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+# Commonalities Consumption and Bundling Design
+
+> **Scope:** Design proposal for consuming `CAMARA_common.yaml` and similar shared schemas in CAMARA API repositories, including validation, synchronization, reviewer visibility, and release-time bundling.
+>
+> **Related discussion:** [Commonalities issue #577](https://github.com/camaraproject/Commonalities/issues/577)
+
+---
+
+## Executive Summary
+
+Several CAMARA API repositories need a supported way to consume shared schemas from `CAMARA_common.yaml` without copy-paste. This became urgent after recent Commonalities schema updates, including OWASP-related changes, because repeated manual copying into API repositories does not scale and destroys provenance.
+
+This proposal recommends:
+
+1. **Controlled local copy on `main`:** API repositories consume Commonalities schemas through a local cached copy, referenced via relative `$ref`.
+2. **`release-plan.yaml` as source of truth:** `dependencies.commonalities_release` defines the intended Commonalities dependency.
+3. **CI-managed synchronization:** the local cached Commonalities file is treated as cache, not as a manually maintained source file.
+4. **Source-only `main`, bundled release artifacts:** bundled API definitions are not committed on `main`, but are generated for PR review and committed on snapshot/release branches and tags.
+5. **In-place replacement:** source files and bundled files occupy the same path (`code/API_definitions/api-name.yaml`). On `main` the file may contain external `$ref` to `common/` or `modules/`; on snapshot/release branches these are replaced with the referenced content. There is no separate source or output directory.
+
+This design aligns Commonalities consumption with the release automation concepts already introduced for CAMARA release preparation.
+
+---
+
+## 1. Motivation and Problem Statement
+
+Section 2.1 of the CAMARA API Design Guide points to `CAMARA_common.yaml` as a shared source of common schemas, but does not define a standard consumption model. In practice this has led to:
+
+- copy-paste of shared schemas into API repositories
+- unclear provenance of consumed Commonalities content
+- avoidable maintenance effort whenever Commonalities evolves
+- inconsistent tooling support across repositories
+
+The immediate pressure is increased by recent updates in `CAMARA_common.yaml`, where API repositories should be able to adopt shared schema changes without re-solving the same problem by local duplication.
+
+---
+
+## 2. Design Goals
+
+The solution should provide:
+
+- **Traceability:** the exact Commonalities release used by an API repository must be identifiable
+- **Tooling compatibility:** source files must work with standard OpenAPI tooling and local development workflows
+- **Reviewer visibility:** codeowners must be able to inspect the effective API impact, including changes caused by shared schema updates
+- **Release artifact quality:** published releases must expose complete standalone API definitions
+- **Identical layout across branches:** the repository structure does not change between `main` and release branches — only file content changes (source → bundled). Tools and processes that operate on `code/API_definitions/` work the same way regardless of branch.
+- **Low contributor friction:** the model should remain understandable and practical for normal API repository contributors
+
+---
+
+## 3. Repository Model on `main`
+
+API repositories should adopt a controlled local copy model with a canonical layout:
+
+```text
+code/
+  API_definitions/   # source API definitions
+  common/            # local cached copy of CAMARA_common.yaml
+  modules/           # optional project-local reusable schemas
+```
+
+Rules on `main`:
+
+- API source files reference Commonalities content via relative `$ref` into `code/common/`
+- project-local reusable schemas may be placed in `code/modules/` and also referenced via relative `$ref`
+- remote URL-based `$ref` are not used for normative schema consumption
+- bundled standalone API definitions are not committed on `main`
+
+### 3.1 Source of Truth
+
+`release-plan.yaml.dependencies.commonalities_release` is the authoritative declaration of the intended Commonalities dependency.
+
+The local `code/common/CAMARA_common.yaml` file is only a cache of that declaration. It is not a manually curated source.
+
+### 3.2 Cache Ownership
+
+Manual edits to `code/common/CAMARA_common.yaml` are not supported. The cache is expected to be synchronized by automation.
+
+---
+
+## 4. Dependency Synchronization Model
+
+The synchronization mechanism should be permanent, not a one-time migration helper.
+
+Supported triggers:
+
+- automatic trigger after relevant `release-plan.yaml` changes
+- manual trigger to re-sync `code/common/CAMARA_common.yaml` later if required
+
+Expected behavior:
+
+- synchronization is idempotent
+- if no change is needed, no PR is created
+- the synchronization result is surfaced through a normal PR
+- snapshot creation validates that the cache is exactly in sync with the declared dependency
+
+This follows an already established principle in CAMARA release discussions:
+
+- `release-plan.yaml` defines the intended target
+- PR validation on `main` reports what still needs to change before a release can be created
+- the final hard block occurs at snapshot creation time
+
+An out-of-sync Commonalities cache is therefore expected to be:
+
+- **a warning on `main`**
+- **a blocker for snapshot creation**
+
+---
+
+## 5. Bundling Decision
+
+Bundled API definitions should **not** be committed on `main`.
