sdk(feature): Decide support contract for dynamically declared planes

[matdev83]

Context

Follow-up from the extension-plane review-corrections work. Merged spec-only PR #557 froze the release-bounded v1 contract for dynamically declared planes and required production implementation plus merged-main certification before this issue could close.

Selected v1 contract

The completed v1 contract is:

• expose one stable ErrUngeneratedPlane classification;
• reject ungenerated Plane[T] contributions fail-closed;
• make generated canonical policy/storage authoritative so copied same-ID descriptors cannot redefine standard-plane semantics;
• remove arbitrary map[string]any / reflection-backed plane contribution, freeze, validation and replay fallback;
• directly prove contribution freeze, request freeze/materialization, FrozenPlaneSet/FeatureBundle validation, ordinary replay and candidate replay.

Completion evidence

The requested production behavior and its focused verification are complete:

• feat(pre-oss): closed-plane contract on generated planes (1.x+2.x) #576 implemented the closed generated-plane contract and sdk(feature): Decide support contract for dynamically declared planes #554 architecture/public-contract tests;
• feat(pre-oss): move tool-call repair into feature (3.x) #582/feat(pre-oss): move secret-guard into feature + compose adapter (4.x) #578/feat(pre-oss): relocate compaction detector to infra (5.x) #579/feat(pre-oss): runtimebundle adapters + zero feature imports (6.x) #580/feat(pre-oss): ownership ratchets, SDK fixture, docs, evidence (7.x+8.x) #581 completed the broader pre-OSS ownership migration and release evidence through Task 8.3;
• chore(pre-oss): pin inventory SHAs to merged main #584/fix(pre-oss): baseline SHA validated as mainline ancestor #585/fix(pre-oss): hermetic git identity in inventory SHA test #586 repaired merged-main residual-inventory SHA verification;
• ci: add pre-OSS exact race gate #588 added the exact Linux race gate;
• fix(runtime): synchronize concurrent terminal state #589/test(runtime): isolate parallel stream assembly state #590 fixed races exposed by that gate;
• fix(feature): make generated plane policy canonical #591 made generated plane policy canonical on merged main at d784a8344888dd9de2141a13d4bf723125d4b08c and added fail-closed/global-mutation regression ratchets;
• exact Linux race run 33891386913 executed against that merged SHA and completed successfully;
• the task: Implement Kiro spec pre-oss-core-slimming #571 closeout record states generator/check, SDK/featurebundle/archtest/speccheck, external fixture, runtime-sensitive/migrated-feature suites and PR CI/QA are green.

That satisfies this issue's production-contract and merged-main/Linux-race acceptance boundary, so #554 is correctly closed.

Relationship to #571 / #398

#571 remains the top-level OSS Base pre-OSS work order because its canonical Kiro Task 8.4/archive/completion metadata still needs repository closeout. That remaining spec-closeout work does not reopen this already-proven #554 production contract.

Do not add #554 directly as a blocker of #398; keep the release gate transitive through #571.

Merged planning PR #559 / post-split #572 remains later milestone work and is not a dependency of this completed issue.