diff --git a/backend/src/Taskdeck.Api/appsettings.json b/backend/src/Taskdeck.Api/appsettings.json
index 40338b182..5de38540a 100644
--- a/backend/src/Taskdeck.Api/appsettings.json
+++ b/backend/src/Taskdeck.Api/appsettings.json
@@ -113,7 +113,7 @@
     "HstsMaxAgeDays": 365,
     "HstsIncludeSubDomains": false,
     "HstsPreload": false,
-    "ContentSecurityPolicy": "default-src 'none'; base-uri 'self'; frame-ancestors 'none'; form-action 'self'; connect-src 'self'; img-src 'self'; font-src 'self'; style-src 'self'; script-src 'self'",
+    "ContentSecurityPolicy": "default-src 'none'; base-uri 'self'; frame-ancestors 'none'; form-action 'self'; connect-src 'self'; img-src 'self'; font-src 'self'; style-src 'self'; script-src 'self'; manifest-src 'self'",
     "XFrameOptions": "DENY",
     "ReferrerPolicy": "no-referrer"
   },
diff --git a/backend/src/Taskdeck.Application/Services/SecurityHeadersSettings.cs b/backend/src/Taskdeck.Application/Services/SecurityHeadersSettings.cs
index 1911ddf1b..15697c80a 100644
--- a/backend/src/Taskdeck.Application/Services/SecurityHeadersSettings.cs
+++ b/backend/src/Taskdeck.Application/Services/SecurityHeadersSettings.cs
@@ -28,7 +28,7 @@ public sealed class SecurityHeadersSettings
     // removing 'unsafe-inline' does not break Vue reactivity.
     [Required(AllowEmptyStrings = false)]
     public string ContentSecurityPolicy { get; set; } =
-        "default-src 'none'; base-uri 'self'; frame-ancestors 'none'; form-action 'self'; connect-src 'self'; img-src 'self'; font-src 'self'; style-src 'self'; script-src 'self'";
+        "default-src 'none'; base-uri 'self'; frame-ancestors 'none'; form-action 'self'; connect-src 'self'; img-src 'self'; font-src 'self'; style-src 'self'; script-src 'self'; manifest-src 'self'";
 
     [Required(AllowEmptyStrings = false)]
     public string XFrameOptions { get; set; } = "DENY";
diff --git a/backend/tests/Taskdeck.Api.Tests/SecurityHeadersApiTests.cs b/backend/tests/Taskdeck.Api.Tests/SecurityHeadersApiTests.cs
index dabd5b0f8..c374e274f 100644
--- a/backend/tests/Taskdeck.Api.Tests/SecurityHeadersApiTests.cs
+++ b/backend/tests/Taskdeck.Api.Tests/SecurityHeadersApiTests.cs
@@ -4,6 +4,7 @@
 using Microsoft.AspNetCore.Mvc.Testing;
 using Microsoft.Net.Http.Headers;
 using Taskdeck.Api.Tests.Support;
+using Taskdeck.Application.Services;
 using Xunit;
 
 namespace Taskdeck.Api.Tests;
@@ -78,6 +79,36 @@ public async Task SecurityHeaders_CspFontSrc_ShouldAllowOnlySameOriginFonts()
         fontSrcDirective.Should().NotContain("fonts.gstatic.com");
     }
 
