diff --git a/db/migrate/20260827134208_expand_coplan_reference_urls.co_plan.rb b/db/migrate/20260827134208_expand_coplan_reference_urls.co_plan.rb
new file mode 100644
index 00000000..2d1c40e0
--- /dev/null
+++ b/db/migrate/20260827134208_expand_coplan_reference_urls.co_plan.rb
@@ -0,0 +1,51 @@
+# This migration comes from co_plan (originally 20260827000000)
+class ExpandCoplanReferenceUrls < ActiveRecord::Migration[8.1]
+  def up
+    if connection.adapter_name == "PostgreSQL"
+      remove_url_index_and_expand_column
+      add_digest_column
+      add_digest_index
+    else
+      add_digest_column
+      add_digest_index
+      remove_url_index_and_expand_column
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration,
+      "reference URLs may exceed the former 255-character limit"
+  end
+
+  private
+
+  def add_digest_column
+    add_column :coplan_references, :url_digest, :virtual, type: :string, limit: 64,
+      as: digest_expression, stored: true
+  end
+
+  def add_digest_index
+    add_index :coplan_references, [ :plan_id, :url_digest ], unique: true,
+      name: "index_coplan_references_on_plan_id_and_url_digest"
+  end
+
+  def remove_url_index_and_expand_column
+    remove_index :coplan_references, column: [ :plan_id, :url ]
+    if connection.adapter_name == "Mysql2"
+      execute "ALTER TABLE coplan_references MODIFY url TEXT CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL"
+    else
+      change_column :coplan_references, :url, :text, null: false
+    end
+  end
+
+  def digest_expression
+    case connection.adapter_name
+    when "Mysql2"
+      "SHA2(url, 256)"
+    when "PostgreSQL"
+      "encode(sha256(url::bytea), 'hex')"
+    else
+      raise "Unsupported database adapter: #{connection.adapter_name}"
+    end
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 6f8cba98..457ddcec 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.1].define(version: 2026_08_24_120000) do
+ActiveRecord::Schema[8.1].define(version: 2026_08_27_134208) do
   create_table "active_admin_comments", id: { type: :string, limit: 36 }, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "author_id"
     t.string "author_type"
@@ -385,9 +385,10 @@
     t.string "target_plan_id", limit: 36
     t.string "title"
     t.datetime "updated_at", null: false
-    t.string "url", null: false
+    t.text "url", null: false, collation: "utf8mb4_bin"
+    t.virtual "url_digest", type: :string, limit: 64, as: "sha2(`url`,256)", stored: true
     t.index ["plan_id", "key"], name: "index_coplan_references_on_plan_id_and_key", unique: true
-    t.index ["plan_id", "url"], name: "index_coplan_references_on_plan_id_and_url", unique: true
+    t.index ["plan_id", "url_digest"], name: "index_coplan_references_on_plan_id_and_url_digest", unique: true
     t.index ["source"], name: "index_coplan_references_on_source"
     t.index ["target_plan_id"], name: "index_coplan_references_on_target_plan_id"
   end
diff --git a/engine/db/migrate/20260827000000_expand_coplan_reference_urls.rb b/engine/db/migrate/20260827000000_expand_coplan_reference_urls.rb
new file mode 100644
index 00000000..5a756f9f
--- /dev/null
+++ b/engine/db/migrate/20260827000000_expand_coplan_reference_urls.rb
@@ -0,0 +1,50 @@
+class ExpandCoplanReferenceUrls < ActiveRecord::Migration[8.1]
+  def up
+    if connection.adapter_name == "PostgreSQL"
+      remove_url_index_and_expand_column
+      add_digest_column
+      add_digest_index
+    else
+      add_digest_column
+      add_digest_index
+      remove_url_index_and_expand_column
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration,
+      "reference URLs may exceed the former 255-character limit"
+  end
+
+  private
+
+  def add_digest_column
+    add_column :coplan_references, :url_digest, :virtual, type: :string, limit: 64,
+      as: digest_expression, stored: true
+  end
+
+  def add_digest_index
+    add_index :coplan_references, [ :plan_id, :url_digest ], unique: true,
+      name: "index_coplan_references_on_plan_id_and_url_digest"
+  end
+
+  def remove_url_index_and_expand_column
+    remove_index :coplan_references, column: [ :plan_id, :url ]
+    if connection.adapter_name == "Mysql2"
+      execute "ALTER TABLE coplan_references MODIFY url TEXT CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL"
+    else
+      change_column :coplan_references, :url, :text, null: false
+    end
+  end
+
+  def digest_expression
+    case connection.adapter_name
+    when "Mysql2"
+      "SHA2(url, 256)"
+    when "PostgreSQL"
+      "encode(sha256(url::bytea), 'hex')"
+    else
+      raise "Unsupported database adapter: #{connection.adapter_name}"
+    end
+  end
+end
diff --git a/spec/models/coplan/reference_spec.rb b/spec/models/coplan/reference_spec.rb
index 84744083..0775a888 100644
--- a/spec/models/coplan/reference_spec.rb
+++ b/spec/models/coplan/reference_spec.rb
@@ -36,12 +36,51 @@
       expect(ref).not_to be_valid
     end
 
