`src/tool/permission.rs` — `PermissionCheck`

The permission decision vocabulary — a small enum, no policy engine.

Key items

• PermissionCheck — Allow, Deny { reason }, Ask { prompt }, Modify { modified_input }.
• Constructors: allow(), deny(...), ask(...), modify(...); predicates is_allow/deny/ask/modify.

Behavior notes

• There is no PermissionPolicy/PermissionSet type — the policy is your function; this enum is the decision.
• Deny.reason surfaces to the model verbatim (via the middleware’s error text) — write concrete reasons.
• Ask resolution and Modify validation are the caller’s responsibilities (the middleware denies unresolved Asks; Modify bypasses schema re-validation).
• Tool::is_read_only and ToolContext::is_non_interactive are the companion flags policies read.

Deep dive: Permissions.