+    [Fact]
+    public async Task SecurityHeaders_CspManifestSrc_ShouldAllowOnlySameOriginManifests()
+    {
+        using var client = _factory.CreateClient();
+
+        var response = await client.GetAsync("/health/live");
+
+        response.StatusCode.Should().Be(HttpStatusCode.OK);
+        response.Headers.TryGetValues("Content-Security-Policy", out var cspValues).Should().BeTrue();
+        var csp = cspValues.Should().ContainSingle().Subject;
+        var directives = csp.Split(';', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+
+        directives
+            .Should()
+            .ContainSingle(directive => directive.StartsWith("default-src ", StringComparison.Ordinal))
+            .Which.Should().Be("default-src 'none'");
+
+        directives
+            .Should()
+            .ContainSingle(directive => directive.StartsWith("manifest-src ", StringComparison.Ordinal))
+            .Which.Should().Be("manifest-src 'self'");
+
+        // The code-side default must carry the same directive, so a deployment whose
+        // configuration omits SecurityHeaders:ContentSecurityPolicy behaves the same way.
+        new SecurityHeadersSettings().ContentSecurityPolicy
+            .Split(';', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
+            .Should()
+            .Contain("manifest-src 'self'");
+    }
+
     [Fact]
     public async Task SecurityHeaders_ShouldBePresent_OnUnauthorizedResponses()
     {
diff --git a/docs/platform/CONFIGURATION_REFERENCE.md b/docs/platform/CONFIGURATION_REFERENCE.md
index d3b040d75..678fb9d92 100644
--- a/docs/platform/CONFIGURATION_REFERENCE.md
+++ b/docs/platform/CONFIGURATION_REFERENCE.md
@@ -626,7 +626,7 @@ Development when the key is unset (`SettingsRegistration.cs`). Consumed by
 | `SecurityHeaders:HstsMaxAgeDays` | `int` | `365` | `max-age` value for HSTS in days. | No |
 | `SecurityHeaders:HstsIncludeSubDomains` | `bool` | `false` | Include `includeSubDomains` in HSTS. | No |
 | `SecurityHeaders:HstsPreload` | `bool` | `false` | Include `preload` in HSTS. | No |
-| `SecurityHeaders:ContentSecurityPolicy` | `string` | `default-src 'none'; base-uri 'self'; frame-ancestors 'none'; form-action 'self'; connect-src 'self'; img-src 'self'; font-src 'self'; style-src 'self'; script-src 'self'` | Raw CSP string. SEC-29: `'unsafe-inline'` removed from `style-src` — API serves JSON (Swagger excluded from CSP), no inline styles needed. | No |
+| `SecurityHeaders:ContentSecurityPolicy` | `string` | `default-src 'none'; base-uri 'self'; frame-ancestors 'none'; form-action 'self'; connect-src 'self'; img-src 'self'; font-src 'self'; style-src 'self'; script-src 'self'; manifest-src 'self'` | Raw CSP string. SEC-29: `'unsafe-inline'` removed from `style-src` — API serves JSON (Swagger excluded from CSP), no inline styles needed. | No |
 | `SecurityHeaders:XFrameOptions` | `string` | `DENY` | Value for `X-Frame-Options`. | No |
 | `SecurityHeaders:ReferrerPolicy` | `string` | `no-referrer` | Value for `Referrer-Policy`. | No |
 
diff --git a/docs/platform/PWA_OFFLINE_BEHAVIOR.md b/docs/platform/PWA_OFFLINE_BEHAVIOR.md
index 317084dd2..69144629d 100644
--- a/docs/platform/PWA_OFFLINE_BEHAVIOR.md
+++ b/docs/platform/PWA_OFFLINE_BEHAVIOR.md
@@ -168,9 +168,10 @@ Workbox handles cache versioning automatically via content hashing in precache m
 ## PWA Installability
 
 The generated frontend assets meet Chrome's PWA installability criteria when the deployment serves
-the same-origin manifest under its CSP. Exact packaged-desktop proof currently finds that the API
-CSP omits `manifest-src`, so Chrome blocks `manifest.webmanifest` on that surface; issue `#2045`
-tracks the directive and packaged reproof. The generated contract includes:
+the same-origin manifest under its CSP. The API's production CSP default (both the shipped
+`appsettings.json` and the code-side `SecurityHeadersSettings` default) now includes
+`manifest-src 'self'` (PR `#2626`); the packaged-desktop installability reproof is still owed and
+issue `#2045` tracks it. The generated contract includes:
 
 - Valid `manifest.webmanifest` with `name`, `short_name`, `start_url`, `display: standalone`, and icons (192x192 and 512x512 PNG).
 - Service worker with fetch handler (provided by Workbox).