+
+Instead:
+
+- `main` keeps source files only (containing `$ref` to `common/` and `modules/`)
+- PR workflows generate bundled artifacts and bundled diffs for reviewer visibility
+- release automation replaces external `$ref` with the referenced content in place on snapshot/release branches and tags — the file path (`code/API_definitions/api-name.yaml`) stays the same
+
+### 5.1 Rationale
+
+Committing generated bundled files on `main` would:
+
+- pollute PRs and git history with generator output
+- increase merge conflicts
+- obscure the real source-level changes
+- create a risk that contributors start editing generated files directly
+
+Keeping source only on `main` preserves a clean development model while still allowing reviewers and consumers to see the complete API through generated outputs.
+
+---
+
+## 6. Reviewer Visibility and Diff Priorities
+
+The issue discussion highlighted that codeowners want to see the effective API changes, especially when `CAMARA_common.yaml` changes. That need is valid, but it does not require committing bundled files on `main`.
+
+PR workflows should therefore provide review surfaces in the following priority order:
+
+1. **Source diff**
+   The normal git diff remains the primary review surface.
+
+2. **Bundled artifact**
+   The fully bundled API for the PR head should be uploaded as an artifact for each affected API.
+
+3. **Bundled diff**
+   A diff between the bundled API from the PR base and the bundled API from the PR head should be generated for affected APIs.
+
+4. **Optional API-aware summary**
+   A compact semantic summary of changes in paths, operations, schemas, responses, and examples may be added later.
+
+This gives reviewers the complete effective API view without polluting `main`.
+
+---
+
+## 7. Validation Policy
+
+Validation should depend on the operational context.
+
+### 7.1 PR Validation on `main`
+
+Purpose:
+
+- validate declared intent
+- provide early feedback
+- allow merge of planned-but-not-yet-releaseable states
+
+Behavior:
+
+- invalid configuration remains blocking
+- most release-readiness issues are warnings
+- out-of-sync `code/common/CAMARA_common.yaml` is a warning, not a blocker
+- warning messages should point to the expected sync PR or manual sync trigger
+
+Mental model:
+
+- `release-plan.yaml` defines the target state
+- PR validation indicates what still needs to be changed before a release snapshot can be created
+
+### 7.2 Validation Before Snapshot Creation
+
+Purpose:
+
+- ensure the exact source commit intended for release is ready
+
+Behavior:
+
+- previously tolerated release-readiness warnings become blockers unless explicitly allowed
+- local source references must resolve
+- `code/common/CAMARA_common.yaml` must exactly match the declared `commonalities_release`
+- APIs intended for release must pass the stricter release profile
+
+Mental model:
+
+- the last PR before snapshot creation should be green
+- technically, snapshot creation still re-validates the exact source commit
+
+### 7.3 Snapshot/Release Artifact Validation
+
+Purpose:
+
+- validate the bundled release artifact rather than the editable source state
+
+Behavior:
+
+- bundled API definitions must validate as standalone artifacts
+- release metadata and dependency provenance must be correct
+- release branches and tags expose consumer-facing artifacts, not editable source structure
+
+---
+
+## 8. Commonalities Content Expectations
+
+`CAMARA_common.yaml` must be directly consumable via `$ref` without preprocessing. This requires two changes on the Commonalities side, which can be addressed independently:
+
+### 8.1 Placeholder Removal
+
+`CAMARA_common.yaml` currently contains placeholder patterns (`{{SPECIFIC_CODE}}`, `{{field}}`) inside Generic error response schemas and examples. These make the file unparseable as a `$ref` target because the placeholder values are not valid OpenAPI content.
+
+The recommended approach is to **comment out** placeholder-containing lines rather than delete them:
+
+- Commented lines are ignored by YAML parsers, bundling tools, and Spectral
+- The placeholders remain visible as human-readable documentation, showing API teams where to add API-specific content
+- The Generic error responses retain their common error codes (e.g., `INVALID_ARGUMENT`, `NOT_FOUND`) as valid enum values
+- The change is minimal — approximately 30 lines across the file
+
+This makes `CAMARA_common.yaml` immediately consumable without requiring structural refactoring.
+
+### 8.2 API-Specific Error Code Extension
+
+APIs need a way to add their own error codes beyond the common ones provided by the Generic responses. This is a separate concern from placeholder removal — it does not need to be solved before `CAMARA_common.yaml` becomes consumable.
