ui(iso): inline-editable Output name + default to speaker display name

src/TeamsISO.App/MainWindow.xaml

@@ -637,17 +637,28 @@
                             </DataGridTemplateColumn.CellTemplate>
                         </DataGridTemplateColumn>
 
-                        <!-- Col 4 — Output name (mono). The NDI source name TeamsISO
-                             will broadcast this participant as. -->
-                        <DataGridTemplateColumn Header="Output" Width="130" IsReadOnly="True">
+                        <!-- Col 4 — Output name (mono, INLINE EDITABLE). The NDI source
+                             name TeamsISO will broadcast this participant as. Defaults
+                             to the speaker's display name; type to override per-row,
+                             clear the field to revert to the default. EditableOutputName
+                             handles both directions (see ParticipantViewModel comment).
+                             UpdateSourceTrigger=LostFocus so we don't restart the NDI
+                             sender on every keystroke — only when the operator
+                             commits by tabbing away or pressing Enter. -->
+                        <DataGridTemplateColumn Header="Output" Width="130">
                             <DataGridTemplateColumn.CellTemplate>
                                 <DataTemplate>
-                                    <TextBlock Text="{Binding OutputName}"
-                                               FontFamily="{StaticResource Wd.Font.Mono}"
-                                               FontSize="12"
-                                               Foreground="{DynamicResource Wd.Text.Secondary}"
-                                               VerticalAlignment="Center"
-                                               TextTrimming="CharacterEllipsis"/>
+                                    <TextBox Text="{Binding EditableOutputName, UpdateSourceTrigger=LostFocus, Mode=TwoWay}"
+                                             FontFamily="{StaticResource Wd.Font.Mono}"
+                                             FontSize="12"
+                                             Background="Transparent"
+                                             BorderThickness="0"
+                                             Padding="0"
+                                             Foreground="{DynamicResource Wd.Text.Secondary}"
+                                             CaretBrush="{DynamicResource Wd.Text.Primary}"
+                                             VerticalAlignment="Center"
+                                             VerticalContentAlignment="Center"
+                                             ToolTip="NDI source name. Defaults to the speaker — type to override, clear to revert."/>
                                 </DataTemplate>
                             </DataGridTemplateColumn.CellTemplate>
                         </DataGridTemplateColumn>
@@ -1009,7 +1020,7 @@
                                         <TextBox Text="{Binding Settings.OutputNameTemplate, UpdateSourceTrigger=LostFocus}"
                                                  FontFamily="{StaticResource Wd.Font.Mono}"
                                                  FontSize="11"/>
-                                        <TextBlock Text="Tokens: {name}, {guid}, {machine}, {timestamp}. Default: TEAMSISO_{guid}."
+                                        <TextBlock Text="Tokens: {name}, {guid}, {machine}, {timestamp}. Default: {name} — the speaker's display name."
                                                    Style="{StaticResource Wd.Text.Body}"
                                                    FontSize="11"
                                                    Foreground="{DynamicResource Wd.Text.Tertiary}"

src/TeamsISO.App/Services/OutputNameTemplate.cs

@@ -1,16 +1,18 @@
 using System.IO;
+using System.Linq;
 using System.Text;
 
 namespace TeamsISO.App.Services;
 
 /// <summary>
 /// User-editable template for the NDI source name a participant's ISO is
-/// published as. Default <c>"TEAMSISO_{guid}"</c> matches the original
-/// hard-coded <c>DefaultOutputName</c> in <c>IsoController</c>; operators
-/// can switch to <c>"TEAMSISO_{name}"</c> for human-readable output names
-/// (recommended for downstream switchers that key on name patterns), or
+/// published as. Default <c>"{name}"</c> renders the speaker's display name
+/// directly, which is what downstream switchers want when they key on
+/// readable identifiers. Operators can override globally to
+/// <c>"TEAMSISO_{guid}"</c> for the legacy stable-id behavior, or
 /// <c>"TEAMSISO_{machine}_{name}"</c> when multiple TeamsISO machines feed
-/// the same NDI network.
+/// the same NDI network and you want the source name to carry both.
+/// Per-participant overrides take priority over whatever template is set.
 ///
 /// Tokens expanded in <see cref="Render"/>:
 ///   <c>{name}</c>      participant display name, sanitized (alphanumeric + underscore)
@@ -18,11 +20,29 @@ namespace TeamsISO.App.Services;
 ///   <c>{machine}</c>   sanitized PC hostname (Environment.MachineName)
 ///   <c>{timestamp}</c> current local time as <c>yyyyMMdd_HHmmss</c>
 ///
+/// Empty-name fallback: if the rendered result is empty/whitespace (e.g.
+/// template was <c>"{name}"</c> and the participant joined with no display
+/// name yet), <see cref="Render"/> falls back to <c>TEAMSISO_{guid}</c> so
+/// the NDI sender always has a usable, unique identifier.
+///
 /// Persisted to <c>%LOCALAPPDATA%\TeamsISO\output-name-template.txt</c>.
 /// </summary>
 public static class OutputNameTemplate
 {
-    public const string DefaultTemplate = "TEAMSISO_{guid}";
+    /// <summary>
+    /// Default template — renders just the speaker's display name. Was
+    /// <c>"TEAMSISO_{guid}"</c> in pre-v1 builds; switched 2026-05-16 so
+    /// new installs get human-readable source names out of the box.
+    /// </summary>
+    public const string DefaultTemplate = "{name}";
+
+    /// <summary>
+    /// Stable fallback used when the rendered template produces an empty
+    /// string (typically because a participant has no display name yet).
+    /// Mirrors the engine's legacy DefaultOutputName so the NDI sender is
+    /// always uniquely identifiable.
+    /// </summary>
+    private const string EmptyNameFallback = "TEAMSISO_{guid}";
 
