refactor(agent-loop): drop the steering/message session event

Steer, inject, and followup now land as durable user/message events on the
session surface; the steering/message event type and its ConversationNode
kind are removed from the client projection. Update tests, docs, generated
catalogs, and agent notes to match, and align the steering e2e fixture and
prompt inventory assertions with the durable user/message landing.

packages/goal/tool-goal/src/authority.ts

@@ -70,8 +70,7 @@ export function goalToolExecution(ctx: Context, exec: ToolRunContext): GoalToolE
 function hasDirectHumanInput(ctx: Context, execution: GoalToolExecution): boolean {
   if (!ctx.agents.roots().includes(execution.agent)) return false
   return execution.events.some(event =>
-    (event.type === 'user/message' && event.data.source.kind === 'user')
-    || (event.type === 'steering/message' && event.data.message.source.kind === 'user'))
+    event.type === 'user/message' && event.data.source.kind === 'user')
 }
 
 /** Whether this turn is the current goal's exact admitted round. */

packages/goal/tool-goal/tests/tool-goal.spec.ts

@@ -305,16 +305,13 @@ describe('goal tool execution authority', () => {
     const humanTurn = openTurn(root, { kind: 'user' })
     const created = ctx.goals.create(root.agent, { objective: 'steer me' })
     closeTurn(root, humanTurn)
-    const round = openTurn(root, {
+    openTurn(root, {
       kind: 'goal', goalId: created.id, revision: created.revision, round: 1,
     })
-    root.session.append('steering/message', {
-      turn: round,
-      message: createUserMessage({
-        content: [{ type: 'text', text: 'pause now' }],
-        source: { kind: 'user' },
-      }),
-    }, { surfaceOp: 'append' })
+    root.session.append('user/message', createUserMessage({
+      content: [{ type: 'text', text: 'pause now' }],
+      source: { kind: 'user' },
+    }), { surfaceOp: 'append' })
     const paused = await execute(ctx, 'update_goal', {
       goal_id: created.id, revision: created.revision, action: 'pause',
     }, root.agent)