+
+Possible extension mechanisms include `allOf` composition, property overrides, or defining API-specific responses that reference only the shared `ErrorInfo` schema. The right approach may vary by API pattern and can be worked out incrementally as APIs adopt the `$ref` model.
+
+Example/template API source files should demonstrate the recommended extension pattern once it is established.
+
+---
+
+## 9. Relationship to Release Automation
+
+The current release automation direction already provides part of the required model:
+
+- `release-plan.yaml` already carries `dependencies.commonalities_release`
+- release-state derivation already exposes that dependency
+- release automation already resolves the semantic Commonalities version
+- release metadata already records dependency provenance
+- source-commit traceability already exists through `src_commit_sha` and `source/rX.Y` reference tags
+
+The main missing pieces are:
+
+- synchronization of the local Commonalities cache
+- bundling/dereferencing of API source files during snapshot creation
+- PR-time generation of bundled review artifacts and bundled diffs
+
+### 9.1 Release Branch Strategy
+
+The release process applies in-place replacement (see executive summary, point 5):
+
+- on `main`, `code/API_definitions/api-name.yaml` is the source file which may contain external `$ref` to `common/` or `modules/`
+- on snapshot/release branches, the same file at the same path is replaced with the standalone bundled version
+- the `common/` and `modules/` directories are removed from the snapshot branch since their content is now embedded in the bundled files
+
+This follows the same pattern as the existing release automation transformer, which replaces `info.version` and server URLs in place on the snapshot branch. No separate output directory is created.
+
+This keeps the familiar filename in all contexts while maintaining a clean source model on `main`.
+
+---
+
+## 10. Bridge Strategy Before Validation Framework v1
+
+A broader `validation-framework-v1` is expected to take time. It should eventually provide:
+
+- one shared validation core
+- context-specific profiles
+- a common findings model for hints, warnings, and errors
+- multiple reporting surfaces
+- replacement of MegaLinter-based validation
+
+Before that is ready, a minimal bridge can still enable the Commonalities consumption model.
+
+### 10.1 Minimal Bridge Scope
+
+Short-term work should:
+
+- keep `pr_validation v0` mostly intact
+- introduce narrow pilot support for repositories adopting the local Commonalities model
+- add synchronization support for `code/common/CAMARA_common.yaml`
+- add strict pre-snapshot validation and bundling into release automation
+
+This allows early adoption for pilot repositories without waiting for the complete validation rewrite.
+
+### 10.2 Tooling Ref Consistency
+
+If pilot repositories use non-`v0` refs of `camaraproject/tooling`, each reusable workflow must be internally consistent with its own tooling ref.
+
+This is especially relevant for PR validation:
+
+- changing only the caller ref is not sufficient if the workflow still hardcodes internal calls to `@v0`
+- pilot behavior should therefore resolve its internal actions, scripts, and configuration from the same tooling ref
+
+This matters for cooperation between PR validation and release automation during the pilot phase.
+
+---
+
+## 11. Recommended Phased Plan
+
+### Phase 1: Decision and Pilot Preparation
+
+- confirm the controlled local copy model
+- confirm source-only `main` plus bundled release artifacts
+- align Commonalities on direct consumability of shared content
+- select pilot repositories
+
+### Phase 2: Pilot Implementation
+
+- implement sync PR generation for `code/common/CAMARA_common.yaml`
+- generate bundled artifacts and bundled diffs in PR workflows
+- add strict pre-snapshot validation and bundling to release automation
+
+### Phase 3: Generalization
+
+- introduce the shared validation core in validation framework v1
+- replace MegaLinter-centered PR validation
+- roll the model out across API repositories
+
+---
+
+## 12. Decisions Requested
+
+1. Confirm the controlled local copy model as the standard way to consume Commonalities schemas.
+2. Confirm that bundled API definitions are not committed on `main`.
+3. Confirm that PR workflows must provide bundled artifacts and bundled diffs for reviewer visibility.
+4. Confirm that an out-of-sync Commonalities cache is a warning on `main`, but a blocker for snapshot creation.
+5. Confirm that Commonalities should evolve `CAMARA_common.yaml` toward direct consumability without placeholders.
+
+---
+
+## 13. Expected Follow-Up Artifacts
+
+The expected follow-up artifacts around this design are:
+
+- a summary comment in [Commonalities issue #577](https://github.com/camaraproject/Commonalities/issues/577) linking to this design and the ReleaseManagement discussion
+- a ReleaseManagement enhancement issue that serves as the umbrella for implementation work
+- implementation issues in tooling, Commonalities, and pilot API repositories linked back to that umbrella