0.7.1: narrow Step::Base#run_once ArgumentError rescue to Runner setup

[justi]

Summary

Follow-up to the Codex review P2 finding on PR #13 (v0.7.0), acknowledged there as a known limitation and tracked for v0.8. This is the first v0.8-planned deliverable from the local v0.8 roadmap — small enough to ship as a 0.7.x patch rather than wait for the batch.

Before: Step::Base#run_once wrapped the entire Runner chain in rescue ArgumentError to convert DSL misconfiguration (e.g. prompt has not been set) into :input_error. Side effect: any ArgumentError raised from adapter code during Runner#call — wrong arity, bad config arg, any programmer bug — was silently coerced into :input_error and re-tried as if the user had supplied bad input.

After: the rescue is scoped to the Runner-construction phase only. DSL configuration errors still produce :input_error. ArgumentError raised during Runner#call propagates to the caller.

The InputValidator inside Runner continues to handle Dry::Types::CoercionError, TypeError, ArgumentError in its own scoped rescue and returns :input_error for bad-input cases. That path is unchanged.

Why it matters

The narrative of v0.7 (CHANGELOG + README + ADR-0020) was "programmer errors propagate, provider errors become :adapter_error". The AdapterCaller already respected that — narrow rescue to RubyLLM::Error + Faraday::Error. But run_once's broader rescue ArgumentError was a backdoor that let adapter-code ArgumentError bugs slip back into :input_error and become retry targets.

This closes that backdoor. Programmer bugs raised during an adapter call now surface loudly instead of being disguised as "user gave bad input."

Test plan

• bundle exec rspec — 1341 examples, 0 failures, 8 pending (all pending are API-key-gated live LLM tests)
• New regression specs in retry_integration_spec.rb under "transport error handling":
  • it "propagates ArgumentError from adapter code (programmer bug, not bad input)" — adapter raising ArgumentError now propagates instead of being coerced into :input_error.
  • it "still converts DSL misconfiguration ArgumentError to :input_error (prompt missing)" — prompt has not been set still becomes :input_error. Existing BUG 48 adversarial spec (step without prompt → :input_error) also still passes, verifying the narrow path works.
• Version bump 0.7.0 → 0.7.1; CHANGELOG entry added.

Semver positioning

Technically a behavioral change — callers previously relying on ArgumentError from adapter code to produce :input_error results will now see the exception propagate. Shipped as patch (0.7.1) rather than minor (0.8.0) because:

• No external user base (the previous deprecation-warning cycle was rejected on this same basis in ADR-0020).
• v0.8.0 is reserved for the larger reach expansion (Chat#with_contract spike) per local ADR-0021.
• CHANGELOG documents the change clearly.

[Copilot]

Pull request overview

This PR narrows Step::Base#run_once’s ArgumentError handling so that only DSL/setup-time misconfiguration is converted into an :input_error result, while ArgumentError raised during adapter execution propagates (treating it as a programmer/runtime error rather than “bad input”).

Changes:

• Scope rescue ArgumentError to the Runner construction phase in Step::Base#run_once, allowing adapter-phase ArgumentError to bubble up.
• Add regression specs covering (a) propagating adapter ArgumentError and (b) still converting missing-prompt DSL misconfiguration to :input_error.
• Bump version to 0.7.1 and document the behavioral change in the changelog.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
lib/ruby_llm/contract/step/base.rb	Refactors run_once to only rescue ArgumentError during Runner setup, not during Runner#call.
spec/ruby_llm/contract/step/retry_integration_spec.rb	Adds regression coverage for adapter-phase ArgumentError propagation and prompt-missing :input_error.
lib/ruby_llm/contract/version.rb	Version bump to 0.7.1.
CHANGELOG.md	Documents the behavioral change in 0.7.1.
Gemfile.lock	Updates the local gem version entry to 0.7.1.

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