `settings=` must be a real
     every row** is the assertion; the view is entered by emitting `::clicked` on the menu's own `Help`
     row, so the row's handler is exercised and not just the stack.
   - `[helpui] help view: rows=5 expected=5 rows_bad=0 back=1 toggle=1 entries='…'` — the summary, with
-    `toggle=1` being the contextual-help row's check, which *is* `settings.contextual_help`.
+    `toggle=` being the contextual-help row's check, which *is* `settings.contextual_help`. It reads `0`
+    on a fresh config (the default) and `1` on one where the setting is on; the probe's next step drives
+    it both ways, which is why the example here is the `1` side.
   - `[helpui] toggle: off -> hints=0 ids={}; on -> hints=8 ids={…}; setting=on` — the toggle's effect
     read both ways through the row itself. **`hints=0` with `off` is the assertion**: off means the
     affordances are *gone*, not greyed, so anything else is a row that hid its buttons instead of
@@ -1088,7 +1098,10 @@ configuration that carries settings, is the defect this exists for — a saved h
 ## `[sources] waveforms` and the waveform load
 
 ```
-[sources] chooser ui: page='sources' title='Sources' icon=yes page='waveforms' title='Waveforms' icon=yes visible='sources' switcher_wired=1 buttons=[prefs=1 new_host=1 open=1 cancel=1]
+[sources] chooser ui: page='sources' title='Sources' icon=yes page='waveforms' title='Waveforms' icon=yes visible='sources' switcher_wired=1 buttons=[prefs=1 new_host=1 open=1 cancel=1] help=[button=1 docs=1 tour=1 toggle=1 on=0]
+[sources] chooser help: tour requested
+[sources] chooser help: tour_pending=1
+[sources] chooser help: toggle=1 setting=1 file=/tmp/…/udpscope/settings.toml
 [sources] waveforms: 1 recent /tmp/rt.npy(ok) page=waveforms
 [sources] picked waveform /tmp/rt.npy
 [udpscope] waveform loaded: /tmp/rt.npy signals=4 samples=20001 rows=20001 decim=1 span=2.000000s rate=10000 time=[-2.000000..0.000000]
@@ -1097,7 +1110,7 @@ configuration that carries settings, is the defect this exists for — a saved h
 
 | field | value it must read | the defect a wrong reading names |
 | --- | --- | --- |
-| `chooser ui:` | both pages with a `title` and an `icon=yes`, `switcher_wired=1`, and all four buttons `1` | the chooser's `.ui` losing an id: the code names the missing one and refuses the window, and this line is the frame that *did* build -- a page with `icon=NO` is one the switcher cannot draw |
+| `chooser ui:` | both pages with a `title` and an `icon=yes`, `switcher_wired=1`, all four buttons `1`, and `help=[button=1 docs=1 tour=1 toggle=1 on=0]` | the chooser's `.ui` losing an id: the code names the missing one and refuses the window, and this line is the frame that *did* build -- a page with `icon=NO` is one the switcher cannot draw, and a `help=` field at `0` is a help row (or the button that opens it) the dialog no longer carries |
 | `waveforms:` | one entry per remembered export, with `(ok)` or `(missing)`, and `page=waveforms` once the page is shown | the Waveforms page not built, or a stale path offered as if it were openable |
 | `picked waveform` | the selected path | a pick that carries no file: `--open` is what the mode reads |
 | `signals=`, `rows=` | the export's `cols=` and `rows=` | a reader mis-slicing its records, or the columns bound to the wrong channels |
@@ -1106,6 +1119,21 @@ configuration that carries settings, is the defect this exists for — a saved h
 | `span=`, `rate=`, `time=[…]` | the exported window and rate, `[-window, 0]` | the plan not covering the whole file (the tail arrives as the whole picture) or the display epoch not pinned to the file's last stamp |
 | `frames=0 packets=0` beside `channels=N` | 0 — no acquisition | a socket opened for a file, which would also make the starvation notice live |
 
+The chooser's **help menu** — `Documentation`, `Guided tour` and `Enable contextual help`, the three
+affordances the window's Help view carries, moved in front of a user who has not started yet — has two
+probe legs, both of which then fall through to the normal first-row pick so the run they affect is the
+run they report:
+
+- `UDPSCOPE_PROBE_CHOOSER_TOUR=1` emits `::clicked` on `Guided tour`, and `[sources] chooser help:
+  tour_pending=1` reads the request back out of the `Config` the run will be handed. **`tour_pending=1`
+  is the assertion**: the tour is drawn on a window that does not exist yet, so the entry can only work
+  by setting that field, and the reading it *started* is the exit dump's `help layer:` — `tour=running
+  … auto=0 requested=1`, `requested=1` being this path (see `help layer:` above).
+- `UDPSCOPE_PROBE_CHOOSER_HELP=1` sets the `Enable contextual help` row active and reads the settings
+  file back: `toggle=1 setting=1 file=<settings.toml>`. **`setting=1` beside `toggle=1`** is the pair
+  that matters — the row *is* the setting, and the app is built from the file and not from the dialog,
+  so the file is where it has to have landed.
+
 ## `[drop-probe]`
 
