Document breaking change: 'dotnet watch' logs to stderr instead of stdout in .NET 10 RC 2 (#48925)

Author: Copilot

docs/core/compatibility/10.0.md

@@ -112,6 +112,7 @@ If you're migrating an app to .NET 10, the breaking changes listed here might af
 | [`dotnet package list` performs restore](sdk/10.0/dotnet-package-list-restore.md) | Behavioral change | Preview 4 |
 | [`dotnet restore` audits transitive packages](sdk/10.0/nugetaudit-transitive-packages.md) | Behavioral change | Preview 3 |
 | [`dotnet tool install --local` creates manifest by default](sdk/10.0/dotnet-tool-install-local-manifest.md) | Behavioral change | Preview 7 |
+| [`dotnet watch` logs to stderr instead of stdout](sdk/10.0/dotnet-watch-stderr.md) | Behavioral change | RC 2 |
 | [project.json not supported in `dotnet restore`](sdk/10.0/dotnet-restore-project-json-unsupported.md) | Source incompatible | Preview 7 |
 | [SHA-1 fingerprint support deprecated in `dotnet nuget sign`](sdk/10.0/dotnet-nuget-sign-sha1-deprecated.md) | Behavioral change | Preview 1 |
 | [MSBUILDCUSTOMBUILDEVENTWARNING escape hatch removed](sdk/10.0/custom-build-event-warning.md) | Behavioral change | Preview 1 |

docs/core/compatibility/sdk/10.0/dotnet-watch-stderr.md

@@ -0,0 +1,38 @@
+---
+title: "Breaking change: 'dotnet watch' logs to stderr instead of stdout"
+description: "Learn about the breaking change in .NET 10 where 'dotnet watch' emits its internal-facing log messages to stderr instead of stdout."
+ms.date: 10/08/2025
+ai-usage: ai-generated
+ms.custom: https://github.com/dotnet/docs/issues/45871
+---
+# 'dotnet watch' logs to stderr instead of stdout
+
+Starting in .NET 10, [`dotnet watch`](../../../tools/dotnet-watch.md) emits its internal-facing log messages to the `stderr` channel instead of `stdout`. This change is part of a general trend towards `dotnet` CLI commands not obscuring the `stdout` channel. That channel is often reserved for special semantics when running certain kinds of applications, like LSP or MCP servers.
+
+## Version introduced
+
+.NET 10 RC 2
+
+## Previous behavior
+
+Previously, [`dotnet watch`](../../../tools/dotnet-watch.md) emitted log messages to `stdout`.
+
+## New behavior
+
+Starting in .NET 10, [`dotnet watch`](../../../tools/dotnet-watch.md) emits log messages to `stderr`.
+
+## Type of breaking change
+
+This change is a [behavioral change](../../categories.md#behavioral-change).
+
+## Reason for change
+
+This change is part of a general trend towards `dotnet` CLI commands not obscuring the `stdout` channel, which is often reserved or assumed to have special semantics when running certain kinds of applications, like LSP or MCP servers. In general, the .NET CLI should get out of the way of your applications.
+
+## Recommended action
+
+Most users shouldn't need to take any action. If you need the `dotnet watch` messages on `stdout`, you can redirect the `stderr` stream to `stdout`. For example, use `2>&1` to redirect the `2` file descriptor for `stderr` to the `1` file descriptor for `stdout`.
+
+## Affected APIs
+
+None.

docs/core/compatibility/toc.yml

@@ -130,6 +130,10 @@ items:
                 href: sdk/10.0/dotnet-package-list-restore.md
               - name: "`dotnet tool install --local` creates manifest by default"
                 href: sdk/10.0/dotnet-tool-install-local-manifest.md
+              - name: "`dotnet watch` logs to stderr instead of stdout"
+                href: sdk/10.0/dotnet-watch-stderr.md
+              - name: HTTP warnings promoted to errors in package list and search
+                href: sdk/10.0/http-warnings-to-errors.md
               - name: MSBUILDCUSTOMBUILDEVENTWARNING escape hatch removed
                 href: sdk/10.0/custom-build-event-warning.md
               - name: MSBuild custom culture resource handling
@@ -138,16 +142,14 @@ items:
                 href: sdk/10.0/nu1510-pruned-references.md
               - name: NuGet packages with no runtime assets aren't included in deps.json
                 href: sdk/10.0/deps-json-trimmed-packages.md
-              - name: PackageReference without a version raises error
-                href: sdk/10.0/nu1015-packagereference-version.md
-              - name: PrunePackageReference privatizes direct prunable references
-                href: sdk/10.0/prune-packagereference-privateassets.md
-              - name: HTTP warnings promoted to errors in package list and search
-                href: sdk/10.0/http-warnings-to-errors.md
               - name: NUGET_ENABLE_ENHANCED_HTTP_RETRY environment variable removed
                 href: sdk/10.0/nuget-enhanced-http-retry-removed.md
               - name: NuGet logs an error for invalid package IDs
                 href: sdk/10.0/nuget-packageid-validation.md
+              - name: PackageReference without a version raises error
+                href: sdk/10.0/nu1015-packagereference-version.md
+              - name: PrunePackageReference privatizes direct prunable references
+                href: sdk/10.0/prune-packagereference-privateassets.md
           - name: Windows Forms
             items:
               - name: API obsoletions