fix(harvest): exclude sub-agent transcripts and agent-generated sessions from task mining

[codeL1985]

Problem

Harvest mines machine-generated prompts as if they were user tasks. On a machine with memory/observer plugins installed (e.g. claude-mem) and regular Agent-tool use, ~80% of mined tasks were not authored by the user:

1. Sub-agent sidechain transcripts — Claude Code stores them at <session>/subagents/agent-*.jsonl; os.walk sweeps them in, so every Task/Agent spawn's prompt becomes a "recurring user task" (one session contributed 19 near-duplicate tasks).
2. Other tools' agent sessions — plugins like claude-mem run their own observer agents whose transcripts look like normal multi-turn sessions, so the single-turn heuristic from Mining counts headless claude -p calls and sub-agent fan-out as user tasks, inflating recurring-task signal #62 never catches them.
3. Expanded slash-command bodies — Claude Code injects the full command markdown as a user message; _is_meta_prompt only skips short /cmd forms, so the plugin's own /skillopt-sleep command body got mined as a task (self-harvest).

Downstream effect: the optimizer trains and gates on prompts the user never wrote.

Fix

• Skip subagents/ directories and agent-*.jsonl files in the transcript walk (structural, no heuristics).
• New _AGENT_SESSION_MARKERS + _is_agent_session(): drop sessions whose FIRST user prompt is a known agent brief. Ships with markers for claude-mem and this plugin's own command; user-extensible via SKILLOPT_SLEEP_AGENT_MARKERS (comma-separated), mirroring the existing SKILLOPT_SLEEP_NEG_FEEDBACK pattern.
• _is_meta_prompt: also skip prompts containing <command-message>/<command-name> or starting with # /.

Verification

On a real ~/.claude with claude-mem installed: harvest went from 120 sessions / mostly machine-generated tasks to 55 sessions / 38 tasks, all genuinely user-authored.

🤖 Generated with Claude Code

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