 ```

src/config.hpp

@@ -59,6 +59,13 @@ struct Config {
   /// live source. File mode and source mode are exclusive -- there is no acquisition behind a file,
   /// and the chooser's Waveforms page sets this rather than the connection fields.
   std::string open_waveform;
+
+  /// The source chooser's "Guided tour" entry. The tour is drawn on the application's own window,
+  /// which does not exist while the chooser runs, so the request rides on the one value `main()`
+  /// owns and hands to both the chooser and the front end (`open_waveform` and the preferences'
+  /// relative time cross the same way) and the window starts the tour once it is up and laid out.
+  /// It is *not* a preference: it describes this request and nothing else, so nothing persists it.
+  bool tour_pending = false;
 };
 
 /// Parses argv. On `--help` prints usage to stdout and exits(0); on a bad

src/help_window.cpp

@@ -3,7 +3,9 @@
 
 #include <adwaita.h>
 
+#include <functional>
 #include <string>
+#include <vector>
 
 #include "build_info.hpp"
 #include "layout_store.hpp"
@@ -44,27 +46,55 @@ void on_dialog_closed(AdwDialog* dialog, gpointer slot) {
   *static_cast<AdwDialog**>(slot) = nullptr;
 }
 
-/// The launch is asynchronous and can fail -- no help viewer installed, no handler for the
-/// `help:` scheme, or a document no viewer can find -- and it runs in another process, so
-/// nothing raises a window of ours. Report the failure here rather than leaving a click that
-/// silently did nothing; the detail names the identifier a viewer looks for.
+/// What an asynchronous launch needs to survive the call: the window it is attributed to (held,
+/// because the call outlives the stack frame that made it) and the caller's reporter, if it asked
+/// for one. One small struct rather than two `gpointer`s, because a callback that takes both through
+/// one `user_data` still has to get them there.
+struct HelpLaunch {
+  GtkWindow* parent = nullptr;
+  std::function<void(bool, const std::string&)> done;
+};
+
+/// The launch failed. Report it rather than leaving a click that silently did nothing -- and say
+/// *which* thing is missing: `gtk_uri_launcher_launch_finish()` reports that the URI could not be
+/// handed over, which is the handler's absence, while a document that is not installed is a
+/// different failure the launcher cannot tell it from. `help_installed_path()` settles that from the
+/// file system, so a missing *document* is not reported as a missing *handler*: with the manual
+/// installed the message names the viewer, and without it the message names the document, its
+/// expected path and the install command -- and a viewer as well, because that second possibility
+/// cannot be ruled out from here.
 void on_help_launched(GObject* source, GAsyncResult* result, gpointer user) {
-  GtkWindow* parent = user != nullptr ? GTK_WINDOW(user) : nullptr;
+  auto* launch = static_cast<HelpLaunch*>(user);
   GError* error = nullptr;
-  if (!gtk_uri_launcher_launch_finish(GTK_URI_LAUNCHER(source), result, &error)) {
+  const bool ok = gtk_uri_launcher_launch_finish(GTK_URI_LAUNCHER(source), result, &error);
+  if (!ok) {
+    const std::string installed = help_installed_path();
     GtkAlertDialog* alert = gtk_alert_dialog_new("Could not open the help manual");
-    const std::string detail =
-        std::string(error->message) +
-        "\n\nThe manual is installed under $XDG_DATA_DIRS/help/C/help:" UDPSCOPE_HELP_NAME
-        "; a desktop help viewer (for example `yelp`) that handles the `help:` URI is needed "
-        "to read it.";
+    std::string detail = error != nullptr ? error->message : std::string("the launch failed");
+    detail += "\n\n";
+    if (!installed.empty()) {
+      detail += "The manual is installed at " + installed +
+                ", so what is missing is a viewer for the `help:` URI it is opened with: install "
+                "one (for example `yelp`) or make it the desktop's default for that scheme.";
+    } else {
+      detail += "The manual does not look installed: nothing named \"help:" UDPSCOPE_HELP_NAME
+                "\" was found under $XDG_DATA_HOME/help/<lang>/" UDPSCOPE_HELP_NAME "/ or "
+                "$XDG_DATA_DIRS/help/<lang>/" UDPSCOPE_HELP_NAME "/. Install it with\n\n"
+                "    cmake --install build --prefix ~/.local\n\n"
+                "which writes ~/.local/share/help/C/" UDPSCOPE_HELP_NAME "/ -- the directory "
+                "`help:" UDPSCOPE_HELP_NAME "` resolves to. If there is no `help:` viewer either, "
+                "install one as well (for example `yelp`).";
+    }
     gtk_alert_dialog_set_detail(alert, detail.c_str());
-    gtk_alert_dialog_show(alert, parent);
+    gtk_alert_dialog_show(alert, launch->parent);
     g_object_unref(alert);
-    g_error_free(error);
   }
-  // `parent` was referenced for the duration of the async call.
-  if (parent != nullptr) g_object_unref(parent);
+  if (launch->done) {
+    launch->done(ok, ok || error == nullptr ? std::string() : std::string(error->message));
+  }
+  if (launch->parent != nullptr) g_object_unref(launch->parent);
+  delete launch;
+  if (error != nullptr) g_error_free(error);
 }
 
