diff --git a/Reports/README.md b/Reports/README.md
index 5f6a790..1312ee3 100644
--- a/Reports/README.md
+++ b/Reports/README.md
@@ -39,11 +39,22 @@ feeding it get run:
 ./scripts/Assert-PfbDerivedArtifacts.ps1 -Artifact Reports/PfbDeadKeyReport.json
 ```
 
-Add `-KeepWorkDirectory` to keep the regenerated output on disk: when the check reports a
-difference, that output is by definition what the comparison demanded, so copying it over the
-committed copies is the reliable fix. The gate pins its spec set to `Data/PfbCapabilityMap.json`'s
-own `generatedFrom` list rather than reading whatever `tools/specs/` happens to hold, so a
-newly published REST version does not show up as artifact drift.
+When the check reports a difference, the output that run produced is by definition what the
+comparison demanded, so writing it over the committed copies is the reliable fix. `-UpdateCommitted`
+does exactly that and then exits 0, listing the repo-relative path of every file it wrote:
+
+```powershell
+./scripts/Assert-PfbDerivedArtifacts.ps1 -Artifact Reports/PfbDeadKeyReport.json -UpdateCommitted
+```
+
+Only artifacts the run found stale are written, so `git status` afterwards names exactly what
+moved. Nothing turns the switch on implicitly — without it the gate never touches the working
+tree, which is what lets the same script serve as the CI check. To inspect the regenerated output
+before overwriting anything, use `-KeepWorkDirectory` instead and copy the files by hand.
+
+The gate pins its spec set to `Data/PfbCapabilityMap.json`'s own `generatedFrom` list rather than
+reading whatever `tools/specs/` happens to hold, so a newly published REST version does not show
+up as artifact drift.
 
 | File | Answers | Generated by |
 |---|---|---|
diff --git a/Tests/AssertDerivedArtifacts.Tests.ps1 b/Tests/AssertDerivedArtifacts.Tests.ps1
index 200e077..3a0adeb 100644
--- a/Tests/AssertDerivedArtifacts.Tests.ps1
+++ b/Tests/AssertDerivedArtifacts.Tests.ps1
@@ -175,11 +175,61 @@ Describe 'Assert-PfbDerivedArtifacts parameter contract' {
         $names | Should -Contain 'KeepWorkDirectory'
     }
 
+    It 'exposes -UpdateCommitted as a switch, so remediating is opt-in and takes no value' {
+        # A [switch], specifically. As a [bool] it would bind positionally and by conversion --
+        # -UpdateCommitted $false still enters the branch under a truthy conversion mistake, and
+        # a stray positional argument could set it. The whole safety property here is that
+        # nothing turns this on except a caller typing it.
+        $parameter = @($gateAst.ParamBlock.Parameters |
+            Where-Object { $_.Name.VariablePath.UserPath -eq 'UpdateCommitted' })
+
+        $parameter.Count | Should -Be 1 -Because 'the remediation switch is the documented fix path in the stale-artifact message'
+        $parameter[0].StaticType.Name | Should -Be 'SwitchParameter'
+        $parameter[0].DefaultValue | Should -BeNullOrEmpty -Because 'a default that enabled writing would make the gate rewrite the working tree on an ordinary check'
+    }
+
     It 'declares PowerShell 7, since the generators it invokes require it' {
         $gateSource | Should -Match '#Requires -Version 7\.0'
     }
 }
 
+Describe 'Assert-PfbDerivedArtifacts remediation semantics' {
+
+    It 'writes into the repository only underneath the -UpdateCommitted guard' {
+        # The load-bearing property of this gate is that checking does not mutate. There are two
+        # Copy-Item calls in the script: one stages specs into the scratch tree, one overwrites a
+        # committed artifact. Only the second may run unconditionally-never. Asserted by
+        # containment rather than by grepping for the switch name, because a Copy-Item moved one
+        # brace out of the guard still sits a few lines from the word "UpdateCommitted" and would
+        # keep a text match green while the gate silently rewrote Data/ on every run.