     private static string TemplatePath =>
         Path.Combine(
@@ -87,7 +107,30 @@ public static class OutputNameTemplate
 
         // Final sanitize on the rendered result — protects against a template
         // that includes literal characters NDI doesn't accept.
-        return SanitizeForNdi(result);
+        var sanitized = SanitizeForNdi(result);
+
+        // Empty-name fallback. The default template "{name}" can render to
+        // an unusable result for participants whose DisplayName hasn't been
+        // populated yet (Teams sometimes delivers the displayName a tick
+        // after the participant join event). Two failure modes to catch:
+        //
+        //   • DisplayName == "" → "{name}" expands to "" → sanitized "".
+        //   • DisplayName == "   " → "{name}" expands to "___" because the
+        //     sanitizer converts whitespace to underscores.
+        //
+        // Neither is a meaningful NDI source identifier, so we substitute
+        // TEAMSISO_{guid}. The Any(char.IsLetterOrDigit) check covers both
+        // cases — anything without at least one alphanumeric is unusable.
+        // We apply this AFTER token expansion (not on the raw input) so a
+        // template like "PFX_{name}" with empty displayName still works:
+        // it renders to "PFX_" which contains alphanumerics and is left
+        // alone.
+        if (string.IsNullOrWhiteSpace(sanitized) || !sanitized.Any(char.IsLetterOrDigit))
+        {
+            sanitized = SanitizeForNdi(EmptyNameFallback.Replace("{guid}", guid));
+        }
+
+        return sanitized;
     }
 
     private static string SanitizeForNdi(string s)

src/TeamsISO.App/ViewModels/GlobalSettingsViewModel.cs

@@ -486,10 +486,13 @@ public sealed class GlobalSettingsViewModel : ObservableObject
 
     /// <summary>
     /// Output-name template applied when the operator enables an ISO without
-    /// a per-participant CustomName. Default <c>"TEAMSISO_{guid}"</c> matches
-    /// the engine's hard-coded behavior; switch to <c>"TEAMSISO_{name}"</c>
-    /// for human-readable NDI source names. See <see cref="OutputNameTemplate"/>
-    /// for the supported tokens.
+    /// a per-participant CustomName. Default <c>"{name}"</c> renders the
+    /// speaker's display name directly (changed from the legacy
+    /// <c>"TEAMSISO_{guid}"</c> in 0.9.0-rc19, since downstream switchers
+    /// almost always want human-readable identifiers). Switch back to a
+    /// guid-based template if you need stable IDs that survive participant
+    /// name changes. See <see cref="OutputNameTemplate"/> for the supported
+    /// tokens.
     /// </summary>
     public string OutputNameTemplate
     {

src/TeamsISO.App/ViewModels/ParticipantViewModel.cs

@@ -422,15 +422,20 @@ public sealed class ParticipantViewModel : ObservableObject
         set
         {
             if (SetField(ref _customName, value))
+            {
                 OnPropertyChanged(nameof(OutputName));
+                OnPropertyChanged(nameof(EditableOutputName));
+            }
         }
     }
 
     /// <summary>
     /// The NDI source name TeamsISO will broadcast this participant as. Prefers
     /// the operator's <see cref="CustomName"/> when set; otherwise renders the
-    /// engine's default template (typically <c>TEAMSISO_{guid}</c>). Bound by
-    /// the v2 participants table's mono "output name" column.
+    /// active template (default <c>"{name}"</c>, falling back to
+    /// <c>TEAMSISO_{guid}</c> when the participant has no display name yet).
+    /// Bound by the v2 participants table's mono "output name" column for
+    /// read-only display contexts.
     /// </summary>
     public string OutputName =>
         string.IsNullOrWhiteSpace(_customName)
@@ -440,6 +445,39 @@ public sealed class ParticipantViewModel : ObservableObject
                 _participant.DisplayName)
             : _customName;
 
