Replace the bespoke store Lua object with ordinary tool calls

[gregjkal]

Summary

Remove the bespoke store Lua object and make store operations ordinary tool calls, so Store is just another entry in the RunConfig ToolCatalog.

Details

Discussed in #cppa-wg21-org on 2026-09-09 and again on 2026-09-10.

• Today store is a table injected into the Lua VM whose keys call back into the host. The PromptForge Prompting Language document (## Store) describes it as the agent's virtual file system.
• Proposed shape:

  tool_call("store.write_file", ...)

  with optional pure-Lua sugar if wanted:

  local store = tables:new()
  store.append_file = tool_call("store.append")

• Guiding rule from Vinnie: if something currently written in Rust can be expressed in Lua using a lower-level primitive, keep the primitive and delete the Rust. tool_call becomes a first-class operation returning a Task-like future (async, awaitable, can fail, returns a result on success).

Rationale

• Simplifies the execute::run contract (crates/promptforge-core/src/execute.rs) by dropping the store argument and the custom API.
• Fewer categories of "happenings" makes record-and-replay for agent persistence (Agent persistence: record every tool call and assistant response, restore agent windows by replay #29) simpler.
• The same operations Lua has become available to the LLM by opt-in, since they are tools.

Related

• Agent persistence: Agent persistence: record every tool call and assistant response, restore agent windows by replay #29
• Tool packs and Task tool: Tool packs and a Task tool for orchestration #31