The privilege set said unbind, the router said no,
so the phone deleted local and the server did not know.
One route, one guard on If-Match, and the card is gone —
the change log tells the next sync what it is syncing on.

Assisted-by: Claude Opus 5 via Claude Code

diff --git a/lib/pro_tacts/web.rb b/lib/pro_tacts/web.rb
index 17bb878..401ca67 100644
--- a/lib/pro_tacts/web.rb
+++ b/lib/pro_tacts/web.rb
@@ -298,7 +298,7 @@ module ProTacts
         # support (RFC 6352 section 6.1); the header is RFC 4918 section 10.1.
         r.options do
           response["DAV"] = "addressbook"
-          response["Allow"] = "OPTIONS, PROPFIND, REPORT, PUT"
+          response["Allow"] = "OPTIONS, PROPFIND, REPORT, PUT, DELETE"
           ""
         end
 
@@ -364,9 +364,12 @@ module ProTacts
               # all — the PUT they prompted was what log/unhandled
               # captured them for. DAV:write covers PUT and PROPPATCH
               # (RFC 3744 section 3.2), and PUT is the one of the pair
-              # answered; DAV:bind is adding a member to the collection
-              # (section 3.9) and DAV:unbind removing one (section 3.10),
-              # neither of which has a route yet.
+              # answered; DAV:unbind is removing a member from the
+              # collection (section 3.10), which DELETE answers.
+              # DAV:bind is adding one (section 3.9), and the create it
+              # names — POST to the collection with DAV:add-member — has
+              # no route: PUT to the member URI is how both clients
+              # create, so nothing has asked for it.
               collection_response = <<~XML
                 <d:response>
                   <d:href>/dav/addressbook/</d:href>
@@ -545,6 +548,14 @@ module ProTacts
             # same fall-through-to-404 the GET handler gives it.
             write_card(id) if id.match?(Contact::ID_FORMAT)
           end
+
+          # DELETE removes the card at the member URI (RFC 4918 section
+          # 9.6) — the DAV:unbind privilege the collection advertises,
+          # and what iOS sends when a contact is deleted on the phone.
+          r.delete String do |filename|
+            id = filename.delete_suffix(".vcf")
+            remove_card(id) if id.match?(Contact::ID_FORMAT)
+          end
         end
       end
     end
@@ -675,6 +686,38 @@ module ProTacts
       nil
     end
 
+    # The whole of the DELETE, a private method for write_card's reason:
+    # a Roda route block cannot return early.
+    #: (String id) -> String?
+    def remove_card(id)
+      # An unmapped URI is a 404, not a silent success: RFC 4918 section
+      # 9.6 gives DELETE no idempotent status, and a client deleting what
+      # it believes exists is owed the disagreement. Falls through to the
+      # not_found handler the way the GET and PUT of a bad id do.
+      existing = store.contact(id)
+      return unless existing
+
+      # The lost-update conditional, RFC 7232 section 3.1, on the same
+      # terms the PUT gets it: a client that names the representation it
+      # means to remove must not remove one that changed underneath it.
+      # No recorded session has sent one on a DELETE — the iOS delete
+      # carried none, which section 3.1 leaves unconditional and
+      # allowed, and macOS has sent no DELETE at all. Answered anyway,
+      # because ignoring the header is the lost update it exists to
+      # refuse, and the PUT's own check is right here to reuse.
+      if_match = request.env["HTTP_IF_MATCH"]
+      return plain_412 if if_match && !if_match_satisfied?(if_match, existing)
+
+      # The change-log entry Store#delete leaves in the same transaction
+      # is what a syncing client is told: sync-collection answers a
+      # removed member as href plus 404 (#missing_response).
+      store.delete(id)
+      response.status = 204
+
+      # Bodyless for the 204, write_card's reason.
+      nil
+    end
+
     # The whole of the edit POST, a private method for the same reason
     # write_card is one: a Roda route block cannot return early, so each
     # refusal is a value the block ends with rather than a branch it
diff --git a/sig/gems/roda.rbs b/sig/gems/roda.rbs
index 016ad48..0d28283 100644
--- a/sig/gems/roda.rbs
+++ b/sig/gems/roda.rbs
@@ -26,6 +26,7 @@ class Roda
 
