promptkit/docs/roadmap/implementation.md

Public Facade Refactor Implementation Plan

Scope And Authority

Implement the public facade roadmap without changing the consumer API or execution behavior. This plan owns implementation sequence; the feature roadmap owns the target state and compatibility requirements. The provisional profile policy is a separate, subsequent scope. Do not update catalog dependencies, introduce standard profiles, change profile stability promises, or prepare a release in these stages.

Read AGENTS.md, the development guide, and all three policies before starting: architecture, documentation, and testing. Use existing GoDoc and canonical consumer/format documentation to distinguish intentional contracts from incidental implementation. If a relocation appears to require a consumer-facing change, stop and report it rather than silently changing the contract. Existing exported declarations are not removal candidates merely because a guide does not mention them.

Each numbered stage is one implementation prompt. Complete stages in order; keep the repository building and maintain one active production path after each stage. Update affected durable documentation when its described ownership changes, rather than leaving inaccurate descriptions until the final stage. For each stage, run focused tests while developing and the complete maintainer validation workflow before acceptance. Report changes, validation results, and any unresolved failures. Do not use live providers, credentials, sibling repositories, module replacements, or a Go workspace to validate the result.

Implementation Decisions

• Add internal/engine as the composition owner. It owns engine construction, defaults, source assembly, catalog loading, registry and capacity construction, and runner/repairer wiring. It delegates execution to internal/usecase; it does not become a second runner.
• Keep root-defined public types, errors, options, conversions, collaborator adapters, and formatting. Root Engine holds a private *engine.Engine. The internal engine exposes only the domain-level operations needed for the existing facade methods. No public bridge methods or internal aliases.
• Preserve root Option and its sealed apply(*engineOptions) error mechanism. Ultimately, private root engineOptions wraps an internal engine.Options value whose private state and setters own source construction and option accumulation. Root options remain closures applying in caller order; do not replace them with a deferred list that changes when errors or copies occur.
• Put the memory profile repository in internal/profile. Existing domain, profile validation, and JSON-copy helpers remain the owners of their rules. Do not duplicate validation in the facade and repository.
• Keep public error classification and redacted public error construction in the root. Internal construction returns descriptive errors; NewEngine translates construction failures to ErrInvalidConfig as it does today. Runtime errors continue through mapPublicError at the public boundary.
• Keep PreparedExecution root-defined with its existing private use-case handle. Pass that internal handle through engine delegation without copying its execution state or creating another lifecycle owner. Private root references to specialized internal packages are allowed.
• Do not impose a single internal import on the root, introduce a generic builder framework, add caching, broaden validation, or migrate all private helpers merely to reduce root line count. Straightforward public convenience constructors and boundary conversions may remain where they are.

Stage 1: Establish The Compatibility Baseline

Purpose: make the compatibility review concrete before moving ownership.

1. Read the root declarations and tests, the consumer guide, component overview, sources document, and runner document. Identify existing contract coverage for constructor options, profile sources, injection, errors, and prepared execution. Read their owning internal tests before adding new coverage.
2. Record the pre-refactor commit ID in this plan and capture an exported API inventory for the final comparison. Include exported declarations, named types, fields and tags, interface signatures, value and pointer method sets, constants, error variables, and serialization/formatting contracts. go doc -all is a useful starting point, not a complete method-set comparison. Temporary comparison output belongs outside tracked source; do not introduce a permanent snapshot of private structure or freeze every future API addition.
3. Use existing tests first. Add only missing, consequential public regression coverage for relocation risks: source replacement versus backend accumulation, option application/capture timing, ownership of injected values and profiles, nil/zero facade behavior, and typed error translation. Keep public behavior tests in the external test package where practical. Do not duplicate full source, transport, capacity, or runner matrices.
4. In particular, inspect the existing contracts around WithProfiles copying during option application and WithBackend capturing the queue-capacity pointer value during option creation. Preserve explicit zero versus unset. Keep errors from an invalid earlier option observable even if a later option would replace it. Do not add reflection-based typed-nil rejection or eagerly read lazy consumer sources as part of the refactor.

Acceptance: the pre-refactor baseline is identified, necessary regression coverage passes, and no production ownership or behavior has changed. If the existing tests already cover these risks, do not add tests solely to fill this stage; record the coverage reviewed and proceed.

Completion

• Pre-refactor baseline commit: 7a858c2365e1a3625de67a46f5c488e0fe31856b.
• Captured the exported API inventory outside the tracked repository for the final comparison.
• Reviewed existing public coverage for source replacement, backend accumulation, option error and capture timing, injected-value and profile ownership, nil and zero facade behavior, prepared execution, and typed error translation. The existing tests cover these relocation risks without a duplicate matrix.

