promptkit/docs/internal/sources.md

# Internal Sources And Validation

## Purpose

This document describes Promptkit's implemented internal source, artifact,
rendering, and output-validation behavior. The
[architecture policy](../policy/architecture.md) owns the library boundary and
dependency rules. None of these internal packages is a supported consumer API,
and the root engine assembles them behind its public source options and values.
The [framework format reference](../formats.md) owns the exact file fields,
validation modes, built-in catalog, and source precedence.

## Prompt Definitions

`internal/promptdef` uses one source-neutral flow for prompt selection and
normalization. That flow scans normalized YAML ID and version metadata,
requires one strictly decoded document per file, classifies errors for the
selected definition, detects duplicates, and normalizes the exact match.
Small operating-system and `fs.FS` adapters own discovery, byte reads, display
paths, content opening, and root containment. Each lookup remains a
point-in-time scan: definitions and catalogs are not cached, and file-backed
message content is opened only for the exact selected candidate.

Operating-system sources enforce containment against canonical roots and
targets so symlinks cannot escape. Injected `fs.FS` sources enforce containment
in their clean relative path namespace. A single-file source uses the selected
prompt file's containing directory as its root. Every content path must be
relative and is opened from its exact parsed text after a separate blank check;
contained parent components and whitespace-bearing names remain valid.

Exact prompt inspection performs one point-in-time lookup through that same
repository and validates referenced message content before returning declared
metadata. It does not parse templates or read profile, input, or schema
sources, and it does not retain the definition for a later execution.

Its package tests own prompt selection, strict decoding, definition validation,
duplicate detection, and source containment:
[prompt-definition repository tests](../../internal/promptdef/repository_test.go).

## Profiles And Built-Ins

`internal/profile` loads and validates execution profiles from an
operating-system filesystem or an `fs.FS`. A file contains exactly one YAML
document and its trimmed YAML `id` is its only selection identity; filenames do
not confer authority. Each point lookup reads discovered files once for their
metadata and reuses the selected file's bytes for strict decoding; unrelated
profiles are not fully decoded. Strict selected decoding recognizes the
optional `backend` field, trims its value, and requires a model plus at least
one non-blank backend or endpoint. File-backed `extra_params` values are
validated and defensively copied through the shared bounded JSON-value owner
before a profile is published. OpenAI-compatible reserved-field policy remains
with the model-client and backend-registry owners.

The overlay repository consults the next repository only when the
higher-precedence repository reports that a profile is absent. A reliably
selected malformed profile stops fallback, while an unrelated malformed file
does not become authoritative through its filename. Loading does not check
backend registry membership because the available registry belongs to the
assembled engine; the runner checks membership during preparation and exact
profile inspection.

The root engine assembles profile repositories in precedence order: in-memory
profiles, one ordinary configured source, an application fallback source, then
the embedded built-in catalog. An explicit file or `fs.FS` profile source
replaces `Config.ProfileDir` within the ordinary configured-source category.

Exact profile inspection performs one point-in-time lookup through those
profile sources and checks the resolved target without reading prompt, input,
or schema sources. It does not retain that lookup for a later execution.

`internal/profile/builtin` embeds the maintained built-in profile catalog.
Every embedded profile selects `openrouter` and inherits its endpoint and
credential environment-variable name from the built-in backend registry rather
than repeating those values. Profile loading and overlay behavior are owned by
the [profile repository tests](../../internal/profile/repository_test.go),
while catalog completeness, the backend-selection invariant, and duplicate IDs
are owned by the
[built-in repository tests](../../internal/profile/builtin/repository_test.go).

## Ordinary Artifacts

`internal/artifact` accepts explicitly typed inline references even when their
body is empty. It also resolves unrestricted, caller-selected paths only when
they identify regular operating-system files, checking that condition before
and after opening the file. It copies content into an artifact, records
metadata and an opaque content-equality value, and applies a content-type
fallback.

Regular files are read synchronously in bounded chunks. Cancellation is
checked before opening, before and after every read, and before publishing the
artifact, so a canceled read never publishes partial content. The ordinary
reader does not detach file reads into background goroutines.

This ordinary reader does not implement an inbound HTTP security boundary. In
particular, it does not constrain files to an application root or impose an
HTTP request-size policy. Scriptorium's restricted HTTP reader remains an
application concern outside Promptkit. The
[artifact reader tests](../../internal/artifact/reader_test.go) own the
implemented reader behavior and failures.

## Rendering

`internal/prompt` renders definition messages as Go templates using named
artifacts and variables. Within one render, each referenced artifact body is
converted to text lazily and cached by input name for reuse across the session
and every message; the cache is not shared across renders. Conversion uses
bounded chunks and preserves the artifact bytes exactly.

Session and message parsing and execution remain synchronous. The renderer
checks cancellation before and after each parse and execution boundary,
between artifact conversion chunks, around each message, and before publishing
the complete prompt. It cannot interrupt template work already in progress and
never publishes a partial prompt after observing cancellation. It carries
message roles, session IDs, and cache control into the rendered prompt. The
[renderer tests](../../internal/prompt/renderer_test.go) own rendering behavior.

## Schemas And Output Validation

`internal/validate` provides validators backed by an operating-system
filesystem or an `fs.FS`. Invalid generated content is returned as a validation
result; inability to load, register, or compile a schema is an operational
error.

For executable preparation, the built-in validators create a frozen validation
plan. None, basic, and JSON modes retain the effective output contract without
source access. JSON Schema mode loads the root document, resolves and compiles
every transitive reference during preparation, and retains the compiled
validator. The provider-facing structured-output metadata uses that same
captured root document.

`PrepareExecution` also completes prompt and profile selection, artifact
loading and hashing, session and message rendering, and target resolution.
`RunPrepared` uses the retained source-derived state and validation plan; it
does not reopen prompt, profile, input, or schema sources and does not rerender
the request. By contrast, ordinary `Prepare` produces a preparation value only:
a later `Run` performs its own source resolution and preparation.

The [validator tests](../../internal/validate/standard_validator_test.go) own
basic, JSON, JSON Schema, source resolution, schema loading, compilation,
frozen-reference behavior, and content-failure behavior. Prepared execution
orchestration is owned by the
[use-case tests](../../internal/usecase/prepared_execution_test.go).