kiro-cli v3: SessionStart hooks run when the first prompt is sent, not when the session starts #12109

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• I have searched for duplicate or closed issues

Operating System

Amazon Linux 2023 (x86_64)

Kiro Version

kiro-cli 2.34.0 (agent engine V3), interactive kiro-cli chat

Bug Description

An agent's SessionStart hooks do not run when kiro-cli chat --agent <name> opens the session. They run only when the user sends the first prompt. A hook meant to prepare the session (log the start, load project status, warm a cache) therefore runs late, and does not run at all if the user only uses slash commands or ! shell escapes.

Steps to Reproduce

1. In an empty folder, create .kiro/agents/hookagent.json:

   {"name":"hookagent","description":"two SessionStart hooks","prompt":"You are terse.","tools":["read"],
    "permissions":{"rules":[{"capability":"fs_read","effect":"allow"}]},
    "hooks":[{"name":"a","trigger":"SessionStart","action":{"type":"command","command":"echo \"$(date +%T) hook-A\" >> /tmp/hook.log"}},
             {"name":"b","trigger":"SessionStart","action":{"type":"command","command":"echo \"$(date +%T) hook-B\" >> /tmp/hook.log"}}]}

2. Run : > /tmp/hook.log; kiro-cli chat --agent hookagent and trust the workspace.
3. Wait 25 seconds without typing. In another terminal, run cat /tmp/hook.log. Observed: empty.
4. Send any prompt, for example Reply with only OK., and check the log again.

Observed in one run: session ready at 08:07:32; log still empty after 25 s idle; prompt sent at 08:08:27; log then shows 08:08:28 hook-A and 08:08:28 hook-B. A second prompt adds nothing, so the hooks run once per session, but at the first prompt.

Expected Behavior

SessionStart hooks run when the session is created, before the first prompt. If first-prompt timing is intended, the hooks documentation should say so, because the trigger name says "session start".

Conversation ID

No response

Additional Context

• Both hooks run, in order; only the timing is in question.
• Related, not the same: --agent-engine v3 --no-interactive: agent hooks never fire and the knowledge tool is absent — non-interactive client sends no _meta.kiro capabilities #11281 (hooks never fire with --no-interactive), Agent-type SessionStart hooks do not fire in a copied/newly-registered workspace (fire in the original) #11387 (SessionStart does not fire in a copied workspace), Add an onSessionStart (or onAgentActivate) hook that fires once when a chat session begins or when the user switches to an agent #8910 (feature request for a session-start hook in the IDE).