feat(cms): compose Session hero image into the upload form (8.F)

Session upload now carries a deferred hero-image input; the submit handler
creates the release then POSTs the held hero to the existing resource-addressed
endpoint. Hero is optional with a non-blocking warn-if-missing gate. The
per-row hero upload in CmsSessionBrowser remains the replace/correct path.

DeepDrftManager/Components/Pages/Tracks/AlbumHeaderFields.razor

@@ -66,6 +66,8 @@
 
     <MediumFields @bind-Medium="MediumBinding"
                   @bind-ReleaseType="ReleaseTypeBinding"
+                  HeroImageFile="HeroImageFile"
+                  HeroImageFileChanged="HeroImageFileChanged"
                   Disabled="Disabled" />
 </MudPaper>
 
@@ -85,6 +87,11 @@
     [Parameter] public IBrowserFile? SelectedImageFile { get; set; }
     [Parameter] public EventCallback<IBrowserFile?> SelectedImageFileChanged { get; set; }
 
+    // Session-only — the held hero-image file, threaded through MediumFields to SessionFields.
+    // Ignored for Cut/Mix media. The parent (BatchUpload) owns it and uploads it after create.
+    [Parameter] public IBrowserFile? HeroImageFile { get; set; }
+    [Parameter] public EventCallback<IBrowserFile?> HeroImageFileChanged { get; set; }
+
     // BatchEdit only: when set (and no new file picked), preview the release's current cover.
     // The parent nulls this to drop the preview when the admin clears the existing cover.
     [Parameter] public string? ExistingImagePath { get; set; }

DeepDrftManager/Components/Pages/Tracks/BatchUpload.razor

@@ -26,6 +26,7 @@
                        Medium="_medium"
                        MediumChanged="OnMediumChanged"
                        @bind-SelectedImageFile="_selectedImageFile"
+                       @bind-HeroImageFile="_heroImageFile"
                        Disabled="_uploading" />
 
     @if (_medium == ReleaseMedium.Cut)
@@ -108,6 +109,12 @@
     private IBrowserFile? _selectedImageFile;
     private string? _imagePath;
 
+    // Session-only: the hero image is resource-addressed and cannot be uploaded until the release
+    // exists, so it is held here and POSTed to api/release/{id}/session/hero-image after create.
+    private IBrowserFile? _heroImageFile;
+    // Set true once the admin has acknowledged the missing-hero warning, so a second submit proceeds.
+    private bool _heroWarningAcknowledged;
+
     private string _albumName = string.Empty;
     private string _artist = string.Empty;
     private string _genre = string.Empty;
@@ -244,6 +251,18 @@
             return;
         }
 
+        // A Session's hero is its primary visual identity on the public detail page. It is optional —
+        // a Session can be authored without one and set later from the Sessions browser — but a missing
+        // hero is usually an oversight, so warn (do not block). The first submit without a hero shows the
+        // warning and primes acknowledgment; a second submit proceeds.
+        if (_medium == ReleaseMedium.Session && _heroImageFile is null && !_heroWarningAcknowledged)
+        {
+            _heroWarningAcknowledged = true;
+            _errorMessage = "No hero image selected. A Session usually needs one — you can add it now, "
+                + "or submit again to create the Session without it (set the hero later from the Sessions browser).";
+            return;
+        }
+
         // For single-track media (Session/Mix) the track name is derived from the Release Name —
         // no separate Track Name input is shown. Sync here so the stored name always matches.
         if (MediumRules.CardinalityOf(_medium).IsSingleTrack && _tracks.Count > 0)
@@ -336,6 +355,34 @@
                             }
                         }
 
+                        // Session hero image is resource-addressed, so it is uploaded here — after the
+                        // release exists and we have its id — within the same submit gesture. Non-blocking:
+                        // the Session is persisted; a failed hero upload is recoverable from the Sessions
+                        // browser's per-row Set/Replace hero action.
+                        if (_medium == ReleaseMedium.Session
+                            && _heroImageFile is { } heroFile
+                            && result.Value.ReleaseId is { } sessionReleaseId)
+                        {
+                            try
+                            {
+                                await using var heroStream = heroFile.OpenReadStream(maxAllowedSize: 50_000_000);
+                                var heroResult = await CmsReleaseService.UploadSessionHeroImageAsync(
+                                    sessionReleaseId, heroStream, heroFile.Name, heroFile.ContentType);
+                                if (!heroResult.Success)
+                                {
+                                    var heroError = heroResult.Messages.FirstOrDefault()?.Message ?? "Unknown error";
+                                    Logger.LogWarning("Batch upload: hero image upload failed for release {ReleaseId} ('{TrackName}'): {Error}",
+                                        sessionReleaseId, row.TrackName, heroError);
+                                    Snackbar.Add("Session uploaded, but the hero image failed. Set it from the Sessions browser.", Severity.Warning);
+                                }
+                            }
+                            catch (Exception heroEx)
+                            {
+                                Logger.LogError(heroEx, "Batch upload: exception uploading hero image for release {ReleaseId}", sessionReleaseId);
+                                Snackbar.Add("Session uploaded, but the hero image failed. Set it from the Sessions browser.", Severity.Warning);
+                            }
+                        }
+
                         // Mix uploads fire the server-side high-res waveform trigger (§3.4). The CMS
                         // computes nothing — the API derives the datum from the audio it just stored.
                         // Non-blocking: the track is persisted; a failed trigger is recoverable from

