Advertise cwd in the agent tool schema (#6314)

The multi-checkout spawn refusal tells the caller to specify cwd, but the
schema hid it — discoverable only by failing. Advertise it with the
worktree/disambiguation semantics; exact-list test updated, discoverability
test pins the new description.

Docs follow-up pending: SUBAGENTS.md still files cwd under parse-accepted
compat. Held out of this commit to avoid churning around contributor PR
#6335, which touches the same table; will update once it lands.

crates/tui/src/tools/subagent/mod.rs

@@ -9480,6 +9480,10 @@ impl ToolSpec for AgentTool {
                     "type": "boolean",
                     "description": "When true, create a fresh git worktree and branch for this child before it starts. Use for parallel edit tasks that must not collide with the parent checkout."
                 },
+                "cwd": {
+                    "type": "string",
+                    "description": "Working directory for this child. With worktree=true it becomes the worktree root; otherwise the child's workspace. Pass it when the parent directory holds several checkouts and the spawn names no single repository."
+                },
                 "write_roots": {
                     "type": "array",
                     "items": { "type": "string" },

crates/tui/src/tools/subagent/tests.rs

@@ -5694,6 +5694,7 @@ fn subagent_tool_schemas_advertise_real_type_and_role_vocabulary() {
         "all_parked",
         "allowed_tools",
         "coordination_contracts",
+        "cwd",
         "deliverables",
         "detail",
         "detached",
@@ -5731,7 +5732,8 @@ fn subagent_tool_schemas_advertise_real_type_and_role_vocabulary() {
         "worktree_base",
         "worktree_branch",
         "worktree_path",
-        "cwd",
+        // "cwd" deliberately advertised since #6314: the multi-checkout
+        // refusal names it as the remedy, so the schema must teach it.
         "deliberate",
         "dependencies",
         "acceptance",
@@ -5786,6 +5788,15 @@ fn agent_start_schema_documents_hidden_spawn_requirements() {
         model.contains("resolved route"),
         "model description should point at per-role resolved routes: {model}"
     );
+    // #6314: the multi-checkout refusal tells the caller to specify cwd,
+    // so the schema must advertise it before the first failure.
+    let cwd = schema_property_description(&schema, "cwd");
+    for needle in ["worktree", "several checkouts"] {
+        assert!(
+            cwd.contains(needle),
+            "cwd description should teach {needle:?}: {cwd}"
+        );
+    }
 }
 
 #[test]