docs(rfc): add declarative artifact families and generation profiles

[MaoMengww]

Which issue or RFC does this PR close?

Refs #1424

Rationale for this change

Family identity is already a free string at the domain-value level (ArtifactRef.family), but every execution path keeps its own closed set
— artifact classes, authorization profiles, ID prefixes, processing bindings, contract enums — so changing the set of families requires
platform source and contract changes and "extend without forking" does not hold today. This RFC defines two governed extension points to
close that gap without executing extension code: what class of derived artifact is produced (declarative Artifact families), and how that
content is generated (Scope-owned generation profiles).

What changes are included in this PR?

• Adds synchronized English and Chinese RFC documents.
• Declarative Artifact families: a data-only extension package (powercontext.extension.json plus JSON Schema documents), closed manifest
  validation, fail-fast activation with per-family failure isolation, and no extension code on the production path.
• Multi-version content schemas: several schema_versions per family, current_schema_version for new writes, the schema content marker
  as the version authority, and schema_version columns on pc_artifacts and pc_artifact_candidate_versions with RESTRICT composite
  foreign keys into the new pc_extension_families description table.
• Content validation through thin wrapper types (RootModel[dict[str, Any]], ArtifactDraft/Artifact subclasses) reusing the existing
  strict decode seam, with the manifest schema as the only authority and document-scoped $ref resolution.
• Fixed platform rules for retrieval projection and context rendering, plus projection rebuild on activation and upgrade.
• Generation profiles: the built-in generation-profile family, immutable revisions, profile content model (target family, prompt
  reference, model catalog entry, bounded settings, output cap, empty-result field, failure policy), resolution keyed by profile key and
  frozen per operation.
• Model catalog as server configuration, with the existing InferenceConfig.generation_* normalized into a default entry, and profile
  limits min'd against catalog bounds.
• Generation provenance: a structured record plus a derived digest whose input contract is frozen by digest_input_version, covered by a
  new pc_artifact_generation_provenance table and candidate-side columns carried into Revision lineage at approval.
• A generic POST /v1/generation/generate endpoint (profile-driven generation, or a manual proposal when only family is given), plus a
  read-only GET /v1/extensions discovery endpoint that makes default-deny explicable through four per-family states.
• Registry-driven family dispatch replacing the closed family sets, contract changes (read-path family enums opened, write-path unions kept
  closed), and the deactivate/downgrade/reinstall state machine with historical readability from the family description table.
• Author tools (extension init/validate/lock/diff) and administrator tools (extension enable/print-config,
  generation-profile), plus a config wizard step; validate performs structural lint and a skeleton dry run so an unconstrained schema
  cannot pass.
• Documents drawbacks, alternatives, prior art, unresolved questions, and acceptance criteria covering external behavior.

Are there any user-facing changes?

No released behavior changes. This PR adds design documents only.

Design decisions worth calling out for reviewers:

• The platform performs no content migration: historical Revisions are validated and rendered under the version each recorded.
• Opening the family enums on read paths is an intentional breaking change for typed integrations when implemented, and must ship with make api-generate and make contract-test.
• Not in the first slice: code-hook extension points, automatic triggering, tags and cross-Scope publication for extension families, and
  Dashboard presentation.

How was this change tested?

make docs-test: no issues.
uv run prek run --files ...: all hooks passed.

AI usage statement

Claude Code assisted me with research, design, and review.

[Teingi]

The Family/Profile split and reuse of Candidate → Review → Revision make sense. I suggest resolving the four contract gaps below before implementation.

For S1, I would focus on one Runbook plus one generation profile, covering exact evidence → Candidate → human Review → retrieval/context contribution → exact reads after deactivation. The lock/diff tools, config wizard, and built-in family integration could follow separately.

I checked the wrapper/codec round trip and the target-version example against the repository on SQLite. These comments concern the proposed design; extension support itself is not implemented in this PR.

[MaoMengww]

@Teingi Done. singleton target frozen at candidate creation (including the expected-absence state), provenance as a complete resolution-time snapshot with a frozen digest input contract, acceptance 2 split by domain as 2a–2d, one fixed recursive rule for array and nested-object rendering (acceptance 25–27), and Example 1 switched to an extension family — and built-in family integration moved to Future possibilities because its payoff is low (parameter tuning is already covered by deployment configuration and Prompt customization). Slices: S1 = one Runbook extension family + one generation profile; S2 = lock/diff, enable / print-config, the config wizard, and discovery-endpoint refinements

[Teingi]

Rechecked at 751c82f1. The singleton target/expected-absence rule, recursive rendering, and built-in-family scope are now addressed. Two P2 contract gaps remain below. I replayed the CAS checks against ArtifactRepository on SQLite and verified the projection counterexample with SQLite FTS5. These are RFC design findings; extension support is not implemented by this PR.

[MaoMengww]

@Teingi Done:

• Dropped the cross-element phrase guarantee
• Template text now has its own version axis: pc_extension_prompt_templates keyed by template_digest, with provenance bound to it by a RESTRICT foreign key;