coop: support canonical blueprint wire fields

[tomelm]

Summary

• add validated parsing for canonical blueprint fields: requestOptions, structured events, expectedNumberOfEvents, and link
• normalize one-request upstream apiRequests nodes into the existing CLI apiRequest runtime model, including request-key reference rewrites
• keep schema-v2 session events as strings for older CLI readers while preserving structured metadata in additive event_definitions
• validate required structure, supported node types, duplicate keys, and references across the complete blueprint

Compatibility

• no nodes to steps rename and no agent response schema change
• embedded blueprint JSON is unchanged and still round-trips byte-for-byte
• multi-request apiRequests nodes are rejected explicitly because the current runtime models one request per node
• older schema-v2 clients can read new sessions; if an older client rewrites one, event names survive but additive payload metadata may be dropped

Test plan

• go test -count=1 ./pkg/coop/... ./pkg/cmd/coop/...
• env -u CODEX_CI -u CODEX_THREAD_ID -u CODEX_SANDBOX -u CODEX_SANDBOX_NETWORK_DISABLED go test ./... -count=1