core: close the evaluator union and package session bridge

[lemone112]

Summary

• Replace the single-evaluator production seam with one code-owned closed evaluator union: exact encoded-sRGB8 identity and WCAG 2.2. Dispatch is a direct match with concrete evidence variants; no trait object, callback, client registry, or threshold dialect reaches the evaluation loop.
• Add one concrete package projection over the generation-bound Core Session: opaque owner/session, closed lifecycle and error unions, canonical output slots, borrowed certificates, and total Set | Remove | Hold operations.
• Add a schema-ordered observation path for the packed package boundary. It uses one reusable scratch vector and one canonical sort, constructs no keyed port-binding vectors, and performs allocation-free exact replay after scratch growth.
• Acquire the weak owner lease before either observation admission path and map OwnerExpired explicitly.
• Preserve the single raw observation owner and shared transactional commit path for keyed and schema-ordered admission.
• Rebind the fail-closed point-support proof to the exact changed semantic cone and ratchet the canonical WASM budget to the measured 376832-byte artifact from Actions run 29966828219, with zero arbitrary headroom. Gzip remains diagnostic-only.

Scope

• Exactly 11 files stacked on core: make compiled programs the sole session-generation owner #453 (9ff2504…), +1884/-141: seven production/test files and four derived proof/budget attestation files.
• No client vocabulary, recipe taxonomy, JSON/hex hot path, resource cap, compatibility fallback, WASM export, or controller change.
• The canonical authored-declaration lowerer into CompiledCoreProgramV1 is intentionally the next stack slice; this PR does not introduce an adapter-authored second Program dialect.

Regression coverage

• Mixed exact + WCAG evidence in one Program, including joint selection across every admitted case and report-only non-gating behavior.
• Ready, Stale, Failed-with-remove, Failed-with-hold, exact replay, changed same-revision rejection, malformed width, and duplicate scenario IDs.
• External-crate RED contract proves package code sees only the concrete owner/session bridge, not generic evaluator or Session machinery.
• Weak-owner expiry remains a closed package error.
• Point-support algebra/claims remain unchanged; the verifier renews only exact source binding after the observation/session refactor.
• The WASM contract pins the measured raw artifact and rejects any uncoordinated budget mutation.

Verification

• Rust 1.96 full workspace: 714 passed, 6 ignored
• Integration suites and doctests
• External package bridge RED test
• clippy --workspace --all-targets -- -D warnings
• rustfmt check on the exact production/test overlay
• point-support independent verifier
• canonical WASM budget contract test
• exact-head GitHub CI
• exact-head Native conformance
• CodeRabbit

This is a stacked draft. Review only against agent/weak-session-owner; do not merge independently.

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[lemone112]

Superseded by the reviewed cumulative squash merge #465 (24fd1f4). The lower stacked branch was intentionally not merged on its own because its intermediate head was not the safe terminal public boundary.