 }  // namespace
@@ -108,6 +138,37 @@ const char* about_icon_name() {
   return adw_about_dialog_get_application_icon(ADW_ABOUT_DIALOG(g_about));
 }
 
+std::string help_installed_path() {
+  // The freedesktop Help System Specification's own search order: `$XDG_DATA_HOME` first, then every
+  // `$XDG_DATA_DIRS` entry in order. Yelp resolves `help:<id>` the same way, so this is a reading of
+  // where the document *would* be found rather than a second, private convention.
+  std::vector<std::string> roots;
+  roots.emplace_back(g_get_user_data_dir() != nullptr ? g_get_user_data_dir() : "");
+  const char* const* dirs = g_get_system_data_dirs();
+  for (int i = 0; dirs != nullptr && dirs[i] != nullptr; ++i) roots.emplace_back(dirs[i]);
+  for (const std::string& root : roots) {
+    if (root.empty()) continue;
+    const std::string base = root + "/help";
+    GError* error = nullptr;
+    GDir* dir = g_dir_open(base.c_str(), 0, &error);
+    if (dir == nullptr) {
+      if (error != nullptr) g_error_free(error);
+      continue;
+    }
+    // `<lang>` is a directory of its own (`C`, `en`, `it`, ...), so the document is looked for one
+    // level below the `help` root rather than straight under it.
+    while (const char* lang = g_dir_read_name(dir)) {
+      const std::string candidate = base + "/" + lang + "/" UDPSCOPE_HELP_NAME;
+      if (g_file_test((candidate + "/index.page").c_str(), G_FILE_TEST_IS_REGULAR)) {
+        g_dir_close(dir);
+        return candidate;
+      }
+    }
+    g_dir_close(dir);
+  }
+  return std::string();
+}
+
 HelpReport help_self_check() {
   HelpReport report;
 
@@ -141,14 +202,16 @@ HelpReport help_self_check() {
   return report;
 }
 
-void show_help(GtkWindow* parent) {
+void show_help(GtkWindow* parent, std::function<void(bool, const std::string&)> done) {
   // The freedesktop `help:` URI, handed to whatever the desktop registered for it -- Yelp on
-  // GNOME. The launch is asynchronous, so the parent is referenced across it and released in
-  // the callback; `parent` may legitimately be nullptr (the chooser runs before any window
-  // exists).
+  // GNOME. The launch is asynchronous, so both the parent and the reporter are carried across it in
+  // a heap `HelpLaunch` and released in the callback; `parent` may legitimately be nullptr (the
+  // chooser runs before any window exists).
+  auto* launch = new HelpLaunch;
+  launch->parent = parent != nullptr ? GTK_WINDOW(g_object_ref(parent)) : nullptr;
+  launch->done = std::move(done);
   GtkUriLauncher* launcher = gtk_uri_launcher_new("help:" UDPSCOPE_HELP_NAME);
-  gtk_uri_launcher_launch(launcher, parent, nullptr, on_help_launched,
-                          parent != nullptr ? g_object_ref(parent) : nullptr);
+  gtk_uri_launcher_launch(launcher, parent, nullptr, on_help_launched, launch);
   g_object_unref(launcher);
 }
 

src/help_window.hpp

@@ -4,6 +4,7 @@
 #include <gtk/gtk.h>
 
 #include <cstddef>
+#include <functional>
 #include <string>
 
 namespace udpscope {
@@ -23,7 +24,20 @@ const char* about_icon_name();
 /// window of our own. `parent` is the window the launch is attributed to (and the one an
 /// error is reported on); the viewer is a separate process, so nothing here can be closed
 /// with `close_help_windows()`.
-void show_help(GtkWindow* parent);
+///
+/// `done`, when the caller gives one, is called with the *launch*'s outcome: whether the
+/// `help:` URI was handed to a viewer, and the error text when it was not. It says nothing
+/// about the viewer itself — that process may fail for its own reasons and this side cannot
+/// see them — so it is the self-check's reading of the path and not a promise that a window
+/// appeared. The failure alert is shown either way; the callback is an extra, not instead.
+void show_help(GtkWindow* parent, std::function<void(bool ok, const std::string& error)> done = {});
+
+/// Where `help:<id>` resolves to on this system: the first of `$XDG_DATA_HOME/help/<lang>/<id>/`
+/// and `$XDG_DATA_DIRS/help/<lang>/<id>/` that holds an `index.page`, or an empty string when no
+/// such directory does. This is the specification's own resolution, and the distinction a launch
+/// failure turns on: a missing *document* (install it) and a missing *handler* (install a viewer)
+/// are different problems with different fixes, and only the file system can tell them apart.
+std::string help_installed_path();
 
