feat(mecak8s): expose opt-in Cedar authority policies for caller-scoped tool restrictions

Problem

Mecatl includes an opt-in Cedar-backed AuthorityEvaluator, but mecak8s does not expose the composition settings needed to select it. mecated provides --authority-evaluator=cedar and --cedar-authority-policy, while mecak8s has neither flag nor corresponding app.Config wiring.

This prevents a Kubernetes deployment from applying caller-identity-aware policy to built-in tools. For example, an OIDC-authenticated bot account should be denied WebSearch while other authenticated callers retain it.

Desired outcome

Make the Cedar authority evaluator available to mecak8s through operator-controlled deployment configuration.

Acceptance criteria

• mecak8s exposes an explicit evaluator selection and static Cedar-policy source equivalent to mecated's --authority-evaluator and --cedar-authority-policy.
• The settings are passed to app.Config.AuthorityEvaluator and app.Config.CedarAuthorityPolicy.
• The Helm chart provides an operator-safe way to supply the policy file (for example, a mounted ConfigMap or Secret) and the corresponding command arguments.
• Cedar remains opt-in; the existing local evaluator remains the default.
• Selecting Cedar without a readable/valid policy fails startup rather than weakening enforcement.
• With OIDC enabled, a Cedar policy can deny Tool::"WebSearch" for one exact (issuer, subject) bot principal, without denying it for another authenticated principal.
• Add offline coverage for CLI/config-to-composition wiring and the bot-specific denial path; update the owning user/deployment documentation.

Notes

This is distinct from --permission-config: permission rules govern approval behavior generally, whereas Cedar is the identity-aware execution authority layer. Cedar is tightening-only: it may deny a carried capability but cannot grant a tool the session does not already carry.

Relevant code:

• cmd/mecated/main.go — existing Cedar flags
• cmd/mecak8s/flags.go — missing equivalent flags/config mapping
• internal/app/root_authority.go — evaluator selection
• internal/adapter/cedarauthority/cedar.go — policy evaluation and owner requirements
• docs/adr/0234-authority-evaluator-port.md — authority-evaluator decision

Start with cmd/mecak8s/flags.go and compare its configuration mapping with cmd/mecated/main.go, then read internal/app/root_authority.go and internal/adapter/cedarauthority/cedar.go. Inspect the Helm chart and the owning user/deployment documentation for configuration conventions. Done means Cedar flags and policy delivery reach app.Config, local remains the default, invalid policies fail startup, and offline coverage verifies wiring and bot-specific denial.