What is SessionStart?

A set of automatic actions that runs when a coding session starts or is compacted, meaning its conversation history is shortened to save space. It provides namespace hints at startup and runs a follow-up loop after compaction.

Use it to run startup or post-compaction scripts automatically during a coding session.

It helps restore useful session context and continue automated follow-up after the conversation is shortened. The input does not specify the exact contents of the hints or loop.

SessionStart — Hook by sd0xdev

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods

npx agentmods add hooks/sd0xdev/sd0x-harness/session-start

Clone the repo

git clone --depth 1 https://github.com/sd0xdev/sd0x-harness

Per session not measured What this adds to a session before it is invoked.

When invoked not measured Not applicable: nothing here is loaded into a session.

Security scan A 0 findings. Scan, not verified.

Origin original No closer match found in the catalogue.

Security

Grade A, and why

SessionStart scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the commands this hook runs, not an audit. A hook is shell that executes on your machine at the event it names, which is why every command in it is printed with what was found.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

hooks/hooks.json · 22 lines

What it actually says

{
  "SessionStart": [
    {
      "matcher": "startup|compact",
      "hooks": [
        {
          "type": "command",
          "command": "${CLAUDE_PLUGIN_ROOT}/scripts/namespace-hint.sh"
        }
      ]
    },
    {
      "matcher": "compact",
      "hooks": [
        {
          "type": "command",
          "command": "${CLAUDE_PLUGIN_ROOT}/hooks/post-compact-auto-loop.sh"
        }
      ]
    }
  ]
}

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2d ago First seen · 22 lines scan A 0dbf482722d4

Subscribe to this mod's changes

SessionStart is a hook published in the GitHub repository sd0xdev/sd0x-harness (188 stars, last pushed 2d ago), licensed MIT. Its token cost is not measured: a hook is shell that never enters the context. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

agent-harness claude-code claude-code-plugin codex harness-engineering skills

SessionStart

Getting it into your agent

Grade A, and why

Nothing flagged

What it actually says

What this file has done since we first saw it

Other hooks, from other repositories

PreToolUse

SessionStart

PostToolUse

TaskCompleted

PostCompact

SubagentStop