 /// What UDPSCOPE_PROBE_HELP_MS reports about the manual *in the tree*. `topics` is the
 /// number of `<id>.page` files other than `index.page`, and `index` says whether

src/settings.cpp

@@ -84,9 +84,10 @@ bool save_settings(const Settings& settings) {
   out << "event_cache_max = " << settings.event_cache_max << "\n";
   out << "relative_time = " << (settings.relative_time ? "true" : "false") << "\n";
   out << "theme = \"" << settings.theme << "\"\n";
-  // The two help keys are the *app's* memory rather than the dialog's: the contextual-help toggle in
-  // the Help menu writes the first, and the first-run tour writes the second. `read_rows()` in the
-  // preferences starts from `load_settings()`, so a dialog save carries them through untouched.
+  // The two help keys are the *app's* memory rather than the dialog's: the contextual-help rows --
+  // the Help menu's and the source chooser's own -- write the first, and the first-run tour writes the
+  // second. `read_rows()` in the preferences starts from `load_settings()`, so a dialog save carries
+  // them through untouched.
   out << "contextual_help = " << (settings.contextual_help ? "true" : "false") << "\n";
   out << "tour_seen = " << (settings.tour_seen ? "true" : "false") << "\n";
   out.flush();

src/settings.hpp

@@ -33,9 +33,11 @@ struct Settings {
   /// "auto", "light" or "dark": what the interface should look like. Kept as the three names libadwaita
   /// uses, so the file says what the setting is rather than what an enum happens to be numbered.
   std::string theme = "auto";
-  /// The contextual-help layer: a small "?" beside each surface it can explain. On by default -- an
-  /// affordance nobody can find is not help -- and off is a decision that survives a restart.
-  bool contextual_help = true;
+  /// The contextual-help layer: a small "?" beside each surface it can explain. **Off by default** --
+  /// a first run shows the interface as a user expects it and the layer is asked for, from the Help
+  /// menu or from the chooser's own help menu, by whoever wants it; on is then a decision that
+  /// survives a restart.
+  bool contextual_help = false;
   /// Whether the guided tour has been offered. A first run has no file carrying this key, so the tour
   /// starts itself once; the flag is written when it *starts*, not when it finishes, because a user who
   /// skips it has still seen it and a second launch with the same tour would be a nuisance.

src/source_dialog.cpp

@@ -5,8 +5,13 @@
 
 #include "waveform.hpp"
 
+#include "help_window.hpp"
 #include "layout_store.hpp"
 #include "settings.hpp"
+// The app's shared chrome -- `ui_impl::menu_button()`/`menu_toggle()` and `install_css()` -- so the
+// chooser's help menu is the *same* menu the window's Help view is, not a second one that merely
+// looks like it. Heavy header, but a row shape copied here would be a row shape that drifts.
+#include "ui_app.hpp"
 #include "ui_prefs.hpp"
 
 #include <adwaita.h>
@@ -127,6 +132,15 @@ struct Chooser {
   /// The preferences, for the button below. Same reasoning as `form` above: a member of the chooser
   /// rather than a heap struct, so nothing can outlive the stack frame that owns it.
   ui_impl::PrefsForm prefs;
+  /// The help menu: the `.ui`'s own `GtkMenuButton` and the three rows built onto it. The rows are
+  /// code for the same reason every other row here is -- each carries a handler, and the toggle
+  /// carries the value the settings file holds -- while the button that opens them is the file's, so
+  /// a `.ui` that lost it is caught by the null check below rather than by an empty popover.
+  GtkWidget* help_button = nullptr;
+  GtkWidget* help_docs = nullptr;
+  GtkWidget* help_tour = nullptr;
+  GtkWidget* help_toggle = nullptr;
+  GtkWidget* help_popover = nullptr;
 
 };
 
