scriptorium/docs/internal/runner.md

Runner Internals

Purpose

internal/usecase.Runner is the core use case orchestrator for prompt preparation and execution.

It owns request validation, prompt/profile resolution, runtime-parameter merge, artifact loading, prompt rendering, structured-output setup, LLM invocation, output validation, and result metadata.

Inputs And Outputs

Primary input type:

• domain.RunRequest

Primary output types:

• domain.PreparedRun from Prepare
• domain.RunResult from Run

LLM boundary types:

• domain.GenerateRequest
• domain.GenerateResponse

Boundaries

Runner coordinates the following interfaces:

• promptdef.Repository
• profile.Repository
• artifact.Reader
• prompt.Renderer
• llm.Client
• validate.Validator
• optional usecase.OutputRepairer

Transport concerns (CLI flags, HTTP DTO parsing, status-code mapping) stay outside runner.

Config Fields Used

Runner does not read app config files directly.

It receives fully constructed repositories/readers/validators from adapters. Effective behavior depends on adapter wiring, including:

• prompt/profile directories
• schema base directory
• selected profile/runtime overrides in request

External Adapters Used

Runner works with adapter implementations via interfaces. Current wiring from CLI/HTTP uses:

• filesystem prompt/profile repositories
• composite artifact reader
• Go-template prompt renderer
• OpenAI-compatible LLM client
• standard validator

State And Resume Behavior

Runner is stateless across requests.

• No durable run-state storage.
• No built-in resume/skip checkpoints.
• Each Run/Prepare executes from request inputs and current repositories.

Failure Behavior

Primary runner error classes:

• ErrInvalidRequest: invalid run request envelope.
• ErrProfileRequired: specific invalid-request reason when neither request profile_id nor prompt default_profile is available.
• ErrAPIKeyEnvMissing: specific invalid-request reason when api_key_env is set but the named environment variable is unset/empty.
• ErrProfileLoad: prompt/profile repository load failures.
• ErrArtifactLoad: artifact read failures.
• ErrPromptRender: template render failures.
• ErrLLMGenerate: outbound model request failures.
• ErrValidation: validation runtime failures (including structured-output schema load/compile failures).

Reason sentinel behavior:

• ErrProfileRequired and ErrAPIKeyEnvMissing are wrapped with ErrInvalidRequest.
• Adapters can use errors.Is for stable reason mapping without matching runner prose.

Validation content failures are not run errors:

• Run can succeed with Validation.Status == failed.
• CLI maps this to exit code 2.
• HTTP returns 200 with failed validation details.

Prepare Flow

Prepare performs:

1. validate request basics (prompt ID present).
2. load prompt definition by ID/version.
3. select profile ID:
   • explicit request profile ID
   • prompt default_profile
   • otherwise return an invalid request with ErrProfileRequired
4. load execution profile.
5. merge effective runtime target:
   • built-in execution defaults
   • selected profile values
   • request overrides
6. verify required api_key_env environment variable:
   • missing/empty env value returns an invalid request with ErrAPIKeyEnvMissing
   • only the environment-variable name is retained; secret value is never returned
7. resolve output contract and structured-output schema payload when json_schema mode is active.
8. read input artifacts.
9. render prompt messages, including any normalized message cache-control metadata.
10. compute prompt/input/render hashes and return PreparedRun.

rendered_prompt_hash includes cache-control metadata when present because it affects the outbound provider request. Prompts without cache control keep the role/content hash behavior.

Prepare does not call the LLM.

Run Flow

Run performs:

1. generate run ID.
2. call Prepare.
3. call LLM with prepared messages/effective target/structured-output spec.
4. build output artifact content type from output format.
5. validate output.
6. optionally attempt bounded repair when repairer is injected and contract allows it.
7. return RunResult with artifact, raw output, validation, hashes, profile/model metadata, token/cache usage, and timestamps.

Repair Hook Boundary

Repair attempts occur only when all are true:

• repairer is injected
• repair_attempts > 0
• validation status is failed
• validation mode is json or json_schema

Current production wiring boundary:

• CLI and HTTP adapters call usecase.NewRunner(...) (no repairer argument).
• Therefore normal CLI/HTTP execution does not perform repair attempts today.

Tests To Inspect Before Changing

• internal/usecase/runner_test.go
• internal/usecase/integration_test.go
• internal/adapter/cli/run_test.go
• internal/adapter/http/handler_test.go

Architectural Invariants

• Run reuses Prepare; prepare logic is not duplicated.
• Effective API-key environment-variable name may appear; resolved secret value must not.
• Structured-output schema document must load before LLM call for json_schema mode.
• Repair loops are bounded by repair_attempts and repairer presence.
• Runner stays transport-agnostic.