+        $guard = @($gateAst.FindAll({
+            param($node)
+            $node -is [System.Management.Automation.Language.IfStatementAst]
+        }, $true) | Where-Object { $_.Clauses[0].Item1.Extent.Text -match '\$UpdateCommitted' })
+
+        $guard.Count | Should -Be 1 -Because 'the remediation branch must be a single identifiable guard, not scattered conditionals'
+
+        $writes = @($gateAst.FindAll({
+            param($node)
+            $node -is [System.Management.Automation.Language.CommandAst] -and
+            $node.GetCommandName() -eq 'Copy-Item'
+        }, $true) | Where-Object { $_.Extent.Text -match '\$committedPath' })
+
+        $writes.Count | Should -Be 1 -Because 'exactly one write targets a committed artifact; a second would need its own review'
+        $writes[0].Extent.StartOffset | Should -BeGreaterThan $guard[0].Extent.StartOffset
+        $writes[0].Extent.EndOffset | Should -BeLessThan $guard[0].Extent.EndOffset
+    }
+
+    It 'reports the updated artifacts by repo-relative path' {
+        # The printed list is the handoff to git: a reader pastes those paths into git diff or
+        # git add. Absolute scratch paths would look identical in the output and be useless in
+        # both commands, which is why the report is built from $_.Artifact -- the plan's
+        # repo-relative key -- rather than from the Copy-Item destination.
+        $gateSource | Should -Match '\$updatedNames\s*=\s*@\(\$updated \| ForEach-Object \{ \$_\.Artifact \}'
+        $gateSource | Should -Match 'git diff --stat --'
+    }
+}
+
 Describe 'Assert-PfbDerivedArtifacts comparison semantics' {
 
     It 'normalizes CRLF to LF before hashing' {
diff --git a/scripts/Assert-PfbDerivedArtifacts.ps1 b/scripts/Assert-PfbDerivedArtifacts.ps1
index e05302b..1df1311 100644
--- a/scripts/Assert-PfbDerivedArtifacts.ps1
+++ b/scripts/Assert-PfbDerivedArtifacts.ps1
@@ -26,8 +26,12 @@
     run while passing in CI -- a gate that is wrong in the direction that trains people to
     ignore it.
 
-    THE WORKING TREE IS NEVER TOUCHED. Regeneration goes to a scratch directory; a gate that
-    rewrites Data/ as a side effect of checking it is not a gate.
+    THE WORKING TREE IS NEVER TOUCHED unless -UpdateCommitted is passed. Regeneration goes to a
+    scratch directory; a gate that rewrites Data/ as a side effect of checking it is not a gate.
+    The objection there is to the side effect, not to the write: -UpdateCommitted is an explicit
+    request to remediate, so a caller who passes it has asked for exactly the thing the default
+    withholds. Nothing infers it -- no environment variable, no CI default -- because the value
+    of the default is that a check stays a check.
 
     Lives in scripts/ rather than tools/ because the workflows call scripts/ (see
     scripts/Publish-Gallery.ps1, scripts/Invoke-PfbCiPester.ps1) and because a developer must
@@ -50,17 +54,33 @@
 .PARAMETER KeepWorkDirectory
     Leave the scratch tree in place and print its path, so a reported difference can be
     diffed by hand instead of being re-derived.
+.PARAMETER UpdateCommitted
+    Overwrite each stale committed artifact with this run's regenerated copy, then exit 0 and
+    list what changed. Without it, a stale artifact is reported and the caller is told to copy
+    the files out of the scratch tree by hand -- the same copy, done manually.
+
+    Only artifacts this run found stale are written, and only within -Artifact when that
+    narrows the set: an up-to-date artifact is left alone rather than rewritten byte-identically,
+    so `git status` after the run names exactly what moved.
+
+    Exit code is 0 on a successful update. Remediating is what was asked for, so doing it is
+    success -- and a non-zero exit from a run that just fixed the problem breaks any caller
+    chaining on it. Callers that want the unremediated answer are the ones that must not pass
+    this switch.
 .EXAMPLE
     ./scripts/Assert-PfbDerivedArtifacts.ps1
 .EXAMPLE
     ./scripts/Assert-PfbDerivedArtifacts.ps1 -Artifact Data/PfbCapabilityMap.json -KeepWorkDirectory
+.EXAMPLE
+    ./scripts/Assert-PfbDerivedArtifacts.ps1 -Artifact Reports/PfbDeadKeyReport.json -UpdateCommitted
 #>
 [CmdletBinding()]
 param(
     [string]$SpecsDirectory,
     [string]$WorkDirectory,
     [string[]]$Artifact,
-    [switch]$KeepWorkDirectory
+    [switch]$KeepWorkDirectory,
+    [switch]$UpdateCommitted
 )
 
 $ErrorActionPreference = 'Stop'
@@ -326,6 +346,35 @@ try {
         $results.Add([pscustomobject]@{ Artifact = $relative; State = $state; Detail = $detail })
     }
 
+    # --- Remediate ------------------------------------------------------------------------
+
+    # Done before the report so one pass of output describes what is now true on disk, rather
+    # than printing STALE and contradicting it two lines later.
