Integrate compaction and reliability checkpoint for beta.4

[Obed0101]

Purpose

Integrate the requested compaction and reliability development checkpoint into dev for the next experimental beta. This is not a claim that the complete readiness specifications are accepted.

Changes

• Native/portable compaction checkpoints and explicitly configured compound-model workflows.
• Shared-backend AI configuration with permission checks and serialized compare-and-swap writes.
• Tool argument replay, bounded retry, targeted cancellation, computer coordinate handling and serialized upgrade-channel transitions.
• AST-backed shell facts and frozen environment fingerprints. Unverified shell execution identities require manual approval; the positive automatic-approval adapters remain unfinished.

Verification

Focused compaction/workflow/configuration/backend/cancellation/upgrade tests passed during implementation. Latest shell, approval and context checks passed, along with package typechecking and staged diff checks. No database migrations or real-user installer runs are included.

Known gaps

See docs/beta-integration-readiness.md. Remaining work includes safe automatic shell approval, durable cold-restart cancellation, Windows deferred channel changes, actual multi-client CLI coverage, live-provider canaries and human/native acceptance. Release remains gated separately by build, security, artifact and platform checks. GitHub reported one high and one low default-branch vulnerability; these are not waived.