fix(agent-kit): provide full thread context to first-time participating roles

When a role participates for the first time (e.g. committer), it previously
only received the system prompt + last step output, missing the full thread
history. This caused hallucination as the role had to guess what happened.

Changes:
- build-continuation-prompt.ts: detect first-time roles and include all
  steps' meta + content for last 2-3 steps (within quota)
- context.ts: add isFirstVisit detection helper
- types.ts: add isFirstVisit field to AgentContext
- hermes.ts: pass isFirstVisit through to prompt builder

Fixes #473

packages/cli-workflow/src/commands/thread.ts

@@ -649,6 +649,7 @@ function buildModeratorContext(uwf: UwfStore, chain: ChainState): ModeratorConte
     detail: step.detail,
     agent: step.agent,
     edgePrompt: step.edgePrompt ?? "",
+    content: null, // Moderator doesn't need content
   }));
   return { start: chain.start, steps };
 }