[superseded] Agent-as-tool delegation — see activeagent#360

[TonsOfFun]

I recommend closing this in favour of activeagent#360. Opening it as a draft so the decision is explicit rather than silent — the work is real and passing, it is just in the wrong repo.

Why I think it belongs in activeagent

docs/framework/v2-extraction-roadmap.md in activeagent draws the line:

• activeagent — execution: agents, providers, tools, telemetry
• solid_agent — persistence: contexts, generations, tool streams, memory, pricing
• the platform — accounts, billing, quotas, hosted UI, multi-tenancy

Delegation is execution, not persistence. And the roadmap lists it explicitly as an activeagent v2 item:

4. Agent-to-agent delegation.tools_function only routes back to self. The platform built call_agent (sub-agent invocation with a Thread.current depth cap) as an app tool. v2: a first-class delegation primitive — invoke another agent class/instance as a tool, with depth limits and shared trace/context correlation.

I built the core version first, was asked to move it here, and only found the roadmap afterwards while researching the records extraction. Flagging it rather than quietly letting whichever PR merges first decide.

What this branch contains, if you want it anyway

The same feature adapted to this gem's conventions, and the adaptation surfaced two things worth keeping regardless of where delegation lands:

• SolidAgent::ModelPricing is better than the Delegation::Pricing I wrote for core. It resolves rates from RubyLLM's registry with a static fallback and a blended default, so max_cost works with no configuration — and mock models correctly price at $0, so a cost budget never trips by accident in tests. If delegation stays in activeagent, that gem needs an equivalent or the two should share one.
• HasTools sets the convention that tools are passed explicitly. So this version uses prompt(tools: delegated_tools) rather than auto-merging, which drops the core patch entirely — no monkeypatching, survives ActiveAgent upgrades. auto_delegate! is opt-in and documented as coupled to a private method.

Also here: an integration harness (test/integration/, rake test:integration) running against a real ActiveAgent::Base and driving the genuine provider tool loop, plus a test-only Fake provider giving backend-swap tests a second service without pulling in a vendor SDK. 55 integration tests, 0 failures; 220 unit unchanged. That harness is useful independent of delegation — if this PR closes, it is worth salvaging.

If you close this

#6 (the records extraction) was deliberately rebased off main rather than stacked on this branch, so closing this one costs nothing there. The one casualty is test/integration/, which lives only here — say the word and I will lift it onto a standalone branch.

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[TonsOfFun]

Closing — superseded by activeagent#360.

Confirmed by diff that this is not a variant of that implementation, it is the same one:

File	Lines	Differences
schema.rb	220	1 — the module name
runner.rb	283	2 — module name, plus one line routing cost through ModelPricing
backend.rb	109	identical in both

Delegation is execution, and docs/framework/v2-extraction-roadmap.md files execution under activeagent — naming agent-to-agent delegation as v2 item 4 specifically. Two copies of the same ~900 lines drifting apart is the worse default.

Two things from this branch are worth keeping and are not carried by #360:

• SolidAgent::ModelPricing is the better cost implementation. activeagent's Delegation::Pricing ships an empty rate table by design, so max_cost silently does nothing until an app registers rates. This one resolves from RubyLLM's registry with a static fallback, and prices mock models at $0 so cost budgets do not trip in tests. activeagent cannot depend on solid_agent, so that gem either grows an equivalent or keeps max_cost opt-in — tracked on #360.
• test/integration/ — a harness driving a real ActiveAgent::Base through the genuine provider tool loop, plus a Fake provider giving backend-swap tests a second service without a vendor SDK. Useful to this gem independent of delegation, and easy to lift onto a standalone branch.

A docs page covering how activeagent's delegation meets this gem's persistence (delegated runs as AgentRun rows, the ledger against ModelPricing, sub-agent contexts under the parent trace) is deferred, not dropped.

#6 is unaffected — it was rebased off main rather than stacked on this branch, so closing this costs it nothing.

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