ConfigKit/docs/roadmap/promptkit-feature-request.md

PromptKit Feature Request: Configuration Input Destinations

Status: consumer feature request; not accepted or implemented.

Requested Capability

Provide a public API through which a consumer can select a destination mapping path for each configuration input. The input's application content contributes beneath that path while retaining ConfigKit's normal composition, precedence, inheritance, validation, diagnostics, and inspection behavior.

PromptKit needs this capability for its proposal 3, Collections With Mounted Configuration Fragments, recorded in PromptKit's docs/roadmap/configuration-collections-mounted-fragments.md. This request describes the public API needs and observable acceptance criteria. It does not prescribe ConfigKit's internal design or an implementation plan.

The reviewed public baseline is ConfigKit v0.7.1. The current layered-loading contract lets consumers choose sources, import policy, filesystem context, and precedence groups, but does not provide an input destination. Existing behavior remains authoritative until an extension is adopted.

Consumer Problem

PromptKit applications assemble independently maintained collections of prompts, inference profiles, and backends. Collections can contain identical local names, such as summarize.alerts, without identifying the same resource. PromptKit wants an effective configuration organized by collection, while letting authors omit repeated collection and resource-container wrappers from individual files.

A file selected from a collection's prompts directory would contain:

summarize.alerts:
  version: "1"
  default_profile: provider/brief
  messages:
    - role: user
      content: Summarize the weather alerts.
  output:
    format: text
    validation_mode: none

Given destination [collections, weatherreporter, prompts], its contribution would appear in the final application configuration as:

collections:
  weatherreporter:
    prompts:
      summarize.alerts:
        version: "1"
        default_profile: provider/brief
        messages:
          - role: user
            content: Summarize the weather alerts.
        output:
          format: text
          validation_mode: none

Another collection can contribute summarize.alerts beneath [collections, homewatch, prompts] without conflicting. After final handoff, PromptKit interprets these as weatherreporter/summarize.alerts and homewatch/summarize.alerts. The profile reference is illustrative and must be supplied separately by the application configuration.

PromptKit will support one installed definition per prompt. Its optional flat version is ordinary domain metadata, not a merge identity. This request does not need identified-record sequences, sequence-root documents, or a custom merge policy.

Authors could write the complete wrappers today, but that repeats assembly details in every fragment. Consumer-side parsing and wrapping would put generic source processing back into PromptKit and complicate source attribution. PromptKit instead wants to select sources and destinations, then receive one final configuration through ConfigKit's supported loading lifecycle.

Minimum Public API

Per-Input Destination

Allow a destination to be attached to each Input passed to LoadLayered. One possible public spelling is an optional Destination Path field on Input. The name and exact signature are suggestions; equivalent public API designs are welcome.

Illustrative consumer code using the proposed field, which does not exist in v0.7.1:

promptInput := configkit.Input{
    Source: configkit.File("/usr/local/share/collections/weatherreporter/prompts/alerts.yml"),
    Destination: configkit.Keys("collections", "weatherreporter", "prompts"),
}

peers := configkit.Underlay{
    Inputs: []configkit.Input{promptInput},
}

The consumer would include peers in its existing LayeredOptions and invoke LoadLayered with its normal root main input and application Definition. This is a partial API sketch, not an executable example or a proposed new loading entry point. A single public layered load is sufficient for PromptKit; it does not require a separate mounting operation on completed results.

The API must let the consumer:

• Express a destination relative to the application configuration root using literal mapping-key segments. Dots, slashes, and numeric-looking text inside a key are not implicit path separators or array indexes. PromptKit's namespace grammar remains its own domain rule.
• Omit the destination to retain existing root placement. An explicitly empty destination should have the same meaning. Mapping destinations are sufficient; sequence-index destinations are not needed by this request.
• Assign different destinations to inputs in the same strict composition group, and assign the same destination to inputs in separate precedence groups.
• Use the destination with existing content-bearing source kinds: host files, native filesystem files, bytes, readers, and mapping sources, subject to their existing acquisition and ownership contracts.
• Retain the existing import opt-in and filesystem context independently of the destination. A configuration destination is not a filesystem root or base directory.

