Add layout dialog helper.

README.md

@@ -135,6 +135,8 @@ web/           the review UI: React + Vite, built by build.zig and embedded
 Layouts.zig    saved tab templates: model, JSON on disk, {{substitution}}
 OpenLayoutDialog.zig  prompts for a layout's parameters
 SaveLayoutDialog.zig  turns the current tab into a saved layout
+PathEntry.zig  a directory field: completion popover plus a Browse button
+paths.zig      what a half-typed path completes to, GTK-free and tested
 Session.zig    libghostty-vt Terminal + parser, fed by the PTY
 Pty.zig        openpt/fork/exec, controlling terminal setup
 script.zig     runs a command for `$(...)` in a layout's directory
@@ -232,6 +234,46 @@ leading `~` is expanded afterwards. An unknown `{{name}}` is left as written
 rather than blanked, so a typo shows up in the pane instead of silently
 producing an empty path.
 
+### Parameter types
+
+A parameter has a **type**, picked beside its name in the layout editor. The
+type only ever changes how the value is *asked for* — every value is text and is
+substituted as text — so it is a better prompt rather than a different layout.
+
+- **Text** is a plain entry, and what every parameter was before types existed.
+- **Directory** is a path field: it completes directory names as you type, and
+  carries a **Browse…** button that opens the file chooser. Which is what most
+  layout parameters already are — a layout is usually aimed at a project.
+
+The completion is shell-shaped rather than GTK-shaped. `Tab` completes as far as
+the matches agree — `~/src/pl` to `~/src/playpen/`, and no further than the
+common prefix when several match — the arrow keys walk the list, `Enter` takes
+the highlighted one, and `Escape` puts the list away. With nothing highlighted,
+`Enter` still opens the layout, so typing a path you already know stays
+type-and-go. Only directories are offered, hidden ones only once you have typed
+the `.`, and a long list says how many it is not showing rather than looking
+like the whole answer. A value still holding `{{a parameter}}` or `$(a command)`
+is left alone: it is not a path yet, so there is nothing to complete it against.
+
+`GtkEntryCompletion` would have been the stock answer. It is deprecated as of
+GTK 4.10, and its inline completion goes to the *first* match rather than to the
+longest common prefix, which among sibling directories guesses wrong more often
+than it helps. The list is a popover that deliberately does not autohide: an
+autohiding popover takes a grab, and the grab would send the next keystroke —
+the one that narrows the list — to the popover instead of the field.
+
+In the file, a type is a string beside the parameter's name, and saying nothing
+means `string`:
+
+```json
+{ "name": "path", "description": "Project directory", "type": "directory" }
+```
+
+A type this build doesn't recognise is asked for in a text box rather than
+refusing the file — unlike a pane `kind`, which is a pane it cannot build. The
+startup list asks for its values the same way, so a directory parameter gets the
+same field there.
+
 ### Directories from a script
 
 A **directory** can also be `$(a command)`, and what the command prints becomes
@@ -293,7 +335,8 @@ one.
     {
       "name": "Project",
       "parameters": [
-        { "name": "path", "description": "Project directory", "default": "~" }
+        { "name": "path", "description": "Project directory",
+          "default": "~", "type": "directory" }
       ],
       "root": {
         "split": "horizontal",
@@ -432,7 +475,9 @@ in principle, but a terminal grid is small.
   reply inline. See [Code review](#code-review)
 - **Saved layouts**: whole tabs — panes, splits, ratios, per-pane directories
   and scripts — opened in one go, parameterised by `{{name}}`, authored by
-  arranging a tab and saving it. See [Layouts](#layouts)
+  arranging a tab and saving it. A parameter can be declared a **directory**, and
+  is then asked for with a completing path field and a file chooser. See
+  [Layouts](#layouts)
 - **A startup list**: the tabs to open at launch, each a layout with its
   parameters filled in, fillable from the tabs you have open now. See
   [Startup tabs](#startup-tabs)
@@ -1115,17 +1160,26 @@ throwaway key has to go inside the same invocation:
 Note that `shot.sh` quotes `$KEYS`, so a chord needs the quoting relaxed for
 the words to reach `wtype` as separate arguments.
 
+**Typed text is unreliable, chords and named keys are not.** `wtype` uploads its
+own keymap for the characters it needs, and GTK goes on interpreting keycodes
+with the keymap it already had until it catches up — so `wtype hello` lands as
+mangled characters or as nothing, while `-k Tab`, `-k Down` and
+`-M ctrl -k comma` land. Drive the UI with chords and named keys; check anything
+that depends on what was *typed* with `zig build test` instead.
+
 **Synthetic clicks do not work.** `swaymsg seat seat0 cursor set/press` is
 accepted and reports success, but the headless backend has no pointer device to
-emit from and the client never sees it. Anything reachable only by clicking has
+emit from and the client never sees it. Neither does the virtual-pointer
+protocol: `wlrctl pointer move/click` reports success and the client sees
+nothing. Anything reachable only by clicking has
 to be reached another way — a keyboard shortcut, or `zig build test` if the
 thing being checked is logic rather than pixels.
 
 `zig build test` runs the unit tests. They cover layout parsing, the
-parameter/`$(...)` substitution pipeline, the palette, the settings file, the
-shortcut table, the emoji table and its search, and — for the review server —
-git's own output formats, the rule for picking a base ref, and the round trip a
-review file makes through disk. Each is its own binary with its own root, since a
+parameter/`$(...)` substitution pipeline, what a half-typed directory completes
+to, the palette, the settings file, the shortcut table, the emoji table and its
+search, and — for the review server — git's own output formats, the rule for
+picking a base ref, and the round trip a review file makes through disk. Each is its own binary with its own root, since a
 test binary has exactly one, and none of those roots links GTK, so they all run
 without a display.