diff --git a/src/app/projects/[projectId]/setup/contractors/ContractorPermissionsTable.tsx b/src/app/projects/[projectId]/setup/contractors/ContractorPermissionsTable.tsx
index 36dd3021..d7bca2b0 100644
--- a/src/app/projects/[projectId]/setup/contractors/ContractorPermissionsTable.tsx
+++ b/src/app/projects/[projectId]/setup/contractors/ContractorPermissionsTable.tsx
@@ -142,7 +142,8 @@ export function ContractorPermissionsTable({
           ? { kind: "blocked", reason }
           : { kind: "needs-confirmation", reason };
       }
-      if (!res.ok) throw new Error(body.error ?? "Couldn't remove the contractor");
+      if (!res.ok)
+        throw new Error(body.error ?? "Couldn't remove the contractor");
       return { kind: "removed" };
     },
     onSuccess: (outcome, { contractor }) => {
@@ -321,7 +322,9 @@ export function ContractorPermissionsTable({
                       <td className="px-4 py-4">
                         <div className="flex items-center gap-3">
                           <span className="flex h-8 w-8 flex-shrink-0 items-center justify-center rounded-full bg-indigo-50 text-sm font-bold text-indigo-700">
-                            {contractor.organisationName.charAt(0).toUpperCase()}
+                            {contractor.organisationName
+                              .charAt(0)
+                              .toUpperCase()}
                           </span>
                           <span className="text-sm font-semibold text-gray-900">
                             {contractor.organisationName}
@@ -391,59 +394,71 @@ export function ContractorPermissionsTable({
                         data-testid={`contractor-permissions-${contractor.organisationId}`}
                       >
                         {/* Full-bleed: the detail table *is* the expanded
-                            space, spanning every column of the row above. */}
+                            space, spanning every column of the row above.
+
+                            The wrapper is a one-row grid whose track animates
+                            0fr → 1fr, so the detail unrolls to whatever height
+                            its own content needs — no measuring, and no effect
+                            to run the animation: mounting starts it. */}
                         <td colSpan={4} className="p-0">
-                          <table className="w-full border-collapse">
-                            <thead>
-                              <tr className="border-b border-gray-200 bg-gray-100/60 text-xs text-gray-600">
-                                <th className="px-4 py-2 text-left font-semibold">
-                                  Workstream
-                                </th>
-                                {PERMISSION_COLUMNS.map((column) => (
-                                  <th
-                                    key={column.key}
-                                    className="w-40 px-4 py-2 text-left font-semibold"
-                                  >
-                                    {column.header}
-                                  </th>
-                                ))}
-                              </tr>
-                            </thead>
-                            <tbody>
-                              {contractor.assignments.map((assignment) => (
-                                <tr
-                                  key={assignment.id}
-                                  className="border-b border-gray-100 last:border-b-0"
-                                  data-testid={`assignment-row-${assignment.id}`}
-                                >
-                                  <td className="px-4 py-2.5">
-                                    <span className="text-sm font-medium text-gray-800">
-                                      {assignment.workstreamName}
-                                    </span>
-                                    {assignment.workOrders > 0 && (
-                                      <span className="ml-2 text-xs text-gray-400">
-                                        {assignment.workOrders}{" "}
-                                        {assignment.workOrders === 1
-                                          ? "work order"
-                                          : "work orders"}
-                                      </span>
-                                    )}
-                                  </td>
-                                  {PERMISSION_COLUMNS.map((column) => (
-                                    <td key={column.key} className="px-4 py-2.5">
-                                      <PermissionState
-                                        granted={assignment[column.key]}
-                                        label={column.header}
-                                        workstreamName={
-                                          assignment.workstreamName
-                                        }
-                                      />
-                                    </td>
+                          <div className="grid animate-disclosure-open motion-reduce:animate-none">
+                            <div className="min-h-0 overflow-hidden">
+                              <table className="w-full border-collapse">
+                                <thead>
+                                  <tr className="border-b border-gray-200 bg-gray-100/60 text-xs text-gray-600">
+                                    <th className="px-4 py-2 text-left font-semibold">
+                                      Workstream
+                                    </th>
+                                    {PERMISSION_COLUMNS.map((column) => (
+                                      <th
+                                        key={column.key}
+                                        className="w-40 px-4 py-2 text-left font-semibold"
+                                      >
+                                        {column.header}
+                                      </th>
+                                    ))}
+                                  </tr>
+                                </thead>
+                                <tbody>
+                                  {contractor.assignments.map((assignment) => (
+                                    <tr
+                                      key={assignment.id}
+                                      className="border-b border-gray-100 last:border-b-0"
+                                      data-testid={`assignment-row-${assignment.id}`}
+                                    >
+                                      <td className="px-4 py-2.5">
+                                        <span className="text-sm font-medium text-gray-800">
+                                          {assignment.workstreamName}
+                                        </span>
+                                        {assignment.workOrders > 0 && (
+                                          <span className="ml-2 text-xs text-gray-400">
+                                            {assignment.workOrders}{" "}
+                                            {assignment.workOrders === 1
+                                              ? "work order"
+                                              : "work orders"}
+                                          </span>
+                                        )}
+                                      </td>
+                                      {PERMISSION_COLUMNS.map((column) => (
+                                        <td
+                                          key={column.key}
+                                          className="px-4 py-2.5"
+                                        >
+                                          <PermissionState
+                                            granted={assignment[column.key]}
+                                            label={column.header}
+                                            workstreamName={
+                                              assignment.workstreamName
+                                            }
+                                          />
+                                        </td>
+                                      ))}
+                                    </tr>
                                   ))}
-                                </tr>
-                              ))}
-                            </tbody>
-                          </table>
+                                </tbody>
+                              </table>
+                            </div>
+                          </div>
                         </td>
                       </tr>
                     )}
@@ -467,7 +482,10 @@ export function ContractorPermissionsTable({
             Work orders can only be imported once every workstream has both a
             stage ladder and a contractor.
           </p>
-          <ul className="mt-3 space-y-1.5" data-testid="contractors-readiness-list">
+          <ul
+            className="mt-3 space-y-1.5"
+            data-testid="contractors-readiness-list"
+          >
             {readiness.incomplete.map((workstream) => (
               <li
                 key={workstream.name}
diff --git a/tailwind.config.js b/tailwind.config.js
index b3b58292..f0b0a768 100644
--- a/tailwind.config.js
+++ b/tailwind.config.js
@@ -190,12 +190,27 @@ module.exports = {
             height: "0",
           },
         },
+        // A disclosure row unrolling to its own content height, without that
+        // height having to be measured: the wrapper is a one-row grid and the
+        // track animates from 0fr to 1fr. Used by the contractor permissions
+        // sub-row (#413) — see `animation["disclosure-open"]`.
+        "disclosure-open": {
+          from: {
+            gridTemplateRows: "0fr",
+            opacity: "0",
+          },
+          to: {
+            gridTemplateRows: "1fr",
+            opacity: "1",
+          },
+        },
       },
       animation: {
         "accordion-down": "accordion-down 0.2s ease-out",
         "accordion-up": "accordion-up 0.2s ease-out",
         "accordion-down": "accordion-down 0.2s ease-out",
         "accordion-up": "accordion-up 0.2s ease-out",
+        "disclosure-open": "disclosure-open 160ms ease-out",
       },
       maxWidth: {
         "8xl": "90rem",