145 lines
7.2 KiB
Markdown
145 lines
7.2 KiB
Markdown
# Captured Configuration Comparison
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Status: Implemented (2026-10-09). PromptKit exposes captured configuration
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comparison through `ConfigurationInspection.Diff`; see the
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[implementation plan](implementation.md) for the completed work and verification.
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## Purpose
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Let consumers compare two captured configuration inspections for operator-facing
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workflows: reviewing a candidate configuration, explaining the effect of an
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overlay, or reporting changes between independently constructed engines.
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PromptKit should expose a thin API over ConfigKit's comparison functionality,
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leaving comparison and sensitivity handling upstream.
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This feature extends inspection, not prompt execution. It does not require
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PromptKit to retain previous engines, manage reloads, or decide whether a
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candidate configuration should be activated.
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## Current Baseline
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PromptKit currently depends on ConfigKit v0.6.0. `Engine.InspectConfiguration`
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returns a captured `ConfigurationInspection` with metadata, source descriptions,
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diagnostics, path explanations, and effective-configuration output, but no
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comparison operation. These methods already expose ConfigKit's public inspection
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types while keeping the typed configuration result private.
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ConfigKit v0.7.0 adds effective-configuration comparison without changing the
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loading contracts used by PromptKit. The reviewed release corresponds to commit
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`8f3396d6f0cbe03af4f92bb2c1a1c9798171dd52`. See its
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[release notes](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.7.0/docs/releases/v0.7.0.md)
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and [public comparison API](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.7.0/diff.go).
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## Target Public API
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Add a method to the existing inspection value:
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```go
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func (v ConfigurationInspection) Diff(other ConfigurationInspection) ([]configkit.Difference, error)
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```
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The receiver supplies the left (earlier) configuration and `other` supplies the
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right (later) configuration. Consumers can compare views from separate engines
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or compare a view with itself. Returning ConfigKit's public `Difference` type is
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consistent with the existing inspection API and avoids a parallel PromptKit
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representation of the same information.
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Comparing either operand's zero inspection value returns `ErrInvalidConfig` and
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no difference records, consistent with existing inspection operations that
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require a captured view. Errors from the underlying comparison remain available
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to the caller; a new comparison-specific error hierarchy is unnecessary.
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## Comparison Meaning And Boundaries
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Delegate to ConfigKit's frozen effective-value comparison. Equal effective
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values produce no records even when their source or resolution histories differ.
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ConfigKit owns comparison granularity, canonical path ordering, and detached
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value snapshots. Its public contract distinguishes absent values from explicit
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nulls, compares mappings recursively, and treats sequences as atomic values.
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Sensitivity classifications from both views protect both sides of the output.
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Pass through ConfigKit's `Redacted` and `HiddenChanged` information rather than
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implementing masking or hidden-change detection in PromptKit. Existing PromptKit
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sensitivity classifications remain applicable. Ordinary prompt and provider
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content is not automatically safe to disclose; consumers still choose where and
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to whom to present reports. See the upstream
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[comparison guidance](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.7.0/docs/config.md#effective-configuration-diffs)
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for the detailed semantics.
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The comparison operates on the configuration captured at the ConfigKit handoff,
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consistent with [ADR 0001](../adr/0001-configuration-boundary.md). It does not
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reread sources, resolve credentials, render prompts, or call providers. It is an
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explicit inspection operation, not an additional step during ordinary prompt
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execution.
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An empty diff means equality of the compared configuration values, not equality
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of engine behavior. For example, a referenced template file can change while its
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configured path stays the same, and secret contents can change while their
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configured reference stays the same. Post-load execution preparation and
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request-specific overrides are not part of this comparison.
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## Work Needed
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### Dependency Adoption
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- Upgrade the ConfigKit requirement to v0.7.0 and update module checksums.
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- Verify PromptKit's existing loading, inspection, and execution behavior against
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the new dependency through the relevant tests and maintained examples.
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- Refresh ConfigKit's version and exact upstream source references in the
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[attribution document](../oss/attribution.md), following the
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[OSS policy](../policy/oss.md). The reviewed release retains its existing
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licensing arrangements.
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### Thin Inspection Integration
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- Provide a private comparison bridge for the retained ConfigKit results in
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`internal/configuration`, preserving the private configuration type and the
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existing inspection operations.
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- Add the public method in `configuration_inspection.go`, delegating through
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that bridge. Keep generic results and internal configuration structures out of
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the public API.
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- Reuse captured inspection state and upstream comparison logic. No changes to
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configuration formats, source precedence, or execution routing are needed.
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### Focused Verification
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- Exercise the public method with independently constructed engines, an equal
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pair, and a representative changed value. Include equal effective values
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produced by different source histories.
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- Verify operand direction, zero-view errors, and propagation of upstream
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records through the private bridge.
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- Verify paired sensitivity protection and hidden-change reporting using
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PromptKit's existing credential-shaped provider fields. Check representative
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presence and sequence behavior without duplicating ConfigKit's comparator
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test suite.
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- Check that comparison uses captured state after source changes and that
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returned records do not let callers mutate retained inspection state.
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- Exercise concurrent inspection comparisons under the race detector. Keep
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tests offline and focused on PromptKit's integration boundary, following the
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[testing policy](../policy/testing.md).
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### Documentation
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- Add GoDoc for the method's direction, errors, snapshot boundary, and upstream
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result semantics.
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- Add a short operator-oriented usage example to the
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[consumer guide](../consumers/pkg-promptkit.md), linking to GoDoc and ConfigKit
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for the detailed contract.
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- Update the [internal source document](../internal/sources.md) to describe the
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private comparison bridge and refresh dependency-specific discussion where
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needed. Record the feature in the applicable release notes when preparing
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its release.
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## Scope And Completion
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This unit of work is the dependency upgrade and a thin inspection comparison
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method, with proportionate tests and documentation. Custom diff algorithms,
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formatters, CLIs, patch application, automatic reloads, and execution-equivalence
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analysis are outside this unit of work.
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The feature is complete when consumers can compare captured inspection views
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through PromptKit, receive ConfigKit's difference records without an additional
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local interpretation layer, and find accurate documentation for the operation
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and its boundaries. The companion [implementation plan](implementation.md)
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defines the staged implementation sequence.
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