     def is: (*untyped matchers) { (*untyped) -> untyped } -> void
     def on: (*untyped matchers) { (*untyped) -> untyped } -> void
+    def delete: (*untyped matchers) ?{ (*untyped) -> untyped } -> void
     def get: (*untyped matchers) ?{ (*untyped) -> untyped } -> void
     def options: (*untyped matchers) ?{ (*untyped) -> untyped } -> void
     def post: (*untyped matchers) ?{ (*untyped) -> untyped } -> void
diff --git a/test/fixtures/macos-exchange/03-options-principal/response b/test/fixtures/macos-exchange/03-options-principal/response
index 6f2b25a..9c0aab3 100644
--- a/test/fixtures/macos-exchange/03-options-principal/response
+++ b/test/fixtures/macos-exchange/03-options-principal/response
@@ -1,5 +1,5 @@
 200
 Content-Type: text/html
 DAV: addressbook
-Allow: OPTIONS, PROPFIND, REPORT, PUT
+Allow: OPTIONS, PROPFIND, REPORT, PUT, DELETE
 
diff --git a/test/pro_tacts/test_web.rb b/test/pro_tacts/test_web.rb
index 0efb48d..a2004e9 100644
--- a/test/pro_tacts/test_web.rb
+++ b/test/pro_tacts/test_web.rb
@@ -40,6 +40,7 @@ class WebTest < Minitest::Test
     assert_equal "addressbook", last_response["DAV"]
     assert_includes last_response["Allow"], "OPTIONS"
     assert_includes last_response["Allow"], "PROPFIND"
+    assert_includes last_response["Allow"], "DELETE"
   end
 
   def test_propfind_root
@@ -513,6 +514,81 @@ class WebTest < Minitest::Test
     end
   end
 
+  ## Deletes
+
+  def test_delete_removes_the_card
+    with_contacts({"aiden" => "Aiden"}) do
+      delete "/dav/addressbook/aiden.vcf"
+
+      assert_equal 204, last_response.status
+      assert_nil last_response["Content-Type"]
+      assert_nil last_response["Content-Length"]
+
+      get "/dav/addressbook/aiden.vcf"
+      assert_equal 404, last_response.status
+    end
+  end
+
+  # RFC 6578 section 3.2: the removal a client syncs on is href plus
+  # 404, with no propstat, and the token has to move for it to arrive.
+  def test_delete_reaches_a_syncing_client_as_a_removal
+    with_contacts({"aiden" => "Aiden", "znorth" => "Zoe"}) do
+      request "/dav/addressbook/", method: "REPORT", input: sync_collection("")
+      token = last_response.body[%r{<d:sync-token>([^<]+)</d:sync-token>}, 1]
+
+      delete "/dav/addressbook/aiden.vcf"
+
+      request "/dav/addressbook/", method: "REPORT", input: sync_collection(token)
+
+      assert_equal 207, last_response.status
+      assert_includes last_response.body, "<d:href>/dav/addressbook/aiden.vcf</d:href>"
+      assert_includes last_response.body, "<d:status>HTTP/1.1 404 Not Found</d:status>"
+      refute_includes last_response.body, "znorth"
+      refute_equal token, last_response.body[%r{<d:sync-token>([^<]+)</d:sync-token>}, 1]
+    end
+  end
+
+  def test_delete_of_a_card_that_is_not_there_is_a_404
+    with_contacts({}) do
+      delete "/dav/addressbook/nobody.vcf"
+
+      assert_equal 404, last_response.status
+    end
+  end
+
+  def test_delete_of_an_id_this_server_cannot_have_is_a_404
+    with_contacts({}) do
+      delete "/dav/addressbook/not.an.id.vcf"
+
+      assert_equal 404, last_response.status
+    end
+  end
+
+  # RFC 7232 section 3.1, the same conditional the PUT honors.
+  def test_delete_with_the_current_etag_removes_the_card
+    with_contacts({"aiden" => "Aiden"}) do
+      get "/dav/addressbook/aiden.vcf"
+
+      delete "/dav/addressbook/aiden.vcf", {}, "HTTP_IF_MATCH" => last_response["ETag"]
+
+      assert_equal 204, last_response.status
+    end
+  end
+
+  def test_delete_with_a_stale_etag_is_refused_and_changes_nothing
+    with_contacts({"aiden" => "Aiden"}) do
+      get "/dav/addressbook/aiden.vcf"
+      before = last_response.body
+
+      delete "/dav/addressbook/aiden.vcf", {}, "HTTP_IF_MATCH" => %("#{"0" * 64}")
+
+      assert_equal 412, last_response.status
+
+      get "/dav/addressbook/aiden.vcf"
+      assert_equal before, last_response.body
+    end
+  end
+
   ## Pictures
 
   # The sizing case on the wire: a 338 KB PUT — the client does not