PromptKit can continue to enumerate an explicitly selected directory and attach the same destination to its returned inputs. ConfigKit does not need a new directory scanner, namespace registry, filename convention, or PromptKit schema. The namespace comes from the application's assembly declaration, not from an implicit interpretation of a directory basename.

Representative Assembly

These are application choices, not ConfigKit-specific reserved paths:

Selected inputs	Destination key segments
Application main document	Root
weatherreporter/collection.yml	collections, weatherreporter
YAML files under weatherreporter/prompts	collections, weatherreporter, prompts
YAML files under homewatch/prompts	collections, homewatch, prompts
YAML files under provider/profiles	collections, provider, profiles
YAML files under provider/backends	collections, provider, backends

Peer collection contributions belong to a single strict underlay group when the application wants conflict detection among them. Intentional operator overrides use later groups or main. Destination selection must not establish precedence or make source traversal order authorize replacement.

Required Observable Behavior

Composition And Precedence

Mounted and explicitly wrapped contributions must have equivalent application values and conflict behavior at their effective destinations. Actual source locations naturally differ and must remain accurate.

Retain the strict composition and layering rules:

• Disjoint mapping entries at the same destination combine.
• Overlapping non-mapping values within a strict group conflict, including equal scalars, nulls, and sequences. Different destinations do not collide merely because the source documents share a local key.
• Later precedence layers recursively override mappings and replace other values. A strict conflict cannot be repaired by an upper layer.
• Empty mappings do not clear lower definitions; ordinary arrays remain atomic. In particular, messages does not acquire sequence-merging behavior.
• Overlapping destination paths and contributions at their ancestors follow those same rules. No namespace-level uniqueness restriction is requested.

Changing only a prompt's version in a later layer changes that field while retaining omitted lower-layer fields. ConfigKit must not treat a domain version label as a request to replace an entire definition.

Imports And Existing Structural Directives

An input with imports enabled must be able to use its existing source-root configkit.imports directive while contributing application data at a nested destination. The directive remains structural configuration, not an application field below that destination.

For the minimum API, imports inherit their importing input's destination, including transitive imports. Import paths continue to resolve relative to their declaring source's filesystem context. A mounted document must not send its imported application fields back to the configuration root accidentally.

Existing opt-in, containment, missing-input, cycle, and repeated-source behavior must remain applicable. A different destination is not a request to bypass the current rejection of a repeated physical source within a strict group.

Sibling extends must resolve against mappings at their effective destinations. For example, two independently supplied profile fragments mounted beneath the same collection's profiles mapping can establish extends: brief once they compose. Inheritance remains ConfigKit-owned; PromptKit does not perform another relationship-resolution pass.

Protected Specification Paths

The distinction between source-local field names and effective application paths is essential. PromptKit's main document will declare version: 1 at the configuration root. A separate collection metadata file can contain:

version: "2.4.0"

Mounted at [collections, weatherreporter], that field is an ordinary collection release label. It must not be rejected as an attempt to contribute the protected root specification field. The same applies to a prompt's nested optional version. Only the main-owned specification declaration uses the application's configured VersionRule.

Conversely, placement must not permit an underlay or imported fragment to claim or replace the actual protected specification path or an ancestor that would replace it. The public contract must define protection in terms of effective application paths, rather than reserving the spelling version in every source. Protection must remain valid with imports, inheritance, overlays, and explicit CLI overrides.

PromptKit needs one main-owned specification check with the existing lifecycle. It does not need main mounted away from the root, integer-to-string conversion for every nested version, or separate compatibility checks for every fragment.