@@ -596,14 +610,90 @@ void open_chooser_preferences(Chooser& c) {
   });
 }
 
+/// The chooser's help menu: the same three affordances the window's Help view carries, because a
+/// user who has not started yet is exactly the one who does not know how to start. The rows are
+/// `ui_impl::menu_button()`/`menu_toggle()` -- the app's own menu-row shape, so the two menus read
+/// as one program -- and the popover carries the same `.udpscope-menu` class, which is what trims
+/// the rows; `install_css()` therefore runs before this, in `choose_source()`.
+///
+/// No row shows an accelerator. The window's Help rows show "F1"/"Ctrl+T" because the window handles
+/// those keys; this dialog binds none of them, and a shortcut printed beside an action that does not
+/// answer to it is the "documented and does nothing" failure the shortcut tables are checked for.
+void build_chooser_help(Chooser& c) {
+  c.help_popover = gtk_popover_new();
+  gtk_widget_add_css_class(c.help_popover, "udpscope-menu");
+  GtkWidget* box = gtk_box_new(GTK_ORIENTATION_VERTICAL, 0);
+  gtk_widget_set_margin_top(box, 6);
+  gtk_widget_set_margin_bottom(box, 6);
+  gtk_widget_set_margin_start(box, 6);
+  gtk_widget_set_margin_end(box, 6);
+
+  c.help_docs = ui_impl::menu_button("Documentation", nullptr);
+  gtk_widget_set_tooltip_text(c.help_docs,
+                              "the udpscope manual, opened in the desktop help viewer");
+  g_signal_connect(c.help_docs, "clicked", G_CALLBACK(+[](GtkButton*, gpointer user) {
+                     Chooser& ch = *static_cast<Chooser*>(user);
+                     gtk_popover_popdown(GTK_POPOVER(ch.help_popover));
+                     // No window of the app exists yet: the manual is a separate process reached
+                     // through the `help:` URI, so this needs no more of the app than the chooser
+                     // itself. The parent may be null, and this dialog is the right attribution.
+                     show_help(GTK_WINDOW(ch.window));
+                   }),
+                   &c);
+  gtk_box_append(GTK_BOX(box), c.help_docs);
+
+  c.help_tour = ui_impl::menu_button("Guided tour", nullptr);
+  gtk_widget_set_tooltip_text(c.help_tour,
+                              "walk over the plot, the side panel, the trigger, the signals and "
+                              "the status line, once the window is up");
+  g_signal_connect(c.help_tour, "clicked", G_CALLBACK(+[](GtkButton*, gpointer user) {
+                     Chooser& ch = *static_cast<Chooser*>(user);
+                     gtk_popover_popdown(GTK_POPOVER(ch.help_popover));
+                     // The tour lives on the window the app builds, which does not exist yet, so the
+                     // request rides on the `Config` this call was handed and the app starts it once
+                     // the window is up -- see `Config::tour_pending`.
+                     ch.cfg->tour_pending = true;
+                     std::fprintf(stderr, "[sources] chooser help: tour requested\n");
+                     std::fflush(stderr);
+                   }),
+                   &c);
+  gtk_box_append(GTK_BOX(box), c.help_tour);
+
+  // The check *is* the setting, exactly as in the window's menu: the row is stated before the handler
+  // is connected, so a row that opens checked does not write the file while the dialog is still being
+  // built. The chooser cannot re-sync anything (there is no "?" layer here), so the handler only has
+  // to leave the setting where the app will read it.
+  c.help_toggle = ui_impl::menu_toggle("Enable contextual help", nullptr,
+                                       load_settings().contextual_help);
+  gtk_widget_set_tooltip_text(c.help_toggle,
+                              "a small \u201c?\u201d beside each surface of the main window, saying "
+                              "what that surface is for");
+  g_signal_connect(c.help_toggle, "toggled", G_CALLBACK(+[](GtkToggleButton* button, gpointer) {
+                     Settings s = load_settings();
+                     s.contextual_help = gtk_toggle_button_get_active(button) != FALSE;
+                     // Written in full, the way the window's toggle writes it: the keys this row does
+                     // not own are carried through from the file rather than dropped.
+                     if (!save_settings(s)) {
+                       std::fprintf(stderr, "[sources] chooser help: could not write %s\n",
+                                    settings_path().c_str());
+                       std::fflush(stderr);
+                     }
+                   }),
+                   &c);
+  gtk_box_append(GTK_BOX(box), c.help_toggle);
+
+  gtk_popover_set_child(GTK_POPOVER(c.help_popover), box);
+  gtk_menu_button_set_popover(GTK_MENU_BUTTON(c.help_button), c.help_popover);
+}
+
 /// `UDPSCOPE_PROBE_PICK_MS`: activate the first row, the way a click does.
 /// `UDPSCOPE_PROBE_NEWHOST=host:port` drives the form instead of a row. The crash surface of a
 /// dialog built, filled and destroyed is as much the point as the values, the same way
 /// `UDPSCOPE_PROBE_FIELDS_MS` is in `ui.cpp`.
 /// The chooser's frame, read back from the `.ui` it was built from: the two pages by name and title, the
-/// switcher wired to the stack, and the four buttons the code resolved. `[help] ui=` does the same against
-/// its tables -- the frame is what the file holds, so the frame is what is read, while the rows a user sees
-/// are read by the probes that drive them.
+/// switcher wired to the stack, the four buttons the code resolved, and the help menu's three rows.
+/// `[help] ui=` does the same against its tables -- the frame is what the file holds, so the frame is
+/// what is read, while the rows a user sees are read by the probes that drive them.
 void report_chooser_ui(const Chooser& c) {
   std::fprintf(stderr, "[sources] chooser ui:");
   for (GtkWidget* w = gtk_widget_get_first_child(c.page_stack); w != nullptr;
@@ -617,14 +707,21 @@ void report_chooser_ui(const Chooser& c) {
                  adw_view_stack_page_get_icon_name(page) != nullptr ? "yes" : "NO");
   }
   std::fprintf(stderr,
-               " visible='%s' switcher_wired=%d buttons=[prefs=%d new_host=%d open=%d cancel=%d]\n",
+               " visible='%s' switcher_wired=%d buttons=[prefs=%d new_host=%d open=%d cancel=%d] "
+               "help=[button=%d docs=%d tour=%d toggle=%d on=%d]\n",
                adw_view_stack_get_visible_child_name(ADW_VIEW_STACK(c.page_stack)),
                adw_view_switcher_bar_get_stack(ADW_VIEW_SWITCHER_BAR(c.switcher)) ==
                        ADW_VIEW_STACK(c.page_stack)
                    ? 1
                    : 0,
                c.prefs_button != nullptr ? 1 : 0, c.new_host != nullptr ? 1 : 0,
-               c.waves_open != nullptr ? 1 : 0, c.cancel_button != nullptr ? 1 : 0);
+               c.waves_open != nullptr ? 1 : 0, c.cancel_button != nullptr ? 1 : 0,
+               c.help_button != nullptr ? 1 : 0, c.help_docs != nullptr ? 1 : 0,
+               c.help_tour != nullptr ? 1 : 0, c.help_toggle != nullptr ? 1 : 0,
+               c.help_toggle != nullptr &&
+                       gtk_toggle_button_get_active(GTK_TOGGLE_BUTTON(c.help_toggle))
+                   ? 1
+                   : 0);
   std::fflush(stderr);
 }
 
