improve dropdown presentation ui

static/portal-table.css

@@ -343,7 +343,7 @@
     flex: 1;
     grid-template:
       'null-control value-control' max-content
-      'helpers helpers' auto / max-content auto;
+      'helpers helpers' 1fr / max-content 1fr;
 
     &:has(:focus) {
       border-left-color: #07f;

svelte/src/datum-editor.svelte

@@ -11,7 +11,10 @@ example within the `<TableViewer />` or `<ExpressionEditor />`.
     editor_state_from_datum,
     type EditorState,
   } from "./editor-state.svelte";
-  import { type Presentation } from "./presentation.svelte";
+  import {
+    type DropdownOption,
+    type Presentation,
+  } from "./presentation.svelte";
 
   const BLUR_DEBOUNCE_MS = 100;
 
@@ -67,6 +70,8 @@ example within the `<TableViewer />` or `<ExpressionEditor />`.
     }
   });
 
+  let filtered_dropdown_options: DropdownOption[] = $state([]);
+
   export function focus() {
     if (
       current_presentation.t === "Dropdown" ||
@@ -86,12 +91,16 @@ example within the `<TableViewer />` or `<ExpressionEditor />`.
     if (blur_timeout !== undefined) {
       clearTimeout(blur_timeout);
     }
-    blur_timeout = setTimeout(() => on_blur?.(ev), BLUR_DEBOUNCE_MS);
+    blur_timeout = setTimeout(() => {
+      on_blur?.(ev);
+      filtered_dropdown_options = [];
+    }, BLUR_DEBOUNCE_MS);
   }
 
   function handle_focus(ev: FocusEvent) {
     if (blur_timeout === undefined) {
       on_focus?.(ev);
+      update_dropdown_filter();
     } else {
       clearTimeout(blur_timeout);
     }
@@ -106,6 +115,29 @@ example within the `<TableViewer />` or `<ExpressionEditor />`.
     on_change?.(value);
   }
 
+  function handle_textinput_input(input_value: string) {
+    if (!editor_state) {
+      console.warn("text input oninput() preconditions not met");
+      return;
+    }
+    editor_state.text_value = input_value;
+    if (input_value !== "") {
+      editor_state.is_null = false;
+    }
+    handle_input();
+  }
+
+  function update_dropdown_filter() {
+    if (current_presentation.t === "Dropdown") {
+      filtered_dropdown_options = current_presentation.c.options.filter(
+        (option) =>
+          option.value
+            .toLocaleLowerCase("en")
+            .includes(editor_state?.text_value.toLocaleLowerCase("en") ?? ""),
+      );
+    }
+  }
+
   function handle_keydown(ev: KeyboardEvent) {
     if (ev.key === "Enter") {
       on_restore_focus?.();
@@ -113,6 +145,33 @@ example within the `<TableViewer />` or `<ExpressionEditor />`.
       // Cancel edit before blurring, or else the table will try to commit it.
       on_cancel_edit?.();
       on_restore_focus?.();
+    } else if (
+      current_presentation.t === "Dropdown" &&
+      filtered_dropdown_options.length > 0
+    ) {
+      const current_option_idx = filtered_dropdown_options.findIndex(
+        (option) =>
+          option.value.toLocaleLowerCase("en") ===
+          (editor_state?.text_value.toLocaleLowerCase("en") ?? ""),
+      );
+      if (ev.key === "ArrowUp" || (ev.key === "Tab" && ev.shiftKey)) {
+        // Prevent shifting focus with tab key. User can still use enter or esc.
+        ev.preventDefault();
+        handle_textinput_input(
+          filtered_dropdown_options[Math.max(current_option_idx - 1, 0)].value,
+        );
+      } else if (ev.key === "ArrowDown" || (ev.key === "Tab" && !ev.shiftKey)) {
+        // Prevent shifting focus with tab key. User can still use enter or esc.
+        ev.preventDefault();
+        handle_textinput_input(
+          filtered_dropdown_options[
+            Math.min(
+              current_option_idx + 1,
+              filtered_dropdown_options.length - 1,
+            )
+          ].value,
+        );
+      }
     }
   }
 
@@ -176,15 +235,8 @@ example within the `<TableViewer />` or `<ExpressionEditor />`.
         bind:this={text_input_element}
         value={editor_state.text_value}
         oninput={({ currentTarget }) => {
-          if (!editor_state) {
-            console.warn("text input oninput() preconditions not met");
-            return;
-          }
-          editor_state.text_value = currentTarget.value;
-          if (currentTarget.value !== "") {
-            editor_state.is_null = false;
-          }
-          handle_input();
+          handle_textinput_input(currentTarget.value);
+          update_dropdown_filter();
         }}
         class="datum-editor__text-input"
         type="text"
@@ -223,11 +275,10 @@ example within the `<TableViewer />` or `<ExpressionEditor />`.
         />
       </div>
     {/if}
-    <div class="datum-editor__helpers" tabindex="-1">
+    <div class="datum-editor__helpers">
       {#if current_presentation.t === "Dropdown"}
-        <!-- TODO: This is an awkward way to implement a keyboard-navigable listbox. -->
         <menu class="datum-editor__dropdown-options">
-          {#each current_presentation.c.options as dropdown_option}
+          {#each filtered_dropdown_options as dropdown_option}
             <!-- FIXME: validate or escape dropdown_option.color -->
             <li
               class={[
@@ -251,7 +302,10 @@ example within the `<TableViewer />` or `<ExpressionEditor />`.
                   editor_state.is_null = false;
                   text_input_element.focus();
                   handle_input();
+                  text_input_element.blur();
+                  on_restore_focus?.();
                 }}
+                tabindex="-1"
                 type="button"
               >
                 {dropdown_option.value}

svelte/src/field-details.svelte

@@ -8,6 +8,7 @@ field. This is typically rendered within a popover component, and within an HTML
 <script lang="ts">
   import {
     type Presentation,
+    RFC_3339_S,
     all_presentation_tags,
     all_text_input_modes,
   } from "./presentation.svelte";
@@ -66,7 +67,7 @@ field. This is typically rendered within a popover component, and within an HTML
       return { t: "Text", c: { input_mode: { t: "SingleLine", c: {} } } };
     }
     if (tag === "Timestamp") {
-      return { t: "Timestamp", c: {} };
+      return { t: "Timestamp", c: { format: RFC_3339_S } };
     }
     if (tag === "Uuid") {
       return { t: "Uuid", c: {} };
@@ -144,6 +145,7 @@ field. This is typically rendered within a popover component, and within an HTML
           <select
             class="field-details__dropdown-option-color"
             name="dropdown_option_colors"
+            value={option.color}
           >
             {#each COLORS as color}
               <option value={color}>{color}</option>

svelte/src/presentation.svelte.ts

@@ -62,6 +62,8 @@ const dropdown_option_schema = z.object({
   value: z.string(),
 });
 
+export type DropdownOption = z.infer<typeof dropdown_option_schema>;
+
 const presentation_dropdown_schema = z.object({
   t: z.literal("Dropdown"),
   c: z.object({