Typed Loading, Diagnostics, And Inspection

The destination must be visible consistently through the ordinary public loading and inspection surface:

• Final typed configuration and application callbacks use effective destination paths. Defaults, resolution, and validation retain the existing single-load lifecycle; fragments are not independently validated as whole applications.
• Metadata and presence queries distinguish omission, explicit null, and other explicit values at the mounted paths.
• Diagnostics identify the effective conflicting or invalid path and the real contributing source locations. Consumers can determine which source and placement produced a value without recreating that relationship themselves.
• Effective rendering, explanations, history, and configuration comparison agree with the final configuration. Existing sensitivity and disclosure rules apply to mounted fields, including application path-based secret classification.
• Unsupported destination forms and destination-related loading failures use the normal structured error boundary. Exact new diagnostic codes, if needed, are for ConfigKit to define.

PromptKit does not require a separate mount registry or new inspection facade. Existing inspection APIs are sufficient if they expose accurate effective paths, source attribution, and placement information. ConfigKit should document how source-local locations relate to effective paths.

Source-Relative Resources And Lifecycle

For a mounted field such as content_file: ./summary.md, obtaining its effective origin and calling Result.SourceContext or Resolution.SourceContext must still identify the declaring source's filesystem and base directory. The same holds when that field survives an override or is inherited into another mapping. Its configuration destination must not change the meaning of the relative file reference.

Retain existing source ownership, load completion, result lifetime, containment, and resource-access behavior. Destinations must participate in documented load limits without creating a way to bypass them; this request does not prescribe new limit values or their accounting machinery.

Optional Follow-Ups, Not Prerequisites

Import destinations in YAML. A destination on an import directive could let publishers describe assembly in configuration rather than Go. Proposal 3 recommends destinations relative to the importing document's destination, with omission retaining that destination. This is useful, but per-input placement through the public API is sufficient for initial PromptKit adoption. No new directive spelling is selected by this request.

Independent specification headers. A collection entry document might later declare its own supported specification version. That needs a distinct contract for checking the header and determining its role in the composed configuration. Mounting collection release metadata does not supply this capability. Keep it a separate request if PromptKit decides it is necessary.

Cross-collection inheritance. Nested collection profiles are not immediate siblings across collections. Current sibling inheritance remains sufficient for the initial proposal, with authored definitions flattened where necessary. Generic cross-path inheritance could be considered separately if consumer needs justify revisiting the deferred scope. Mounting must not silently reinterpret extends: provider/brief as a cross-collection reference.

PromptKit also does not request collection installation, automatic directory discovery, remote fetching, namespace ownership enforcement, dependency solving, live reload, filename-derived identity, or arbitrary document transformations. Its qualified resource IDs, optional prompt version semantics, collection inventory, and execution APIs remain PromptKit responsibilities.

Public Acceptance Scenarios

Evaluate the extension through supported public loading and inspection APIs:

Scenario	Expected consumer-visible result
Destination omitted or empty	Existing root-placement behavior
Same fragment shape mounted under two distinct collection keys from independent sources	Two separate effective resources
Disjoint inputs at the same destination in one group	Mapping contributions combine
Equal or unequal overlapping scalar fields in one group	Structured composition conflict with both source locations
Same destination across deliberate precedence tiers	Existing recursive overlay behavior
Version-only prompt override	Label changes; omitted prompt body fields survive
Nested mounted import without a destination directive	Imported fields contribute at the inherited destination
Local profile inheritance across mounted peer fragments	Parent resolves at the effective sibling scope
Collection metadata containing version mounted below root	Ordinary nested field, independent of root VersionRule
Mounted/imported contribution actually targeting the protected version path	Rejected under version ownership rules
Mounted field using source-relative content, including inheritance	Original declaring resource context remains available
Mounted explicit null and omitted field	Distinct effective presence information
Mounted validation error or secret field	Effective paths, physical locations, and existing disclosure rules agree
File, native filesystem, byte, reader, or mapping input with equivalent content	Equivalent application values, subject to existing source contracts
Unsupported destination or failed load	Normal structured failure, no usable partial result

The minimum usable outcome is a consumer that selects collection sources and destinations, performs one ordinary layered load, and receives final typed configuration with reliable diagnostics and inspection. It should need no consumer-side source rewriting, generic merging, or provenance reconstruction.