Plan independent defaults for both configuration comparison sides

docs/roadmap/future.md

@@ -48,8 +48,11 @@ only; do not inspect or monitor unreleased work in anticipation of adoption.
 
 Independent per-side domain selectors and opt-in comparison assertions are now
 included in the [working roadmap](promptkit-v0.19.0.md#additional-configkit-operator-workflows).
-Roadmap OD-9 selects explicit application-declared right-side bindings with
-inheritance and collection replacement; empty-collection grammar remains open.
+Roadmap OD-9 selects independent ordinary defaults for both sides and explicit
+application-declared right-side bindings. Configuration selections and overrides
+apply only to their own side; omission never inherits from the opposite side.
+Whether to standardize empty collections overriding nonempty application defaults
+remains open; clearing inherited comparison values is no longer needed.
 OD-10 selects an optional assertion outcome with a distinct difference status.
 These accepted plans do not change the currently implemented behavior.
 
@@ -85,8 +88,9 @@ projections. Further presentation refinements should follow practical feedback.
 
 Transient acquisition overrides are included as an opt-in loader capability in
 [roadmap OD-11](promptkit-v0.19.0.md#od-11-transient-configuration-overrides).
-Loader composition, numeric conversion, unusual path syntax, and comparison-side
-clearing remain design tasks. Persistent configuration editing remains deferred.
+Comparison overrides follow OD-9's independent-side model. Loader composition,
+numeric conversion, and unusual path syntax remain design tasks. Persistent
+configuration editing remains deferred.
 
 Discovery, import defaults, collection identities, and field-level resolution
 recording remain available through application loaders. Discovery tracing,

docs/roadmap/promptkit-v0.19.0.md

@@ -149,7 +149,9 @@ Transient configuration overrides are included under OD-11 as an opt-in loader
 capability. `config validate --set /workers=0` and
 `config show --set /server/port=8080` apply temporary overrides during acquisition
 without editing source files. Numeric conversion, unusual pointer keys, loader
-composition, and comparison-side grammar remain to be finalized.
+composition, and supplemental input grammar remain to be finalized. Comparison
+overrides follow OD-9's independent-side model: `--set` affects only the left
+side and `--against-set` only the right.
 
 ### Compatibility and native semantics
 
@@ -301,12 +303,13 @@ Diagnostic filters affect the presented records, not the underlying acquisition
 outcome; retain the source references needed to interpret selected records.
 
 **Independent comparison selections.** Extend the per-side typed-input design
-in [ADR 0012](../adr/0012-typed-configuration-comparison-pairs.md). Capture
-applicable selector bindings for each side, prepare and check both inputs before
-comparison, and preserve the existing shared invocation state. Resolve omitted
-right selectors, explicit empty values, repeated selectors, and flag-name
-collisions under OD-9. Domain interpretation and loader caching remain with the
-application; the comparison provider still receives two selections.
+in [ADR 0012](../adr/0012-typed-configuration-comparison-pairs.md), deliberately
+replacing its left-to-right inheritance and shared application-selector rules.
+Initialize each side from ordinary application defaults and apply only that
+side's explicitly supplied configuration selections and overrides under OD-9.
+Prepare and check both inputs before comparison and preserve the existing shared
+invocation state. Domain parsing, default interpretation, and loader caching
+remain with the application; the comparison provider still receives two selections.
 