DeepDrftManager/Components/Pages/Tracks/MediumFields.razor

@@ -1,4 +1,5 @@
 @using DeepDrftModels.Enums
+@using Microsoft.AspNetCore.Components.Forms
 
 @* The single dispatch point for medium-conditional form fields. All five upload/edit forms embed this
    one component; the @switch below is the ONLY place medium-specific form shape is decided. Adding a
@@ -26,7 +27,9 @@
                        Disabled="Disabled" />
             break;
         case ReleaseMedium.Session:
-            <SessionFields />
+            <SessionFields HeroImageFile="HeroImageFile"
+                           HeroImageFileChanged="HeroImageFileChanged"
+                           Disabled="Disabled" />
             break;
         case ReleaseMedium.Mix:
             <MixFields />
@@ -42,5 +45,9 @@
     [Parameter] public ReleaseType ReleaseType { get; set; } = ReleaseType.Single;
     [Parameter] public EventCallback<ReleaseType> ReleaseTypeChanged { get; set; }
 
+    // Session-only — the held hero-image file, uploaded after create. Ignored for Cut/Mix.
+    [Parameter] public IBrowserFile? HeroImageFile { get; set; }
+    [Parameter] public EventCallback<IBrowserFile?> HeroImageFileChanged { get; set; }
+
     [Parameter] public bool Disabled { get; set; }
 }

DeepDrftManager/Components/Pages/Tracks/SessionFields.razor

@@ -1,10 +1,51 @@
+@using Microsoft.AspNetCore.Components.Forms
+
 @* Session-medium fields. The hero image is resource-addressed (POST api/release/{id}/session/hero-image)
-   and therefore set after the release exists — managed per-row in the Sessions browser, not at create
-   time when no release id is yet assigned. This section states that contract so the admin knows where
-   the hero image is managed; it carries no input of its own. *@
+   and therefore cannot be uploaded until the release exists. The file is selected here, held by the
+   parent form, and uploaded after the create call returns a release id — the same deferred-upload
+   pattern AlbumHeaderFields uses for cover art ("Will upload on submit"). The hero is optional; the
+   parent warns (does not block) when a Session is submitted without one. *@
 <MudItem xs="12">
-    <MudAlert Severity="Severity.Info" Dense="true" Variant="Variant.Outlined">
-        Sessions are single-track live releases. After upload, set the hero image from the
-        <strong>Release Archive → Sessions</strong> browser.
-    </MudAlert>
+    <MudField Label="Hero Image" Variant="Variant.Outlined" InnerPadding="false">
+        <MudStack Spacing="3">
+            <MudText Typo="Typo.body2" Color="Color.Default">
+                Sessions are single-track live releases. The hero image is the session's primary visual identity.
+            </MudText>
+
+            @if (HeroImageFile is { } selectedHero)
+            {
+                <MudStack Row="true" AlignItems="AlignItems.Center" Spacing="2">
+                    <MudText Typo="Typo.body2" Color="Color.Default">Selected: @selectedHero.Name</MudText>
+                    <MudIconButton Icon="@Icons.Material.Filled.Clear"
+                                   Color="Color.Error"
+                                   Size="Size.Small"
+                                   Disabled="Disabled"
+                                   OnClick="ClearHeroFile"
+                                   aria-label="Cancel hero image selection" />
+                </MudStack>
+            }
+            else
+            {
+                <MudText Typo="Typo.body2" Color="Color.Default">No hero image — optional, but recommended.</MudText>
+            }
+
+            <InputFile OnChange="HandleHeroFileSelected" accept="image/*" disabled="@Disabled" />
+            @if (HeroImageFile is not null)
+            {
+                <MudText Typo="Typo.caption">Will upload on submit.</MudText>
+            }
+        </MudStack>
+    </MudField>
 </MudItem>
+
+@code {
+    [Parameter] public IBrowserFile? HeroImageFile { get; set; }
+    [Parameter] public EventCallback<IBrowserFile?> HeroImageFileChanged { get; set; }
+    [Parameter] public bool Disabled { get; set; }
+
+    private Task HandleHeroFileSelected(InputFileChangeEventArgs e) =>
+        HeroImageFileChanged.InvokeAsync(e.File);
+
+    private Task ClearHeroFile() =>
+        HeroImageFileChanged.InvokeAsync(null);
+}