Expand mount create-draft identity to every adapter-valid noncanonical filename

[khaliqgant]

Problem

The mount and CLI currently attach contentIdentity kind mount-writeback-create-draft only to resource-space-UUID and factory-create JSON filenames. Adapter file-native create routing accepts additional noncanonical JSON basenames such as customer escalation.json.

AgentWorkforce/relayfile-adapters#252 intentionally mirrored the current mount predicate so direct helper writes and mount echoes share byte-identical identities for the production UUID helper path. Widening the adapter alone cannot coalesce other valid draft names because the later mount echo carries no matching identity.

Required change

• Define create-draft classification from the same routing contract used by adapter file-native writeback, or expose a shared contract that both repos consume.
• Emit mount-writeback-create-draft identity for every adapter-valid create filename, with the existing workspace + normalized remote path + exact-content-SHA256 key and TTL.
• Add RED direct-write to mount-echo coverage for a descriptive noncanonical basename.
• Preserve canonical update routing and delete semantics.

Context

Found by Codex review on relayfile-adapters#252. The scoped production incident path uses the covered resource-space-UUID filename; this issue tracks full contract parity.