Stage 2: Relocate The Memory Profile Repository

Purpose: move a self-contained repository before changing engine assembly.

1. Introduce internal/profile.NewMemoryRepository accepting internal profile definitions. Move the map-backed repository and lookup implementation from root profiles.go to that package. Preserve normalized duplicate-ID detection, definition validation, missing-profile classification, inheritance metadata, and independently owned values on storage and lookup.
2. Separate public field conversion from repository normalization as necessary. Root WithProfiles converts at application time and invokes the new internal constructor. Use the existing definition-normalization and JSON-copy owners once at the repository boundary; preserve rejection of invalid extra values and deep-copy guarantees without an unnecessary second validation pass. Audit other callers before changing the responsibilities of toDomainProfile.
3. Remove the root repository implementation. Leave public Profile and OpenAICompatibleProfile unchanged, including the convenience constructor's documented copy behavior; do not strengthen that contract incidentally.
4. Move private repository tests to internal/profile, adapting inputs to internal values. Retain representative public WithProfiles integration and conversion coverage at the root. Add only uncovered copy/validation cases. Update the internal source document and inventory for the new owner.

Acceptance: WithProfiles uses the internal repository in the active engine; public behavior is unchanged and no duplicate root repository remains.

Completion

• Moved the in-memory repository, normalization, validation, and defensive copies into internal/profile.
• Kept public conversion and WithProfiles application timing at the root.
• Moved focused repository coverage to internal/profile and retained facade-level copy timing coverage.
• Updated the implemented component and source ownership documentation.

Stage 3: Move Engine Assembly And Delegation Inward

Purpose: establish the internal engine while leaving source-option relocation for the next prompt.

1. Add internal Config, Options, and Engine types. Internal Config carries the existing construction settings, not a new consumer configuration API. For this stage, Options may carry the already-prepared collaborators, repositories, backend definitions, and source-presence flags from the root option state. Do not lose distinctions between an absent source and an explicitly supplied empty source. Stage 4 removes this transitional mapping.
2. Move the assembly portion of root NewEngine, after option application, into internal/engine.New, including maintained module imports and newProfileRepository. Preserve the existing assembly semantics:
   • prompt-source requirement and configured source defaults;
   • validated maintained catalogs and engine-local backend registry;
   • raw profile precedence: memory, ordinary configured source, application fallback, maintained catalog; an explicit ordinary source replaces Config.ProfileDir, and one resolver wraps the complete overlay;
   • schema default and supplied validator selection;
   • supplied or default client and artifact reader selection; and
   • one capacity manager per engine, one capacity wrapper around the selected client, and that same wrapped client used by runner and repairer.
3. Give internal Engine domain-level forwarding methods for the existing prepare, run, prepared-execution, and inspection operations. Keep runner orchestration and prepared-handle lifecycle in internal/usecase. Do not add another queue, retry loop, mutex, source cache, or execution state machine.
4. Change root Engine to hold the internal engine. Root NewEngine still applies options and maps constructor errors. Root methods still check nil/zero receivers, convert/validate public requests at their existing boundary, convert results, and translate runtime errors. Do not wrap an error twice or expose internal typed provider errors instead of public ones.
5. Adapt tests that inspect private runner fields to the new owner or, where feasible, observable contract assertions. Reuse existing tests for prepared handle engine binding, shared copied-handle state, consumption/discard, cancellation, redaction, repair, and capacity. Add an assembly test only if a consequential wiring obligation is otherwise untested.
6. Update architecture, component inventory, sources, and runner documentation to describe the implemented split. Remove the superseded root assembly path.

Acceptance: all public operations route through one internal engine and the existing runner; maintained catalogs and component wiring are internally owned. Prepared-execution behavior and public error contracts remain unchanged.

Completion

• Added internal/engine as the owner of engine assembly and runner delegation.
• Kept the public facade's option application, conversions, nil checks, prepared-execution wrapper, and error translation at the root.
• Updated architecture, component, source, and runner documentation for the implemented ownership split.

Stage 4: Move Option State And Source Construction Inward

Purpose: finish the ownership split without changing the public option API.

