Find a past agent session by topic and load its context into the current conversation. Searches the session-brain topic graph, ranking by relevance, topic membership, and time decay, then loads the winning transcript. Use when the user says "/wiki-sessions <topic>", "which session did I do X in", "find the session where I fixed X", "when did I last work on Y", "what was that session about Z", "load the session where I set up X", "have I done this before". Read-only — never writes to the vault. Requires a graph built by the session-brain skill.