diff --git a/internal/workflows/maintenance/branch_docs_impact.rb b/internal/workflows/maintenance/branch_docs_impact.rb
new file mode 100644
index 00000000..b351dce8
--- /dev/null
+++ b/internal/workflows/maintenance/branch_docs_impact.rb
@@ -0,0 +1,97 @@
+# typed: true
+# frozen_string_literal: true
+
+#: self as Roast::Workflow
+
+# Gets the committed diff of the current branch vs origin/main, then analyzes it for potential
+# documentation impacts, and optionally applies fixes. This is meant to be run as a pre-merge check, to
+# catch any potential documentation issues before they get merged into main.
+#
+# Accepts a `--fix` flag to apply any suggested fixes in place. Otherwise, it just reports the analysis
+# and recommended fixes without applying them.
+
+config do
+  agent do
+    provider :claude
+    model "claude-opus-4-7"
+    quiet!
+  end
+  chat do
+    provider :openai
+    model "gpt-5"
+    quiet!
+  end
+end
+
+execute do
+  cmd(:diff) do
+    merge_base = %x(git merge-base origin/main HEAD).strip
+    fail!("could not determine merge-base with origin/main — run `git fetch origin main` first") if merge_base.empty?
+    "git diff #{merge_base} HEAD"
+  end
+
+  agent(:analyzer) do
+    skip! if cmd!(:diff).text.strip.empty?
+    fail!("diff too large (#{cmd!(:diff).text.bytesize} bytes) to analyze — narrow the branch or exclude generated files") if cmd!(:diff).text.bytesize > 500_000
+    <<~PROMPT
+      You are checking whether a git diff makes any existing documentation stale.
+
+      Rules:
+      - Use ONLY the diff below. Do not run any commands.
+      - Be thorough about finding real issues — do not be conservative.
+      - But do NOT speculate about docs you cannot see in the diff.
+      - No markdown headers, no preamble, no caveats, no "limitations" sections.
+
+      Output format — pick exactly one:
+
+      If nothing in the diff affects existing docs, output a single line:
+        No documentation impact.
+
+      Otherwise, output one block per affected doc, separated by blank lines:
+        <doc/path.md>
+        Stale because: <one sentence>
+        Fix: <one sentence>
+
+      --- DIFF START ---
+      #{cmd!(:diff).text}
+      --- DIFF END ---
+    PROMPT
+  end
+
+  chat(:report) do
+    skip! if cmd!(:diff).text.strip.empty?
+    <<~PROMPT
+      Based on the following analysis, summarize the impact of the changes in this branch on the project's documentation.
+      Highlight any significant improvements or regressions, and provide recommendations for any additional documentation updates that may be necessary.
+      Do not suggest updates that are not needed.
+      Do not be verbose. Be super concise.
+
+      Analysis:
+      #{agent!(:analyzer).response}
+    PROMPT
+  end
+
+  agent(:fixer) do
+    skip! unless arg?(:fix)
+    skip! if cmd!(:diff).text.strip.empty?
+    skip! if agent!(:analyzer).response.strip == "No documentation impact."
+    <<~PROMPT
+      Apply the documentation fixes suggested in the analysis below. Edit the
+      affected files in place. Do not modify any code files; docs only.
+
+      #{agent!(:analyzer).response}
+    PROMPT
+  end
+
+  ruby(:output) do
+    if cmd!(:diff).text.strip.empty?
+      puts "No changes vs origin/main — nothing to analyze."
+    else
+      files = cmd!(:diff).out.scan(%r{^diff --git a/.+ b/(.+)$}).flatten
+      puts "Files considered (#{files.size}):"
+      files.each { |f| puts "  #{f}" }
+      puts "ANALYSIS:\n#{chat!(:report).response}"
+      puts(agent?(:fixer) ? "Fixes applied." : "(Next time, run with `-- fix` to auto-apply suggested edits)")
+    end
+  end
+end