1. Replace the root collaborator/flag record with a private wrapper around engine.Options. Move the construction state into private fields of that internal type. Remove Stage 3's transitional root-to-internal state mapping. Internal setters correspond to the existing source, profile, backend, client, and artifact options; no generic option registry or callback framework.
2. Move filesystem/fs.FS repository and validator construction, fileSource, source-presence flags, replacement rules, and backend accumulation into internal option methods. Invoke them during each root option's apply, not collectively after all options. Preserve current file checks and lazy source loading; do not add path restrictions or normalize actual paths beyond the existing contract. Preserve separate blank checks for whitespace-bearing valid paths.
3. Keep public-to-internal conversion and public collaborator adapters at the root. Preserve closure capture and validation timing from Stage 1, including queue-capacity capture, profile copies, nil options, and ordinary interface nil checks. Internal methods consume internal values/interfaces without importing root types. Do not copy injected client or reader implementations.
4. Root NewEngine now performs only ordered option application, configuration translation, internal construction, and public error translation. Review the remaining root imports/helpers: retain boundary work, remove dead assembly helpers, and do not relocate formatting or conversion for appearance alone.
5. Move implementation-only option/source setup tests with their owner, while retaining public timing and error assertions at the facade. Update affected documentation immediately. No exact private field layout becomes a test requirement.

Acceptance: the root no longer constructs repositories, validators, registries, capacity managers, catalogs, or runners. Public options still have their existing names, signatures, ordering, capture, and error behavior. No transitional state mapping or duplicate source-assembly path remains.

Completion

• Wrapped the root option state around internal engine options with private construction state.
• Moved filesystem and file source setup, source replacement, profile repository construction, validator construction, and backend accumulation into internal option methods.
• Kept ordered public option application, boundary conversion, collaborator adaptation, and error translation in the root facade.
• Updated current architecture and internal ownership documentation.

Stage 5: Guard The Public Boundary And Dependency Direction

Purpose: protect the intended architecture without freezing private layout.

1. Add a focused root architecture test using Go type information. Load the compiled root package with standard-library go list export data and go/importer/go/types; avoid a new production dependency or parsing only surface syntax. It must work in the ordinary offline maintainer workflow once normal module dependencies are available.
2. Inspect exported declarations, public field types, function signatures, interface methods, and both pointer and value method sets. Follow nested type expressions and aliases with a visited set to avoid recursion. Reject references to this module's internal types in accessible public surfaces, public aliases to those types, and internal anonymous embedding that exposes implementation methods. Account for generics if encountered rather than silently ignoring their signatures or constraints.
3. Permit private internal fields and the sealed Option method. Do not follow inaccessible fields as if they were public contracts or reject all aliases indiscriminately. Check accessible promoted methods even if the embedded field itself is unexported. Do not require the root to import only internal/engine, or impose rules on unrelated third-party internals.
4. Check production package imports, using package metadata, for any dependency from this module's internal/ packages to its root. Exclude external test packages from that restriction. Do not assert an exact internal package list.
5. Exercise the boundary checker with a small in-memory fixture set: allowed private internal state and sealed option; forbidden direct/nested internal signature or field; forbidden internal alias and promoted method. Keep the test helper local and proportionate, not a reusable architecture framework.

Acceptance: the completed refactor passes the checks; representative violations fail for the intended reason, and ordinary private implementation changes remain possible. No ConfigKit checkout or other sibling is needed.

Stage 6: Complete Compatibility And Documentation Review

Purpose: verify the whole refactor, not just successful compilation of each move.

1. Compare the final exported API against the Stage 1 commit, including method sets, fields/tags, type ownership, interfaces, and public error identities. Review any difference; no API additions/removals/redesigns are authorized. Inspect supported serialization and formatting alongside the existing tests.
2. Review the final root package for retained business assembly or duplicated repositories, and the internal engine for duplicated runner behavior. Review test moves for lost assertions and duplicate matrices. Existing specialized packages should still own their detailed behavior tests; facade tests should prove conversion, compatibility, and representative assembled behavior.
3. Finish the durable documentation review: architecture owns dependency rules; the internal overview inventories owners; sources and runner docs explain their current implementation. Correct stale links and root-assembly claims. Keep public GoDoc authoritative and avoid adding consumer migration steps, format rules, or new guarantees for an internal relocation. No separate ADR is needed merely to restate the existing facade policy.
4. Run the entire maintainer workflow, including race tests, vet, build, both offline examples, formatting, local links, and repository hygiene checks. Review the complete diff against the baseline. Report any environmental validation blocker explicitly; do not call an unrun check successful.
5. Report completion against the feature roadmap criteria. Retain these two temporary documents for the maintainer's completion review; their later retirement follows documentation policy. Do not start the profile-policy work or tag a release as part of this plan.

Acceptance: compatibility review finds no unauthorized changes, all required validation passes, documentation matches the implemented architecture, and the refactor is ready for independent review before subsequent feature work.

Open Questions

None requiring a product decision for this scope. The refactor preserves the existing API and behavior; the provisional catalog policy and its release decisions remain outside this plan.