+    it "enforces database uniqueness when a writer omits the generated digest" do
+      create(:reference, plan: plan, url: "https://example.com")
+      attributes = {
+        id: SecureRandom.uuid,
+        plan_id: plan.id,
+        url: "https://example.com",
+        reference_type: "link",
+        source: "extracted",
+        created_at: Time.current,
+        updated_at: Time.current
+      }
+
+      expect { described_class.insert_all!([ attributes ]) }.to raise_error(ActiveRecord::RecordNotUnique)
+    end
+
+    it "stores URLs longer than a database string" do
+      url = "https://example.com/?query=#{"x" * 500}"
+      ref = create(:reference, plan: plan, url: url)
+
+      expect(ref.reload.url).to eq(url)
+      expect(ref.url_digest).to eq(Digest::SHA256.hexdigest(url))
+    end
+
+    it "updates the database-generated digest when the URL changes" do
+      ref = create(:reference, plan: plan, url: "https://example.com/old")
+
+      ref.update!(url: "https://example.com/new")
+
+      expect(ref.reload.url_digest).to eq(Digest::SHA256.hexdigest(ref.url))
+    end
+
     it "allows same url on different plans" do
       other_plan = create(:plan)
       create(:reference, plan: plan, url: "https://example.com")
       ref = build(:reference, plan: other_plan, url: "https://example.com")
       expect(ref).to be_valid
     end
+
+    it "treats case-sensitive URL paths as distinct" do
+      create(:reference, plan: plan, url: "https://example.com/Report")
+
+      expect {
+        create(:reference, plan: plan, url: "https://example.com/report")
+      }.to change(described_class, :count).by(1)
+    end
   end
 
   describe ".classify_url" do
diff --git a/spec/requests/api/v1/operations_spec.rb b/spec/requests/api/v1/operations_spec.rb
index 7e2e61e1..4cf66280 100644
--- a/spec/requests/api/v1/operations_spec.rb
+++ b/spec/requests/api/v1/operations_spec.rb
@@ -38,6 +38,24 @@
     expect(body["revision"]).to eq(plan.current_revision + 1)
   end
 
+  it "applies content containing a URL longer than a database string" do
+    url = "https://example.com/?query=#{"x" * 500}"
+
+    post api_v1_plan_operations_path(plan),
+      params: {
+        lease_token: lease_token,
+        base_revision: plan.current_revision,
+        operations: [
+          { op: "replace_exact", old_text: "Some content here.", new_text: "Read [the report](#{url}).", count: 1 }
+        ]
+      },
+      headers: headers,
+      as: :json
+
+    expect(response).to have_http_status(:created)
+    expect(plan.references.find_by!(url: url).source).to eq("extracted")
+  end
+
   it "apply operations fails without lease" do
     CoPlan::EditLease.find_by(plan_id: plan.id)&.destroy
 
diff --git a/spec/services/coplan/references/extract_from_content_spec.rb b/spec/services/coplan/references/extract_from_content_spec.rb
index d06c99b4..290ba107 100644
--- a/spec/services/coplan/references/extract_from_content_spec.rb
+++ b/spec/services/coplan/references/extract_from_content_spec.rb
@@ -116,5 +116,13 @@ def update_content(plan, content)
       expect(plan.references.count).to eq(1)
       expect(plan.references.first.url).to eq("https://example.com")
     end
+
+    it "extracts URLs longer than a database string" do
+      url = "https://example.com/?query=#{"x" * 500}"
+      update_content(plan, "Visit [the report](#{url}) for more info.")
+
+      expect { described_class.call(plan: plan) }.to change(plan.references, :count).by(1)
+      expect(plan.references.first.url).to eq(url)
+    end
   end
 end