@@ -638,6 +735,26 @@ gboolean pick_probe(gpointer user) {
   // What the `.ui` contributed, before anything is driven: the pages, the switcher and the buttons.
   report_chooser_ui(c);
 
+  // `UDPSCOPE_PROBE_CHOOSER_TOUR=1` and `UDPSCOPE_PROBE_CHOOSER_HELP=1` drive the help menu's two
+  // stateful rows the way a click does, and then fall through to the pick below -- the point of the
+  // tour entry is that it crosses *into the run this chooser starts*, so a probe that stopped here
+  // would assert nothing. The tour is read back out of the `Config` the run will be handed, which is
+  // the carrier; the toggle is read back out of the settings file it writes, since the app is built
+  // from that file and not from the dialog.
+  if (g_getenv("UDPSCOPE_PROBE_CHOOSER_TOUR") != nullptr && c.help_tour != nullptr) {
+    g_signal_emit_by_name(c.help_tour, "clicked");
+    std::fprintf(stderr, "[sources] chooser help: tour_pending=%d\n", c.cfg->tour_pending ? 1 : 0);
+    std::fflush(stderr);
+  }
+  if (g_getenv("UDPSCOPE_PROBE_CHOOSER_HELP") != nullptr && c.help_toggle != nullptr) {
+    gtk_toggle_button_set_active(GTK_TOGGLE_BUTTON(c.help_toggle), TRUE);
+    const Settings back = load_settings();
+    std::fprintf(stderr, "[sources] chooser help: toggle=%d setting=%d file=%s\n",
+                 gtk_toggle_button_get_active(GTK_TOGGLE_BUTTON(c.help_toggle)) ? 1 : 0,
+                 back.contextual_help ? 1 : 0, settings_path().c_str());
+    std::fflush(stderr);
+  }
+
   // `UDPSCOPE_PROBE_CHOOSER_PREFS=1`: the preferences opened from *here* rather than from the app's
   // menu -- the entry point that exists because this dialog runs before `App`. It is driven through
   // the same fill-and-apply the app's probe uses, and reports what the run about to start will get,
@@ -906,15 +1023,24 @@ bool choose_source(Config& cfg) {
   c.new_host = GTK_WIDGET(gtk_builder_get_object(c.ui, "new_host_button"));
   c.waves_open = GTK_WIDGET(gtk_builder_get_object(c.ui, "waves_open"));
   c.cancel_button = GTK_WIDGET(gtk_builder_get_object(c.ui, "cancel_button"));
+  c.help_button = GTK_WIDGET(gtk_builder_get_object(c.ui, "help_menu_button"));
   if (c.window == nullptr || c.page_stack == nullptr || c.switcher == nullptr || c.list == nullptr ||
       c.wave_list == nullptr || c.prefs_button == nullptr || c.new_host == nullptr ||
-      c.waves_open == nullptr || c.cancel_button == nullptr) {
+      c.waves_open == nullptr || c.cancel_button == nullptr || c.help_button == nullptr) {
     std::fprintf(stderr, "[sources] chooser ui: source-chooser.ui is missing an id this code reads\n");
     std::fflush(stderr);
     return false;
   }
   adw_view_switcher_bar_set_stack(ADW_VIEW_SWITCHER_BAR(c.switcher), ADW_VIEW_STACK(c.page_stack));
 
+  // The help menu's rows are the window's own `menu_button()`/`menu_toggle()`, so its popover wants
+  // the same stylesheet the overflow menu is drawn with (`.udpscope-menu`, which trims a row to a
+  // menu row rather than Adwaita's 34 px button). The app installs it in `on_activate()`, which is
+  // *after* this dialog, so it has to be installed here first; `install_css()` is idempotent, so
+  // the later call is the no-op it reads as.
+  ui_impl::install_css();
+  build_chooser_help(c);
+
   g_signal_connect(c.list, "row-activated", G_CALLBACK(on_row_activated), &c);
   g_signal_connect(c.wave_list, "row-activated", G_CALLBACK(on_wave_activated), &c);
   g_signal_connect(c.waves_open, "clicked", G_CALLBACK(on_wave_open_clicked), &c);