 **Comparison assertions.** Base a difference outcome on native record presence,
 including hidden changes whose redacted snapshots look equal. Equal effective
@@ -813,17 +816,25 @@ Default tests remain offline and independent of real credentials.
 - [ ] Source-ID selection works on successful and failed acquisitions. Path,
   explicitness, severity, and code filters preserve the selected evidence and
   source references without masking the acquisition outcome.
-- [ ] Independent comparison selectors preserve the chosen inheritance and
-  repeatable-value rules, side-specific checks, and shared-state lifecycle.
-  Explicit empty right-side collection selection is designed and covered.
+- [ ] Comparison sides start independently from ordinary application defaults.
+  Supplied config/overlay selections, domain selectors, and their presence apply
+  only to their own side, including repeatable values. Cover left-only,
+  right-only, both-side, neither-side, and partially supplied right selections;
+  no omitted right field inherits from the left. Preserve side-specific checks
+  and the shared-state lifecycle. Command-wide controls remain shared.
+- [ ] A superseding ADR records OD-9's replacement of ADR 0012's inheritance and
+  shared-selector application rules. Update canonical CLI/API contracts and
+  examples with implementation, including cases that now require repeating a
+  common nondefault selection on both sides.
 - [ ] Assertion mode distinguishes equality, native differences (including
   hidden changes), usage errors, and operational failures with statuses
   `0`, `3`, `2`, and `1` respectively, without changing ordinary diff outcomes.
   Report-delivery failures remain observable.
 - [ ] Only supplied CLI overrides reach opted-in loaders under OD-11, with typed
-  values and safe flag labels,
-  selected comparison-side behavior, native errors, and returned provenance
-  preserved. No tests independently re-establish ConfigKit override semantics.
+  values and safe flag labels. `--set` applies only to the left comparison side,
+  and `--against-set` only to the right; omission supplies no CLI override records
+  for that side. Native errors and returned provenance are preserved. No tests
+  independently re-establish ConfigKit override semantics.
 - [ ] Default validation remains concise; `--details` selects the additional
   diagnostic report with a text template. Core automatically selects text when
   that template is supplied, while explicit formats still win. Changing format
@@ -897,11 +908,13 @@ The core ownership, JSON representation conventions, text printing/templates,
 universal-format, automatic-selection, and joint format-delivery decisions are
 now agreed above. Remaining details are listed under
 [remaining core reporting implementation details](#remaining-core-reporting-implementation-details).
-Provider JSON number decoding and namespace applicability are agreed in OD-2
-and OD-3. Outstanding integration choices are empty comparison collections and
-binding design in OD-9, and override grammar/acquisition details in OD-11. Exact helper
-names and report layouts otherwise remain ordinary implementation choices, not
-unresolved scope.
+Provider JSON number decoding, namespace applicability, and independent comparison
+defaults are agreed in OD-2, OD-3, and OD-9. Outstanding operator choices are
+whether to standardize explicit empty collections when application defaults are
+nonempty (OD-9), and configuration-override numeric conversion, unusual-path
+grammar, and loader composition (OD-11). Inheritance-clearing flags are no longer
+needed. Exact helper signatures, typed binding composition, flag collision
+handling, and report layouts remain implementation choices, not unresolved scope.
 
 ### OD-1: Preview command and report presentation
 
@@ -1324,20 +1337,62 @@ or aggregate path-selected display is selected for this adoption.
 
 ### OD-9: Independent comparison selector bindings
 
-**Agreed:** applications declare which domain selectors support right-side
-comparison values, with explicit metadata for their `--against-*` spellings.
-Do not generate comparison flags for every application option automatically.
-Omission inherits the left value and presence; an explicit right value replaces
-it. For repeatable selectors, the supplied right collection replaces the
-inherited collection rather than appending to it. This supports comparisons
-such as two campaigns without requiring different files or repeating every
-unchanged selection.
+**Agreed comparison model:** initialize the left and right sides independently
+from the configuration the application ordinarily loads without CLI configuration
+selections or overrides. Ordinary loading retains application discovery, files,
+defaults, environment handling, and resolution; it does not mean an empty or
+defaults-only configuration.
 
