Provenance now flows as a function parameter through the entire tool
dispatch chain: thought::dispatch → memory::dispatch → store methods.
Removed task_local (TASK_AGENT), thread_local (TASK_PHASE), and env
var (POC_PROVENANCE) from the tool dispatch path. The env var remains
only as a fallback for non-tool paths (CLI commands, digest).
Phase names are passed from knowledge.rs → llm.rs → api.rs, and
api.rs updates the provenance string between steps. No globals needed.
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