src/ui.cpp

@@ -5142,8 +5142,15 @@ void on_activate(GtkApplication* application, gpointer user) {
   // A first run is the run whose settings file does not say the tour has been offered -- see
   // `tour_autostart()`. Delayed rather than fired on the first tick: the window has to be up and
   // laid out for the tour to have anything to point at, and a tour that opened on the frame the
-  // window appeared would be a spotlight on a widget with no allocation yet.
-  if (!app->settings.tour_seen) g_timeout_add(1500, tour_autostart, app);
+  // window appeared would be a spotlight on a widget with no allocation yet. The source chooser's
+  // own "Guided tour" entry arrives as `Config::tour_pending` (the request has to outlive the dialog
+  // that made it -- the tour is drawn on *this* window) and gets the same delay for the same reason,
+  // through its own callback so the two are told apart in the readings.
+  if (app->model->config().tour_pending) {
+    g_timeout_add(1500, tour_start_requested, app);
+  } else if (!app->settings.tour_seen) {
+    g_timeout_add(1500, tour_autostart, app);
+  }
 
   // Bubble phase on purpose: a focused GtkEditable or GtkButton wins its own keys, so typing
   // 'm' into the window entry does not toggle the measurements pane and Space does not

src/ui/source-chooser.ui

@@ -33,6 +33,17 @@
                 <property name="tooltip-text" translatable="yes">the event cache, relative time and the interface's theme — the same dialog as the main window's menu, and the only place relative time can still change this run</property>
               </object>
             </child>
+            <!-- The help menu: the same three affordances the window's Help view carries, because a
+                 user who has not started yet is exactly the one who does not know how to start. Only
+                 the button is here — its rows carry a handler and a setting, so they are code, the
+                 same division every other row in this file follows. Beside `_Preferences`, because
+                 both act on the *program* rather than on a source. -->
+            <child type="start">
+              <object class="GtkMenuButton" id="help_menu_button">
+                <property name="icon-name">help-about-symbolic</property>
+                <property name="tooltip-text" translatable="yes">the manual, a guided tour after start-up, and the contextual help</property>
+              </object>
+            </child>
             <child type="end">
               <object class="GtkButton" id="cancel_button">
                 <property name="label" translatable="yes">_Cancel</property>

src/ui_app.hpp

@@ -255,6 +255,18 @@ struct App {
   /// The first-run auto-start: set by the timer that fires it, and read by the probe and the dump.
   /// The decision itself is `settings.tour_seen`, which is the whole of "this has happened before".
   bool tour_auto_started = false;
+  /// The chooser's own "Guided tour" request (`Config::tour_pending`), recorded when its timer runs.
+  /// A separate flag from the auto-start because it is a *different* thing: the user asked for the
+  /// tour before the window existed, rather than never having seen it.
+  bool tour_requested = false;
+  /// The self-check's reading of the manual's launch (`UDPSCOPE_PROBE_HELP_MS`). The launch is
+  /// asynchronous and the viewer is another process, so the outcome arrives in a callback and the
+  /// probe prints it from a timer afterwards; `attempted` is set at the call, because a launch that
+  /// never called back is itself a reading.
+  bool dbg_help_launch_attempted = false;
+  bool dbg_help_launch_done = false;
+  bool dbg_help_launch_ok = false;
+  std::string dbg_help_launch_error;
   /// The help layer's own dump readings, captured on the tick while the window is alive (nothing
   /// here may be read in the dump -- see `docs/claude/verification.md`).
   std::string dbg_context_help;
@@ -1743,6 +1755,10 @@ int tour_step_count(const App& app);
 int tour_step_index(const App& app);
 /// The first-run auto-start's callback, scheduled only when `settings.tour_seen` is false.
 gboolean tour_autostart(gpointer user);
+/// The chooser's "Guided tour" request (`Config::tour_pending`): the same delayed start, but it
+/// sets `tour_requested` rather than `tour_auto_started`, so the probe and the dump can tell the two
+/// apart. Scheduled only when the config carries the request.
+gboolean tour_start_requested(gpointer user);
 /// Captures the layer's own readings and the bounds of the surfaces the help's figures label, while
 /// the window is alive -- the dump runs after it is destroyed and may not ask GTK anything.
 void capture_help_state(App& app);

src/ui_probe.cpp

@@ -4444,16 +4444,33 @@ UiShortcuts ui_shortcut_rows(const char* path) {
   return out;
 }
 
+/// Prints the manual launch's outcome, which arrives in a callback (the launch is asynchronous and
+/// the viewer is another process) -- so the line is written from a timer a moment later rather than
+/// from `help_probe`. `done=0` is a launch that never called back, which is a reading of its own.
+gboolean help_launch_report(gpointer user) {
+  App* a = static_cast<App*>(user);
+  const std::string installed = help_installed_path();
+  std::fprintf(stderr, "[help] launch attempted=%d done=%d ok=%d error='%s' installed=%s\n",
+               a->dbg_help_launch_attempted ? 1 : 0, a->dbg_help_launch_done ? 1 : 0,
+               a->dbg_help_launch_ok ? 1 : 0, a->dbg_help_launch_error.c_str(),
+               installed.empty() ? "(not found)" : installed.c_str());
+  std::fflush(stderr);
+  return G_SOURCE_REMOVE;
+}
+
 gboolean help_probe(gpointer user) {
   App* a = static_cast<App*>(user);
   const HelpReport report = help_self_check();
   const std::string session =
       layout_path(a->model->config().server, a->model->config().port);
 