-Domain parsing stays in the declared typed bindings; no generic selector
-language is introduced. Review the refinement of ADR 0012 and flag collision
-handling before implementation. Exact helper signatures and an explicit way to
-select an empty right-side collection remain open. An empty string element is
-not necessarily an empty collection; do not equate them implicitly.
+Apply each side's explicitly supplied values only to that side:
+
+- `--config`, `--overlay`, application configuration selectors, and `--set`
+  affect the left side.
+- Their declared `--against-*` counterparts affect the right side.
+- Every omitted field retains that side's ordinary application default and
+  unsupplied state. Never copy the opposite side's value or supplied state,
+  even when other fields on the right are explicitly supplied.
+- Repeatable selectors follow their declared typed binding behavior on their
+  own side. Left-side elements are never copied into the right collection.
+- Command-wide controls such as `--scope`, `--format`, `--details`, and `--check`
+  govern the comparison as a whole and remain outside this separation.
+
+| Invocation after `app config diff` | Left selection | Right selection |
+| --- | --- | --- |
+| `--config candidate.yml` | `candidate.yml` | Ordinary configuration |
+| `--config before.yml --against-config after.yml` | `before.yml` | `after.yml` |
+| `--config base.yml --against-overlay experimental` | `base.yml` | Ordinary configuration with the selected overlay |
+| `--config base.yml --against-config base.yml --against-overlay experimental` | `base.yml` | `base.yml` with the selected overlay |
+| `--against-config candidate.yml` | Ordinary configuration | `candidate.yml` |
+| No side-specific flags | Ordinary configuration | Ordinary configuration |
+
+The examples retain normal application interpretation of file and overlay
+selectors. Explicitly selecting the same nondefault input on both sides requires
+supplying it on both sides. Equal selections remain allowed and do not skip
+acquisition or comparison.
+
+Applications declare which domain selectors support right-side values, with
+explicit metadata for their `--against-*` spellings. Do not generate comparison
+flags for every application option automatically. A configuration selector
+without a right-side binding still affects only the left when supplied; it is
+not implicitly shared. Domain parsing stays in declared typed bindings; no
+generic selector language is introduced. Retain the two input preparations and
+checks, one shared invocation state, and existing provider lifecycle.
+
+This deliberately replaces the previous inheritance model, including existing
+config/overlay behavior and shared application selectors. When implementation
+lands, record the change in a superseding ADR for the affected decisions in
+ADR 0012, retaining its accepted decision text as history, and update current
+CLI/API contracts and examples. Exact helper signatures and flag collision
+handling remain implementation design tasks.
+
+**Remaining collection question:** omission already means the ordinary collection
+for that side, so no flag is needed to clear inherited left-side values. The
+earlier proposed `--against-clear-*` flags are not selected. Explicitly replacing
+an application's nonempty default collection with an empty collection is a
+separate, symmetric question for either side: decide whether it needs a standard
+capability or should remain with application-declared bindings. No empty-collection
+grammar is selected here, and an empty string element is not implicitly an empty
+collection.
 
 ### OD-10: Comparison assertion outcomes
 
@@ -1367,6 +1422,20 @@ required. The loader contract must state how it combines these records with
 any existing application-owned overrides; the generic adapter cannot inject
 them into an arbitrary loader after the load has completed.
 
+**Agreed comparison behavior:** `--set` supplies override records only to the
+left side; `--against-set` supplies records only to the right. Each side starts
+from its ordinary configuration under OD-9. Omission supplies no CLI override
+records for that side; it never inherits records from the other side. Normal
+application-owned overrides are part of ordinary loading and are not erased by
+omitting these flags.
+
+For example, `config diff --set /workers=4` compares the left configuration with
+that override against the ordinary right configuration. Adding
+`--against-set /workers=8` explicitly overrides the right configuration as well.
+Repeat the same `--set` assignments as `--against-set` assignments when both
+sides should use them. There is no shared CLI override baseline and no
+`--against-clear-set` flag is needed to undo inheritance.
+
 Prefer inline assignments for ordinary one-value experiments. This is the
 largest remaining loader integration design item; revisit scope explicitly if
 the required acquisition changes prove disproportionate rather than silently
@@ -1383,11 +1452,6 @@ dropping the agreed feature. Settle these details before implementation:
 - Follow the released mapping-path constraints, including root/index and
   schema-version restrictions, without extending them into a generic patch
   language. Empty, false, zero, and null remain intentional supplied values.
-- For comparison, recommend `--set` as the shared baseline and
-  `--against-set` as a right-side replacement list when supplied, following
-  OD-9's agreed repeatable-selector rule. Define an explicit way to select
-  an empty right list before finalizing this grammar; appending or replacing
-  individual paths would need a different selected rule.
 - Reflect native CLI origins and subsequent resolution in existing reports.
   Test CommandKit parsing, forwarding, and outcome/report adaptation, leaving
   ConfigKit's override algorithm to its own tests.