+    $updated = @()
+    if ($UpdateCommitted) {
+        foreach ($result in @($results | Where-Object { $_.State -eq 'STALE' })) {
+            $committedPath   = Join-Path $repoRoot $result.Artifact
+            $regeneratedPath = Join-Path $outRoot $result.Artifact
+
+            # Copy-Item rather than read-transform-write: the committed artifacts carry no BOM,
+            # and a round-trip through Set-Content is one -Encoding default away from adding
+            # one. Preserving bytes also settles the line-ending question instead of reopening
+            # it -- the comparison above already normalized CRLF, so a whole-file copy lands
+            # exactly the content the gate demanded, and git's autocrlf handles the checkout
+            # form on commit. A partial rewrite is what would produce mixed endings; this is not
+            # one.
+            $parent = Split-Path -Parent $committedPath
+            if (-not (Test-Path -LiteralPath $parent)) {
+                New-Item -ItemType Directory -Path $parent -Force | Out-Null
+            }
+            Copy-Item -LiteralPath $regeneratedPath -Destination $committedPath -Force
+
+            $result.State  = 'UPDATED'
+            $result.Detail = 'overwritten from this run''s regeneration'
+        }
+        $updated = @($results | Where-Object { $_.State -eq 'UPDATED' })
+    }
+
     # --- Report ---------------------------------------------------------------------------
 
     foreach ($result in $results) {
@@ -340,11 +389,15 @@ try {
         $rows = foreach ($result in $results) { "| ``$($result.Artifact)`` | $($result.State) |" }
         $heading = '### Derived artifact check'
         if ($stale.Count -gt 0) { $heading = "$heading -- $($stale.Count) stale" }
+        if ($updated.Count -gt 0) { $heading = "$heading -- $($updated.Count) updated" }
         $lines = @($heading, '', "Pinned to REST $($pinnedVersions[0])-$($pinnedVersions[-1]) via ``Data/PfbCapabilityMap.json`` ``generatedFrom``.", '', '| Artifact | Result |', '|---|---|') + @($rows)
         ($lines -join [Environment]::NewLine) | Out-File -FilePath $env:GITHUB_STEP_SUMMARY -Append
     }
     if ($env:GITHUB_OUTPUT) {
-        "stale_count=$($stale.Count)" | Out-File -FilePath $env:GITHUB_OUTPUT -Append
+        @(
+            "stale_count=$($stale.Count)"
+            "updated_count=$($updated.Count)"
+        ) | Out-File -FilePath $env:GITHUB_OUTPUT -Append
     }
 
     if ($stale.Count -gt 0) {
@@ -359,9 +412,9 @@ try {
         throw @"
 $($stale.Count) committed artifact(s) do not match a fresh regeneration: $($staleNames -join ', ').
 
-RELIABLE FIX -- take the output this run already produced, which is by definition exactly what the comparison demanded:
-    ./scripts/Assert-PfbDerivedArtifacts.ps1 -Artifact $($staleNames -join ',') -KeepWorkDirectory
-then copy <work>/out/Data/* and <work>/out/Reports/* over the committed copies and commit them.
+RELIABLE FIX -- rerun with -UpdateCommitted, which writes the output this run already produced, and which is by definition exactly what the comparison demanded:
+    ./scripts/Assert-PfbDerivedArtifacts.ps1 -Artifact $($staleNames -join ',') -UpdateCommitted
+then review the diff and commit. To inspect before overwriting anything, use -KeepWorkDirectory instead and copy <work>/out/Data/* and <work>/out/Reports/* over the committed copies by hand.
 
 Running the generators bare instead:
     $($fixSteps -join "`n    ")
@@ -369,6 +422,24 @@ only reproduces this output when tools/specs/ holds EXACTLY the $($pinnedVersion
 "@
     }
 
+    if ($updated.Count -gt 0) {
+        # The paths are printed bare, one per line, so each is selectable on its own AND the
+        # block as a whole pastes into a git command -- the two things a reader does next.
+        $updatedNames = @($updated | ForEach-Object { $_.Artifact } | Sort-Object)
+        $unchanged = $results.Count - $updated.Count
+
+        Write-Host ''
+        Write-Host "Updated $($updated.Count) committed artifact(s) from this run's regeneration:"
+        foreach ($name in $updatedNames) { Write-Host "    $name" }
+        if ($unchanged -gt 0) {
+            Write-Host "$unchanged checked artifact(s) were already up to date and were not rewritten."
+        }
+        Write-Host ''
+        Write-Host 'Review, then commit:'
+        Write-Host "    git diff --stat -- $($updatedNames -join ' ')"
+        return
+    }
+
     Write-Host "All $($results.Count) checked artifact(s) are up to date."
 } finally {
     if ($KeepWorkDirectory) {