+    /// <summary>
+    /// Two-way binding endpoint for the inline-editable Output column. Reads
+    /// resolve to whatever name will actually be broadcast (<see cref="OutputName"/>);
+    /// writes set <see cref="CustomName"/> with a couple of UX niceties:
+    ///
+    ///   • Clearing the field (empty / whitespace) reverts to the template
+    ///     default — the user doesn't have to remember the template syntax to
+    ///     "undo" a customization.
+    ///
+    ///   • Typing a value that exactly matches the resolved default is treated
+    ///     as a no-op (CustomName stays empty), so the participant continues
+    ///     to follow the template when their display name changes upstream.
+    ///     Without this, typing the auto-suggested value would silently
+    ///     "pin" the participant to a stale name forever.
+    /// </summary>
+    public string EditableOutputName
+    {
+        get => OutputName;
+        set
+        {
+            var trimmed = (value ?? string.Empty).Trim();
+            var defaultRendered = Services.OutputNameTemplate.Render(
+                Services.OutputNameTemplate.Get(),
+                _participant.Id,
+                _participant.DisplayName);
+
+            CustomName = string.IsNullOrWhiteSpace(trimmed) ||
+                         string.Equals(trimmed, defaultRendered, StringComparison.Ordinal)
+                ? string.Empty
+                : trimmed;
+        }
+    }
+
     public AsyncRelayCommand ToggleIsoCommand { get; }
 
     /// <summary>Copy the participant's NDI source FullName to the clipboard. Useful for pasting into Studio Monitor.</summary>
@@ -464,6 +502,12 @@ public sealed class ParticipantViewModel : ObservableObject
         OnPropertyChanged(nameof(SourceMachine));
         OnPropertyChanged(nameof(SourceFullName));
         OnPropertyChanged(nameof(IsOnline));
+        // OutputName/EditableOutputName both derive from _participant.DisplayName
+        // when no per-participant CustomName is set — re-notify so the Output
+        // column tracks upstream Teams name changes for participants who
+        // haven't been manually renamed.
+        OnPropertyChanged(nameof(OutputName));
+        OnPropertyChanged(nameof(EditableOutputName));
     }
 
     private async Task ToggleIsoAsync()
@@ -479,10 +523,11 @@ public sealed class ParticipantViewModel : ObservableObject
             else
             {
                 // Resolve the output name: explicit per-participant CustomName
-                // wins; otherwise expand the operator's template (defaults to
-                // "TEAMSISO_{guid}" which matches the engine's old hard-coded
-                // behavior). Passing the rendered name to EnableIsoAsync as
-                // customName overrides the engine's DefaultOutputName path.
+                // wins; otherwise expand the operator's template (default is
+                // "{name}" since 0.9.0-rc19, with an empty-name fallback to
+                // TEAMSISO_{guid} inside Render). Passing the rendered name
+                // to EnableIsoAsync as customName overrides the engine's
+                // DefaultOutputName path.
                 var resolvedName = string.IsNullOrWhiteSpace(_customName)
                     ? Services.OutputNameTemplate.Render(
                         Services.OutputNameTemplate.Get(),

src/tests/TeamsISO.App.Tests/Services/OutputNameTemplateTests.cs

@@ -15,10 +15,34 @@ public class OutputNameTemplateTests
     private static readonly Guid TestId = new("11223344-5566-7788-99aa-bbccddeeff00");
 
     [Fact]
-    public void Render_DefaultTemplate_ProducesGuidPrefix()
+    public void Render_DefaultTemplate_RendersSpeakerDisplayName()
     {
         var name = OutputNameTemplate.Render(OutputNameTemplate.DefaultTemplate, TestId, "Jane");
-        // Default is "TEAMSISO_{guid}" → first 8 hex of TestId, uppercase.
+        // Default is "{name}" since 0.9.0-rc19 — produces the speaker name
+        // directly so downstream switchers see human-readable identifiers.
+        // Previously was "TEAMSISO_{guid}"; see DefaultTemplate's xmldoc.
+        name.Should().Be("Jane");
+    }
+
+    [Fact]
+    public void Render_DefaultTemplate_EmptyName_FallsBackToGuidPrefix()
+    {
+        // The "{name}" default would render to an empty string for a
+        // participant with no display name yet (Teams sometimes delivers
+        // DisplayName a tick after the join event). The empty-name
+        // fallback substitutes TEAMSISO_{guid} so the NDI sender is
+        // always uniquely identifiable. Without this, the engine would
+        // throw on an empty sender name.
+        var name = OutputNameTemplate.Render(OutputNameTemplate.DefaultTemplate, TestId, "");
+        name.Should().Be("TEAMSISO_11223344");
+    }
+
+    [Fact]
+    public void Render_DefaultTemplate_WhitespaceName_FallsBackToGuidPrefix()
+    {
+        // Mirror of the empty-name case — whitespace-only display names
+        // sanitize down to empty and should trigger the same fallback.
+        var name = OutputNameTemplate.Render(OutputNameTemplate.DefaultTemplate, TestId, "   ");
         name.Should().Be("TEAMSISO_11223344");
     }