-  // The manual is not opened here: it lives in another process (Yelp, through the `help:` URI)
-  // and neither it nor this box can draw a window for it, so there is nothing to open, read
-  // back or close. `help_self_check()` above is the assertion -- the set is on disk where the
-  // build says it is. The two AdwDialogs below are still built, read and closed for real.
+  // The manual is *launched* here and read no further: it opens in another process (Yelp, through
+  // the `help:` URI) and neither it nor this box can draw a window for it, so there is nothing to
+  // read back or close. `help_self_check()` above is the assertion on the *set* being on disk where
+  // the build says it is; the launch is the assertion on the *path*, and its outcome is reported by
+  // `help_launch_report()` once the launch's callback has run. The failure alert the callback shows
+  // is deliberately left up -- it is what a user sees, and the probe must not report a failure as a
+  // silence. The two AdwDialogs below are still built, read and closed for real.
   show_about(GTK_WINDOW(a->window), session);
   show_shortcuts(GTK_WINDOW(a->window));
   // Read while it is open: the icon is the point of the dialog carrying one, and
@@ -4461,6 +4478,18 @@ gboolean help_probe(gpointer user) {
   const std::string about_icon = about_icon_name();
   close_help_windows();
 
+  // The manual's path: on a successful launch no window is left behind, so this cannot be observed
+  // any other way; `show_help()`'s reporter is the only hook that runs on that path.
+  a->dbg_help_launch_attempted = true;
+  a->dbg_help_launch_done = false;
+  a->dbg_help_launch_ok = false;
+  a->dbg_help_launch_error.clear();
+  show_help(GTK_WINDOW(a->window), [a](bool ok, const std::string& error) {
+    a->dbg_help_launch_done = true;
+    a->dbg_help_launch_ok = ok;
+    a->dbg_help_launch_error = error;
+  });
+
   int accel_count = 0;
   int gesture_count = 0;
   (void)app_accels(&accel_count);
@@ -4479,6 +4508,10 @@ gboolean help_probe(gpointer user) {
                build_info::kCommit, build_info::kTimestamp, config_dir().c_str(),
                about_icon.c_str());
   std::fflush(stderr);
+  // The launch's outcome needs its callback to have run; a moment is enough for a local
+  // `g_app_info_launch_default_for_uri()`, and `done=0` in the line is how a launch that never
+  // called back reads.
+  g_timeout_add(600, help_launch_report, a);
   return G_SOURCE_REMOVE;
 }
 

src/ui_tour.cpp

@@ -342,6 +342,16 @@ gboolean tour_autostart(gpointer user) {
   return G_SOURCE_REMOVE;
 }
 
+gboolean tour_start_requested(gpointer user) {
+  App* app = static_cast<App*>(user);
+  if (app->window == nullptr || app->tour_overlay == nullptr) return G_SOURCE_REMOVE;
+  // Not `tour_auto_started`: the chooser's entry is the user asking for the tour before the window
+  // existed, and the reading has to say which of the two started it.
+  app->tour_requested = true;
+  start_tour(*app);
+  return G_SOURCE_REMOVE;
+}
+
 // --- the dump's readings ----------------------------------------------------
 
 namespace {
@@ -381,10 +391,11 @@ void capture_help_state(App& app) {
   char layer[512];
   std::snprintf(layer, sizeof(layer),
                 "contextual=%s hints=%d ids={%s} icon=dialog-question-symbolic(%s); tour=%s steps=%d "
-                "step=%d auto=%d",
+                "step=%d auto=%d requested=%d",
                 app.settings.contextual_help ? "on" : "off", hints, ids.empty() ? "" : ids.c_str(),
                 icon_ok ? "ok" : "MISSING", app.tour_running ? "running" : "idle",
-                tour_step_count(app), tour_step_index(app), app.tour_auto_started ? 1 : 0);
+                tour_step_count(app), tour_step_index(app), app.tour_auto_started ? 1 : 0,
+                app.tour_requested ? 1 : 0);
   app.dbg_context_help = layer;
   app.dbg_tour_steps = tour_step_count(app);
   app.dbg_tour_step = tour_step_index(app);

src/ui_widgets.cpp

@@ -37,6 +37,13 @@ GtkBuilder* ui_load(App& app, const char* resource) {
 /// the whole side panel. Scoped to `.udpscope-compact` so it cannot reach any other
 /// button in the window.
 void install_css() {
+  // Idempotent, because it is no longer installed from one place: the source chooser runs before the
+  // application (it draws a menu built from the same `menu_button()` rows) and has to have the
+  // stylesheet before it shows them, while `on_activate()` still installs it for every run. A second
+  // provider would be a second copy of the same rules on the display.
+  static bool installed = false;
+  if (installed) return;
+  installed = true;
   static const char kCss[] =
       "row.udpscope-compact { min-height: 0; padding: 1px 0; }\n"
       // A popover menu row: Adwaita gives a button a 34 px minimum height and 8 px of padding,