fix(session): validate session ID path and update tests

Move session ID detection above tree-navigation active check
so invalid inputs get clear feedback via empty_policy=notify.
Update tests to match new behavior.

Author: jensenojs

lua/opencode/commands/handlers/session.lua

@@ -180,24 +180,32 @@ local function compute_target_index(current_idx, total, direction, wrap)
 end
 
 function M.actions.navigate_session_tree(direction, interaction, wrap, empty_policy)
-  local active = state.active_session
-  if not active then
-    if empty_policy == 'notify' then vim.notify('No active session', vim.log.levels.WARN) end
-    return
-  end
-
-  -- If direction is not a known navigation direction, treat it as a target session ID
+  -- If direction is not a known navigation direction, treat it as a target session ID.
+  -- This path runs before the tree lookup so invalid inputs get clear feedback.
   if direction
     and not tree_directions[direction]
     and direction ~= 'forward'
     and direction ~= 'backward'
   then
+    empty_policy = empty_policy or 'notify'
+    if not state.active_session then
+      if empty_policy == 'notify' then
+        vim.notify('No active session to navigate from', vim.log.levels.WARN)
+      end
+      return
+    end
     if interaction == 'picker' then
       return session_runtime.select_session(direction)
     end
     return session_runtime.switch_session(direction)
   end
 
+  local active = state.active_session
+  if not active then
+    if empty_policy == 'notify' then vim.notify('No active session', vim.log.levels.WARN) end
+    return
+  end
+
   local dir = tree_directions[direction]
   if dir then
     local target_id = dir.get_target(active)

tests/unit/commands_handlers_spec.lua

@@ -517,11 +517,15 @@ describe('opencode.commands.handlers', function()
   end)
 
   -- normalize_navigate_args tests via command_defs
-  it('normalize_navigate_args rejects invalid direction', function()
+  it('non-direction string is treated as session ID, notifies when no active session', function()
     local session_handler = require('opencode.commands.handlers.session')
-    local ok, err = pcall(session_handler.command_defs.navigate_session_tree.execute, { 'up' })
-    assert.is_false(ok)
-    assert.equal('invalid_arguments', err.code)
+    local state = require('opencode.state')
+    local notify_stub = stub(vim, 'notify')
+    state.session.clear_active()
+    local ok = pcall(session_handler.command_defs.navigate_session_tree.execute, { 'up' })
+    assert.is_true(ok)
+    assert.stub(notify_stub).was_called()
+    notify_stub:revert()
   end)
 
   it('normalize_navigate_args rejects invalid interaction', function()

tests/unit/formatter_spec.lua

@@ -585,9 +585,9 @@ describe('formatter', function()
     end)
 
     assert.are.same({
-      text = '[S]elect Child Session',
+      text = '[S] Open this Session',
       type = 'navigate_session_tree',
-      args = { 'child', 'picker' },
+      args = { 'ses_child' },
       key = 'S',
       display_line = 1,
       range = { from = 2, to = 5 },