skills/ce-compound/references/modes.md

# Depth and session-history: why neither is a question

Both are decisions the agent is better positioned to make than the user. Depth depends on the context budget the agent can observe and the user cannot. Session-history value is unknowable a priori to *either* party — the payoff is an unrelated earlier session the current agent was never in — so a cheap probe resolves it instead of a prompt.

**Full is the right choice for essentially every documented learning.** Its token cost is small next to the engineering work that produced the learning, and it is dwarfed by the value of a doc that compounds. Lightweight buys back context at the cost of cross-referencing, overlap detection, and semantic grounding validation, so it is for real context pressure only. If Lightweight turns out to be the wrong call for the user's taste, re-running is a rare, cheap correction — cheaper than taxing every run with a prompt.

**The session-history probe is near-free on wall-clock** because it runs alongside the research subagents, and it escalates to the expensive extraction and synthesis only when genuinely relevant candidate sessions turn up (`references/session-history.md`). This support exists only inside the compounding workflow; there is no standalone session-history product surface.

## Auto-Invoke

Completion phrases such as "that worked", "it's fixed", "working now", and "problem solved" identify the completion checkpoint; they do not establish that a learning is worth documenting. Auto-invoke only when the Preconditions in `SKILL.md` qualify the learning.

An explicit invocation with optional context requests immediate evaluation without waiting for auto-detection. It does not waive the solved, verified, and durable-learning preconditions.